Introduction -Setting Final Corrected

1 Chapter 1 : Introduction

Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal

1 Introduction

1.1 Background

Constructed wetlands (CWs) have been defined as „„engineered systems, designed

and constructed to utilize the natural functions of wetland vegetation, soils and their

microbial populations to remove contaminants in surface water, groundwater or

waste streams” and which is to as nature‟s kidneys (ITRC, 2003). CWs can be used

as part of decentralized wastewater treatment systems, due to their characteristics as

low construction cost, low-technology systems, relatively low operational &

maintenance cost and requires significantly less energy. Denny et al., (1997) pointed

out that CWs are particularly suitable for developing countries as well as any rural or

low density area in the world, whereas conventional systems are appropriate in

industrialized regions and densely populated areas with guaranteed power supplies,

easily replaceable parts, and available of skilled manpower to ensure operation and

maintenance requirement.

Wolverton (1987) pointed out that the scientific basis for waste water treatment in a

vascular aquatic plant system is the cooperative growth of both the plants and the

microorganisms associated with the plants. A major part of the treatment process for

degradation of organics is attributed to the microorganisms living on and around the

plants roots. Once microorganisms are established on aquatic plants root, they form

a symbiotic relationship in most cases with the higher plants. This relationship

normally produces a synergic effects resulting in increased degradation rates and

removal of organic compounds from the wastewater surrounding the plant root

systems. Also, microorganisms can use some or all metabolites released through

plant roots as a food source. By each using the other waste products, this allows a

reaction to be sustained in favor of rapid removal of organics from wastewater.

Generally, common reed (Phragmites australis) is among the most popular plants

used in constructed wetlands because of high tolerance and abundance in several

areas of the world (Kadlec and Knight 1996).

The first experiments aimed at the possibility of wastewater treatment by wetlands

plants were undertaken by Käthe Seidel in Germany in 1957 at the Max Plank

Institute in Plön (Seidel, 1995). From 1995, Seidel carried out numerous experiments



on the use of wetland plants and especially Bulrush (Schoenoplectus = Scirpus

lacustris) for the treatment of various types of wastewater. In the mid-1960s, Seidel

began collaboration with Reinhold Kickuth from Göttingen University, but the

collaboration ended after a few years due to person reasons (Kadlec and Wallace,

2009). After then Kickuth developed a HSSF wetland process, which is also known

as root zone method (RZM). Constructed wetlands with sub-surface horizontal flow

drew more attention in Europe during the 1980s and 1990s with vertical flow and

their combination (Cooper et al., 1996; Vymazal et al., 1998). The first European

national guideline was published in Germany by ATV (Abwassertechnische

Vereinigung) in 1989 (ATV H 262, 1989) followed by European Guidelines (2008).

According to the inventory almost 3000 CWs existed in Lower Saxony in1994 and

more than 50000 small constructed wetlands were in operation by 2003 with majority

of system built to upgrade septic tank efficiency (Vymazal and Kröpfelová, 2008,

Vymazal 1998).

Similarly, CWs with sub-surface technology was started in North America during the

early 1970s. Similarly, Tanner et al. (2000) reported that many communities in New

Zealand have been using constructed wetlands as a cost effective means of

secondary and tertiary wastewater treatment. Since the mid 1980s, the concept of

using constructed wetlands has gained increasing support in Southern Africa. At

present, CWs are in operation, in Asian countries like India, China, Korea, Taiwan,

Japan, Nepal, Malaysia and Thailand for various types of waste wastewater (Kadlec

and Wallace, 2009).

CWs can be divided into two types, first is free-water surface type (FWS) in which the

water level is over the surface, and second is subsurface type (SF), in which the

water level is maintained below the surface. The subsurface can be further

categorized into two types based on the flow pattern, one with horizontal subsurface

(HSF) and another with vertical subsurface flow (VSF) (Vymazal, et. al., 2010). The

illustration of each system can be seen in the figure below. The free water surface

constructed wetlands (FWS) closely resemble natural wetlands because they look

like ponds containing aquatic plants that are rooted in the soil layer on the bottom.

The water flows through the leaves and stems of the plants. Their design and

operation is very close to pond systems.



The main focus is based on the constructed wetlands with subsurface flow. This is

due to several researches indicating that the pollutant removal efficiency is better

than in FWS per unit of land, implying the area requirement is lower. These systems

also pose no problem of mosquito or other insects breeding as well as the human,

probably children, exposure to surface wastewater. Some disadvantages of this type

are higher cost and have lower ecological value comparing to the FWS wetlands,

which are of minor concerns. The HSF and VSF systems do not resemble natural

wetlands because they have no Surface flow of water. They contain a bed of media

which is typically gravel and sand, but also soil or crushed rocks can be also used.

Within the media, emergent macrophytes are planted and the water is introduced

beneath the surface of the media and is flowing through the roots and rhizomes of

the plants. Conventionally, the flow in HSF systems is continuous, hence it creates a

“saturated” condition within the wetland body whereas the flow in VSF systems is

commonly intermittent, which results in an “unsaturated” and thus aerobic condition.

A simple and effective operation and maintenance system is essential for operating a

wastewater treatment system. Centralized wastewater management systems are

difficult to operate because of the difficulties in maintaining the long sewer networks

and treatment plant. So the constructed wetland as polishing biotopes in Gadenstedt

was constructed in 1998 as a part of decentralized waste water treatment system

covering the area of 1.1 hectare. The project„‟ Ecotechnological treatment of waste

water and sewage sludge in Lahstedt‟‟ was registered and officially sponsored project

at the world exhibition EXPO 2000 in Hanover. After achieving the good results, the

Lahstedt Municipality has decided to expand and improvement in the sewage plants

in another locality of Municipality like Oberg, Münstedt, Adenstedt, and Groß-

Lafferde. Likewise, small community of 600 residents in Berel introduced CWs

system in 2008 to ensure environment protection and better effluent quality before

discharging into the water receiving course. CWs are working as secondary

treatment plant and in the combination with pond system. The overall efficiency of

treatment plants achieved by removing 92% COD, 95% BOD, 96% NH4-N, 81% TN

and 55% TP at Gadenstedt and similarly 86 % COD, 94% BOD, 81% NH4-N, and

52% TP at Berel.



Decentralized system of treating wastewater ,with constructed wetlands, can provide

not only a more economical and energy efficient means of achieving treatment

objective , but also a resource in the form of reclaimed water available for landscape

irrigation or creation of wildlife habitats. Such an approach is more in line with the

philosophy of sustainable development and suitable technology for developing

countries.

1.2 Objectives

The objectives of this thesis were to evaluate the treatment efficiency of the

constructed wetland built in Gadenstedt and Berel. Similarly other objectives are as

follows:

Visiting in the study area.

Analysis of data of influent and effluent concentration of BOD, COD, NH4-N, TN,

TP

To study the efficiency of CWs to reduce BOD,COD,NH4-N,TN,TP

To examine the hydraulic characteristics of the flow-through system.

Economic analysis of power consumption and cost.

Evaluate the effect of influent pH and temperature effects

To focus as Constructed Wetlands are suitable technology in the context of

Nepal

1.3 Methodology

Literature Reviews Literature review is one of the most important methodologies, which helps to bring

clarity and focus in the research subjects. The literatures relevant to the study subject

were studied from available books, journals, previous thesis, reports and internet

sites to formulate the subject matter, develop conceptual study framework, select

study area, and later discuss the results. Further, before visiting field various

published/unpublished national and international reports and maps related to the

study area were collected and studied, which attributed to understand more deeply.



Data collections Data collections are the secondary methodology that has been used during the

research study for this thesis. Both primary and secondary data collections have

been made.

Primary data collection: Field visit, sample taken of wastewater, direct measurement pH and temperature in

field and measurement of influent and effluent concentration of BOD, COD, NH4-N,

TN, and TP in the central Laboratory were observed and data collected. Similarly

discharge, power consumption were also collected directly in field.

Secondary data collection (Data regarding the climate and hydrology from the relevant organizations) The existing data in relevant to this thesis writing from the different organizations can

be categorized into this group. The data and information from the various

meteorological departments, research organizations come under this category. An

enormous number of such data and information have been used in this study.

Analysis, Discussion and Interpretation of the data The primary and secondary data obtained from the field and laboratory is processed

for further analysis and interpretation.

Conclusions and Recommendations Depending upon the analysis and interpretations of the data conclusions and

recommendations has been suggested for the future.

Report Writing Finally, the report is prepared after data processing and analyzing along with

evaluation and interpretation of the field data, laboratory inferences and maps. All the

results and discussion will be synthesized and presented in the reports. It is obvious

that all these stages will be carried out with the iterative and frequent consultative

approach.



1.4 Structure of Thesis

Thesis Layout This thesis, presented in ten chapters, will give more information to the reader about

the constructed wetlands of Gadenstedt and Berel. This research work is basically

concerned with the investigation of constructed wetlands, types of wetlands used for

waste water treatment, method of reduction of organic matter (BOD, COD) and

nutrients (N,P) ,types of vegetation used in the treatment plants , soil properties, and

design process of subsurface vertical flow and horizontal flow CWs. Besides, the

thesis is presenting the present scenario of wastewater treatment in Nepal and

suitability of CWs technology transfer to Nepal.

Chapter 1 presents a general introduction about the thesis, objectives of the study,

the methodology used. Chapter 2 describes an overview of Organization

involvement (Ingenieurbüro Blumberg, Wasserverband Peine, and Lahstedt

Municipality) and their responsibility. Chapter 3 discuss about wastewater treatment

through Constructed Wetlands and its importance and implication. This chapter

focuses to wastewater qualities basically chemical, physical, and Biological

characteristics and Nutrients. This chapter also provides description on treatment

requirements guidelines, types of constructed wetlands and treatment mechanism.

Chapter 4 outlines a description on the theoretical approaches and methodology of

basic design recommendation and design principle of horizontal and vertical

subsurface CWs. This chapter also indicates the soil clogging and soil aeration in

vertical flow CWs. Chapter 5 explain an overview of soil used in substrate for

wastewater treatment process in the CWs. Chapter 6 shows the scenario of

Macrophytes used and its function for the wastewater decomposition in the CWs.

Chapter 7 describes the scenario of wastewater treatment in Nepal. Chapter 8

presents a brief description of study area geography, topography; climate, hydrology

and detail about project structure of Gadenstedt and Berel. This chapter describes

also the field data analysis of BOD, COD, NH4-N, TN, and TP. Chapter 9 presents

the analysis and discussions of the results of wastewater effluent from the CWs.

Especially focus to BOD, COD, NH4-N, TN, TP, and pH and temperature analysis.

Also focus to economic analysis of power consumption in two study area and



highlighted about CWs as a suitable technology in Nepal. Chapter 10 deals the

conclusions and recommendations that have been lay out from the investigation of

result analysis of BOD, COD, N, P, pH value in concern to the improvement of CWs

efficiency.

8 Chapter 2: Organization involvement


2 Organization involvement

2.1 Ingenieurbüro Blumberg

Blumberg Engineers is associated with a network of consulting firms in Germany,

Europe and other countries round the world. Involvement of Ingenieurbüro Blumberg

is in planning, designing, and construction as well as monitoring and supervision of

various engineering projects of water and wastewater treatment for more than 20

years. Ingenieurbüro has experiences in the successful application of wastewater

and water treatment systems, having completed over 350 large and small scale

projects worldwide, including industrial project across several sectors over the last 20

years. They have also long experience of constructed wetlands for the wastewater

treatment of small community, industrial effluent, agricultural effluent and road run-

off. Ingenieurbüro works closely with municipalities and districts for the promotion of

wastewater treatment by constructed wetlands as an eco-technology. They are

providing consulting services in the environment sector. Especially, Ingenieurbüro

involves in monitoring and supervision as well as provides technical advice for the

betterment in the Lahstedt municipality and Berel wastewater treatment project after

the construction.

2.2 Wasserverband Peine

The Wasserverband Peine has been working in the drinking water supply and

industrial water since 1952. In 1996, Wasserverband Peine has involved in the

wastewater treatment sector and especially providing services in the region of Peine,

Baddeckenstedt, Borsum and Dransfeld. The regional office in Baddeckenstedt is

responsible for the water sample collection, analysis and data recording of Berel

wastewater treatment plant.

2.3 Lahstedt municipality

Lahstedt Municipality has given more importance on the conservation of nature and

the environment and municipality are operating „‟ community sanitation Lahstedt „‟ in

the five villages of the municipality. Municipality has their own central laboratory,

which is responsible for monitoring, water sample collection, analysis and data

recording of Gadenstedt.

9 Chapter 3: Wastewater treatment through Constructed Wetlands


3 Wastewater treatments through the Constructed wetlands

(Literature review)

3.1 Constructed Wetlands

Constructed wetland treatment systems are engineered systems that have been

designed and constructed to utilize the natural processes involving wetland

vegetation, soils, and their associated microbial assemblages to assist in treating

wastewater (Vymazal, 1998). There are three types of wetlands categorizes

according to flow type like free water surface flow, horizontal subsurface flow and

vertical subsurface flow. They all have macrophytes coverage of varying degree and

the flow is usually driven under gravity system. In constructed wetlands, pollutants

are removed through a unique combination of physical, chemical and biological

processes, including sedimentation, precipitation, adsorption to soil particles,

assimilation by plant tissue and microbial transformations.

Bastian et al.,(1993) described that constructed wetlands have been designed not

only for the single purpose of treating wastewater but also implemented for multi use

objective such as treated wastewater effluent using as a water source for creation

and restoration of wetland habits for wildlife and environmental enhancement. The

efficiency of CWS for the pollutants removable is largely depends upon the bed size,

composition of substrate, type of vegetation, flow pattern, environmental conditions

and wastewater composition. The degree of control is larger than in a natural wetland

where species composition and performance may change over time. The treatment

methods by CWs were developed in Germany in 1952 at the Max Planck Institute in

Plön (Seidel 1995) and in the mid-1980 in Europe (Copper, 1996).

CWs are suitable to treat the wastewater coming from single house, small

community, as well as industrial effluent; land fill leachate, agricultural effluent and

road run-off. A relatively large amount of treatment plants are currently in use in

Europe and North America. Most of them are small, but for example in Denmark,

where the total amount is about 100 plants, there are more than 30 plants

constructed for 5 000-6 000 person equivalents (Leonardson, 1994).



Due to simple construction, low cost and large buffering capacity, CWs with

subsurface flow have been constructed in Africa, Asia, and South America.

3.1.1 Application and Importance of Constructed Wetlands

Constructed wetlands are an appropriate technology for small communities in rural

and suburban areas. Many rural projects with activated sludge plants failed because

it was not properly operated, often no skilled stuff is available or the energy costs is

no longer affordable. Constructed wetlands may also be applied for primary,

secondary or tertiary treatment and may need a pre treatment before discharging into

constructed wetlands. In general, influent and effluent constitutes of these

characteristics; data shown in Table 3.1

Table 3.1: Wastewater treatment plant Shenyang (China) for 6000 people

(Source: Ingenieurbüro Blumberg, Gottingen)

CWs are used in various fields to increase the water quality and at various treatment

levels as described below.

In domestic wastewater treatment, CWs treated the disposal of single houses or

small dwelling cluster. But it required to pretreatment in the septic tanks. CWs are

mostly used as secondary treatment. In animal wastewater treatment, livestock

wastewater includes dairy manure, milk house wash water, run off from cattle

feeding, poultry and swine manure are collected and treated. The strength of

wastewater is higher than for municipal applications, with BOD, TSS and ammonia

often above 100 mg/l (Kadlec and Wallace, 2009). In mine water treatment, a large

number of treatment wetlands were built the 1980s to treat acids mine drainage in the

United States (Wieder, 1989). CWs were in used at more than 300 sites in the United

States in 1989, to increase the pH and reduce concentration of iron and /or

manganese at coal mine sites.

Industrial wastewater from food processing is containing more bio-degradable and

nitrogen. CWs are used to reduce of nutrients and organic. Application area of CWs

2006/07 Influent Parameters Effluent Parameters

COD 191.0 mg/l 11.8 mg/l

BOD5 69.63 mg/l 11.00 mg/l

NH3-N 39.2 mg/l 1.07 mg/l

Total P 4.61 mg/l 0.37 mg/l



is now in wine, starch, alcohol, sugar and meat processing industries. Pulp and paper

mill are using CWs to reduce the effluent value in limitation. Process water and storm

water coming from petroleum refineries are being treated by constructed wetlands as

using advanced secondary and tertiary treatment (Knight et al., 1997). When the

inorganic and organic degraded water combines with the rainfall and groundwater,

then leachates are produced with more toxic and damaging surrounding

environment. In modern lined landfills, leachates are collected from the lined cells

and treated by constructed wetlands, which is one of rapidly developing technology,

with both surface flow and sub surface flow.

After the rainfall, pollutants concentration and loads are generally low range in the

undeveloped area, low density residential and commercial. Similar pollutants

concentration can be found high range in the high density resident and commercial

as well as large industrial area. The use of constructed wetlands, usually with

accompanying ponds, is now a routine best management practice (BMP) for

controlling the quality of runoff (Kadlec and Wallace, 2009). In agricultural runoff

treatment, concentration of main contaminants like suspended solids, nitrate,

phosphorus and chemicals depend upon farming practices, rainfall intensity soil type

and topography. CWs are only the economically feasible means of controlling

phosphorus, nitrogen and ability to abate the pulse of some pesticides.

Nevertheless, this lesson deals mainly with the conventional use of constructed

wetlands, which are to treat the pre-treated municipal wastewater, or so-called

primary effluent. The typical treatment cycle is shown in Figure 3.1.

Fig 3.1: Constructed Wetlands in the treatment cycle

Constructed

Wetlands

Secondary

Treatment

Primary

Treatment

Disinfection

or

Tertiary

Treatment

Raw

Wastewater

Primar

y

Effluent

Second

ary

Effluent

Final

Discharge



3.1.2 Horizontal Subsurface Flow Constructed Wetlands

In a horizontal subsurface flow CWs, water flows from inlet to outlet in the horizontal

path through a bed of a relatively homogenous medium, like gravel, sand or stones of

different sizes.

HSF wetlands are typically comprised of inlet piping, clay or synthetic liner, filter

media, emergent vegetation, berms, and outlet piping with water level control. The

main objective of impermeable layer made of plastic or soil with very low

permeability, to prevent seepage of wastewater mixing into the groundwater. During

the passage through the wetland, wastewater will come into contact with a network of

aerobic, anoxic and anaerobic zone (Vymazal, 1998). The decomposable parts of the

wastewater are transformed by microorganisms which are attached as bio-film in

plant roots and the filter medium. The vegetation in the wetland consists of emergent

macrophytes (rooted aquatic plants with leaves above the water surface).

Fig 3.2: Cross section of an HSF constructed wetland. (Picture from Ingenieurbüro Blumberg)

It is recommended to let clean water enter over CWs surface during the planting

phase. Plant growth may be inhibited by the high oxygen demand in wastewater

coming from a septic tank effluent. The wastewater can be introduced after a few

weeks of plant growth. The role of macrophytes is discussed in detail in chapter 6 of

this thesis report. Similarly, removable of organic matter, TSS, nitrogen and

phosphorus reduction are described in section 3.6 of this chapter.



Wastewater needs to be pre-treated in a septic tank or similar, to remove solids,

before entering at HSF wetland. If without pretreatment allowed to enter into the

wetland, these could effectively clog the medium and prevent water passage and

subsequent treatment.

Kickuth developed a concept of wastewater treatment through constructed wetlands

with horizontal flow and known as „‟ Root Zone Method‟‟ system. This method was

put in operation in Germany in 1974. Soil was used as a medium as a result low

hydraulic conductivity and suffered from surface runoff. But the problem was

overcome by the use of more porous media e.g. gravel (Vymazal, 1998). In Europe,

the most common term for HSF constructed wetlands is the Reed Bed Treatment

System‟‟ (RBTS) because of frequently used plant is Common Reed (Phragmites

australis). Detail design criteria and recommendation of HSF constructed wetlands

are described in chapter 4.

3.1.3 Vertical Subsurface Flow (VSF) Constructed Wetlands

In VF CWs, wastewater is distributed over the whole surface area of beds and

allowed to flow vertically through bed material. The earliest VSF Constructed

Wetlands in Europe were so-called „‟ infiltration fields‟‟ in the Netherlands and this

system is also known as Seidel-System or Max Planck Institute Process (Brix, 1994).

Fig 3.3: Detail cross- section of Vertical Flow Subsurface CWS



The water is fed under the intermittent loading system and then the water percolates

down through the sand medium. This enables diffusion of oxygen from the air into the

bed. As a result, VF CWs are far more aerobic than HF CWs and provide suitable

conditions for nitrification. VF CWs do not provide any denitrification and are also

very effective in removing organics and suspended solids. Removal of phosphorus is

low unless media with high sorption capacity are used. As compared to HF CWs,

vertical flow systems require less land. The system is typically comprised of a

preliminary settling/distribution ditch, alternative infiltration compartments with

soil/sand media, a discharge via drain and an effluent ditch as shown in fig 3.3. The

bed is planted with emergent wetlands plants (typically Phragmites). Detail design

criteria and recommendation of VSF constructed wetlands are described in chapter 4.

3.1.4 General advantage and disadvantage

Constructed wetlands are widely acceptance and many advantages compared

to conventional treatment systems, and some of them are presented here.

CWs are simple in construction, low operation and maintenance costs with or

without low energy demand. They have high ability to tolerate fluctuations in

flow, high process stability, so they can stand low loading for an extended

period of time, e.g. during a vacation, and also handle extra large loads during

a short period, and still keep a good effluent quality . Untreated water is not

exposed to the atmosphere during the treatment process, hence there are less

odor problems and the risk associated with human or wildlife exposure to

pathogenic organism is minimized and fewer problems with mosquitoes

(Kadlec and Wallace,2009). They are used to enhance aesthetic of open

spaces, help for recreational and educational opportunities. Reed harvesting

as a regenerative energy source may contribute to generate electricity

(biogas). The treated effluent water might be acceptable as irrigation water for

cash crops, lawns, public parks and golf course.

They generally require larger land areas than conventional wastewater systems. But

compared to FWS constructed wetlands, SSF constructed wetlands require less land



area. They can tolerate temporary water level draw downs, but not complete drying

(a base flow of water is required).The Evapotranspiration rate of aquatic macrophytes

in treatment wetlands is high thus reducing the water volume available for irrigation.

Some disadvantages with HSF wetlands are risk of shortcuts on the surface between

inflow and outflow and possibility of clogging if pre-treatment is insufficient. In

temperate regions the performance might be decreased during winter. Constructed

wetlands are regarded as an attractive alternative for small to medium-sized

communities in sparsely populated areas and in developing countries (Brix, 1993).

3.2 Characteristics of Wastewater.

In order to design wastewater treatment systems, it is very necessary to understand

the nature of wastewater. The treatment capacity and treatment efficiency of systems

are calculated based upon the wastewater characteristics because the effluent

quality depends upon the influent characteristics. Wastewater generally includes a

large variety of contaminants and can be very complex in composition, originating

from households, industries and storm water collection. In this project no industrial

wastewater will be considered, only domestic and stormwater.

Fig 3.4: A range of possible source of household wastewater showing wastewater from toilet, kitchen, bathroom, laundry and others. (Source: http://www.unep.or.jp/ietc/publications/freshwater/sb_summary/2.asp)

Typical components of wastewater are microorganisms, biodegradable and other

organic material, nutrients, metals and other inorganic material coming from

household and paved surface area. Domestic wastewater can be categorized into

http://www.unep.or.jp/ietc/publications/freshwater/sb_summary/2.asp



two groups like black water and grey water. Black water is especially generated from

the WC, containing faeces and urine. Grey water is wastewater coming from the

kitchen, bathroom and laundry (Ujang and Henze 2006). The water treated in the

constructed wetland is especially domestic and surface run-off from pavement. This

literature study focuses on the parameters that were tested in the project. Chemical,

physical and biological characteristics are described below.

3.2.1 Chemical Characteristics

Organic material Wastewater contains a vast number of organic materials that are comprise of

carbohydrates, fat, proteins, higher fatty acids and soluble organic acids, originate

from kitchens and bathrooms, and toilets. It is hard to determine all organic materials

in detail but they share common characteristics that can be tested in more collective

analyses. The parameters included in the analyses of this study, except for organic

nitrogen, are listed below.

Table 3.2: Analysis of domestic waste water by the American Public Health Association (Source: Wastewater Technology, by W.Fresenius and W. Schneider, 1989)

Biochemical oxygen demand, (BOD5) BOD indicates the amount of biodegradable substances in wastewater, and is widely

used and recognized as an important parameter in wastewater treatment processes.

It is a measure of the oxygen consumption of microorganisms, when oxidizing

organic matter in wastewater, at 20°C. For the measurement of BOD5, the test is

normally runs for five days, and the result is then more properly designated as BOD5.

It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen

consumed per liter of solution. If the concentration of BOD5 is near to 300 mg/l, 200

Substances mg/l

Pollution

High Average Low

Total solids 1000 500 200

Suspended solids 600 350 120

Total dissolved solids 500 200 100

Total nitrogen 85 50 25

Chloride8as CaCO3) 175 100 15

Alkalinity 200 100 50

Fats 40 20 0

BOD5 300 200 100

http://en.wikipedia.org/wiki/Milligram

http://en.wikipedia.org/wiki/Litre

http://en.wikipedia.org/wiki/Mass

http://en.wikipedia.org/wiki/Solution



mg/l , then it is called high and average level of polluted wastewater as per the

American Public Health Association as shown in table 3.2.

Chemical oxygen demand (COD) COD describes the amount of chemical oxidant, usually potassium dichromate,

required to oxidize the organic matter. It is expressed in milligrams per liter (mg/L),

which indicates the mass of oxygen consumed per liter of solution.

Table 3.3: Per capita contributions of domestic wastewater characteristics

PH The pH is a useful and important parameter in measuring the conditions of

wastewater during the whole treatment process. The pH is a logarithmic index of the

concentration of hydrogen ions (H+) in water solution. A pH value of 7 indicates

neutral conditions. Above 7 is basic and below is acid. Especially metabolic reactions

in biological processes are highly pH dependant and sensitive to low pH levels or

changes in pH.

3.2.2 Physical Characteristics

These characteristics are concerned with detection of wastewater by using the

physical senses like temperature, odor, color, and feel of solid material.

Suspended solids and total solids Suspended solids represent that fraction of total solids in any wastewater that can be

settled gravitationally. Suspended solids can further be classified into two fractions

like organic which is volatile and inorganic which is fixed. However, organic matter is

Item Range of values in wastes (g/capita-day)

BOD , 5 days,20 °C 45 - 54

COD 1.5 to 1.9 x BOD5

Total solids 170 - 220

Suspended solids 70 -145

Grit (inorganic, 0.2 mm and above)

5 -15

Alkalinity (as CaCO3) 20 - 30

Chlorides 4 - 8

Total nitrogen, as N 6 -12

Total phosphorous, as P 0.6 – 4.5

http://en.wikipedia.org/wiki/Milligram

http://en.wikipedia.org/wiki/Litre

http://en.wikipedia.org/wiki/Mass

http://en.wikipedia.org/wiki/Solution



present in the form of either setteable form or non-setteable (dissolved or colloidal)

form. If the organic fraction of suspended solids present in sewage is discharged

untreated into streams, it leads to sludge deposits and subsequently to anaerobic

conditions. These are also the main cause of clogging effects in the constructed

wetlands. The wastewater are characterized as high, average and low level polluted

as per the concentration of suspended solid, dissolved solids and total solids if they

meet the above mentioned requirement in table 3.2.

Temperature Temperature affects chemical and biological processes in a profound way. The rate

of chemical reactions and biological activity increases with increased temperature.

Similarly, metabolism and growth of microorganisms are affected by this but only up

to a certain level, after which the rate becomes lower and eventually lethal

temperatures stop the growth altogether. Different microorganisms tolerate different

temperature intervals.

Turbidity Turbidity in water is caused by suspended matter, e.g. clay or silt, small organic and

inorganic particles, plankton and protozoa. Therefore, turbidity is sometimes used as

surrogate for gravimetric measurement of suspended matter. The particle size of the

present substances ranges between 1 to 300 μm. The turbidity can be measured by

a decrease in the intensity of the radiation passed through the liquid or by the

intensity of the stray light. Turbidity is often measured using a turbidimeter, consists

of nephelometer, light source and photometer (Kadlec and Wallace, 2009). The unit

for turbidity measured with this instrument is nephelometric turbidity units (NTU).

3.2.3 Biological Characteristics

Microorganisms A microorganism is unicellular or lives in a colony of cellular organisms that is too

small to be seen by the human eye. The study of microorganisms is called

microbiology, a subject that began with Anton van Leeuwenhoek's discovery of

microorganisms in 1675, using a microscope microscope1.

1 Information share from http://en.wikipedia.org/wiki/Microorganism

http://en.wikipedia.org/wiki/Microorganism



Microorganisms are very diverse and classified into two major groups like

prokaryotes and eukaryotes. The prokaryotes are divided into two groups like

bacteria and archaea. The eukaryotes can be divided into three groups, fungi, algae

and protozoa. Microorganisms are the cause of many infectious diseases. The

organisms involved include pathogenic bacteria, causing diseases such as plague,

tuberculosis and anthrax; protozoa, causing diseases such as malaria, sleeping

sickness and toxoplasmosis; and also fungi causing diseases such as ringworm,

aspergilosis. Bacteria are unicellular and can have a number of different shapes and

sizes (0.1-40 μm). They are universally present in human feces, with normal

population of about 1011 organisms per gram (Kadlec and Wallace, 2009).

3.3 Nutrients

Nitrogen, phosphorus and potassium -- there are valuable nutrients contained in

wastewater. Excessive amounts of nutrients, especially nitrogen and phosphorus,

speed up the eutrophication process. Eutrophication is the slow, natural nutrient

enrichment of streams and lakes and is responsible for the "aging" of ponds, lakes,

and reservoirs. As algae grow and then decompose, they deplete the dissolved

oxygen in the water. Excess nutrients in water usually results toxicity to aquatic life

like fish, offensive odors, unsightliness, and reduced attractiveness of the water for

recreation and other public uses. Similarly excessive nitrate (NO3-) in drinking water

can cause human and animal health problems, particularly for small babies.

3.3.1 Nitrogen

Nitrogen occurs in different forms in municipal or domestic wastewater are ammonia

(NH4+),nitrite (NO2

-), nitrate (NO3-), nitrous oxide (N2O) and nitrogen gas (N2). In the

atmosphere, concentration of nitrogen is up to 78 %. Similarly, organic nitrogen is

also present in wastewater in the form of amino acid, urea and uric acids. Amino

acids are the main component of proteins, which is essential to all form of life. Urea

(CNH4O) and uric acid (C4N4H403) are the simplest form of organic matter in aquatic

system. Nitrogen in domestic sewage comprises about 60% ammonia and 40%

organic nitrogen (Wallace and Kadlec, 2009). The wastewater can be defined as

high, average and low level of pollution, if total nitrogen concentration exceeds up to

85, 50 and 25 mg/l respectively (see table3.2). Nitrogen removal process is described

in detail in section 3.6 of this chapter.

http://en.wikipedia.org/wiki/Pathogenic_bacteria

http://en.wikipedia.org/wiki/Bubonic_plague

http://en.wikipedia.org/wiki/Tuberculosis

http://en.wikipedia.org/wiki/Anthrax

http://en.wikipedia.org/wiki/Malaria

http://en.wikipedia.org/wiki/African_trypanosomiasis

http://en.wikipedia.org/wiki/African_trypanosomiasis

http://en.wikipedia.org/wiki/Toxoplasmosis

http://en.wikipedia.org/wiki/Ringworm

http://en.wikipedia.org/wiki/Candidiasis



3.3.2 Phosphorus

Phosphorus is an important constituent of all life. This nutrient occurs naturally in

most plants and animals and readily enters the food supply of humans from these

sources. It is one of the 20 most abundant elements in the solar system, and the 11th

most abundant in the earth‟s crust (MPCA, 2007). Human activities, however, have

resulted in excessive loading of phosphorus into many freshwater systems.

Excessive amounts of phosphorus may lead to the increased growth of algae and

other microorganisms, causing water quality to degrade. Water containing large

amounts of algae can become unsafe to drink and can cause vomiting and diarrhea.

Contact with algal blooms can cause skin irritation, thus impacting on the recreational

use of water.

In domestic wastewater, phosphorus exists in the form of orthophosphate,

dehydrated orthophosphate and organic phosphorus. Most phosphorus is conversed

into orthophosphate forms (H2PO4-, HPO4

2-, and PO43-) under the biological oxidation

(Cooper and Job, 1996). In wetlands, lakes, ponds and rivers particulate phosphate

may be deposited by sedimentation, trapped by macrophytes stems or sorbed to

biofilms.

3.4 Treatment requirements

3.4.1 Legislation

In Germany, a framework act of the Federation, the Federal Water Act

(Wasserhaushaltsgesetz) provides fundamental requirements for water management

measures. According to Article 7a of the Act, a permit for the discharge of wastewater

shall be granted only if the pollutant load of the wastewater in question is kept as low

as is possible through application of appropriate procedures using the best available

technology. The Federal Government shall establish relevant requirements, by

means of ordinances approved by the Bundesrat that are in keeping with the best

available technology2.

2 Promulgation of the New Version of the Waste Water Ordinance of 17. June 2004,this ordinance will come

into force on 1 January 2005 http://www.bmu.de/english/water_management/doc/3462.php

http://www.bmu.de/english/water_management/doc/3462.php



European Communities (EC) developed a Waste Water Treatment Regulations 2005.

These Regulations contain general binding rules requiring sanitary authorities to

ensure that waste water treatment plants do not cause a nuisance through odours or

noise emissions. The Regulations set a legal requirement for waste water treatment

plants to be designed, constructed, operated and maintained so as to avoid causing

nuisance from odor emissions or noise. Operators of such plants, including sanitary

authorities, must indicate to the Environmental Protection Agency each year all steps

taken to comply with the Regulations and, on request from the Agency, must furnish

copies of all complaint records.

The Urban Waste Water Treatment Directive of EC has already contributed to an

improvement of the quality of big European rivers by reducing BOD levels by 20-

30%, of phosphorus concentrations by 30-40% and of NH4-N levels by around 40%.

Austria, Denmark and Germany, plus with certain restrictions the Netherlands have

shown that successful and timely implementation is possible, leading to significant

improvements in water quality by achieving compliance rate of about 2/3 of the

pollution load covered by the 1998 and 2000 deadlines (H. Blöch ,2005). The

Austrian Water Act (1959/1990) is based on the principle of provision with respect to

water considering whole environment and its relationship with water and wastewater

are taken into consideration. The effluent values from treatment plant should be

within limiting values, which is legally regulated (Vymazal, Brix, 1998).

Table 3.4: Effluent standards of different European countries for small scale discharges into the surface water (modified data of Diederik P. L. Rousseaua, Peter A. Vanrolleghemb, and Niels De Pauwa)

Country Remarks COD BOD SS TN NH4-N TP Reference

Belgium 250 60 50 - - - VLAREM II (1995)

Germany 1000 – 5000 PE

110 25 - - - - Joachim (2000)

Austria 500 – 5000 PE

75 20 - - 5 2 AES ,1996

Poland < 2000 m

3

day-1

150 30 50 30 6 5 Kempa (2001)

Czech 500 – 2000 PE

120 30 35 - - - Czech Law No. 61/2003

Italian 125 25 35 35 15 10 Italian Law (1999)

Netherlands 750 150

250 30

70 30

- -

- -

- -

Debets (2000)

Sweden 10 15 0.3 – 0.5

Linde and Alsbro (2000)



Wastewater coming from domestic use, industry, agriculture or any other activity that

can contaminate the water of lakes, rivers and aquifers, should be treated before

discharge. To protect the environmental and water course, effluent from wastewater

treatment systems should be standard limit governed by national law. Some of the

European country has set the standard norms of effluent wastewater as shown in

table 3.4.

3.4.2 Guidelines

A over growing population, unrelenting urbanization, increasing scarcity of good

quality water resources and rising fertilizer prices are the driving forces behind the

accelerating upward trend in the use of wastewater, excreta and greywater for

agriculture and aquaculture. The health risks associated with this practice have been

long recognized, but regulatory measures were, until recently, based on rigid

guideline values whose application often was incompatible with the socio-economic

settings where most wastewater use takes place.

In 2006, WHO published a third edition of its guidelines for the safe use of

wastewater, excreta and grey water in Agriculture and Aqua culture. These

guidelines are divided into four volumes, which propose a flexible approach of risk

assessment and risk management linked to health-based targets that can be

established at a level that is realistic under local conditions. Some of the

recommendations regarding reuse of treated wastewater for irrigation purposes and

decentralized wastewater treatment systems will be presented here. To reuse water

for activities and areas with public access, for example parks and irrigation of crops

that will be eaten raw or that are not commercially processed, WHO (2004)

recommends that there should be no detectable faecal coliforms /100 ml of water,

and BOD values of less than 10 mg O2/l. This is called unrestricted irrigation. For

restricted irrigation, when irrigating areas with limited or no public access and cereal

crops, industrial crops, fodder crops, pasture and trees, the recommendations from

USEPA (2004) are faecal coliform concentrations of less than 200 faecal coliforms

/100 ml and BOD and SS levels of less than 30 mg/l. In the guidelines from WHO

(1989) on safe wastewater reuse, the recommended limit was 1000 faecal coliforms

/ml for unrestricted irrigation. in the new guidelines from 2006, WHO validated their

earlier general recommendation of 1000 E.coli/100 ml for unrestricted wastewater



use in agriculture, but other values were also given, e.g. 105 E.coli/100 ml for drop

irrigation of higher crops (WHO, 2006).

3.5 Hydraulics in Constructed Wetlands

3.5.1 Retention Time (RT) and Hydraulic Loading Rate (HLR)

Nominal retention time is defined as the wetland water volume involved in flow

divided by the volumetric water flow. Alternatively, it can be described a measure of

retention time, it takes for the whole water volume of a wetland to be replaced. It is

defined as RT = V/Q, where V is the total water volume and Q is the flow through the

wetland. The assumptions are steady-state conditions, i.e. the inflow is equal to the

outflow (Q = Q in = Q out), and no mixing of the water column. The total volume of the

wetland is occupied by the medium, e.g. sand, gravel. These medium having the

porosity holds water. The actual retention time for a constructed wetland is given by

the following expression (Kadlec and Wallace, 2009):

…… (1)

…... (2)

A = surface area of the wetland (m2), h = depth of water-filled part of the wetland (m)

= porosity, % expressed as decimal, Q = average flow through the bed (m3/d)

= detention time (d), q = hydraulic loading rate (m/d)

Above expression in eqn. 1, takes into consideration the porosity of the medium but

not plant roots, biofilms or non degradable residues. Over longer time, the

accumulation of non-degradable residues in the pore spaces and the spreading of

plant roots will also add resistance to the flow. Eventually this could lead to clogging

of the medium and unwanted surfacing of the wastewater. The void fraction, also

termed media porosity, ranges usually from 0.3 - 0.45 depending on the soil material

chosen, e.g. sand, gravel or clayey soils (Vymazal, 1998a). In surface flow systems,

the “reactive” volume is defined as the volume of the free water body above the

substrate minus the portion occupied by the submerged plant parts, e.g. stems,

leaves, detritus, but also settled solids. The porosity of surface flow wetlands has



proved difficult to exactly measure, thus, porosity values for surface flow wetlands in

the literature are highly variable. For example, Reed (1995) recommended wetland

porosity values ranging from 0.65 - 0.75 for fully vegetated surface flow beds.

To meet advanced treatment standards in surface flow as well as in subsurface flow

wetlands, the HRT should be at least 5 days (Vymazal, 1998a; WPCF, 1990). Reed

(1995) suggested a hydraulic retention time of at least 6 to 8 days to ensure

adequate nitrification rates. It can be concluded that there are no universally

applicable recommendations in the literature.

Hydraulic loading rate also play important role in the treatment efficiency of CWs.

There is also relationship between nominal detention time and hydraulic loading rate

as expressed in eqn. 2. From the expression, it can be seen that hydraulic loading

rate is inversely proportional to nominal detention time for the given wetlands depth

(Kadlec and Wallace, 2009). Hydraulic loading rate therefore embodies the notion of

contact duration, just as nominal detention time does.

Horizontal subsurface flow wetlands

2.0 - 5.0 cm/d for secondary treatment (Vymazal, 1998)

< 20 cm/d for tertiary treatment (Vymazal, 1998)

Vertical flow wetlands

6.0 cm/d (Mennerich, 2003)

The required energy to overcome the resistance of the medium, plant roots and

residues, is provided by the difference in hydraulic head between the inlet and the

outlet of the wetland. The time it takes for the water to pass from the inlet to the outlet

of the wetland may be less than the nominal retention time since the velocity of the

water may be higher in certain channels of the bed and shortcuts can be formed.

According to USEPA (2000) the actual retention time has frequently been reported to

be 40-80 % less than the theoretical retention time. This is one of the reasons to loss

of pore volume, preferential flow and dead volume, i.e. stagnation pockets sometimes

exits.

3.5.2 Porosity and Permeability

Porosity can be defined as the ratio of fraction volume of voids over the total volume

of materials. Soil porosity refers that pore spaces are filled with air, other gases, or



water. Large pores known as macropores allow the ready movement of air and the

drainage of water. They are also large enough to accommodate plant roots and the

wide range of tiny animals that inhabit the soil (Brady and Weil, 1999; Munshower,

1994). Clay soils have numerous micropores which help to hold large quantities of

water, but since they have few macropores cause very slow infiltration rates. The

pores in the clays may be so small and hold water so tenaciously that the water is not

available to plants. Sandy soils with numerous macropores but few micropores have

higher infiltration and percolation rates but a lower water-holding capacity than other

soil textures. (Munshower, 1994).

Permeability is the measure of a soil‟s ability to transmit water and it is largest for

coarse gravel with same size grains. In a less sorted sample, the small grains fill the

voids between the large grains and lower the permeability. The permeability can be

expressed with a coefficient, called hydraulic conductivity.

Fig 3.5: Permeability test model with different material (Gravel, Sand, Silt and clay) (Source: http://techalive.mtu.edu/meec/module06/Permeability.htm)

3.5.3 Soil clogging

Clogging is a well known phenomenon in soil filter as well as Constructed wetlands

and occurs in the wetlands bed by different mechanism like sediment deposition,

chemical precipitation and Biomat formation. Clogging caused soil pore spaces

decrease which restricts the flow of water through the bed media. Mostly suspended

(minerals) solids deposited within the inlet region of HSF wetland beds due to the low

flow velocity and such kind of deposition occurs within the 5% of the wetland bed

(Kadlec and Wallace, 2009). Biological clogging occurs when bacterial growth or its

by-products reduce the pore diameter. Biological clogging frequently associated with

organic and inorganic solids, which are entrapped by biofilms for the formation of

http://ecorestoration.montana.edu/mineland/guide/analytical/physical/porosity.htm




http://techalive.mtu.edu/meec/module06/Permeability.htm



Biomet. Kadlec and Watson (1993) found approximately 10% voids blocked by

volatile and inorganic solids. Especially, the combined effects of short-term and long

term bed clogging are reducing the hydraulic conductivity of the inlet zone of the HSF

bed and upper 0-15 cm of bed in VSF CWs. Purification efficiency drops significantly

when constant ponding occurs. Clogging is dependent on the height of organic mass

loading.

Therefore the system has to be designed large enough so that resting periods in

parts of the filter bed can occur. Another possibility to avoid clogging is to keep the

load so low that it does not occur due to the natural degradation processes. The

experiences with soil clogging in constructed wetlands differ widely, since the

problem depends on many factors (Platzer and Mauch, 1997). Sufficient soil (or bed)

aeration is the main factor for the proper functioning of VFBs and wastewater needs

to be pumped onto the VFBs intermittently (4-12 times per day). Communal

constructed wetlands with VF CWs should have at least 4 beds in order to feed them

intermittently loading on a regular basis like some beds 6 weeks in operation and 2

weeks of rest for better oxygenation.

The hydraulic loading should not exceed 150 L/(m²·d) for domestic wastewater under

normal conditions (during rain events, a hydraulic loading up to 500 L/(m²·d) can be

acceptable). The TSS loading should be less than 5 g/(m²·d) and this requires

efficient pre-treatment and organic loading (COD) should not exceed 20 g/ m²·d

(Winter and Goetz, 2003). Adequate plants with developed rhizome/root system play

an important role in maintaining and restoring soil conductivity and withstand against

the clogging.

3.6 Treatment mechanisms in Constructed Wetlands

Constructed Wetlands are effective in treating many contaminants, including organics

(BOD, COD), suspended solids, nitrogen and phosphorus as well as, and also in

reducing metals, organics and pathogens from wastewater (Vymazal, 1998). In a

subsurface flow wetland TSS and BOD are generally removed effectively while the

removal of nutrients (P and N) are variable and depends on loading rate, type of

substrate, oxygen supply and composition of wastewater (Brix 1993). The major



processes for removal of pollutant are complex within the wetland system as

described as below.

3.6.1 Organic compounds removal (BOD and COD)

The organic strength of wastewater can be measured as BOD (Biochemical Oxygen

Demand) and COD (Chemical Oxygen Demand). However, BOD is the more

important and frequently used parameter for domestic or municipal wastewaters

(Kadlec and Knight, 1996). Settable organics are rapidly removed in wetland system

under quiescent condition by deposition and filtration. Organic compounds are

degraded aerobically as well as anaerobically. Firstly, organic compounds are

biologically decomposed by the heterotrophic microorganisms under aerobic

condition and converted to water and carbon dioxide (Vymazal, 1998). Similarly,

anaerobic degradation is a multi-step process that occurs within constructed

wetlands in the absence of dissolved oxygen (Cooper et al. 1996). Anaerobic

degradation is much slower than aerobic degradation. The oxygen needed to support

the aerobic process is supplied directly from the atmosphere via diffusion or oxygen

leakage from macrophytes roots in the rhizosphere (Cooper, 1996)

The removal rate of organic matter is temperature-dependent since higher

temperatures have a positive effect on microbial activity. The growth rate,

reproduction, metabolism and the mobility of organisms, e.g. rates of biochemical

reactions, usually double when temperature is increased by 10°C within the given

tolerance range of an organism. The decomposition of BOD in all types of

constructed wetland systems is usually very efficient and has been reported to be on

the range of 70 - 95 % (Reed, 1995) for pre-treated municipal or domestic

wastewaters. However, the BOD removal rate is poorer at low input concentrations

due to the internal background production of about 1 - 6 mg/L BOD. COD removal

performance is usually slightly lower than of BOD since some groups of organic

compounds cannot be biologically decomposed by microorganisms. This results in

background levels ranging from 30 to 100 mg/L COD (Kadlec and Knight, 1996).

3.6.2 Removal of Suspended Solid (SS)

Suspended solids are setteable and floatable particles in wastewater consisting of

organic and inorganic matter. The major removable process of setteable suspended

solids is sedimentation and filtration. Non-settling or colloidal solids are removed at



least partially, by bacterial growth (which results in the settling of some colloidal

solids and the microbial decay of others) and collusions with the adsorption to other

solids (plants, pond bottom, suspended solids) (stowell et al. 1981).

Kadlec and Wallace (2009) found the median values of inlet and out let TSS

concentration in 31 vertical flow wetlands were 90 mg/l and 12 mg/l respectively, with

the removable efficiency of 87%. Similarly, by the experiments showed that

suspended solids are efficiently removed in both types of constructed wetlands and

TSS effluent concentrations are generally less than 20 mg/L and often less than 10

mg/L in both types of constructed wetlands (Brix, 1994). According to Reed (1995)

and Kadlec and Knight (1996), TSS background concentrations of about 2 - 5 mg/L

TSS can be expected.

The influent should be at least primary pre-treated to avoid the high TSS

concentrations typically found in raw wastewaters. Suspended solid of wastewater

are filtered and settled within the first few meters beyond the inlet zone. These could

lead a major threat for good performance of subsurface flow systems (Vymazal,

1998).

3.6.3 Nitrogen Removal

Nitrogen (N) in municipal wastewater is usually present as organic compounds, e.g.

urea and amino acids, and as inorganic form, almost exclusively ammonium (NH4+).

The removal mechanisms for nitrogen in constructed wetlands are manifold and

include ammonification, nitrification-denitrification, plant uptake and matrix adsorption

(Vymazal et al. 1998).

3.6.3.1 Ammonification

Ammonification is the process where the bacterial conversion of organic N into

inorganic N, especially NH4+-N in untreated wastewaters, which is also known as

mineralization. Ammonification rates are fastest in the oxygenated zone and

decrease in the facultative anaerobic zone. Reedy and Patrick et al. (1984) described

about the Ammonification process which are highly dependent on temperature, pH

value ,C/N ratio of the residue, available nutrients in the system and soil condition

(texture and structure) From the literature data, that the rate ammonification

increased by double with a temperature increase of 10°C.



Fig 3.6: Nitrogen transformation in constructed wetlands (Cooper et al., 1996)

3.6.3.2 Nitrification

Nitrification is the biological transformation of ammonium to nitrate with nitrite as an

intermediate in the reaction sequence. Nitrification is a chemoautotrophic process

and energy for growth of nitrifying bacterial is derived by the oxidation of ammonia

and carbon dioxide is used as a carbon source for synthesis of new cells (Cooper

and Job, 1996). Nitrification includes two consecutive processes where ammonium-N

is oxidized by autotrophic bacteria to nitrite (NO2-), after it is formed, immediately is

oxidized to nitrate (NO3 -). Nitrite occurs therefore in very low concentrations while

nitrate may occur in high concentrations.

The first step: ammoniacal nitrogen is converted to nitrite in the presence of Nitrosomonas bacteria:

1) NH4+ + 1.5O2 NO2

- + 2H+ + H2O

The second step: Nitrite is converted to nitrate in the presence of Nitrobacter bacteria:

2) NO2 - + 0.5O2 NO3

-

Ammonification

Organic N

NH4+

NO2-

NO3-

N2,N2O

Biomass

uptake

Biomass

uptake

Anaerobic zone Aerobic zone

Volatilisation Matrix

adsorption Biomass

uptake

N2,N2O

gas



Equations 1) and 2) can be comprised as follows that describes the entire nitrification process:

3) NH4

+ + 2 O2 NO3 - + 2 H+ + H2O

According to Vymazal (1998), nitrification is influenced by temperature, pH value,

concentration of ammonium-N and dissolved oxygen. Especially, temperature and pH

have a major effect on the rate of nitrification. The optimum temperature for

nitrification ranges from 25 °C to 35 °C in water and from 30 °C to 40 °C in soils.

Temperatures below 15 °C affect the nitrification rate more significant compared to

temperatures between 15 °C and 35 °C. Minimum temperatures for growth of

Nitrosomonas and Nitrobacter are 5 °C and 4 °C, respectively (Cooper, 1996).

Nitrifying bacteria are sensitive organism and susceptible to a wide range of

inhibitors. Nitrification can exists on the optimum pH ranges from 7.5 to 8.6, however,

can also occur at much lower pH values (Vymazal, 1998).

3.6.3.3 Denitrification

The biological reduction of nitrate (NO3-) to nitrogen gas (N2) by facultative

heterotrophic bacteria is called Denitrification. “Heterotrophic” bacteria need a carbon

source as food to live. There are several genera of heterotopic bacteria including,

Achromobacter, Aerobacter, Alcaligenes, Bacillus, Brevibacterium, Flavobacterium,

Lactobacillus, Micrococcus, Proteus, Pseudomonas and Spirillum are capable of

dissimilatory nitrate reduction (Cooper, 1996).

Denitrification occurs when oxygen levels are depleted and nitrate becomes the

primary oxygen source for microorganisms. The process is performed under anoxic

conditions, when the dissolved oxygen concentration is less than 0.5 mg/L, ideally

less than 0.2. When denitrifying bacteria break apart nitrate (NO3-) to gain the oxygen

(O2), the nitrate is reduced to nitrous oxide (N2O), and, in turn, nitrogen gas (N2). In

unbalanced equation form:

NO3-

→ NO2 - →NO → N2O → N2

Since nitrogen gas has low water solubility, it escapes into the atmosphere as gas

bubbles. Free nitrogen is the major component of air, thus its release does not cause

any environmental concern. Since denitrifying bacteria are facultative organisms,

they can use either dissolved oxygen or nitrate as an oxygen source for metabolism

and oxidation of organic matter. If dissolved oxygen and nitrate are present, bacteria



will use the dissolved oxygen first. That is, the bacteria will not lower the nitrate

concentration. Denitrification occurs only under anaerobic or anoxic conditions.

Conditions that affect the efficiency of denitrification include nitrate concentration,

anoxic conditions, and presence of organic matter, pH, temperature, alkalinity and

the effects of trace metals.

Cooper et al. (1996) pointed out that optimum pH values for denitrification are

between 7.0 and 8; however, pH value rised due to the alkalinity production during

denitrification. Denitrification is also strongly temperature dependent and proceeds at

very slow rates, at temperature below 5°C.

3.6.3.4 Plant uptake

Nitrogen removable mechanism also depends upon plant uptake system especially

macrophytes which are used in CWs will take up nitrogen in its mineralized state and

incorporate it into its biomass and tissue through their root system. However, the

potential nitrogen uptake capacity by plants is limited by its productivity (growth rate)

and the nutrient content in the plant tissue.

The uptake capacity of emergent macrophytes, when the biomass is harvested, is

roughly on the range of 1000-2500 kg N ha-1yr-1 and highly productive Water

Hyacinth (Eichhornia crassipes) have higher uptake capacity up to nearly 6000kg N

ha-1yr-1 whereas submerged macrophytes is lower range of about 700 kg N ha-1yr-1

(Brix,1994a, Vymazal,1998). Similarly, Gersberg et.al (1985) pointed out that the

amount of nitrogen removed with biomass under optimum condition can be achieved

10-16% of the total removed nitrogen. Furthermore, nitrogen is only temporarily

stored in the emergent plant biomass and will return back to the wetland system by

decomposition process through an annual cycle of growth and die back. Regularly

harvesting of the aboveground biomass can be realized in order to improve the total

nitrogen removal efficiency. Although wetland plants show generally a high

productivity and can incorporate considerable amounts of nitrogen into their biomass,

the uptake rates are relatively insignificant compared to the total nitrogen loading

charged into the constructed wetland (Brix, 1994a).



3.6.3.5 Sediment adsorption

Removal of nitrogen through matrix adsorption (fixation of nitrogen at soil particles)

accounts for the third pathway nitrogen can be removed from wastewater. In a

reduced state of ammonium N is stable and can be adsorbed onto active sites of the

bed matrix. However, cation exchange in the bed matrix is not a long-term sink for

NH4-N removal and NH4-N sorption in continuous flow will be equilibrium with NH4-N

sorption solution. Only in the intermittent loading of a system will show rapid

removals of NH4-N by adsorption mechanism due to depletion of NH4-N during rest

periods (Cooper, 1996). This process amounts to about another 10 % of the total

nitrogen removal rate and can be considered as insignificant (Wissing, 2002).

3.6.4 Phosphorus Removal

Phosphorus in wastewater occurs mostly in the form of phosphates and organic

phosphorus. The main mechanisms for phosphorus removal in subsurface flow

systems are chemical and physical adsorption, precipitation in the soil matrix and

plant uptake. The adsorption and retention of phosphorus in wetland soils depends

primarily on the soil type and chemical composition, and further, surrounding

conditions such as pH value, redox potential (Vymazal et al.1998). In acid soils,

inorganic P is adsorbed on hydrous oxides of Fe and Al and may precipitate as

insoluble Fe phosphates and Al phosphates. Precipitation as Ca-P is the dominant

transformation at pH greater than 7.0 (Cooper, 1996).

Soil with high amounts of clay has a large capacity to bind P than non-cohesive,

coarser-textured soils (gravel beds), but the permeability is low. Hence there have

been hydraulic problems in constructed wetlands. The P removal can be improved

using a filter medium that has a large capacity to bind P, like gravel with high

amounts of calcium or iron.

Like nitrogen, phosphorus is taken up through the root system and transports it to the

growing tissues, particularly at the beginning of the growing season (in temperate

regions during the early spring). The uptake capacity of emergent macrophytes is

lower as compared to nitrogen and phosphorus removal by plant uptake is roughly

50-100 kg P ha-1yr-1(Brix, 1994a). However, the wetland vegetation acts only as a



temporary storage, thus, phosphorus removal through plants is limited to seasonal

uptake during the vegetation period. Phosphorus contents for plants such as reeds

ranges from 0.9 to 1.35 mg/g (dry weight) for stems, 1.0 to 1.7 for leaves, and 0.9 to

1.63 for whole shoots (Davies, 1993).Phosphorus removal by plant harvesting is also

found often less than 10% of the annual load even in lightly loaded wetlands

(Herskowitz, 1986) and Hurry et al. (1990) pointer out the uptake of phosphorus by

plant in constructed wetland is only 7 %.

3.6.5 Pathogen Removal

Bacteria and viruses are important organisms from a public point of view as well as

protozoan pathogens and helminth worms are also of particular importance in tropical

and subtropical countries. Pathogens are removed in constructed wetlands by the

suitable combination of physical, chemical and biological process (Cooper, 1996).

In the physical factor, filtration and sedimentation are major processes, which may be

involved in the reduction of pathogens in wetlands. Chemical factors include

oxidation, UV radiation, exposure to biocides excreted by some plants and

absorption to organic matter. Biological removal mechanisms include antibiosis,

predation by nematodes, protists and zooplankton, attack by lytic bacteria and

viruses and natural die-off (Cooper et al. 1996). The die-off rates of all the bacteria

and coliphage were greater in the water column than the sediment. The die-off rates

of fecal coliforms in the water and sediment were 0.256 log10 day-1 and 0.151 log10

day-1, respectively (Karim, 2004).

With the literature survey of 60 constructed wetlands around the world, the removal

efficiency of total coliforms (TC) and fecal coliforms (FC) in constructed wetlands with

emergent macrophytes is high, usually 95 to >99% while removal of fecal

streptococci is lower, usually 80–95%. Whereas TC and FC in the outflow

concentrations are usually in the range of 102 to 105 CFU/ 100 ml while for fecal

streptococci (FS) the range is between 102 and 104 CFU/ 100 ml. Bacterial removal

efficiency is a function of inflow bacteria number, therefore, the outflow numbers of

bacteria are more important (Vymazal, 2005). The removal efficiency also depends

upon the hydraulic retention time.

34 Chapter 4: Criteria for the design of subsurface flow CWs


4 Criteria for the design of subsurface flow CWs

Constructed wetlands are usually designed as a secondary treatment for removal of

suspended solids (SS) and organic matter (BOD and COD) and as a tertiary

(advanced) treatment for nutrient removal (nitrogen and phosphorus). Primary

treatment occurs normally conventionally in septic tanks having three-room digesters

or Imhoff tanks, but also in pond systems. They also remove pathogens, heavy

metals and organic contaminants.

4.1 Basic design recommendations

4.1.1 General consideration about planning /necessary conditions

The general considerations for being able to use constructed wetlands for wastewater treatment are: Retention, enhancement and interpretation of existing ecological, landscape and

cultural values, such as trees and other native vegetation and sites of archeological

significance should be considered. These are valuable assets that will be of interest

to the local community and help to create a unique sense of place. A successful

physical pre-treatment is necessary for a good performance of all constructed

wetlands. Enough space should be availability because it is a “low-rate system” with

a higher space requirement than technical systems. Construction place of CWs

should be fully receiving sunlight instead of shadow. Urbanization and population

developments have to be considered when calculating the expected wastewater flow

rate to the constructed wetland. The use of locally indigenous species in wetland

plantings ensures that plants are adapted to local environmental conditions and that

the character of the wetland is „in keeping‟ with the surrounding landscape

The substrate used should not contain loam, silt or other fine material, nor should it

consist of material with sharp edges. Uniform distribution of the wastewater in the

inlet area and surface area. A sufficient hydraulic capacity of the beds has to be

proven by application of Darcy´s law. The surface of the beds should be flat to omit

unequal distribution or surface run off so that short circuits can be avoided. Basic

design of CWs has to take into account suspended solids and organic load. CWs

beds have to be designed considering nitrification and denitrification using oxygen

consumption, soil aeration, and availability of carbon source as additional criteria.



4.1.2 Design life

The exact design life of constructed wetlands cannot be calculated but only be

expected to have at least 30-40 years. This is one of assumption based on different

literature study. The design life will be long till CWs fulfill the objective of treatment.

There are no theoretical reasons which would indicate that constructed wetlands

would stop working after a certain length of time (at least for removal of organic

matter, nitrogen and pathogens).

The design life is determined by the design life of major components involved in

constructed wetland such as influent pump, plastic pipes, plastic lining, gravel and

sand. The pumps and feeding pipes can easily be replaced if necessary. The gravel

and sand will never need replacement. The exact design life of the plastic lining is

also unknown and the condition of the plastic lining can also not be verified in an

operational constructed wetland. If a constructed wetland ever has to be abandoned,

it is easy to use the space of the former constructed wetland for other purposes, or to

just let the plants grow wild.

4.1.3 Design parameters

There are several design parameters or approaches for subsurface flow CWs which

are used at different points in the design calculations, depending on the type of

wastewater and climate:

Average flow rate of wastewater (m3/s)

Surface area per person equivalent (in m²/p.e.)

Organic loading per surface area (in g BOD or gCOD/(m² d))

Hydraulic load (in mm/d or m3/(m2·d))

Oxygen consumption and input.

Detention time (day)

Hydraulic gradient (m/m or %)

Base slope (m/m or %)



4.2 Design principles of subsurface flow CWs

The focus of this chapter is the general principles for horizontal flow (HF) and vertical

flow (VF) constructed wetlands, which are both subsurface flow type constructed

wetlands. The filter bed is based on sand and plant roots (the gravel in the bed does

not have a filtering function, but just covers the drainage pipe and avoids puddles on

the surface layer). Detailed design of a subsurface flow CWs are described below

detail as per the literature information achieved.

4.2.1 Horizontal flow (HF) CWs

In the beginning HF CWs had some problems with surface run-off and therefore often

poor treatment results, but nowadays well-designed HF CWs are widely accepted as

a robust and low maintenance treatment system. HF CWs are an interesting option

especially in locations without energy supply and low hydraulic gradient.

Kickuth has first proposed the equation, which has been widely used for the sizing of

HSF system for the domestic treatment.

Ah = Qd (ln Co – ln Ct) / KBOD where, KBOD = KT d n …... (3) KT = K 20(θ

R) (T-20) …. (4)

t = V.n / Qd = LW d n / Qd = Ah d n/ Qd …(5) HLR = 100 Qd / Ah … (6)

Where Ah = treatment area of the wetland (m2

), Ct = outlet effluent pollutant

concentration (mg/l), Co = influent pollutant concentration (mg/l), KBOD = rate constant

(m/d) , K20= rate constant at reference temperature 20o

C (day-1

), KT

= Rate constant

at temperature dependent (day-1

), n = porosity (percent, expressed as decimal

fraction), Qd = average daily flow rate through the wetland (m3

/day), t = hydraulic

residence time (day-1), T = operational temperature (

o

C), V = volume of wetland

available for water flow (m3

), W = width of the wetland (m), L = length of wetlands

beds, d = depth of the wetland (m), θR

= temperature coefficient for rate constant.



Table 4.1 Shows the parameters for the design of the two types of constructed

wetlands (FSW & SSFW) based on the Reed et al. (1995) equation.

Table 4.1: Temperature coefficient for rate constant in design equations (Source: Design manual of waste stabilization pond and constructed wetlands, S. Kayombo)

Similarly, dimension of beds are derived from Darcy‟s Law. Cross section is of beds

can be calculated by the equation (Reed et al. 1998, Cooper et al. 1996) as:

Ac = Qs / Kf (dH/ds) ... (7)

W = Ac / d …. (8)

Where Ac is the cross-sectional area of wetland bed (d*W) perpendicular to the flow

direction (m2), d is the depth (m), Kf is the hydraulic conductivity of the medium

(m3/m2.day), and dH/ds is the slope of the bed (m/m).

The most important criteria and recommendations developed for HSF constructed

wetlands are summarized as follows (Cooper et al. 1996, Vymazal et al 1998, Kadlec

et al., 2009, ATV 1997):

Specific surface area for secondary treatment is about 5 m2 PE-1 and for

tertiary treatment is 1 m2 PE-1

Organic loading should be less than 150 kg BOD5 ha-1 d-1 (usually

recommended 80 kg BOD5 ha-1 d-1)

While the top surface of the filter is kept horizontal to prevent erosion, the bed



bottom slope should be 0.5 - 1%, whereas in most cases 1% is used from inlet

to outlet to allow for easy drainage.

The depth of filter beds of HSSF CWs is normally around 0.6 – 0.8 m (allow an

additional 15 cm freeboard for water accumulation).

The hydraulic loading should be 40 mm/d for secondary treatment condition

and 200 mm/d for tertiary treatment.

Detention time in wetland should be more than 5 days.

Hydraulic conductivity of media 10-3 – 3x10-3 m/s (86 -260 m/d).

Media used in Bed are especially washed gravel, crushed stones (3-6 mm)

Media porosity should be 30 – 45 %.

In most of system, plastic liner or membrane such as HDPE or LDPE has

been used with thickness 0.5 – 1.0mm.

Hydraulic gradient should maintain 2- 5 %.

Minimum area of each the reed bed of 20 m2.

4.2.2 Vertical flow (VF) CWs

VF CWs are more suitable than HF CWs, when there is a space constraint as they

have higher treatment efficiency and therefore need less space. Kadlec and Knight

(1996) developed a first-order decay, plug flow model for all pollutants, including

BOD, TSS, total phosphorous (TP), total nitrogen (TN), ammonia nitrogen (NH4-N),

oxidized nitrogen (NO3-N, NO2-N ), and faecal coliform (FC). Their model is based on

areal rate constants instead of temperature rate constant. The Kadlec and Knight

model may be less sensitive to different climatic conditions:

…. (9)

Where Q = average flow rate through the wetland (m3/day), = treatment area of

the wetland (m2), Ce = target effluent concentration (mg/l), Ci = target influent

concentration (mg/l), C* = background pollutant concentration (mg/l), k = first order

aerial rate constant (m/d).

K-values especially depend on different the parameter of the environmental and

operation circumstances. Table 4.2 gives the first order areal rate constant, which

has been deduced from measurements of practically operated plants:



Parameter Areal rate constant (k)

m/yr m/d

BOD 20 - 60 0.055 – 0.16

COD 10 – 40 0.027 – 0.11

NH4-N 10 – 40 0.027 – 0.11

TN 12 – 20 0.033 – 0.055

TP 1 – 2 0.0027 – 0.033

FC 70 – 95 0.19 – 0.26

Table 4.2: Values of areal rate constant (Vymazal et al. 1998)

In VSF CWs, wastewater is intermittently pumped onto the surface and then drains

vertically down through the filter layer towards a drainage system at the bottom. The

drainage pipes are covered with gravel. The treatment process is characterized by

intermittent short-term loading intervals (4 to 6 doses per day) and long resting

periods during which the wastewater percolates through the unsaturated substrate,

and the surface dries out. The intermittent batch loading enhances the oxygen

transfer and leads to high aerobic degradation activities. VF CWs therefore always

need pumps or at least siphon pulse loading.

Some of basic design criteria and recommendations for VF CWs are summarized for

better efficiency achievement (Cooper et al. 1996, Vymazal et al 1998, Kadlec et al.,

2009, ATV et al., 1997):

The specific surface area is required 1m²/p.e. for BOD removal only and 2 m²/p.e.

for additional nitrification is needed and bed depth is used on the range of 0.5 -0.8

m. Some VF CWs was designed in Austria, with specific area 4 -5 m²/p.e and

main layer bed depth was 0.6-0.8 m.

The organic loading per surface area should be limited to 20 gCOD/(m²·d) in

colder climates and in warm climates with about 60-70 gCOD/(m²·d)

(corresponding to approximately 30-35 g BOD/(m²·d), with 90% nitrification .

Bottom slope of 0.5 - 1% in direction to the outlet.

Nowadays mostly sand and gravel are used for media with permeability of 10-3 –

10-4 m/s.

The depth of the sand filter beds should be at least 50 cm, with an additional 20

cm of gravel at the base (to cover the drainage pipes), 15 cm gravel on the top of

the bed and 15 cm freeboard for water accumulation. The gravel on top is there to

prevent free water accumulation on the surface, and could in actual fact be



omitted in case of constructed wetlands without free access for members of the

public.

The hydraulic loading for VF CWs in colder climate should not exceed 100 - 120

mm/d and in summer hydraulic rates up to 200 mm/d of pre-treated wastewater

could be applied without negative influence.

Minimum area of each reed bed size 10 m2.

41 Chapter 5: Substrate in Subsurface flow CWs


5 Substrate in Subsurface flow CWs

Wetland substrates support the wetland vegetation, provide suitable sites for

biochemical and chemical transformations, and provide sites for storage of removed

pollutants. The different filter media such as soil, sand, gravel, organic materials

which are used in constructed wetlands are known as substrates.

Table 5.1: typical kf values (Cooper et al. 1996)

The provision of a suitably permeable substrate in relation to the hydraulic and

organic loading is the most critical design parameter of subsurface flow systems.

Most treatment problems occur when the permeability is not adequately designed for

the applied load. Some of the horizontal flow CWs which were built from 1985 to

1989 in Europe, used soil as a substrate, where it was assumed that the hydraulic

conductivity would increase. Some of these suffered from surface-flow and this led to

channeling and scouring of the surface which results in areas of the bed being

starved of water and this in turn led to poor reed growth and poor treatment. Similar

problem occurred with plants built in Germany and Denmark (Cooper, 1996).

As a result of these problems, WRc decided in 1986/87 to recommend the use of

gravels in UK system at Little Stretton (Seven Trent Water) and Gravesend (Southern

Water) especially washed gravel of different size like 3-6 mm, 5-10mm and 6-12 mm.

(Cooper, 1996). In Germany with VF CWs with reed beds was built with soil of

hydraulic conductivity of 3x 10-3 m/s and latter it was advised in the European

Guidelines of 1990 (Cooper, 1990) „‟ not to assume a hydraulic conductivity greater

than that of the original media.‟‟ Conventional wisdom regarding intermittent sand

filters suggested clean washed sand with an effective size of 0.2-0.5mm with less

than 1 % by weight passing through a 0.1mm sieve (Reed et al., 1988). At oaklands

Soil Texture kf (m/s)

Fine to course gravel 10-3 - 1

Fine to course sand 10-7 – 10-2

Karst limestone 10-4 – 10-2

Sandstone 10-8 – 10-4

Silt loess 10-9 – 10-5

Glacial till 10-12 – 10-4

Unweathered marine clay 10-12 – 10-9

Shale 10-13 – 10-9

42 Chapter 5: Substrate in Subsurface flow CWs


Park in UK, VF beds are filled with different layer by graded gravel usually with a top

layer of washed sharp sand as given in table 5.2.

Substrate Depth Size

Top layer

8 cm Sharp sand

15 cm 6 mm washed pea -gravel

10 cm 12 mm round washed gravel

Bottom layer 15 cm 30 – 60 mm round washed gravel

Table 5.2: Graded gravel used in different layer as recommended by Burka at Oaklands Park. (Vymazal et al., 1998)

In additional, large stones were placed around the drainage pipe, which formed the

under drain system. In Austria, substrate profile of VF system was divided into two

major substrate as top and bottom layer. Top layer consists of protection layer of

depth 20 cm filled with 8/16 mm grain size, main layer of depth 60 cm filled with 0/4

and 4/8 mm mixing in 1:1 ration and transitional layer of depth 10 cm filled with 4/8

mm grain size. In the bottom, drainage layer of depth 20 cm filled with 16/32 mm

gravel (Vymazal, 1998).

Similarly in the case of Phytofilt system, beds contains four layer in which top layer of

depth 0.3 m filled with soil ,upper filter layer of depth 0.4 m filled with sand/gravel

having conductivity (kf) value 5.10-3 – 5.10-2 m/s , intermediate filter layer of depth 0.7

m filled with sand /gravel with kf value 5.10-6 – 5.10-5 m/s and lower layer filled up to

0.4 m with kf value 5.10-6 – 5.10-5 m/s. Generally, sand layer needs a thickness of 40

to 80 cm, which has the actual filter bed function of the subsurface flow CWs with a

hydraulic capacity (kf-value) of about 10-4 to 10-3 m/s. The drainage pipes at the base

are covered with gravel and top gravel layer does not contribute to the filtering

process. The recommended grain size distribution for the substrate is like d10 > 0.3

mm or d60/d10 < 4 (Vymazal, 1998). The substrate should not contain loam, silt nor

clay material because of low kf values and hence are not recommended.

Fig 5.1: Example of filter material used in CWs for municipal wastewater treatment in Brazil and Peru (photo by C. Platzer, H.Hoffmann, and source: gtz, 2010).

A B C

43 Chapter 6: Macrophytes used in Constructed Wetlands


6 Macrophytes used in the Constructed wetlands

Macrophytic plants provide much of the visible structured of wetland treatment

system. These macrophytes are very important for physical, chemical and microbial

process in the CWs. A basic understanding of the growth requirement and

characteristics of these wetland plants is essential for successful treatment wetlands

design and operation.

Macrophytes have several properties in relation to the treatment process and most

important effects of the macrophytes are the physical effects that plant tissues

prevent the formation of erosion channel, prevent clogging of bed medium, provide

the surface area for attached microorganisms (Brix, 1994a). Similarly plant uptake of

nutrients is only of quantitative importance in low loaded system which is described

detail in chapter 3 (section 3.6) and more focus is given in this chapter about the

transfer of oxygen to the rhizosphere by leakage from root and type of macrophytes

used in CWs. Moreover, macrophytes have additional site specific values such as

providing a suitable habit for wildlife and giving a system an aesthetically

appearance.

6.1 Type of macrophytes used in CWs

A wide range of macrophytic plants occur naturally in wetlands environment and have

been recognized to have the ability to treat wastewater. The United State Fish and

Wildlife Service has found more than 6700 plant species on their list of obligate and

facultative wetland plant species in the United States (Kadlec, 2009). Four groups of

aquatic macrophytes can be used distinguished on a basis of morphology and

physiology (Wetzel, 2001).

Emergent macrophytes: These are the dominating life form in wetlands and

marsches and grow on water-saturated or submersed soils within a water table

ranges from 50 cm below the soil surface to water depth approximately 150 cm or

more. They produce aerial stems, leaves, roots and rhizome-system. These

emergent macrophytes are like Phragmites australis (Common Reed),

Schoenoplectus (Scirpus) lacustris, Typha latifolia (Cattails),



Fig 6.1: Emergent macrophytes (a) Phragmites australis (b) Schoenoplectus lacustris (c) Typha latifolia (photo –Wikipedia)

Floating - leaved macrophytes: They are rooted in submerged sediments in water

depth of approximately 0.5 to 3 m and possess either floating or slightly aerial leaves

like Nyymphaea odorata, Nuphar luteum(waterlilies), Potamogeton natans (pond

weed).

Freely floating macrophytes: They are not rooted to the substratum and they are

freely floating on in the water surface. These kinds of species are used usually to non

turbulent, protected areas (e.g. Lemna, Spirodella polyrhiza (Duckweed), Eichhornia

crassipes (water Hyacinth).

Submerged macrophytes: These species have their photosynthetic tissue entirely

submerged inside the water surface. Vascular angiosperms (e.g. Myriophyllum

spicatum, Ceratophyllum demersum) occur only to about 10 m of water depth and

nonvascular macroalgae occur to the lower limit of the photic zone (up to 200m, e.g.,

Rhodophyceae).

However, the selection of plant species are required several criteria that are suitable

for use in constructed wetlands under different conditions such as availability in

climate zone, pollutant removal capacity and tolerance ranges, plant productivity and

biomass utilizations. The plants should be selected for constructed wetlands, which

are adapted to the local climate, soil conditions, but also the surrounding plant and

animal communities. A lot of plants that occur in natural wetlands have the potential

for purification of waters as well as higher tolerance capacity. Because, constructed



wetlands receive a permanent wastewater inflow including high organic and nutrient

concentrations. All plants cannot tolerate these conditions and will not survive.

Most common macrophytes are popular and recommended for use in constructed

wetlands like Phragmites australis (common reed), Juncus effusus (soft rush) and

conglomeratus, Scirpus lacustris (common bulrush), Scirpus maritimus (alkali

bulrush), Typha angustifolia (narrow-leaved cattail), Typha domingensis (southern

cattail), Typha latifolia (broad-leaved cattail), Iris pseudacorus (yellow flag), Acorus

calamus (Sweet-flag) (Cooper et al., 1996, Vymazal et al., 1998). The emergent

plants most used in constructed wetlands which are survival, tolerance capacity are

given in table 6.1

Table 6.1: Main aquatic macrophytes used in constructed wetlands (Reed et al., 1988) (*- Temperature range for seed germination: roots and rhizomes can survive in frozen soils.)

The hidden objective of macrophytes used in constructed wetlands can be harvested

biomass and can be utilized for energy production, agricultural purposes, animal or

cattle feed, livestock forage, thatching material, diverse handicrafts. Phragmites

australis is one of the most productive, widespread and variable wetland species in

the world. Due to its climate tolerance and rapid growth, it is the predominant species

used in the constructed wetlands not only in Europe but also in tropical and sub-

tropical region (Cooper, 1996). Table 6.2 gives the summary of the typical

characteristics of the main aquatic macrophytes used in CWs.

Emergent species

Temperature Max. Salinity

tolerance mg/l

Optimum pH

Desirable Survival*

Typha 10 - 30 12 – 24 30,000 4.0 – 10.0

Phragmites 12 – 33 10 – 30 45,000 2.0 – 8.0

Juncus 16 – 26 20,000 5.0 – 7.5

Schoenoplectus 16 – 27 - 20,000 4.0 – 9.0

Carex 14 – 32 - - 5.0 – 7.5



Emergent species

Growth rate

(cover 1st year)

Typical spacing

m

Typical root penetration

in gravel m

Annual

yield (mt /ha) Dry

weight

Habitat value

Typha Rapid dense

0.6 0.3 – 0.4 30 Good nesting cover and food source for

wetlands birds

Phragmites Very rapid

dense 0.6 >0.6 40

Low food values but some values as nesting cover

Juncus Moderate to rapid dense

0.3 – 0.6 0.6 – 0.9 20

Good food source for wetland birds and

nesting for fish when flooded.

Carex Moderate to slow dense

0.15 - < 5

Food source for numerous birds. Good

for habit enhancement.

Table 6.2: Characteristics of main aquatic macrophytes (applied from Cooper et al., 1996)

6.2 Functions of macrophytes in constructed wetlands

The macrophytes growing in constructed wetlands can contribute directly by up

taking nutrient in the treatment processes and indirectly as they support physical,

chemical and microbial processes. The most important effects are the physical effect,

where the presence of vegetation reduces the current velocity, reduces the risk of

erosion, prevent the clogging, increase the water and plant surface area. Similarly,

they provide huge surface area for attached microorganisms and suitable habitat for

wildlife and giving aesthetic appearance for the single house, hotels as well as

floating island. It is well documented that aquatic macrophytes release oxygen from

roots into the rhizosphere. This chapter focuses only about the oxygen release by

macrophytes.

Oxygen release There are many studies which show the ability of some aquatic macrophytes to pass

a supply of oxygen into the rhizosphere through a special helophyte tissue in the

plant stems and roots from the air. The plants, with their roots and rhizomes, provide

the suitable environment for microorganisms‟ growth. Oxygen release rates from



roots depend on the internal oxygen concentration, the oxygen demand of the

surrounding medium and permeability of the root wall (Vymazal, 1998).

The ability of macrophytes to transport oxygen and thereby to support of aerobic

microorganism in the rhizosphere is one of the key mechanisms for efficient BOD and

nitrogen removal. The flux of oxygen transferred into the rooting system has been

tentatively quoted to be 4-5 gO2/m2d and later prediction by Armstrong et al., (1990)

based on oxygen release from single adventitious roots plus laterals in a streaming

oxygen –free system, measured polar graphically, yielded 5-12 g O2/m2d; this work

has based on 150 shoots per m2, 10 roots per shoot and a rhizome oxygen

concentration of 17 %. Total flux of gaseous oxygen into the bed substrate of 5.9 g

O2/m2d of which 2.08 gO2/m

2d was through the hollow culms of standing dead culms

of Phragmites australis has been measured Roots and rhizomes used 2.06 g O2/m2d

for the respiration purpose and measured to almost perfectly balance the oxygen

influx through the culms leaving only 0.02 g O2/m2d to be released to the surrounding

matrix. (Brix and Schierup et al., 1990).

Fig 6.2: Oxygen mass balance for Phragmites australis in the constructed reed beds at Kalϕ, April 1988 (g O2/m

2d) (Photo taken: Brix and Schierup, Cooper, Ingenieurbüro Blumberg)



Individual experiments has been conducted in the laboratory to detect the oxygen

release from roots and rhizomes of Phragmites australis, Typha latifolia, Glyceria

maxima and Iris pseudacorus by using oxygen microelectrodes ( Fruergaard ,1987).

With the help of microelectrode, oxygen concentration within the internal gas-space

of roots and rhizomes was measured by microelectrode penetrating into the root and

rhizome wall. Generally, no release of oxygen from the surface of rhizomes and old

roots could be detected even though the internal oxygen concentration was relatively

high as shown in table 6.3. Only young white roots without laterals released oxygen

to the surrounding medium and it was found that the oxygen release rates were

highest in the sub apical region of the roots and decreased with distance from the

root – apex (Brix and Schierup, 1990). The root –apex itself actually consumed

oxygen from the surrounding medium. However form the experiments of four species,

Phragmites showed the highest oxygen release rate and Typha the lowest. At lower

experiment temperatures the release rates would probably have been higher

because of lower tissue respiration.

Table 6.3: Oxygen release from individual roots of Phragmites, Typha latifolia, Glyceria maxima and Iris pseudacorus measured by an oxygen microelectrode (from Fruergaard, 1987)

Species O2 –release

(10 - 8 g cm-2min-1) Internal O2-con

(vol %)

Phragmites australis

Root apex < 0 Not analysed

2mm from apex 6.3 Not analysed

5mm from apex 4.7 Not analysed

9 mm from apex 4.2 Not analysed

60 mm from apex < 0 Not analysed

Rhizome 0 12.3

Typha latifolia

10 mm from apex >0 10.8


65 mm from apex 0 Not analysed

Glyceria maxima



40 mm from apex 2.3 4.7

Iris pseudacorus



70 mm from apex >0 5.8

150 mm from apex 0.62 8.5

49 Chapter 7: Scenario of Wastewater Treatment in Nepal


7 Scenario of Wastewater treatment in Nepal

7.1 Country background

Nepal is a small and beautiful landlocked country lies between two big neighbouring

countries like China on the north side and India on the south, east and west. It is also

known as Himalayan country with total area of 147,181 sq. km (56,827 sq mi) and

divided as per geographically into the three main regions like mountains, hills and

terai regions. Mountains cover 20%, hills fall 63% and terai covers 17% of total area

respectively. It is located between the latitudes 27°42' N and longitudes 85° 19' E

(http://en.wikipedia.org/wiki/Nepal). The altitude varies from some 60 m above sea

level in the terai to 8,848 m the Mt. Everest, which is the highest peak of the world.

Nepal has a population of 29.9 million with an average annual population growth rate

of 1.7 % and life expectancy for males and females is 59 years and 58 years

respectively.Nepal is one of the least developed country with Gross Domestic

Production (GDP) per capita is $ 438 and ranked as low human development

country, at 138 out of 169, with a Human Development Index (HDI) is 0.428 (UNDP,

HDR 2010). The population living below the national poverty line has declined from

42% (1990-1995) to 31% (2003-2004) (www.who.int).

As per the Department of Water Supply and Sewerage (DWSS) under the

Government of Nepal indicates the figure in the period of mid July 2003 to mid July

2007 that 80.4 % of the population have access to drinking water supply and 46 % in

basic sanitation.

Fig 7.1: Map of Nepal showing Mountains, Mid hill and Terai regions (http://www.worldmapfinder.com/De/Asia/Nepal)

China

India

Kathmandu valley

http://www.who.int/



In Nepal, the water resources are regarded having the potential to be the catalyst for

all round development and economic growth of the country. Nepal has a monsoon

type climate. The total rainfall varies between 1,000 to 4,000 mm with an annual

average of 1,814 mm. More than 75% rainfall occurs during four months of the

monsoon period (June - September). Summer temperatures rises more than 40 °C

in Terai and 20°C in hilly region. Similarly in winter, average maximum and minimum

temperatures in the Terai varies from a mild 23°C to a brisk 7 °C while the central

valley‟s experience a chilly 12°C maximum temperature and a minimum temperature

often falling below freezing point. (www.himalayanmart.com)

7.2 Wastewater treatment in Nepal

Wastewater without treatment from household and industry is discharged directly into

receiving the river, which creates serious water pollution problem and so exerts

immense pressure on the urban and semi urban environment. As a result, urban

sanitation has become a major challenge for municipalities and small towns in Nepal.

Wastewater treatment plants are almost non-existent in the country except for a few

in the Kathmandu Valley and outside of valley but even these are not functioning

well. The total wastewater produced in the country is estimated to be 370 million litres

per day (MLD) but installed capacity of wastewater treatment plants is only 37 MLD

fulfilling only 10% of total demand and functioning wastewater treatment plants

account for 17.5 MLD, i.e. 5% of total demand (Nyachhyon, 2006). It is estimated that

only about 12 % of urban households are connected to the sewer system

(www.wateraid.org)

Kathmandu Valley comprises of three districts, Kathmandu, Lalitpur, and Bhaktapur

have total of 150 local administrative units (Village Development Committees and

Municipalities). The Valley encloses the entire area of Bhaktapur district, 85% of

Kathmandu district and 50% of Lalitpur district covering 665 square kilometers and

more than 1.5 million people, (220,000 households) are living. Kathmandu Valley is

the most important urban concentration in Nepal (Pant and Dongol, 2009)

Although there are some waste water treatment systems in Kathmandu Valley (KV),

these are not functional and as a result waste water from the drains and sewers are

discharged directly into the Bagmati, Bishnumati, Dhobi Khola and other small rivers

http://www.himalayanmart.com/



of KV without treatment. The city is becoming an example of a terribly polluted city

with open sewers and unhygienic disposal of waste leading to the pollution of all the

existing rivers in Kathmandu. (Pant and Dongol, 2009)

7.2.1 Wastewater treatment in Kathmandu Valley

Arata et al., (2003) pointed that only 38 % of the population is connected with the

sewer system and collected 47 MLD of total domestic wastewater (approximately 124

MLD) in Kathmandu valley. According to ADB (2000), there are 1340 industries in

and around the Kathmandu Valley, which generate 0.8 MLD of wastewater. Similarly,

56.7 MLD of wastewater is discharged into the different river systems in the valley,

from which 82% of total volume is of domestic origin.

Within the periods of 1975 -1996, there were five municipal wastewater treatments

plant (WWTP) namely Hanumanghat, Sallaghari, Guheshwori, Dhobighat and Kodku

constructed in the Kathmandu valley for the treatment of wastewater with total design

capacity 34.4 MLD.

Fig 7.2: Map of Wastewater Treatment Plants in Kathmandu Valley (Hillary Green, 2003)

Hanumanghat WTP was constructed in 1975 for 0.5 MLD wastewater treatments

coming from some parts of Bhaktapur city. With the reference of ADB (2000) and

BASP (2002), this plant was under the partial function after the construction but it

was found this plant full of sludge and not working at all, and the land being used as



a crop field (Poh et al., 2003). Sallaghari WTP was designed and constructed in

1983 to treat about 1.0 MLD form north and south parts of Bhaktapur with the support

of the German Government. The system was originally designed as an aerated

lagoon but due to operators cost high cause of electricity cost, aeration system was

closed. Since then, the plant has been partially operating as a non-aerated lagoon

system (Asian Development Bank, 2000).

Dhobighat WTP was designed in 1982 for an average flow of 15.4 MLD wastewater

collected from the northeast part of Kathmandu; however it is not functioning due to

the breakdown of the pump station and truncated sewer line along several sectors in

the city. Lack of proper maintenance, stabilization ponds are now serving as a

grazing for cattle and football field for the local people (Arata, 2003).

Kodku WTP was designed and constructed as stabilization pond in 1982 to treat

wastewater coming from Patan (Lalitpur). This plant consisted of primary anaerobic

ponds followed by secondary facultative ponds with several surface mixers and a

system of mixed, shallow tertiary aerobic ponds (Shrestha, 1999). According to the

ADB (2000), the Kodku system is partially operating, as the chlorinator had never

worked since its installation. According to Tetsuji Arata , MIT Nepal Project team

member, , observed in January 2003 that effluent quality was not satisfactory and

even smelled like that of sewer water when discharged into the Bagmati River

(Green, Poh and Richards, 2003).

Treatment plant

Year of establishment

Capacity (mld)

Type of plant

Area coverage Existing situation

Hanumanghat 1975 0.5 Aerated lagoon

Part of Bhaktapur city

Operating inefficient as non-aerated lagoon

Sallaghari 1983 1.0 Aerated lagoon

North and south part of Bhaktapur city

Operating inefficient as non-aerated lagoon and receives wastewater only from southern part of the city

Guhyeswari 1996 16.4 Oxidation ditch

Northeast ern part of Kathmandu (upper Bagmati zone)

In operation

Dhobighat 1982 15.4 Stabilization pond

Wastewater from the northeast part of kathmandu

Out of oder

Kodku 1982 1.1 Stabilization pond

Part of Patan city

Operating inefficiently

Table 7.1: Condition of wastewater treatment plants in Kathmandu valley (Source: http://www.undp.org.np/publication/html/mdg_NAN/Chapter_8.pdf)

http://www.undp.org.np/publication/html/mdg_NAN/Chapter_8.pdf



Fig 7.3: Guheshwori Wastewater Treatment Plant. (Photo from Hillary Green, 2003)

Guheshwori WTP was designed and constructed on the bank of Bagmati River in

1996 for the treatment capacity of 16.4 MLD in the upper Bagmati zone especially

treating the wastewater coming from the north part of Kathmandu valley. The main

objective of this project is to keep Bagmati River clean by preventing the direct

discharge of untreated liquid wastes into the river. It is the only fully operating

treatment plant in the Kathmandu Valley than others mentioned four plants above.

The treatment plant adopts the most advanced technology of wastewater treatment

and the process is extended aeration consisting of a deep oxidation ditch of carrousel

type (WHO, 2008). The plant at Guheshwori has two carrousel type oxidation ditches

each with three aerators and 60 HP are required to drive the aerators Operation and

maintenance cost of plant at Guheshwori is estimated 12.5 million NRs/year (US $

167,000 /year) (Richards, 2003).

Although this plant is partially functioning and the cost of operation is very high so

that the sustainability is questionable (Water aid Nepal). It is the possibility of

treatment plant may be halt in the near future, due to the lack of financial support

from the Nepal Government. It is a hotly debated question among wastewater

professionals whether conventional activated sludge wastewater treatment plants are

appropriate treatment technologies suitable for developing countries like Nepal

(Harleman, 2001). These treatment plants are based on simple lagoon systems

except Guheshwori, where wastewater is treated through natural processes such as

sedimentation and biological degradation in a series of large lagoons. Although these

plants are technically very simple with no mechanized parts but they are still not

functioning well because of poor operation and maintenance and mismanagement



7.3 Constructed Wetlands as an alternative technology in Nepal

Most of the centrally collected wastewater treatment plants in Nepal are not

functioning due to high cost of operation and maintenance and lack off trained human

resources. To mitigate the financial problem and minimize of water pollution, low-cost

natural treatment options like Constructed Wetlands (CWs) and the related Reed Bed

Treatment System (RBT) have been introduced in Nepal since 1997.

Environment and Public Health Organization (ENPHO), a national non-governmental

organization, has introduced constructed wetland (CW) as a low cost, simple,

effective and an appropriate alternative technology for wastewater treatment in

Nepal. ENPHO designed and constructed first wetland system with a two staged sub-

surface flow for Dhulikhel Hospital in 1997 to treat domestic wastewater (Shrestha,

1999). Due to the success of the CW system in Dhulikhel Hospital, since then, the

interest of people has been growing in this technology and more than a dozen

constructed wetlands have been established for various applications such as the

treatment of hospital wastewater, grey water, septage, landfill leachate, institutional,

universities and municipal wastewater. Since 1997 to 2004, there are 12 sub-surface

flow constructed wetland systems in operation for treatment of grey water,

wastewater and fecal sludge as shown in Table 7.2

Table 7.2: List of Constructed Wetlands in Nepal (Source: R. R. Shrestha and P. Shrestha)



Recently, ENPHO has established the first community-based wastewater treatment

system in Madhyapur Thimi Municipality of Nepal using this technology with support

from ADB, UNHABITAT, Water Aid Nepal, and Thimi Municipality. Similarly, the

Urban Environment Improvement Project (UEIP) which is being implemented in eight

urban centres with the assistance of ADB is now in the process of constructing 18

more plants in these towns (Water Aid Nepal, www.wateraid.org)

Location TSS

Removal Rate (%)

BOD5 Removal Rate (%)

COD Removal Rate (%)

NH4 Removal Rate (%)

Dhulikhel Hospital

97 97 94 68

Single house grey water

98 98 94 91

Malpi School 97 99 97 97

Sunga Commnunity

98 97 96 85

SKM Hospital 97 98 94 96

Kathmandu University

87 97 93 99

ENPHO 87 95 88 40

Kapan Monastry

99 99 98 96

Table 7.3: Efficiency of CWs (UN-HABITAT, 2008 and ENPHO, 2004)

In general, the performance of the CWs has been excellent as shown in table 7.3.

After regular monitoring of the systems and analysis of wastewater sample shows

high pollutant removal efficiency achieving more than 90% removal of TSS, BOD and

COD. Plant species, which are locally available called Phragmites Karka, is used in

this process.

In Dhulikhel hospital, the designed system does not need any electric energy as the

wastewater is fed hydro-mechanically into the beds. The total cost of the system

including the sewer lines was US$ 27,000 in 1997, while the cost of the constructed

wetland alone was at US$ 16,400 (Poh, 2003). For the single house, the system

required an investment of only about Rs. 36,000 (US$ 520) and the family is able to

save about 400 liters of water per day (Water Aid Nepal). In SKM hospital , the

system also does not need any electric energy as the wastewater is feed hydro-

mechanically into the beds and total costs of the system including the sewer lines

were US$ 27000 in 2000 (Poh, 2003). In Sunga community, the total cost of the

http://www.wateraid.org/



treatment plant was Rs. 2.5 million in which total construction cost of the wetland

amounted to NRs. 1,800,000 (US$ 26,000) at NRs. 2,900 (US$ 40) per m2 of the

wetland and average O&M cost of the wetland is about NRs. 20,000 (US$ 290) per

year. So, Constructed wetlands (CWs) are a biological wastewater treatment

technology designed to mimic processes found in natural wetland ecosystems and

required less land, less expensive for construction, operation & maintenance as

compare to conventional expensive technology. Hence, they can be considered as

effective, economic and environmentally friendly and sustainable systems for

wastewater treatment.

7.4 Fact finding of CWs in Dhulikhel Hospital and Sunga Community

Dhulikhel Hospital is a community-based hospital located in Dhulikhel Municipality

and approximately 30 kilometer far from Kathmandu. Hospital location is 1,650

meters above sea level and has a sub-tropical climate with an annual rainfall of about

1,456 mm (HMG, 1996).Constructed wetlands is designed and constructed by

ENPHO at Dhulikhel Hospital in 1997 as a first plant in Nepal under the technical

support from a Nepali PhD scholar from University of Natural Resource and Applied

Life Sciences, Vienna, Austria (Shrestha, 1999).

The treatment system was originally designed to treat 10 m3 of wastewater per day,

but it is currently treating about 40 m3 per day as the capacity of the hospital has

increased significantly since 2000. The constructed wetland in Dhulikhel Hospital is a

two-staged subsurface flow system, which consists of a horizontal flow bed surface

area of 140 m2, followed by vertical flow bed of area of 120 m2. Three chambered

sedimentation tank of 16 m3 capacity has been constructed for pre-treatment.

Fig 7.4: Site Plan of the Constructed Wetland System at Dhulikhel Hospital (UN-HABITAT, 2008). (Photo by Dr. Roshan Raj Shrestha)

Vertical Flow Bed

Horizontal Flow Bed



The depth of the horizontal bed is found varies from 0.65 to 0.7 meters and filled with

1-4 mm crushed gravel with conductivity (Kf) of 0.03 m/s having pore volume of 39%.

The inlet and outlet zone was filled with 10-20 mm gravel and inlet pipe of 100 mm

diameter PVC pipe with 20 mm diameter hole at a distance of 2 m connected with a

feeding tank (0.9 m3 per feed). The outlet pipe of pipe 100 mm dia. perforated pipe

with 6 mm diameter perforations. Similarly, the depth of the vertical bed is 1.05 m

(0.75m sand, 0.10 m with 5-8 mm gravel, 0.15m with 10-20 mm gravel and 0.05 m

with sand) and filled with clean sand as main layer with conductivity (Kf) of 0.001 m/s

and a pore volume of 30%. The main inlet pipe of 100 mm diameter connected with 6

branches of 50 mm diameter pipe with 8 mm and 6 mm holes at a distance of 1 m.

Both of the beds were planted with Phragmites Karka, a local variety of reeds that

was easily available. The system does not need any electric energy as the

wastewater is fed hydro-mechanically into the beds (UN-HABITAT, 2008). The total

cost of the system including the sewer lines was US$ 27,000 in 1997, while the cost

of the constructed wetland alone was at US$ 16,400.

Initial tests done in 1997 showed that the plant was able to remove 98% of total

suspended solids (TSS), 98% of BOD5, 96% of COD and 99.9% of total coli forms. It

also removed 80% of the ammonia nitrogen and 54% of phosphate. Follow-up

monitoring in 2003 showed that the plant was still removing 96% of BOD5 and 93%

of TSS and COD (Water Aid Nepal Bulletin).

Month Q

m3/day TSS

mg/l NH4 mg/l

PO4-P mg/l

BOD5 mg/l

COD mg/l

E. Coli. Col /ml

IN OUT IN OUT IN OUT IN OUT IN OUT IN OUT

No of reading

13 12 12 11 11 12 12 13 13 13 13 11 11

Minimum 7 26 0.3 17 0.04 2.2 0.6 31 0 63 4 39000 3

Maximum 40 230 6.7 52 5.4 26 18 210 10 1048 40 8E+08 987

Average 20 83 2.3 33 1.6 8 4 110 3 325 20 1E+08 148

Median 11 41 1.8 19 0.04 2 0.7 41 4 79 18 1E+05 38

Std. Deviation

11 58 1.9 12 2.2 7 5.8 63 3 273 14 2E+08 307

Elimination (%)

97 95 47 97 94 99.9

Table 7.4: Summary statistics of inlet and Outlet concentration and mean efficiency Dhulikhel Hospital Constructed Wetland System (1997 to 2000) (Source: Poh, 2003)

The Hospital as well as the local people is very satisfied with the performance of the

treatment system and the system has become a showpiece for the Hospital. Many



researchers, students, journalists and other people regularly visit the Hospital to see

the constructed wetland in action and learn from it. The Hospital is now in the

process of expanding the system.

Sunga community

Madhyapur Thimi municipality, one of Nepal‟s oldest settlements living Newar

community, is a small municipality located in Kathmandu Valley. It has a population

of 47,751 in 2001 and covers a total area of 11.47 sq. km with 20% residential area,

70% agricultural land and around 10% vacant land. As the town was designated as a

municipality only in 1996, major infrastructure developments like the sewerage

system, water supply and road network are all still in the planning phase. Due to lack

of funds, still wastewater treatment through oxidation ponds was not completed;

however a part of the municipality was connected to sewers in the 1990s. From the

social-economic analysis more than 50% of the populations are still lacking proper

sanitation facilities. Sanitation improvement is one of the most urgent issues in the

municipality that should to be addressed, so the local people of Madhyapur Thimi

and the municipality showed an interest in managing the wastewater through

innovative technology.

Fig 7.5: Solid Waste dumping site before and after the construction of CWs at Sunga wastewater treatment plant, Thimi (Photo by: UN-HABITAT and Water Aid/ Marco Betti)

The people of Sunga village are interested to implement the innovative urban

wastewater treatment technology to improve sanitation, improve water quality of

rivers, and provide alternate water uses other than for drinking purposes and to link

with livelihood opportunities for poor communities. At the request of community



people and the Municipality, in 2005, ENPHO, with support from ADB, UN-HABITAT

and Water Aid Nepal, initiated the construction of a community-based wastewater

treatment plant. Sunga constructed wetlands are also known as the first community-

based wastewater treatment plant in Nepal. In addition to the funding agencies,

Madhyapur Thimi municipality provided the required land for construction along with

the financial assistance for operation and maintenance of the wastewater treatment

plant. Under this initiative, ENPHO joined hands with the local people of Sunga and

built CWs on steep terrain, which was previously a waste dumping site near to a

school at Sunga. This treatment plants has come in operation since October, 2005.

Now the site has a beautiful garden and a model treatment plant that provides a

learning ground for students as well as professionals.

The constructed wetland at Sunga consists of a coarse screen and a grit chamber for

preliminary treatment, an anaerobic baffle reactor (ABR) with capacity of 42 m3 for

primary treatment, Horizontal Flow (HF) followed by Vertical Flow (VF) reed beds for

secondary treatment and two sludge drying beds for treating sludge of area 70 m2.

The total area of the constructed wetland is 375 m2 in which HF and VF beds covers

150 m2 by each (UN-HABITAT, 2008). The treatment plant has a capacity to treat

wastewater from 200 households, but it is urgently treating wastewater from 80

households. The plant receives an average daily flow of 10 m3 of very high -strength

wastewater (average BOD5 of raw wastewater is 900 mg/l).

Monitoring of the performance of the system over its first year of operation shows that

it removes organic pollutants highly efficiently (up to 98% TSS, 97% BOD5 and 96%

COD). It was also found that the ABR was very effective in removing organic

pollutants and could remove up to 74% TSS, 50% BOD5 and 18% COD (UN-

HABITAT, 2008). The effluent values show that there is a significant reduction of

BOD5, COD and TSS as compared to the raw wastewater and these values are

below the legal limits (50mg/l TSS , 50 mg/l BOD5 , 250 mg/l COD ) as specified by

the Government of Nepal for the combined wastewater treatment.

The total cost of the treatment plant was Rs. 2.5 million in which the total construction

cost of the wetland amounted to NRs. 1,800,000 (US$ 26,000) at NRs. 2,900 (US$

40) per m2 of the wetland. The average O&M cost of the wetland is about NRs.

20,000 (US$ 290) per year. As per the tripartite agreement made between ENPHO,



the management committee of Sunga WWTP and Madhyapur Thimi municipality, the

municipality has committed Rs 50,000 annually for operation and maintenance

including remuneration (NRs. 3000/month) and equipment for the caretaker. The

average annual O & M cost of the wetland at present is about NRs. 20,000 (US$ 290)

per year, which is less than the amount allocated by the municipality. It has been

agreed that the surplus amount will be transferred to the operation and maintenance

reserve fund for future maintenance of the plant.

(Source: UN-HABITAT, 2008)

By visually observing CWs operation and treatment efficiency, other surrounding

communities of Sunga village are also interested to implement such kind of treatment

plant. During the handover ceremony on 1st September 2006, many other local

communities requested ENPHO to construct additional similar treatment plants in

other parts of the Municipality. These opinions and demands from the local

community clearly indicate that CWs has been well accepted.

The Sunga constructed wetland is a clear demonstration of the effectiveness of the

community based wastewater management project and its contribution. Due to easy

operation and maintenance, this project has many advantages such as treated

effluent from wastewater can be used as multiple purposes like for irrigation,

gardening, toilet flushing, and washing vehicle. In addition, the project has also

become successful in enhancing the river quality and making the treatment plant

healthier and aesthetically attractive with an enhanced environment thus ensuring

benefits to the community dwellers. This has inspired people to adopt this type of

technology that can be managed by the community itself for the solution of currently

mismanaged wastewater in the city.

Table 7.5: Concentration of pollutants at Sunga (August,2006)

Parameter Units RAW ABR HFCW VFCW

TSS mg/l 796 204 28 16

BOD5 mg/l 950 450 165 30

COD mg/l 1438 1188 213 50

Ammonia mg/l 145.5 408.9 214.1 21

Nitrate mg/l 4.1 36.8 32.6 56.6

Total Phosphorus mg/l 26.4 44.3 20.4 24.3

Fecal Coliform CFU/ ml 1.3E+5 1.3 E+6 1.1E+6 8.1E+3

61 Chapter 8: Case Study of Project Area


8 Case study of Project Area

8.1 Study area of Gadenstedt

8.1.1 Location

Gadenstedt is a small village lies in the Lahstedt municipality of Peine district situated

in the German Federal State Lower Saxony, south-east of Hanover. The population

of Gadenstedt is annually varying and according to present data total Gadenstedt

population has 2434 (see fig 8.2). The highest point lies in Degree Mountain which is

105.2 m above from sea level and the lowest point 70.2 m above sea level lies in is

Fuhse river south of the „‟ lukewarm Thaler mill „‟ in Gadenstedt.

Fig 8.1: Map of Gadenstedt, Lahstedt (source:http://de.wikipedia.org/wiki/Datei:Landkreise_Niedersachsen.svg and

http://www.maplandia.com/germany/niedersachsen/braunschweig/peine/lahstedt/)

The small river which is called Fuse is flowing near to this small village. The

accessibility of Gadenstedt by bus is 25 minutes from Peine. The village Gadenstedt

is the old communities that can be seen a strong traditional cultural.



Fig 8.2: Population graph of Gadenstedt (source: www.lahstedt.de)

8.1.2 Geography and topography

The project area situated in the Gadenstedt of Lahstedt municipality. The

surrounding land of Gadenstedt is flat and used for agricultural purpose. The project

area as per the geographical location lies in 52°14‟48‟‟ north latitude and 10°13‟6‟‟

east longitude. According to the topographic map (1:25000) is the terrain height to 85

meters above sea level.

8.1.3 Climate and hydrology

The annual average temperature and rainfall data are recorded in the metrological

station located in Hildesheim. As per these data, the study area has an annual

average temperature of 9.2°C and annual rainfall 708 mm. However, it was found

maximum temperature of 34°C in July and minimum -4°C in January as per the

recorded data of 2010 at the study area.

8.1.4 Description of the project

Constructed Wetlands has been widely recognized as a simple, effective, reliable and

economical technology compared to several other conventional systems especially

decentralized system of wastewater treatment for rural and semi urban area.

http://www.lahstedt.de/



Considering this advantage, the municipality of Lahstedt focused to introduce such

kind of technology. The municipal area consists of 43 km2 with 5 villages and a total

of 10.100 populations living in the five villages like Gadenstedt, Adenstedt,

Mündstedt, Oberg, and Groß Lafferde. It was decided to use such kind of treatment

processes however requiring extensive land for constructed wetlands and open

lagoons. This resource is cheaply available in the rural area. The Federal

Government of Germany developed the standard guidelines mentioning the rule and

regulation to treat wastewater according to the population. The treatment of

wastewater is a duty prescribed by the law of government authorities.

The project „‟ Ecotechnological treatment of waste water and sewage sludge in

Lahstedt‟‟ was registered and officially sponsored project at the world exhibition

EXPO 2000 in Hanover. The constructed wetland as polishing biotopes in

Gadenstedt was constructed in 1998 for the waste water treatment covering the area

of 1.1 hectare. After achieving the good results, the Municipality of Lahstedt has

decided to expand and improvement in the sewage plants in the locality of Oberg,

Münstedt, Adenstedt, and Groß-Lafferde.

Fig 8.3: Combined waste water biotope in Oberg

In the 2001 combined wastewater biotopes was constructed in Oberg and Münstedt

covering an area of 0.57 ha and 1.4 hectares respectively. Similarly sewage sludge

processing plant covering an area of 0.6 ha was constructed in Groß-Lafferde in

2002. This is one of the innovative ideas for the alternative system on natural method

is gaining popularity not only in the state of Lower Saxony but also in Europe. This is



one of model which show decentralized wastewater treatment under the local level

initiative for the environment protection.

However the main focus is given to waste water treatment through the CWs of

Gadenstedt. The waste water is being treated in Gadenstedt through the combination

of conventional and natural system. The treatment plant is located around 500 m far

in the west side of village. Gadenstedt has an old trickling filter which was

constructed in 1959 and treating the waste water.

Fig 8.4: Isometric view of Gadenstedt and project site (from Google)

An old trickling filter system is also functioning properly but community people are not

interested to replace by new activated sludge systems due to high operation cost.

They are planning to be continuing use of old sewage treatment plant to eliminate the

pollutants from wastewater and will close in near future within the 10 years. After then

they will depend totally upon Constructed Wetland. With the concept of ecological

technology, the project especially designed and constructed in 1998 under the direct

supervision and involvement of Ingenieurbüro Blumberg.

The project was designed with different objective for the wastewater treatment. So

the project was divided into three parts: polishing biotope (reed bed treatment

system); combined waste water biotope (cascade of ponds and reed beds); reed

Gadenstedt

Village

Constructed

Wetlands and

Lagoon area

Screening, Grit chamber,

Trickling filter and Sludge

drying bed



planted dry beds for sewage sludge. A total cost of construction was 1.7 million DM,

whereas Lahstedt municipality shared the cost by 75% and state government of

Lower Saxony by 25 %.

8.1.4.1 Screening

Screening is the first unit operation used at wastewater treatment plants. The main

objective of screening is to remove floating materials like faecal matter, toilet paper

and mineral solids, plastics, stone and metals preventing to damage and clogging of

downstream equipment, piping, and appurtenances. Coarse and fine screens are

used 15-75 mm and 3-12.5 mm.

Fig 8.5: Screening and collection drum (HUBER Screenings Treatment Systems in

Gadenstedt)

A screening compactor is usually situated close to the mechanically cleaned screen

and compacted screenings are conveyed to a dumpster or disposal area. Total 195.7

cubic meter floating materials was screened during the whole year periods, but

values from October and November was not included due to absence of record and

maximum screening material found in January equals to 189.7 cubic meter and

remaining months collected varies from 0.25 to 1.0 cubic meter respectively.

8.1.4.2 Aerated grit chamber

Grit includes sand, gravel, cinder, or other heavy solid materials that are “heavier”

(higher specific gravity) than the organic biodegradable solids in the wastewater.

Screening



Aerated grit chambers are typically designed to remove particles of 70 mesh (0.21

mm) or larger. When wastewater flows into the grit chamber, particles settle to the

bottom according to their size, specific gravity, and the velocity of roll in the tank.

Aerated grit chamber was designed in a rectangular type to treat around the 400 to

600 m3 per day. It was constructed with the cross section area of 2.5 m2 and the

length of 14 m respectively.

Air is introduced in the grit chamber along one side, causing a perpendicular spiral

velocity pattern to flow through the tank. Heavier particles are accelerated and

diverge from the streamlines, dropping to the bottom of the tank, while lighter organic

particles are suspended and eventually carried out of the tank. Grit is collected from

bottom of channel by automatic sand scraper and pumped into the collecting drum.

Total sand was collected 4 m3 in 2010.

Fig 8.6: Grit chamber in Gadenstedt treatment plant (photo by R. Shrestha, drawing from Ingenieurbüro Blumberg)

8.1.4.3 Trickling filter

Trickling filter was constructed in 1959 and one of the oldest treatment plants

operating to treat the wastewater coming from Gadenstedt village. The trickling filter

was filled with the lava and gravel of sizes ranging from 40 to 80 mm corresponding

with specific surface area of ca. 100 m2 /m3. In the trickling filter the treatment

process proceeds from top to bottom. The lava and gravel are providing more surface

area for the development of biofilms when wastewater flows downwards. The

Gritchamber



removal of pollutants from the wastewater involves both absorption and adsorption of

organic compounds by the layer of microbial biofilms. The BOD5 volumetric loading

rate is found 0.1 kg/ m3.d which is less than 0.4 kg/ m3.d and total nitrogen loading

rate is found 0.039 kg/m3.d which is less than 0.1 kg /m3.d. The surface loading rate

is 4.17 m / d. Under operating conditions ca. 2/3 of this can be assumed to be

biologically active. The depth and diameter of trickling filter consists of 3 m and 13 m

respectively.

Fig 8.7: a) Wastewater dosing into the bed through the rotating arm, b) lay out plan of project, c) trickling filter and d) diagram of biological process in trickling filter

BOD 5

NH4 +

NO3 -

Trickling filter

By R. shrestha From Ingenieurbüro Blumberg

By R. shrestha



8.1.4.4 Constructed Wetland as polishing biotopes

Constructed wetland is used as a tertiary treatment plants like a polishing biotopes

which is used to treat effluent coming from the existing trickling filter. Four vertically

flow CWs was designed and constructed in 1998 covering the total area of 1.1 hector

of which 7300 m2 is covered by reeds (Phragmites) in four vertically percolated CWs.

These ground surfaces are sealed with a lining at bottom to prevent wastewater

entering into the ground water.

Fig 8.8: a) Construction phase of Lagoon, b) Bed preparation of Constructed wetlands, c) planting Reeds in bed during the construction period of 1997-1998, d) after the maturation of Reed

The system was designed to treat 500 m3 / day of the wastewater during summer to

more than 2000 m3 / day in winter. But it was found by data analysis of discharge in

the whole year of 2010 that the actual wastewater treated with varies maximum 650

m3 / day to minimum 496 m3 / day. It was assumed that the treatment capacity would

in the future be extended up to 3000 inhabitants in Gadenstedt. The depth of the

vertical beds is 1.5 meter and filled with different filter materials of different depth

considering as a research purposes (Ingenieurbüro Blumberg, 1998). The area of

a b

c d

From Ingenieurbüro

Blumberg

From Ingenieurbüro

Blumberg

From Ingenieurbüro

Blumberg

By R. Shrestha



constructed wetland is divided into four small reed bed areas and materials used in

these beds are categorized into two groups. Top layer of 10 cm depth was filled with

aggregate and second layer was filled with sand (+ 5% limestone) and aggregate 2/8

mixing in 1:1 ratio in the depth from 10 - 80 cm in the bed 1 & 3. Sand (+ 5%

limestone) and root wood mixing also in 1: 1 ratio was filled in 80 – 125 cm depth and

125 – 135 cm depth with aggregate 2/8. Similarly in bed 2 & 4 are also filled with

limestone 0/32 at depth 0-20 cm, Sand (+ 5% limestone) and without root wood in

depth 20-135 cm. Finally bottom layer of four beds (1, 2, 3, and 4) was filled with

coarse aggregate16/32.

However, there are different filter material used for the purpose of wastewater

treatment with an estimated conductivity (Kf) of 10-4 to 10 -3 m/s and a designed pore

volume of 30-40%. The drained basins are lined with a polyethylene membrane. The

planned freeboard allows storage of a volume up to 2.000 m3 above the filter

substrate. The beds were planted with Phragmites Australis (Common Reed).

Technical data of CWs of Gadenstedt

Total size of area 1.1 hectares Surface Area

Vertical subsurface flow reed beds with total size

7500 m2 Surface area

Depth 1.5 metres

Capacity 3000 P.E Person equivalents

Current connected load 2600 P.E Person equivalents

Hydraulic loading 127 m / yr

Depth Bed 1 & 3 Bed 2 & 4

0-10 cm Aggregate 4/8 Limestone 0/32

10 – 20 cm Sand 0/1 + 5% Limestone } Aggregate 2/8 } 1: 1 mixing

20 – 80 cm Sand 0/1 + 5% Limestone Without Root wood 80 – 125 cm Sand 0/ 1 + 5% Limestone

Root wood } 1:1 mixing

125 – 135 cm Aggregate 2 / 8

135 – 150 cm Aggregate 16 /32 Aggregate 16 /32

Table 8.1: Technical data of Constructed Wetlands at Gadenstedt WWTP

New sewer was constructed from the old sewage treatment plant to the nearby

Polishing biotope. Similarly effluent from trickling filter collected in collection chamber

and pump was installed to distribute wastewater on the polishing biotope (reed beds)

under intermittent loading with a low pressure distribution system. First time samples

were analyzed in 1999 to measure the efficiency of CWs and obtained the good



results as shown in fig 8.9. Constructed Wetlands are used as a tertiary treatment

system.

Fig 8.9: Constructed Wetlands used as a tertiary treatment system

Nonetheless, CWs are also used as secondary treatment of municipal wastewater to

check the efficiency and main objective to replace the trickling filter slowly. The

wastewater was treated through the CWs from December 2001 to April 2002 and it

was found by the analysis that removal efficiency of COD, BOD5 and NH4-N in CWs

were 92%, 96% and 44% respectively. Similarly reduction of TN and TP were found

52% and 29% respectively. Influent and effluent values of organic and nutrients can

be seen detail in fig 8.10.

mg/l mg/l mg/l mg/l mg/l mg/l mg/l

COD BOD5 NO2-N NO3-N NH4-N TN TP pH

Influent 40.0 7.7 0.58 17.2 1.4 19.2 4.5 7.4

Effluent 10.0 4.9 0.035 4.7 0.2 4.90 1.0 7.1

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0First Results in 1999



Influent 54.0 16.0 0.30 14.0 2.0 16.0 3.0 7.3

Effluent 15.0 4.0 0.10 9.0 0.7 9.00 2.0 7.4

0.0

10.0

20.0

30.0

40.0

50.0

60.0

October 2004 - Setember 2005

n = 50

n = 20



Fig 8.10: CWs used as secondary treatment system at Gadenstedt WWTP

8.1.4.5 Combined waste water biotope

First of all, domestic wastewater and rain water from paved surfaces area of

Gadenstedt flow together through the combined sewer system into the treatment

plants. During heavy rains a considerable amount of such combined wastewater is

diverted into the open lagoons before entering to the treatment plants. Combined

wastewater biotopes are used to treat large amount of wastewater coming from

paved surface during the rainy season and protected the receiving river being

polluted from organic and inorganic pollutants. This lagoon system was designed to

treat wastewater 123000 m3 per year and 19250 kg COD per year from 38.5 hectare

paved area.

Fig 8.11: Combined wastewater treatment biotope (Lagoon) at Gadenstedt WWTP



Influent 301.0 165.0 0.60 9.8 13.4 22.1 4.1 7.5

Effluent 24.0 4.0 0.10 3.1 7.5 10.70 2.9 7.3

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

December 2001 to April 2002

n = 19



Combined wastewater biotopes of total area covering of 17000 m2 are divided into

three parts, which are called settling pond, unaerated storage pond and reed planted

soil filter. Wastewater is first passed though settling ponds with covering area of 2940

m2 to settle the suspended solids and after then treated in retention pond where

organic pollutants are oxidized by aerobic and anaerobic process. Storage pond has

a covering the area 5070 m2 with a large retention capacity of 13440 m3 and

detention volume of 4680 m3.

Floating islands are also constructed in the storage pond. Marsh plants growing on

floating islands accelerate the sewage purification process and absorb noxious

substances and nutrients dissolved in the waste water. The root zone under the

water provides a suitable place for the growth of microbiofilms (e.g. fixed nitrifying

bacteria). The wastewater is finally treated in a reed planted soil filter covering net

area 1.330 m2 before it is discharged into the receiving river Fuhse.

Gadenstedt

Total size 1700 m2 Surface area

Settling pond 2940 m2 Surface area

Retention pond 5070 m2 Surface area

Permanent retention volume 4680 m3 capacity

Maximum volume of water 13440 m3 capacity

Storage volume 8760 m3 capacity

Reed bed filter 2400 m2 Total Surface area

Hydraulic load on Reed bed filter 132 m/ yr

Table 8.2: Facts and figures about the combined wastewater treatment biotope

(Source: Ingenieurbüro Blumberg, Leaflet of Lahstedt Municipality)

The former method of combined waste water treatment in Gadenstedt did not

conform to legal requirements. The permissible pollutant overflow rate of 250 kg COD

/ ha / yr was clearly exceeded with a figure of 372 kg COD / ha .yr. The specific

overflow load will be below 64 kg COD / ha /yr well within the limit in Lower Saxony.

Samples were taken from December 2001 to April 2002 to analyze the concentration

of organic matter and nutrients. This system is therefore far superior in efficiency to

conventional combined waste water treatment systems with concrete basins.

Construction and maintenance costs are clearly lower. Hydraulic stress impacts on

the receiving river are avoided. A secondary environmental complex with valuable

biotope functions is established.



Figure 8.12: Isometric view of wastewater treatment plant at Gadenstedt

8.1.4.6 Sewage sludge dewatering and mineralization in reed beds

Sewage sludge is the end product of wastewater which is settled in the primary

settling tank and pumped into the reed beds for dewatering and mineralization

process where such kind of sludge is treated with aerobically and anaerobically. This

scarcely known method of dewatering and stabilizing sewage sludge in dry beds

planted with reeds has been in practice in Gadenstedt for nine years. Three reed

beds are used for this purpose covering area of 516 m2 .The roots of the plants which

penetrate the dumped sludge helps to accelerating the dewatering and mineralization

process.

Dewatering process is achieved by evapotranspiration and especially by drains which

are fitted at the bottom of the reed beds. Dry bed also helped in reduction of

pollutants in sewage sludge. It was found that sewage sludge dewatered and

stabilized in the reed beds which are designed for operation approximately 10 to 15

years with energy saving method and after then beds are cleared and refilled with

sludge for the next 10-15 years. However, from the experienced showed that dry

Source: Ingenieurbüro Blumberg

website (http://www.blumberg-

engineers.de/)

Common Reed

in CWs



matter content of over 50 % is currently achieved. The major advantages of dry reed

beds are to store surplus sludge load during the winter months when agricultural use

is prohibited. Transport costs are lowered by volume reduction and new options for

utilization and recycling of this valuable nutrient source in landscaping, horticulture,

tree nurseries, private gardening and recultivation can be explored. It is one of the

natural sludge dewatering and stabilization at reasonable investment and

maintenance costs.

8.1.5 Method and Field works

8.1.5.1 Field work - pH measurement

It is very important to measure the pH value of influent and effluent of waste water

because of the pH value shows the characteristic of water whether it is an acidic or

basic. Pure water is said to neutral with a pH value close to 7.0 at 25 °C. Influent and

effluent of wastewater with a pH lesser than 7 are said to be acidic and a pH greater

than 7 are basic nature. It is measured on a scale of 0 to 14. The term pH is derived

from “p” the mathematical symbol of the negative logarithm (base10) and “H” the

chemical symbol of Hydrogen. The formal definition of pH is the negative logarithm of

the hydrogen ion concentration i.e. pH = -log10 [H] +.

pH variation is dependent upon the hydrogen ions concentration. When hydrogen

ions concentration is low, pH indicates high and water becoming more basic. Water

with low pH cause the acidic or high pH cause basic nature is harmful to the flora and

fauna. Most organisms have adapted to life in water of a specific pH and may die if it

changes even slightly. This is especially true for aquatic life. The most significant

environmental impact of pH involves synergistic effects. Synergy involves the

combination of two or more substances which produce effects greater than their sum.

Changes pH value of water shows the negative impact on the quality of the receiving

river and soil properties. So pH is a critical factor determining the health of a

waterway. pH measurement is important for environmental science, civil engineering,

food science and many other applications.

In addition to controlling various biological processes, pH is also a determinant of

several important chemical reactions. Ammonium changes to free ammonia at pH



above neutral and at higher temperature. The protonation of phosphorus changes

with pH and the hydroxide and oxyhydroxide precipitations of iron, manganese and

aluminum and pH sensitive. (Kadlec und Wallace, 2009)

Limiting pH Values

Minimum Maximum Effects 3.8 10.0 Fish eggs could be hatched, but deformed young are often

produced

4.0 10.1 Limits for the most resistant fish species 4.1 9.5 Range tolerated by trout --- 4.3 Carp die in five days 4.5 9.0 Trout eggs and larvae develop normally 4.6 9.5 Limits for perch --- 5.0 Limits for stickleback fish 5.0 9.0 Tolerable range for most fish --- 8.7 Upper limit for good fishing waters 5.4 11.4 Fish avoid waters beyond these limits 6.0 7.2 Optimum (best) range for fish eggs --- 1.0 Mosquito larvae are destroyed at this pH value 3.3 4.7 Mosquito larvae live within this range 7.5 8.4 Best range for the growth of algae

Table 8.3: Limiting pH values for different aquaculture (Source: CWQRB, 1963)

A pH meter is used to measure the pH

value of water. It is an electronics

instrument consist of a glass electrode

connected to an electronic meter which

helps to measure pH by the activity of

hydrogen ions nears it tips and displays

in digitally on the electronic meter. Three

pH values are measured every day in

the morning and sometimes afternoon

by using pH meter and recorded for the

data analysis. Firstly, pH value of influent waste water is taken at Grit chamber before

entering to the trickling filter. Second measurement is done on the effluent water from

Trickling and third measurement on the effluent coming from constructed wetlands.

Daily measured values of pH are recorded in the dairy by manually. It was found that

pH meter was kept in a wet condition when it was not used to prevent the glass

electrode being dehydrated and cleaned once in a month by using HCl.

Figure 8.13: pH meter (WTW pH 315i)



8.1.5.2 Temperature measurement

Daily meteorological variations in air temperature, cloudiness, windiness and relative

humidity cause responses in the water temperature changes. The annual cycle of

wetland water temperatures follows a sinusoidal pattern with summer maximum and

minimum in winter. Kadlec and Wallace et al. (2009) pointed out four reasons for the

importance of water temperature in treatment wetlands like several key biological

processes, water quality parameter, evaporative water loss processes and functional

in subfreezing conditions even in cold-climate. Several biogeochemical processes

that regulate the removal of nutrients in wetlands are affected by temperature, thus

influencing the overall treatment efficiency (Kadlec and Reddy, 2001). The

temperature conditions in a wetland affect both the physical and the biological

activities in the system. The biological reactions responsible for BOD removal,

nitrification, and denitrification are known to be temperature dependent (Reed et al.,

1995). In the studies highlighted above, it is reasonable to expect temperature to be

significant in wetlands treating the waste water.

To analysis the temperature effects on the biological activity, daily air temperature of

maximum to minimum was recorded by automatic temperature reading equipment

installed in the site and similarly water tempera was also measured by a pH meter

together during pH reading. Daily water temperature is recorded in daily record book

by manually.

8.1.5.3 Sample collection for COD, BOD, NH4-N, TN, TP analysis

Field work Water sample were taken for chemical / physical and biological analysis from three

different places of treatment plants. Water sample were taken from the site using

1000 ml bottle washed with a 2 percent HCl solution and rinsed with distilled water.

Rinsing with acid and distilled water is necessary to remove any contaminant present

in the bottle. The samples were collected mostly in the morning time and once in a

week. Actually sample collection was done four times in every month for physical and

chemical analysis but sometimes found to be 5 to 6 times in a month. There are

always five to six days differences between each start of new sample collections.



Fig 8.14: Influent and effluent sample taken at Gadenstedt WWTP

First influent sampling was taken near to grit chamber and second sample taken

effluent of trickling filter and third was taken effluent of constructed wetlands. More

priority was given sample collection and handling so samples were always deliver to

Laboratory within two hours of last sampling time. It was always kept in mind that if

analysis was not started within two hours, sample should be kept at sample container

below 4 °C from the time of collection. All samples were stored in a dark insulated

box until the return to the laboratory.

Sample were analyzed for COD, BOD5, total Nitrogen (TN), and total phosphorus

(TP) and nitrogen in the form of nitrate (NO3-), nitrite (NO2

-) and ammonia (NH4-N).

Mitsch et. al., (1998) explained that samples, if not analyzed immediately after

collection, were preserved with concentrated H2SO4 and refrigerated for later

analysis. Sample preservation or analysis was completed within 48 hours of

collection.

Lab procedure There is central laboratory located in Groß-Lafferde, where samples ware brought for

the experiment of COD, BOD5, NH4-N, NO3-N, TN and TP from different treatment

plants situated in Lahstedt municipality like Lahstedt, Oberg, Adenstedt, Münstedt

and Groß-Lafferde. In the Lab, wastewater sample was tested by the HACH LANGE

cuvettes test method and this method being much easier, saves space, time and high

efficiency of achieving the reliable data. The method is also known as „‟ operational

analytical method‟‟ and is an alternative to reference DIN method. The sample after

collecting in Gadenstedt treatment plants is returned into the laboratory within the 45



minutes and sample analyses are conducted. The results obtained by this method

are verified by water authority of Peine four times in a year.

Fig 8.15: left: Sample of wastewater in the Laboratory for the analysis .Right: Miss Katharina Ohlemann (Lab technician) using the Homogenizer to homogenize the sample.

Biochemical Oxygen Demand (BOD5) Biochemical oxygen demand represents the amount of oxygen consumed by bacteria

and other microorganisms while they decompose organic matter under aerobic

conditions at a specified temperature. The Biochemical Oxygen Demand in 5 days is

of the sum parameter for the assessment of organic and oxidatively degradable

wastewater pollution. In the operational analytical method, LCK -555 Cuvettes test is

used to analysis BOD5 considering the recommended concentration on the range of

4-1650 mg / l. BOD5 is measured with referring to the Hack Lange booklet3.

First, dilution water was made with reference to the Dr. Lange booklet. Wastewater

sample is homogenized with the help of homogenizer within 30 seconds, which rotate

20000 rpm. Wastewater sample are screened by filter paper and filled into three

cuvettes by opening DosiCap Zip. Reagents (tablets and beads) is poured into

cuvettes with the help of funnel and sealed immediately after funnel is removed and

there should not be air bubbles inside the sample cuvettes. Repeatedly invert the

dilution water and sample cuvettes for 3 minutes until the reagent tablets have been

3 LCK cuvettes method can be found in the internet online for more information in the website

http://shop.hach-lange.com

http://shop.hach-lange.com/



dissolved completely.

After then, the three cuvettes are filled with

required amount of sample and dilution water as

per the table 8.4, using a transfer pipette, ensuring

there are no air bubbles, and seal with the DosiCap

Zip. First cuvettes are filled with 1 ml sample of

influent and 3 ml dilution water considering the

BOD5 measurement ranged 50 – 275 mg /l under

the category of B2. Second and third cuvettes are

filled with 4 ml of sample taking the effluent of

trickling filter and constructed wetlands considering

the low BOD5 concentration under the category A1.

These samples are shaken vigorously for 1 minute

in order to enrich the sample with oxygen and leaved in darkness in the block

thermostat maintaining the temperature at 20°C for 5 days. After the 5 days, cuvettes

are evaluated by photometry, this shows directly the BOD5 in mg/l O2 and data are

recorded as concentration of BOD5 in inflow and out flow of wastewater.

Measuring range

Preliminary dilution in reaction tube

Prepared sample

Dilution factor

(mg/l) Sample Dilution water

Pipette into the cuvette test

For CADAS 200 / LASA 30/50/ 100 / XION 500

A = 4 – 58 A1 = 4 – 19 A2 = 7 – 38 A3 = 11 – 58

4 ml 4 ml 4 ml

- - -

1.8 ml 0.9 ml 0.6 ml

3.5 7.0 10.5

B = 25 – 413 B1 = 25 -138

B2 = 50 – 275 B3 = 75 – 413

1 ml 1 ml 1 ml

1ml 3 ml 5 ml

0.5 ml 0.5 ml 0.5 ml

25 50 75

C = 100 – 1650 C1 = 100 – 550 C2 = 200 – 1100

C3 = 300 -1650

0.4 ml 0.4 ml 0.4 ml

2.8 ml 6.0 ml 9.2 ml

0.5 ml 0.5 ml 0.5 ml

100 200 300

Table 8.4: Sample preparation as per upper limit of measuring range of BOD5

(http://shop.hach-lange.com/shop/action_q/download)

Fig 8.16: SPECTROPHOTOMETER

DR2800 for the measurement of BOD5

and other required data also in Groß-

Lafferde

http://shop.hach-lange.com/shop/action_q/download



Chemical oxygen demand (COD) COD is used to measure the oxygen equivalent of the organic material in wastewater

that can be oxidized chemically using potassium dichromate – sulphuric acid solution

in the presence of silver sulphate as a catalyst. Chloride is masked by mercury

sulphate. The green coloration of Cr3+ is evaluated (www.hach-lange.co.uk).

Fig 8.17: COD measurement of LCK-514, LCK-314 cuvettes kits box and HT200S high temperature Thermostat.

For the COD analysis, Hach - Lange method was followed and selected the LCK -

514 cuvettes test for the inflow wastewater sample considering the COD

concentration range 100 – 2000 mg/l O2 and LCK – 314 cuvette test for the effluent

water with low COD concentration ranging 15 -150 mg/l. Three cuvettes is taken and

filled with 2 ml sample water, initially homogenized with the help of homogenizer and

screened with filter paper. After closing the cuvettes and thoroughly cleaned the

outside, cuvettes are inverted for few times and put into the thermostat for heating

these sample at a temperature 170 ° C for 15 minutes instead of heating at 148°C for

2 hours. When the heating process is completed then hot cuvettes are taken out and

immediately inverted two times after the lock opening of thermostat. These sample

cuvettes is put again in thermostat for cooling down at room temperature (18-20°C).

It is also important to see that sediment must be completely settled before evaluation

is carried out and clean the outside of the cuvette. Cuvettes are evaluated by

spectrophotometer, which shows directly the COD concentration in mg / l O2 of inflow

and out flow of wastewater sample.



Total Nitrogen (TN) Total nitrogen of wastewater was also analysis by LCK – 338 cuvette test as per the

Hach –Lange method and process taken into eight steps. First of all, 0.2 ml sample

was put into the reaction tube and poured the reagents of 2.3 ml solution A and 1

tablet reagent B, whereas A indicate the sodium hydroxide solution and B represents

oxidant tablet. Then reaction tube is

closed immediately and put in the HT

200S thermostat at the temperature

170°C for 15 minutes. After cooling down

the reaction tube into room temperature

(18-20°C) in which 1 micro cap C

reagents is added and inverted a few

times until the streak are vanished. Such

digested sample of 0.5 ml from reaction

tube is filled slowly into the cuvettes test by

pipette and 0.2 ml of D solution reagent is

mixed. Then cuvettes tests are quickly closed and inverted few times until no more

streaks can be seen. After 15 minutes, outside of cuvettes are thoroughly cleaned

and measured the total nitrogen in mg/l O2 by spectrophotometer DR2800. The total

nitrogen compounds are known as the sum of the Kjeldahl-N + NO2-N + NO3-N.

Total phosphorus Total phosphorus was analyzed LCK - 348 cuvette test method. Firstly foil is removed

carefully from the Dosi Cap Zip of cuvettes and opened the Zip, after then filled 0.5

ml sample into the three cuvettes. The Dosi Cap Zip is tightened and shaken the

cuvettes firmly and put these sample into the thermostat for standard heating at

temperature 170°C for 15 minutes. After cooling then mixed 0.5 ml reagent B and

screwed by a grey DosiCap C onto the cuvettes. Cuvettes are inverted for few times

and after 10 minutes also inverted a few times more afterwards thoroughly cleaned

outside of the cuvettes. Finally Cuvettes are put into the spectrophotometer which

displays the concentration of total phosphorus in sample in mg/l.

Fig 8.18: Total nitrogen (TN) measurement of LCK-338 cuvettes kits box with reagents (A, B, C and D)



Ammonium - Nitrogen (NH4-N) The main principle of measurement is ammonium ions

react at pH 12.6 with hypochlorite ions and salicylate

ions in the presence of sodium nitroprusside as a

catalyst to form indophenol blue. In the laboratory,

NH4-N is analyzed very simple and quickly way by

LCK -303 cuvettes test as per described by Hach-

Lange method. Firstly foil is removed carefully from

the DosiCap Zip and opened the cap. In the three

cuvettes, 0.2 ml homogenized sample is filled with the

help of pipette and quickly closed by DosiCap. After

cuvettes are shaken 2- 3 times and kept in rest. After

15 minutes, outside of cuvettes are thoroughly

cleaned and kept in spectrophotometer which displays

the concentration of ammonium nitrogen (NH4-N) in

sample in mg/l.

Fig 8.19: LCK-303 cuvettes test sample for NH4-N and Kit box with instruction of measurement process.

Nitrate - Nitrogen (NO3 - N)

In the laboratory, nitrate nitrogen (NO3-N) is analyzed very quickly by LCK -340 and

LCK- 339 cuvettes test method. In LCK -340 cuvettes test is conducted considering

the concentration of NO3-N high in influent sample in the range of 5- 35 mg/l and

LCK -339 cuvettes test for the NO3-N concentration low in effluent of sample within

the range of 0.23 – 13.5 mg/l.

First test sample is prepared as LCK-340 test method by filling 0.2 ml sample into the

cuvette and mixed 1.0 ml the reagent A solution. Similarly second test sample

prepared as LCK-339 by filling the cuvette with 1.0 ml sample and mixed with 0.2 ml

solution A reagent. After then both cuvettes are closed and inverted a few times until

no more streaks can be seen in the sample. Cuvettes are cleaned thoroughly after 15

minutes and evaluated with the help of spectrophotometer which displays digitally the

concentration of nitrate - nitrogen (NO3-N) in sample in mg/l.



Fig 8.20: LCK -340 and LCK -339 cuvettes kit boxes for NO3-N measurement

Nitrite-Nitrogen (NO2-N) Nitrite is tested in the laboratory by the LCK -342 cuvettes test method. Considering

nitrite nitrogen concentration in the wastewater sample should be low as within the

range of 0.6 – 6.0 mg/l. This analysis is also similar to previous described method of

NH4-N and NO3-N. Three cuvettes is filled with 0.2 ml sample for the test and

immediately closed by the DosiCap. The cuvettes are shaken 2-3 times with firmly

then kept in rest for 10 minutes. After then cuvettes are again inverted few time and

cleaned outside surface of cuvettes. Finally, cuvettes are evaluated with the help of

spectrophotometer which displays digitally the concentration of nitrite - nitrogen

(NO2-N) in sample in mg/l.

8.2 Study area of Berel

8.2.1 Location

Berel is one of the very small village of Baddeckenstedt municipalities and situated in

Wolfenbüttel district (Lower Saxony). This small village lies 20 km south of Peine, 21

km east of Hildesheim and 11 km west of Salzgitter. The Population of Berel was

found from 1996 to 2003 on average 684 inhabitants, (1999 Max 698 inhabitants and

2003 Min 668 inhabitants).



Fig 8.21: Map of Wolfenbüttel district and Berel (Source: http://commons.wikimedia.org/wiki/File:Landkreise_Niedersachsen-en.svg And http://maps.google.de/maps)

8.2.2 Geography and topography

The project area is situated in the Berel of Baddeckenstedt municipality. The

surrounding land of Berel is flat and used for agricultural purpose. The project area

as per the geographical location lies in 52°9‟54‟‟ north latitude and 10°13‟4‟‟ east

longitude. According to the topographic map, this village is 167 meters high from the

sea level.

Fig 8.22: Geographic location of Berel (Source: http://maps.google.de/maps )

52 °9‘ 54‘‘ N

10°13‘ 4‘‘ E

http://maps.google.de/maps



8.2.3 Description of the project

Wastewater was treated by a pond plant system in Berel since 1989; the plant was

originally designed to be naturally ventilated type, consisting of three successive

ponds. After waste regulation system was designed for 600 residents of the Great

Class 1 (<1,000 inhabitants). Village has its own separate sewer to carry out

wastewater coming from private house and rain water from paved surface. The

wastewater is discharged through sewer pipe from the village to the existing pond

treatment plant under the gravity flow system. The treatment plant is located around

600 m southeast of the village at an altitude of about 167 m above sea level. The

site is bounded on the south side of the receiving water Sangebach.

Fig 8.23: View of Berel village and treatment plant (Source: http://maps.google.de/maps)

By 1996, wastewater was treated and purified by pond under the natural system and

found under the legal requirement. After then final effluent values of pond are not

found under the legal limit described by Wolfenbüttel district. It was found the oxygen

deficiency and bad odor. For the better quality control and reduction of COD, BOD

and nutrients in wastewater, two mobile surface aerators have been used in the pond

- 2 since 1996. After then the effluent values were measured from 2004 to 2006 as

shown in fig 8.24 and 8.25, the results also showed the concentration of COD, BOD

and Ntotal were more than legal limit described by Wolfenbüttel. Wolfenbüttel district

Berel village

Berel WWTP

plantplant

http://maps.google.de/maps



recommended the limiting values of COD, BOD5, TN, TP concentration before

discharging into the receiving water course Sangebach are shown in Table 8.5

Monitoring values of the district Wolfenbüttel

Chemical oxygen demand (COD)

100 mg /l

Biological oxygen demand (BOD)

40 mg /l

Phosphor (P total) 8 mg/l

Nitrogen (N total) 40 mg/l Table 8.5: Requirements for waste water at the point of discharge into the Sangebach

Fig 8.24: COD and BOD effluent values of self-monitoring of the treatment plant Berel

Fig 8.25: Ntotal and Ptotal effluent values of self-monitoring of the treatment plant Berel



From 31.01-19.03.2003, around 45 days, the Water Association of Peine investigated

the hydraulic conditions of the sewage system around the catchment area of Pond

treatment plant. The assessment of the external water inputs to the sewage system

was based on the specific water consumption and population of 668 inhabitants.

Total wastewater volume runoff into the sewer pipe was measured 5952 m3 during 45

days in which average water consumption was by inhabitants was 3607 m3

This showed that the difference 2345 m³ wastewater was entered into the pipe from

outside. The external water share was limited to 65% of the waste water runoff.

Regarding the flow characteristics, the low rainfall condition was also observed

during the investigation period. Water Association Peine was concluded that the

more external water into the sewer pipes due to improperly connected drains and

leaky channel coverage layer and ground water discharging into the sewage system.

Community people were interested to improve the water quality as per the required

limit and upgrading the sewage treatment pond safely through constructed wetland.

The project especially was designed and constructed in 2008 under the direct

supervision and involvement of Ingenieurbüro Blumberg. The project cost was

541,830.00 Euro.

8.2.3.1 Screening

Screening is the first unit operation used at wastewater treatment plants. The main

objective of screening is to remove floating materials like faecal matter, toilet paper

and mineral solids, plastics, stone and

metals preventing to damage and clogging

of downstream equipment, piping, and

appurtenances. The Screen system in the

influent of the Berel treatment plant is

designed as a flat fine screen with a gap

width of 3 mm. Because of the relatively low

feed rate to the treatment plant, the

smallest size is provided by the company

Grimmel Water Technology (or equivalent)

The maximum hydraulic capacity of the

Fig 8.26: Screening and automatic

screening waste collected in

dust pin at Berel WWTP



proposed computer system provides a adequate security for future new connections

to the sewage treatment plant in Berel.

Technical data of Screening system

Wastewater supply Q max 10 l/s

Channel width W 500 mm

Channel depth 600 mm

Bar rack width 460 mm

Bar gap width 3 mm

Maximum water level before screening H 200 mm

Machine height from channel bottom 1360 mm

Machine width 800 mm

Machine length 1650 mm

Electrical power around 4.5 kW

Table 8.6: Technical data of screening system installed in Berel

8.2.3.2 Pond system

The treatment plant in Berel was designed in the late eighties as a naturally aerated

pond treatment system. The treatment plant consists of three successive lagoons

with a total surface area of 6,800 square meters. The surface ratio of the ponds is

around 4:3:3. The largest pond 1 has a surface area of 2,700 square meters.

Structurally, the lagoons have been designed with a slope gradient of 1:1.5, a depth

of 1.20 m and a freeboard of 20 cm. The inflow into a pond branches off from the

shaft 109 and terminates in an inlet structure as shown in fig 8.27. In pond 1, a mud

pocket and a floating baffle wall were installed. Baffles walls were constructed in

ponds 1 and 3 to allow the flow through the entire treatment plant. The overflow of

the ponds and the drainage area to the receiving waters consist of a landscaped area

of shallow water depth of 20 to 50 cm with embankment slope 1:1.6. Overflow and for

the period of sludge removal from Pond 1, wastewater is diverted directly from

manhole No. 109 to pond 2 through the manhole No. 110 as shown in fig 8.27

Fig 8.27: Isometric view of Berel WWTP and settling pond



Wastewater was first treated through a combination of physical, biological, and

chemical processes in the pond1, also known as settling pond, where suspended

solids settled and organic material is decomposed by aerobic bacteria under the

biological reaction to reduce the COD, BOD. After then wastewater is pumped into

the constructed wetland. Effluents from constructed wetlands enter the pond 3, which

is working as polishing pond. Finally effluent of polishing pond is discharged into the

receiving small river called Sangebach. For the efficiency of pond system is

described more detail in chapter 9 (result and discussion).

8.2.3.3 Constructed Wetlands (CW)

Constructed wetlands are designed in Berel for a maximum treatment capacity of 600

residents. The calculation and design of CWs is based on the DWA Worksheet A 262

(2006) and the design of the FLL / IÖV worksheet "recommendation for planning,

construction, care and maintenance and operation of constructed wetlands"

2005/2006. Total surface area of constructed wetland is 2400 sq.m and divided into

four equal small reed bed areas having each surface area of 600 sq.m .

Fig 8.28: a) Gravel filling over the drain pipe in the bottom layer of bed, b) Reed planting in the bed, c) Lay out plan of Berel treatment plant (Pond and constructed wetlands) d) Reed after the maturation, e) End cape fitting at distribution pipe

The total depth of the vertical flow beds is 1.0 meter and filled with different filter

materials of different depth (Ingenieurbüro Blumberg, 2006). At the bottom layer,

By Ingenieurbüro Blumberg

By Ingenieurbüro Blumberg By Ingenieurbüro Blumberg

a

b c

d

e



where HDPE drain pipe were laid down

to drain water, was filled with coarse

aggregate of 16/32 mm size up to 0.25 m

depth. Second layer was also filled with

fine aggregate of 5,6/8 mm size up to

0.15 m and top layer of about 0.60 m

depth was filled with fine sand filter

materials. Figure 8.29: shows the structure of the filter

materials used in CWs schematically.

Phragmites communis (common reed) was planted on the surface area of CWs.

Two pumps were installed to deliver controlled amounts of the waste water

intermittently and alternately on the four beds of CWs. The distribution of the waste

water to the four reed bed is controlled by four electrically operated valves.

Wastewater is evenly distributed on the surface through a feed system of HDPE

pipes with low pressure largely maintenance. Possible blockages can be washed out

by removing the end caps of distribution pipes. Bed slope was maintained about 2%

to drain water under gravity system and percolated water was collected by drainage

pipe. These pipes are also connected with main drainage pipe (DN 200) and

collected into the collection chamber after then discharged directly into pond 3.

8.2.4 Method and Field work

8.2.4.1 Field work

At Berel treatment plant, water samples were collected mostly once a week in the

morning time and totally four times in a month for better result analysis. Actually

samples were taken for Lab analysis from four different places of treatment plants

and collected in 1000 ml plastic bottle separately. First influent sampling was taken

near to inlet of settling pond, second sample taken effluent of settling pond, third was

taken effluent of constructed wetlands (1 and 2) and fourth sample was final effluent

of polishing pond. All samples were stored in a dark insulated box until the return to

the laboratory. In Labor, Sample ware analyzed for COD, BOD5, total Nitrogen (TN),

and total phosphorus (TP) and nitrogen in the form of nitrate (NO3-), nitrite (NO2

-) and

ammonia (NH4-N).



Fig 8.30: Water sample collection as shown in circle at Berel treatment plant

A pH meter is used to measure pH value of water, which help to find out whether it is

acidic or basic or neutral nature and with together ph reading, temperature reading is

also recorded. A pH meter is an electronics instrument which displays pH and

temperature values in digitally on the electronic meter after the glass electrode

dipping into the sample and hold at least 60 seconds. Water temperature and pH

values are recorded by manually, when the sample is collected for Laboratory

analysis.

8.2.4.2 Laboratory work

There is branch laboratory of Wasserverband Peine located in Baddeckenstedt,

where samples ware brought for the experiment of COD, BOD5, NH4-N, NO3-N, TN

and TP. In the Lab, wastewater sample was tested by the HACH LANGE cuvettes

test method and this method being much easier, saves space, time and high

efficiency of achieving the reliable data. The procedure of measurement of COD,

NH4-N, NO3-N, TN and TP was same as Gadenstedt treatment plant and detail

described in section 8.1.5.3 of this chapter. Only measurement procedure was

different in the case of BOD5 than HACH LANGE cuvettes method. The



measurement method proceed in the laboratory is also known as „‟ operational

analytical method‟‟ and is an alternative to reference DIN method. The sample after

collecting in Berel treatment plants is returned into the laboratory within the 1 hour

and sample analyses are conducted.

Fig 8.31: left: Mr. Marko Lux (Lab technician) using the Homogenizer to homogenize the sample and right: Sample of wastewater in the Lab for the analysis. (Wasserverband Peine Laboratory at Baddeckenstedt)

Biochemical Oxygen Demand (BOD5)

BOD is measured by using OxiTop® BOD

Respirometer Systems. This method is based on a

pressure measurement in a closed system where

microorganisms in the sample consume the oxygen

and form CO2. This is absorbed by NaOH, creating a

vacuum which can be read directly as a measured

value in mg/l BOD. The sample volume being tested

regulates the amount of oxygen available for a

complete the respirometer system's BOD

measurement. BOD measurement ranges of up to 4,000 mg/l can be measured with

the respirometer system using different sample volumes. The OxiTop® BOD

respirometer systems have two different heads; one is green used for inflow and

yellow for outflow. The influent sample of 164 ml is taken in green head bottle and

yellow head bottle is filled with 432 ml effluent sample after then mixed with 2 tablets

NaOH. These samples are kept inside the heating box at room temperature for 5

Fig 8.32: OxiTop Respirometer for

BOD measurement in Laboratory



days. However, every day one value of effluent and influent are observed and

recorded and continue up to 5 days. The final value after 5 days is measured as

BOD5 values, but there is some constant multiple factor to obtain the exact value of

BOD5 in the case of influent and generally the measured value is multiplied by 10.

Respirometer systems further measured BOD values that can be read at all times

after the period of 5 days, which permits the tracking of check values or

measurements over longer periods.

Chemical oxygen demand (COD) For the COD analysis, Hach - Lange method was followed and selected the LCK -

514 cuvettes test for the inflow wastewater sample considering the COD

concentration range 100 – 2000 mg/l O2 and LCK – 414 cuvette test for the effluent

water with low COD concentration ranging 5 - 60 mg/l. Four cuvettes is taken and

filled with 2 ml sample water, initially homogenized with the help of homogenizer and

screened with filter paper. Detail measurement process of COD is followed as

instruction given and described detail in section 8.1.5.3.

Ammonium nitrogen (NH4-N) In the laboratory, for the measurement of NH4-N, LCK 303 and LCK 305 cuvette test

method is used for the measurement of influent and effluent of wastewater sample of

Berel. Detail processes are same as Gadenstedt sample measurement, which is

described in detail in chapter 8.1.5.3

Nitrate-Nitrogen (NO3 -

N) and Nitrite-Nitrogen (NO2-N) In the laboratory, nitrate nitrogen (NO3-N) is analyzed very quickly by LCK -340 and

LCK- 339 cuvettes test method. In LCK -340 cuvettes test is conducted considering

the concentration of NO3-N high in influent sample in the range of 5- 35 mg/l and LCK

-339 cuvettes test for the NO3-N concentration low in effluent of sample within the

range of 0.23 – 13.5 mg/l. Nitrite is tested in the laboratory by the LCK -342 cuvettes

test method. Considering nitrite nitrogen concentration in the wastewater sample

should be low as within the range of 0.6 – 6.0 mg/l.



Total phosphorus (TP) Total phosphorus was analyzed by LCK - 350 and LCK - 348 cuvettes test method.

Influent and effluent of waste sample taken from settling pond was analyzed by LCK

– 350 cuvette considering the phosphorus concentration on the range of 2-20 mg/l

and effluent from constructed wetland and final polishing pond was analyzed by LCK-

348 cuvette test with low range of phosphorus (0.5-5.0 mg/l).

95 Chapter 9: Results and discussion


9 Results and discussion

The mean value for sampling data are taken for the analysis and other parameters

that are being studied covers the six main wastewater sampling i.e. COD, BOD, NH4-

N,TN,TP and pH. Other analysis including nitrate, nitrite and temperature are

included in this study.

9.1 Chemical Oxygen Demand (COD) of Gadenstedt and Berel WWTP

Fig 9.1: COD influent and effluent values at Gadenstedt WWTP

Chemical Oxygen Demand (COD) is a widely known parameter used to measure the

amount of oxygen required that can chemically oxidize organic matter as well as

inorganic substances present in the wastewater. COD values are much larger than

BOD values due to presence of humic materials in wastewater. For untreated

domestic wastewaters, COD concentration is found on the range of 250 - 1000 mg/l

(Metcalf and Eddy, 1991).

The above graph shows that concentration of COD in wastewater varies from 114

mg/l in November to 460 mg/l in July. The average value of influent of total 52

samples is 257 mg/l. This shows that volumetric loading of COD on the trickling filter

is 0.23 kg/m3.d. The effluent COD concentration is mostly below than 50 mg/l except

in the month of February and July. However, the average value of COD is 38.23 mg/l

Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

COD Influent 293.0 204.5 134.0 264.0 306.0 281.5 460.0 292.0 155.0 214.0 114.0 214.0

COD Effluent of TF 42.0 57.0 37.0 31.7 43.3 34.8 58.4 40.5 24.8 27.6 25.3 22.7

COD Effluent of CWs 17.0 21.0 15.0 12.9 17.7 14.6 19.5 18.3 16.1 15.0 15.0 15.0

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

450.0

500.0

mg

/ l

COD influent and effluent ,Gadenstedt

365

588

455511 486 468 477

558 568 569 555 531

Inflow Discharge (Q) - m3/d



that effluent from the trickling filter. The surface loading rate on the CWs is varied

from 50 l/m2.d to 78 l/m2.d and found average organic loading of 2.68 g/m2.d. Final

COD effluent of CWs is on the range of 14-21 mg/l. (See in Appendix -1 more detail

COD values)

Fig 9.2: COD reduction efficiency of CWs and TF at Gadenstedt WWTP

From the graph 9.2, COD is reduced by the trickling and constructed wetlands on the

range of 72-89 % and 4 -18 % respectively. And overall efficiency plant is found 93 %

where trickling filter contributes up to 84 % and CWs up to 9 %. The graph clearly

shows that effluent level of COD from trickling filter and constructed wetlands are

mostly below the legal limit of 110 mg/l mentioned by German Federal Government

Law and 90 mg/l by specific limit of Lahstedt wastewater treatment plant.

Similarly, in the case of Berel wastewater treatment plant, COD concentration in

wastewater varies on the range of 223 – 820 mg/l. Firstly, wastewater is treated by

settling pond, which helps to reduce the COD by 20 -72 % except August. Effluent

values are found on the range of 72.9 – 350.5 mg/l. Similarly, effluent waster from

settling pond is pumped and dosed over vertically flow CWs at the surface loading

rate of 59 l/m2.d under intermittent system. The water is then drained vertically under

gravity and voids in the filter media are refilled with air from the atmosphere. This


% reduced by CWs 9% 18% 16% 7% 8% 7% 8% 8% 6% 6% 9% 4%

% reduced by TF 86% 72% 72% 88% 86% 88% 87% 86% 84% 87% 78% 89%

86%72% 72%

88% 86% 88% 87% 86% 84% 87%78%

89%

9%18% 16%

7% 8% 7% 8% 8%6% 6%

9% 4%

0%

20%

40%

60%

80%

100%

120%

COD reduction in %, Gadenstedt



mechanism helps to provide sufficient oxygen to oxidize the organic and inorganic

materials present in wastewater.

Fig 9.3: COD influent and effluent values and reduction efficiency at Berel WWTP

COD concentration remains on the range of 18.3- 75.9 mg/l on the effluent of CWs

and overall reduction efficiency is achieved by 44 %.

The surprising results show that final effluent from maturation pond contains more

COD value than effluent value of CWs. Only in the month of January, February and

August COD values are reduced with very low percentage (1-2%) and remaining

months of the year, COD values are increased by 2 – 14 %. COD increased in the

polishing pond is the main cause of algae lifecycle phenomenon.


COD Influent 469.3 820.3 407.5 716.8 496.0 449.0 547.8 336.5 223.0 318.3 224.7 317.8

COD Effluent of SP 297.8 350.5 221.7 231.5 334.0 179.7 154.8 324.7 72.9 255.7 127.0 158.3

COD Effluent of CWs(1+2) 75.9 68.6 34.5 28.0 28.5 30.8 44.5 44.8 37.6 19.1 18.3 30.8

COD Effluent of PP 67.7 59.1 62.2 68.8 43.4 52.8 78.5 44.1 43.1 36.5 42.1 74.8

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0m

g /l

COD influent and effluent , Berel

37%57%

46%

68%

33%

60%72%

4%

67%

20%

43% 50%

47%

34%46%

28%

62%

33%20%

83%

16%

74%

48% 40%

2%1%

-7% -6% -3% -5% -6%

0%

-2% -5% -11% -14%

-20%

0%

20%

40%

60%

80%

100%

120%


Pe

rce

nt

Months

COD reduction at Berel WWTP

% reduction by SP % reduction by CWs(1+2) % reduction by MP

132.0 125.5

190.0

147.0 150.0

94.564.0

87.0

137.5 123.0

219.5 231.0

Inflow Discharge (Q) - m3/d



However, finally COD effluent from MP and CWs are below the legal limit of 150 mg /l

mentioned by German Federal Government law and 100 mg /l by specific limit of

Berel WWTP.

9.2 Biochemical oxygen demand (BOD5) of Gadenstedt and Berel WWTP

Biochemical oxygen demand (BOD) is an approximate measure of the amount of

biochemically degradable organic matter present in a water sample. It is defined by

the amount of oxygen required for the aerobic microorganisms present in the sample

to oxidize the organic matter to a stable inorganic form. The method is subject to

various complicating factors such as the oxygen demand resulting from respiration of

algae in the sample and the possible oxidation of ammonia (if nitrifying bacteria are

also present). Other parameters like pH- value, temperature, or presence of toxic

substances in a sample may affect microbial activity leading to a reduction in the

measured BOD. Therefore, interpretation of BOD results and their implications has

done with great care.

Fig 9.4: BOD5 influent and effluent values at Gadenstedt WWTP

The above graph shows the analysis of BOD5, sample measurement from

Gadenstedt treatment plants. The BOD5 concentration in the wastewater is varied

with a maximum 182 mg/l in July and minimum 56 mg/l in November. The average


BOD5 mg/l Influent 112.0 103.3 70.0 110.8 159.8 139.3 182.2 109.3 94.8 95.5 56.0 76.2

BOD5 mg/l Effluent of TF 10.25 16.8 14.0 10.3 9.3 5.8 10.4 4.3 4.8 4.3 5.5 4.6

BOD5 mg/l Effluent of CWs 4.00 7.3 6.2 4.0 5.3 3.8 2.4 3.3 5.4 4.0 4.0 4.0

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

mg

/ l

BOD5 inflow and outflow ,Gadenstedt

n = 52

BOD5 inflow = 109 mg/l (avg.)



value of BOD5 in influent lies 109 mg/l and these values are much higher than the

recommended by German Federal Government. The effluent BOD5 of trickling filter is

found on the range of 4.3 – 16.8 mg/l with average value 8.35 mg/l that shows the

reduction efficiency of BOD in trickling filter on the range of 80-96%, when comparing

the influent and effluent of trickling filter. Similarly, BOD5 concentration in the final

effluent from the constructed wetlands is found 2.4 – 7.3 mg/l (with average 4.46

mg/l) and reduction efficiency of CWs varies also on the range of 1 – 11 %, when

comparing the TF and CWs with respect to influent concentration.

Fig 9.5: BOD5 reduction in percent by TF and CWs

Above fig 9.4 clearly shows that effluent value of BOD5 from trickling filter and CWs

are mostly below the legal limit of 25 mg /l given by German Federal law and

Gadenstedt WWTP. But only on the month of January, BOD5 level is higher than

legal limit.

The major cause of BOD removable depends upon the trickling filter operation and

development of high growth of microorganisms. During the operation, the wastewater

trickles over the surface of media and develop the visible shiny slime. The organic

material present in the wastewater is absorbed and metabolized by the micro-

organisms in the presence of oxygen under the aerobic condition. They produce

more organisms, carbon dioxide, sulfates, nitrates and other stable byproducts. The

oxygen supply is seemed to be enough to decompose the organic matter and


% reduced by CWs 6% 9% 11% 6% 3% 1% 4% 1% -1% 0% 3% 1%

% reduced by TF 91% 84% 80% 91% 94% 96% 94% 96% 95% 96% 90% 94%

91% 84% 80%91% 94% 96% 94% 96% 95% 96% 90% 94%

6% 9% 11%6% 3% 1% 4% 1%

-1%

0% 3% 1%

-20%

0%

20%

40%

60%

80%

100%

120%BOD5 reduction in % ,Gadenstedt



nitrification. This is one of the evidence of the old trickling filter operating properly

with high efficiency.

In the case of constructed wetlands, they are designed for vertically flow and

intermittent hydraulics loading system. Hydraulic loading rate is found 70 l/m2.d and

organic (BOD5) loading is found 0.59 g/ m2.d. The water is drained by gravity and

voids are refilled with air from the atmosphere considering porosity 30-40 %. This

mechanism helps to provide sufficient oxygen for aerobic process. The substrate

used in constructed wetlands whose hydraulic conductivity was designed 10-3 m/s,

which permit water to flow through the filter media without clogging. This shows that

CWs are in good function whereas CWs is treating as the tertiary treatment plant only

for polishing purpose. BOD reduction in constructed wetlands is assumed that

oxygen is transferred by plant through the roots into rhizomes and aerobic condition

exits which help to decompose the organic matter by micro-organism. There are

different views found in the literature on how much excess oxygen that is available for

biological activity in the root zone of constructed wetlands.

The flux of oxygen transferred into the rooting system has been tentatively quoted to

be 4-5 gO2/m2d (Armstrong et al., 1988). The oxygen transferred into the root zone

by Phragmites australis was 2.08 g /m2.d, but root and rhizomes consumed the

oxygen for respiration was measured 2.06 g /m2.d, which show the perfectly balance

oxygen influx through the culms leaving only 0.02 g/m2.d to be released to the

surrounding matrix and these values are far lower than those quoted (30-150 g/m2d)

for vertical flow system (Brix et al., 1990). It is also much lower than the oxygen

demand of 8 – 10 g O2 /m2d for a bed designed at 5 m2/ pe for BOD removal only

(Cooper et al., 1996). With reference of literature, it is very difficulties to find out such

kind scientific measurement in the study area, but it is concluded that vegetated

plants are more important for better hydraulic conductivity rather than supply of

oxygen.

In the case of Berel, the data taken are not consistency in the case of BOD

measurement. The effluent of BOD5 from settling pond was measured only in the

February and March with the value 200 mg/l and 185 mg/l respectively. The reduction

percentages were 35 % and 12 %. The effluent values of BOD in CWs are an

average value of 22.0, 10.0 and 9.0 mg/l respectively (average 13.67 mg/l) during



January, February and March, which shows removals efficiency of 80 %. The ability

to reduce BOD shows that the microorganisms in constructed wetlands have been

developed well and the wetland has a design that gives sufficient time and internal

surface for degradation of organic matter to occur. These values are below the legal

limit of 40 mg /l stated by German Federal law and 25 mg /l stated by Berel WWTP

for the small treatment plant up to one thousands inhabitants.

Fig 9.6: BOD influent and effluent measured values of wastewater in Berel.

9.3 Ammonium nitrogen (NH4- N) of Gadenstedt and Berel WWTP

The most important inorganic forms of nitrogen in wetlands treating municipal or

domestic wastewater are ammonia (NH4+), nitrate (NO3-), nitrite (NO2-) and nitrous

oxide (N2O) and dissolved element nitrogen or nitrogen gas (N2) (Kadlec and

Wallace, 2009). Ammonia exists in water solution as either as un-ionized ammonia

(NH3) or ionized ammonia (NH4+, ammonium ion), depending upon water temperature

and pH.

At the time of the study, the plant was operating at a design flow of 512.83 m3 per

day with a hydraulic loading rate of NH4-N at the average of 0.017 kg /m3/d. Above

figure shows that the average concentration values of NH4-N in the wastewater is

more than 10 mg/l besides March (8 mg/l) and November (9.7 mg/l) .In the summer

these values can be found maximum on the range of 20-34.3 mg/l and in the winter

values varies from 16-18.3 mg/l respectively. (More detail can be seen in Appendix II)

Jan Feb Mar Apr May June Aug Sep Nov

BOD5 Influent 297.50 310.00 210.00 245.00 147.50 280.00 260.00 158.00 113.33

BOD5 Effluent of SP 200.00 185.00

BOD5 Effluent of CWs(1+2) 22.00 10.00 9.00

BOD5 Effluent of PP 15.33 13.25 14.00 18.25 5.75 22.37 4.75 7.80 12.33

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

mg

/ l

BOD5 influent and effluent , Berel



Fig 9.7: NH4-N influent and effluent values at Gadenstedt WWTP

.Average monthly effluent NH4-N values from TF during colder temperature periods

varied from 1 to 3.3 mg/L. Similarly in summer average monthly value of NH4-N is on

the range of 0.2 mg/l to 2.6 mg/l. Temperatures in winter is ranged between 5°C and

7°C, while the summer water and air temperatures ranged between 14° -18°C and

23-34°C respectively. (See Appendix IV of air and water temperature). Efficiency of

trickling filter for NH4-N removal varies between 80 to 99 % (average 93%).

In the case of Constructed wetlands, NH4-N surface loading is very low as 0.1 g/m2.d.

So NH4-N is reduced by CWs only in four months like January ,February ,May and

July by 10%, 5%, 14%, 6% respectively, otherwise the values are similar to effluent


NH4-N Influent 16.4 18.3 8.0 16.5 15.5 20.1 34.3 26.0 14.1 14.0 9.7 10.9

NH4-N Effluent of TF 3.3 2.7 0.2 0.3 2.3 0.3 2.6 0.6 0.2 0.2 1.0 1.0

NH4-N Effluent of CWs 1.7 1.8 0.2 0.2 0.2 0.2 0.4 0.4 0.3 0.2 1.0 1.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

mg

/ l

NH4-N influent and effluent , Gadenstedt

Table 9.1: NH4-N reduction in percentage by TF and CWs

Month % reduction by TF % reduction by CWs

Overall efficiency

Jan 80% 10% 90%

Feb 85% 5% 90%

Mar 98% 0% 98%

Apr 98% 0% 99%

May 85% 14% 99%

June 98% 0% 99%

July 92% 6% 99%

Aug 98% 1% 99%

Sep 99% -1% 98%

Oct 99% 0% 99%

Nov 90% 0% 90%

Dec 91% 0% 91%



from trickling filter. However, finally NH4-N effluents from CWs are below the legal

limit of 10 mg /l mentioned by Gadenstedt WWTP. Overall efficiency of NH4-N

reduction is found by 96%.

In Berel, NH4-N concentration in the wastewater varies from lowest 34.4 mg/l to

maximum 61mg/l as shown in fig 9.8. After retention in settling pond, effluent values

of NH4-N are found on the range of 17- 41.9 mg/l and discharge into the CWs at the

surface loading rate of 59 l/m2.d and organic loading 1.8 g/m2.d.

Fig 9.8: NH4-N influent and effluent values at Berel WWTP

Concentration of NH4-N effluent from CWs is lower than 10mg/l from April to

December. The effluent values of NH4-N are more than 10 mg/l in three months like

January, February, and March. From the fig 9.9, the efficiency of SP and CWs for

NH4-N reduction varies within 20 - 56 % (with average 38 %) and 22 -70 % (with

average 48%). Similarly, final effluent from maturation pond shows the very low

efficiency of NH4-N reduction only in four months like March. April, May and July on

the range of 1-10% .In the other hand, concentration of NH4-N increased in remaining

months varies from 4 % to 26 % beside above mentioned four months. (More detail

can be seen in Appendix II)


NH4+ Influent 51.6 61.0 50.0 40.7 42.1 48.7 54.8 58.6 42.7 52.4 40.6 34.4

NH4+ Effluent of SP 41.5 41.4 26.9 20.3 27.6 32.0 39.9 41.9 24.5 25.2 17.9 23.4

NH4+ Effluent of CWs(1+2) 18.8 26.3 15.7 6.8 1.8 1.5 1.6 1.3 1.0 0.4 0.4 6.9

NH4+ Effluent of PP 26.9 28.6 12.5 3.0 0.7 4.1 1.1 1.5 4.2 7.3 10.7 12.5

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

mg

/l

NH4 - N influent and effluent ,Berel



Fig 9.9. NH4-N reduction efficiency of Berel WWTP

From the above result analysis of Gadenstedt and Berel wastewater treatment plants,

it can be concluded that ammonium nitrogen is reduced by converting into nitrate

through nitrification process. Biological nitrification takes places in the trickling filter

and constructed wetlands converting ammonia in wastewater to nitrate using aerobic

autotrophic bacteria in the treatment process. Nitrification is actually a two-step

process for removing ammonia from wastewater using two different types of

autotrophic bacteria. In the first step ammonia is oxidize to nitrite by bacteria in the

genus Nitrosomonas under nitritation and then oxidize nitrite to nitrate by bacteria in

the genus Nitrobacter under nitrification (Kadlec and Wallace, 2009). These bacteria

known as “nitrifiers” are strict “aerobes,” meaning there must have free dissolved

oxygen to perform their work. Biological nitrification systems are designed in the

trickling filter and constructed wetlands to completely convert all ammonia to nitrate.

Oxidized nitrogen forms (e.g., nitrite and nitrate) do not bind to solid substrates, but

ammonia is capable of sorption to both organic and inorganic substrates. Because of

the positive charge on the ammonium ion, it is subjected to cation exchange .Ionized

ammonia may therefore be removed from water through exchange with detritus and

inorganic sediments in constructed wetlands. But it is not analyzed how much

ammonia is absorbed in the soil substrate of constructed wetlands. Based on the

-40%

-20%

0%

20%

40%

60%

80%

100%

Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec% reduction by MP -16% -4% 6% 10% 3% -5% 1% 0% -7% -13% -26% -16%

% reduction by CWs 44% 25% 22% 33% 61% 63% 70% 69% 55% 47% 43% 48%

% reduction by SP 20% 32% 46% 50% 34% 34% 27% 28% 43% 52% 56% 32%

20%32%

46% 50%34% 34% 27% 28%

43%52% 56%

32%

44% 25%

22%33% 61% 63% 70% 69%

55%47% 43%

48%

-16%-4%

6%

10%3%

-5%

1%

0% -7% -13%-26%

-16%

NH4 - N reduction in % ,Berel



stoichiometric relationship, Kadlec and Wallace (2009) pointed out theoretically that

total oxygen required 4.57 g per gram of NH3-N oxidized in which 3.43g O2 per gram

of NH3-N oxidized by the first nitritation reaction and 1.14g O2 by the second

nitrification reaction. Similarly, Cooper and Job (1996) explained about approximately

4.3 mg O2 per mg of NH4-N is required to oxidize into nitrate nitrogen and nitrification

occurs only under aerobic conditions at dissolved oxygen levels of 1.0 mg/L or more.

This result shows that oxygen is available in sufficient quantity for microbial activity to

convert ammonium nitrogen into nitrate in the trickling filter and constructed wetlands.

In the case of constructed wetlands, influent wastewater flow vertical through the filter

media and feeding intermittent system, so maximum oxygen entered the bed from

atmosphere via pores and root. But at Gadenstedt, there is very low organic loading

rate in influent of CWs, so there is low efficiency for reduction of ammonium nitrogen.

The efficiency of treatment plant for ammonium nitrogen reduction in Gadenstedt and

Berel is found 86% and 81% respectively. The discharge of ammonium nitrogen from

wastewater treatment plants has a very less amount and it is not challenging for

aquatic life.

9.4 Total nitrogen (TN) analysis of Gadenstedt and Berel WWTP

Total Nitrogen (TN) is the sum of nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N),

ammonia-nitrogen (NH3-N) and organically bonded nitrogen. Total Nitrogen (TN)

should not be confused with TKN (Total Kjeldahl Nitrogen) which is the sum of

ammonia-nitrogen plus organically bound nitrogen but does not include nitrate-

nitrogen or nitrite-nitrogen. TN is sometimes regulated as an effluent parameter for

municipal and industrial wastewater treatment plants, but it is more common for limits

to be placed on an individual nitrogen form, such as ammonia. Treatment plants that

have a TN limit will usually need to nitrify and denitrify in order to achieve the TN

limit.

This graphs shows that total nitrogen concentrations in wastewater varies from

minimum 29.4 mg/l to maximum 47 mg/l with an average value of 39.6 mg/l. The

effluent TN from trickling filter varies from 12.8 – 15.4 mg/l in summer and on the

range of 16.5 – 18.6 mg/l in winter.



Fig 9.10: Total nitrogen (TN) influent and effluent values at Gadenstedt WWTP

Likewise, lowest concentrations of TN in the effluent of CWs are found June, July and

August with an average value of 2.1 mg/l, 3.6 mg/l and 1.3 mg/l respectively. TN

effluent from constructed wetland is found 7.22 mg/l (average), this value is 73% less

than the legal limiting limit of 27 mg/l mentioned by Gadenstedt WWTP and overall

efficiency of TN reduction is found 81 % (trickling filter - 58% and CWs - 23 %).

Influent

mg/l

Effluent of TF

mg/l

Effluent of CWs

mg/l

NH4-N 16,97 1,20 0,61

NO3-N - 14,75 6,61

NO2-N - 0,09 0,07

Nges 39,66 16,07 7,22

N org 16.89 - -

Table 9.2: Annual average value of nitrogen concentration at Gadenstedt WWTP (year 2010, sample n=52)

Nitrogen contains in different form which polluted water is originally present in the

form of organic nitrogen and ammonia. In the table 9.2, organic nitrogen and

ammonia concentration in waste water are 43% and 43 % respectively. From the

above table shows wastewater with TN (39.6 mg/l) in which 43 % concentration as

NH4 –N and 43 % organic nitrogen, entered into the trickling filter, it goes under


TN Influent 44.5 38.4 37.7 43.5 38.6 44.3 47.0 39.6 34.6 29.4 35.9 42.0

TN Effluent of TF 17.7 18.6 16.5 17.3 20.9 15.4 11.5 12.8 12.5 18.7 16.0 16.5

TN Effluent of CWs 12.6 12.1 9.7 8.3 5.8 2.1 3.6 1.3 4.2 7.9 8.0 12.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0m

g /

lTotal Nitrogen influent and effluent ,Gadenstedt



biochemical process which converts organic ammonia nitrogen into ammonia and

further oxidized first into nitrite, then into nitrate. Then effluent of NH4 –N, NO3-N and

NO2-N contains 1.2 mg/l, 14.75 mg/l and 0.09 mg/l respectively. This results show

nitrite and ammonium nitrogen are at minimum concentration (at or near zero) and

nitrate is at a maximum value, the wastewater has been fully nitrified. A fully nitrified

wastewater will have little or no organic nitrogen being utilized as a nutrient by

microorganisms in the treatment process (www.asaanalytics.com/total-

nitrogen.php)

Fig 9.11: Total Nitrogen influent and effluent values of Berel WWTP

In the case of Berel, effluent data of NO3-N, NO2-N and TN was measured in the

constructed wetlands and polishing pond to analysis the efficiency of treatment

process. Data analysis about the ammonium nitrogen was already discussed in

previous section 9.3 of this chapter.

Table 9.3: Monthly average effluent data of different nitrogen form measured in constructed wetlands and polishing pond at Berel WWTP (data - 2010, n = 46 sample)


TN Effluent of CWs 24.7 31.1 44.4 46.4 35.1 29.9 45.9 45.6 32.4 21.1 23.8 13.2

TN Effluent of PP 28.6 29.5 20.8 14.7 5.9 4.7 1.4 4.2 9.8 11.9 14.1 13.4

0.0

10.0

20.0

30.0

40.0

50.0

mg

/ l

Total nitrogen influent and effluent ,Berel

CWs PP

Month NH4-N NO3-N NO2-N TN NH4-N NO3-N NO2-N TN

Jan 18,81 5,74 0,19 24,74 26,9 1,7 0,1 28,6

Feb 26,26 4,65 0,23 31,14 28,6 0,8 0,1 29,5

Mar 15,67 29,44 0,90 44,38 12,5 6,4 1,3 20,8

Apr 6,85 39,16 0,42 46,42 3,0 11,0 0,8 14,7

May 1,80 32,90 0,43 35,12 0,7 5,0 0,2 5,9

June 1,50 28,28 0,11 29,89 4,1 0,4 0,2 4,7

July 1,63 44,23 0,07 45,93 1,1 0,3 0,0 1,4

Aug 1,27 44,23 0,07 45,57 1,5 2,4 0,3 4,2

Sep 0,97 31,35 0,07 32,39 4,2 6,9 0,6 9,8

Oct 0,41 25,97 0,05 21,13 7,3 5,7 1,0 11,9

Nov 0,35 23,38 0,06 23,79 10,7 4,9 0,5 14,1

Dec 6,95 6,17 0,08 13,20 12,5 0,8 0,2 13,4

http://www.asaanalytics.com/total-nitrogen.php




From the above table 9.3, effluent value of NO3-N is low in winter seasons varies

from 4.66 – 6.95 mg/l, when the water temperature was 5-7°C and maximum

effluents during the summer in June and July with the average value of 44.23 mg/l

,when the water temperature is found 14 -18°C (see the temp fig 9.17). The

nitrification process is temperature dependent so nitrification is occurred in CWs

during the summer by Nitrosomonas and Nitrobacter converting ammonia and

ammonium to nitrite and nitrite to nitrate. The reaction is generally coupled and

proceeds rapidly to the nitrate form, which means nitrite produced by Nitrosomonas is

instantly oxidized by Nitrobacter to nitrate and therefore, the concentration of NO2-N

is very less or near to zero (Schneider and Fresenius, et. al 1989).

Similarly, the effluent values of NH4-N from polishing pond are high in winter and

minimum in summer. Nitrate values are on the range of 0.3-11.0 mg/l shows the

denitrification process occurred in the reduced environment of the water column,

where anoxic conditions prevailed. This may be due to the thicker sediment layer- as

dead algae settled in the bottom as sediments that contained more denitrifying

organisms. Nitrates reduce to nitrites, which in turn easily combine to form

substances dangerous to man. Total nitrogen concentration fluctuation is highly

depended upon the nitrification and denitrification process in the treatment system.

TN effluent finally into the receiving water course is 1.4 – 4.7 mg/l in summer and

maximum values in winter varies 13.4 -29.5 mg/l, however, these values are below

the legal limit of 40 mg/l authorized by Berel WWTP.

The WHO recommended as „‟International Standards„‟ for the maximum limit for

nitrate concentration in the drinking water is 50 mg/L, which is equivalent to 11.3 mg/l

as NO3-N (Chilton, 1996). Similarly, Mohaupt et al. (1996) reported that nitrate (NO3-

) concentration in surface water samples in Germany is not higher than 25 mg/l,

which is half the drinking water limit. Concentration of NO3- as low as 10 mg/l are

deem unacceptable for the baby food, which causes methemoglobinemia problem

and nitrite as low as ca. 10 to 20 mg/l are highly toxic for fish (Schneider and

Fresenius et al., 1989). In Europe, the maximum consented level of nitrates in

potable water is 50.0 mg/L (www.environ.ie), while in the USA the EPA has

established a guideline for the maximum level of nitrate nitrogen of 10 mg/L (NO-3-

N), which corresponds, to 45.0 mg/L of nitrates. Nitrogen removal on the other hand

is effected through sediment accumulation, adsorption of ammonium onto the organic



sediments (Howard-Williams, 1985), plant uptake and nitrification-denitrification

processes.

9.5 Phosphorus of Gadenstedt and Berel WWTP

Phosphorus appears in different form in wastewater as orthophosphate, dehydrated

orthophosphate (polyphosphate) and organically bound phosphorus, due to biological

oxidation results in the conversion of most of phosphorus to the orthophosphate

forms ( H2PO4-, HPO4

2-, PO43-)(Cooper el at., 1996). Microbes utilize phosphorus

during cell synthesis and energy transport. As a result, 10 to 30 percent of the

influent phosphorus is removed during traditional mechanical / biological treatment

(Metcalf and Eddy, 1991). Phosphorus is important nutrients for the plants growth

which are used in during the growing seasons.

Fig 9.12: phosphorus influent and effluent values of Gadenstedt WWTP

There is no legal limit specified by German federal Government about the

phosphorus concentration in wastewater before discharging to receiving water course

concerning to the small treatment plant for less than 5000 population. But only

specific legal limit of 5 mg/l phosphorus concentration in effluent water according to

Gadenstedt WWTP. In the fig 9.12, P concentration is found 7.3 mg/l in July and

August and 5.3 mg/l in January, which are higher than legal limit. After then the

remaining month‟s concentration is below the 5 mg/l. Effluent form trickling filter is

found on the range of 1.5 – 4.6 mg/l (average 2.6 mg/l), and final effluent of CWs is

varied from 1.2 mg/l to 2.6 mg/l (average 1.8 mg/l) respectively. P reduction efficiency

by TF and CWs are 37% and 17% respectively.


TP Influent 5.3 3.7 1.8 4.0 3.9 4.3 7.3 7.3 3.0 3.6 2.8 3.1

TP Effluent of TF 1.9 2.4 1.5 2.2 2.9 2.7 4.6 4.6 1.6 2.7 1.8 1.7

TP Effluent of CW 1.5 2.0 1.2 1.5 1.8 1.5 2.6 2.6 2.1 1.6 1.2 1.4

0.01.02.03.04.05.06.07.08.0

mg

/ l

phosphorus influent and effluent , Gadenstedt



Fig 9.13: phosphorus influent and effluent values of Berel WWTP.

In the case of Berel, P inflow concentration was not as high as compare to limiting

values of 8 mg/l given by Berel WWTP and here only in three months, the

phosphorus values are more than limiting values in February, July and October as

12.76 mg/l, 10.18 mg/l and 11.45 mg/l respectively. Phosphorus effluent from settling

pond is average value of 6.27 mg/l, representing 22 % reduction and only the effluent

value varies by 52 % in August. In construction wetland, P is reduced highly by 74%,

58% and 102 % respectively in summer (June, July and August). In winter seasons,

CWs is also functioning properly to trap the phosphorus and reduced by 35 % and in

autumn by 27 % respectively. Final P removable efficiency of CWs is found 41%.

Fig 9.14: Phosphorus reduction efficiency of Berel WWTP


Pges Influent 8.39 12.76 7.70 8.11 8.57 7.57 10.18 6.80 5.65 11.45 6.51 5.58

Pges Effluent of SP 6.74 6.86 4.59 4.91 6.16 7.50 7.81 10.36 4.97 7.26 4.25 3.81

Pges Effluent of CWs(1+2) 2.77 3.01 5.18 2.36 1.77 1.94 1.94 3.38 3.56 2.61 3.20 2.31

Pges Effluent of MP 4.49 4.59 3.93 3.16 3.19 4.25 4.04 2.85 3.14 3.60 4.14 3.75

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

mg

/ l

Phosphorus influent and effluent ,Berel

-60%

-40%

-20%

0%

20%

40%

60%

80%

100%

120%


20%46% 40% 39% 28%

1%23%

-52%

12%37% 35% 32%

47%

30%

-8%

31% 51%

74%

58% 102%

25%

41%16% 27%

-20% -12%

16%

-10% -17%-31% -21%

8%

7%

-9% -14%-26%

phosphorus reduction in % ,Berel

Effluent of SP Effluent of CWs(1+2) Effluent of MP



It was found interesting by the data analysis in fig 9.14 that effluent value of

phosphorus from maturation pond increased in the month of summer like June and

July by 31% and 21% with comparison to constructed wetlands. Similarly in winter

concentration also varies from 12 % in February to 26 % in December. The study

shows that P concentration is increased by average value of 11% in comparison to P

effluent of CWs. However final P concentration on effluent is an average value of

3.76 mg/l, which is nearly 47 % less than the legal limiting values.

The possible mechanisms of phosphorus removal in vertical flow through beds

comprise plant uptake, assimilation by micro-organisms and physico-chemical

processes associated with the bed media. Most of the phosphorus in the soil column

is structural phosphorus, both organic and inorganic. Very small fraction is found in

pore water or as sorbed phosphorus. It is assumed that Phragmites (reed), are

planted in constructed wetlands of Gadenstedt and Berel, uptake phosphorus from

root zone as an important nutrients, which are used during the growing seasons.

Kadlec and Wallace et.al (2009) indicated that especially most plant roots are found

on the top soil layer at the depth of 0-10 cm, which helps to remove phosphorus with

high concentration from this zone by taking up during the cycle of growth.

Phosphorus sorption is heavily influenced by the amount of calcium carbonate,

aluminum oxides and iron oxides and organic matter present in the bed aggregate

(Vohla et al., 2008). But it is also notable that algae growth, death, decomposition in

pond and plant growth, death, decomposition, litter formation may increase in

phosphorus mass during the cold seasons.

Jin et al (2005) estimated that P sorption reactions are endothermic, colder water

temperatures will decrease the apparent sorption capacity of the bed aggregate. By

the study of Gadenstedt, sorption capacity decreased by 10% when the water

temperature was decreased from 18°C to 5°C. Similarly in the case of Berel, sorption

capacity decreased by 8 % after water temperature decreased from 19 °C to 3 °C.

Generally the amount of phosphorus that can be recovered through harvesting of

emergent wetland plants is about 5-10 g/m2 (Vymazal et al., 2005a). Maximum

nutrients by emergent macrophytes was found to be in the range of 200-1560 kg

N/ha and 40 -375 kg P/ha in Florida (Reddy and DeBusk, 1987). Phragmites (reed)



stored the phosphorus in tissue at the rate of 2-3 g P /kg and biomass growth varies

10 – 60 t/ha .yr (www.fao.org). Emergent macrophytes uptake nutrients depend upon

the climate, plant density, loading rate and culture system. It is better to harvest

above ground biomass once a year rather than frequently harvesting should improve

the overall nutrients efficiency. However, it is not found such kind of practice like

harvesting of emergent macrophytes from the constructed wetlands at Gadenstedt

and Berel WWTP.

9.6 pH value of Gadenstedt and Berel WWTP

The physical and chemical environment of a wetland affects all biological process.

Hydrogen ion concentration, measured as pH, influences many biochemical

transformations. It influences the partitioning of ionized and unionized forms of

carbonates and ammonia, and controls the solubility of gases solids, such as

ammonia and solids such as calcite. Hydrogen ions are active in cation exchange

processes with wetlands sedimentation and soils and determine the extent of metal

binding (Kadlec und Wallace, 2009).

Fig 9.15: pH value of influent and effluent of wastewater at Gadenstedt WWTP

In the above fig 9.15, the pH values of influent showed the fluctuation in every month

and found to be average values of 8.0, which showed the wastewater in basic (alkali)

nature. The pH effluent from trickling filter is found low in July and August with

average value 7.54 and maximum value in January, February, March and December

falls under the range of 7.96 to 7.99; however mean value of pH is 7.68. Wastewater

was treated through the trickling filter, water containing organic matter decomposed;

ammonium nitrogen in wastewater is oxidized first to nitrite nitrogen and then to


pH Influent 8.11 8.26 8.03 7.92 7.90 7.91 8.02 7.95 7.88 8.06 8.01 7.98

pH Effluent of TF 7.96 7.98 7.98 7.92 7.84 7.81 7.54 7.57 7.81 7.85 7.82 7.99

pH Effluent of CWs 7.54 7.70 7.54 7.58 7.41 7.18 7.17 7.12 7.16 7.14 7.30 7.48

6.406.606.807.007.207.407.607.808.008.208.40

pH influent and effluent value,Gadenstedt

http://www.fao.org/



nitrate through nitrification. The nitrification process produces acid and acid formation

lowers the pH value.

The pH value of final effluent water from constructed wetlands is found average value

of 7.36 during the analysis, whereas the pH value was lower in summer, autumn and

higher value in winter and spring respectively.

Fig 9.16: pH influent and effluent values of Berel WWTP

Similarly, in the case of Berel treatment plant, pH value of influent water in the first

settling pond was found more than 8.0, showing the alkalinity nature of wastewater.

pH effluent in settling pond is found on the range of 7.24 to 7.57 except October and

November before entering to constructed wetlands. After the oxidation of organic

matter and ammonium-nitrogen in the VF constructed wetlands during the

intermittent hydraulic loading system; aerobic reaction occurred and released the

carbon dioxide forming the carbonic acid, resulting the pH value reduced having

average value 6.7. Final pH effluent from polishing pond is found mean value of 7.68,

the main cause of algal activity. In the pond during the photosynthesis process algae

consumed the CO2 (Carbon Dioxide) after decomposed and leaving an excess of

hydroxyl ions. The major source of carbon dioxide for algae depends upon the

carbonate and bicarbonate ions reaction. As a result, the pH of the water is increased

up to 7.68 (average value) in polishing pond. The potential of increasing the pH of

wastewater to high levels by CO2 stripping through air, N2, O2 and a gas mixture

(95% N2+ 5% CO2) (Cohen and Kirchmann, 2004).


Influent 8.48 8.57 8.25 8.31 8.40 8.25 8.48 8.39 8.11 8.49 8.29 7.95

Effluent of SP 7.52 7.34 7.54 7.55 7.57 7.24 7.50 7.57 7.34 8.03 7.63 7.42

Effluent of CWs(1+2) 7.10 7.14 6.51 6.62 6.59 6.57 6.43 6.41 6.53 6.59 6.85 7.01

Effluent of PP 7.68 7.65 7.67 7.98 7.70 7.67 8.05 7.69 7.40 7.54 7.65 7.45

0.00

2.00

4.00

6.00

8.00

10.00 pH influent and effluent ,Berel

http://www.springerlink.com/content/?Author=Yariv+Cohen



From the data analysis the main factor which affects the pH is the amount of plant

growth and organic material within a body of water. When this material decomposes

carbon dioxide is released. The carbon dioxide combines with water to form carbonic

acid. Although this is a weak acid, large amounts of it will lower the pH. The effluent

value of pH from trickling filter and constructed wetlands is basic nature, whose value

only little bit more than neutral water. pH is not changed drastically and cannot be

consider the synergy effect on the water. pH play a vital role for healthy aquatic

system, can function only within a limited pH range. As a consequence, surface

water discharge permits frequently require 6.5< PH <9.0. Wetland water chemistry

and biology are likewise affected by pH. Many treatment bacteria are not able to exist

outside the range 4.0< pH <9.5 (Metcalf and Eddy Inc., 1991). Denitrifies operate

best in the range 6.5 <pH <7.5 and nitrifies prefer pH =7.2 and higher.

This is one of the suitable environments for wetlands water chemistry for nitrifying

bacteria and microbiological degradation process. The Phragmites australis used in

constructed wetlands can withstand within the pH value of 4.8 to 8.2 (Duke, 1978,

1979). There is no harmful effect on the growth and survivable of Common Reed in

the constructed wetlands. The height of common reed is found to be 2-3 m in the real

field Gadenstedt and Berel. Due to very close value to neutral water, the effluent

water from constructed wetlands and polishing pond did not affect on the quality of

water in receiving river and seemed no danger to aquatic life present in the river.

9.7 Temperature

The water temperature in treatment wetlands is important for several reasons such

as: (1) Temperature modifies the rate of several key biological processes, (2)

Temperature is sometimes a regulated water quality parameter, (3) Water

temperature is a prime determined of evaporative water loss, (4) Cold–climate

wetlands systems have to remain functional in subfreezing condition (Kadlec and

Wallace et al., 2009).

Treatment wetlands are solar powered ecosystems, resulting in annual cyclic

temperatures, where an energy balance is dominated by radiation, heat transfer, heat

gains or losses, heat conduction and convection among the ground, the atmosphere

and the wastewater (Reed et al., 1995). Wetland energy flows are the proper



framework to interpret and predict not only evaporative process, but also wetlands

water temperatures (Kadlec and Wallace et al., 2009).

Fig 9.17: Annual pattern of water and air temperature at Gadenstedt WWTP

From the temperature figure of Gadenstedt and Berel, it is clearly showed that the

annual cycle of wetland water temperature as well as air temperature follows a

sinusoidal pattern, with a summer maximum and a winter minimum. The air

temperature in winter are varies from -4 °C to 0 °C, whereas water temperature

remains 5 - 7 °C. Similarly air temperature was maximum in summer varies from 23

to 34°C and water temperature remains 14 to 18 °C respectively. This is due to the

convection and diffusion method of water surface and transfer heat from air to the

wetland. From the correlation graphs, water temperature is dependent on air

temperature and around the less than 50 % heat is transferred into the wetlands (Tw

= 0.44 Ta, R2 = 0.74).

Evapotranspiration (ET) is the main causes of water losses to the atmosphere

through the water surface, media used and emergent vegetation in constructed

wetlands. But the presence of vegetation which helps to retard evaporation, main

reasons is shading of the surface, increased humidity near the surface and reduction

of the wind velocity at the surface. Another important effects of plants is to provides

insulation that helps protecting the soil from freezing during winter, but on the other

hand, it keeps the soil the soil cooler during the spring (Vymazal et al. 1998). Abtew

(1996) operated vegetated lysimeters for two years in marshes with three vegetation

types: 1) Typha domingensis, 2) a mixture including Pontederia cordata, Saittaria


Air Temp Min -4 0 4 7 9 14 18 15 11 8 4 -4

Air Temp Max 0 5 10 16 18 29 34 23 18 14 9 0

Water Temp average 6 5 7 10 11 14 18 17 15 13 14 7

-10-505

10152025303540

°C

Air and Water temperature ,Gadenstedt



latifolia and Panicum hemitomon, and 3) submerged aquatic Najas guadalupensis

and Ceratophyllum demersum. The annual average water losses (ETp) were 3.6, 3.5,

3.7 mm/d respectively.

Fig 9.18: Relationship between annual average water and air temperature in CWs, at Gadenstedt WWTP (Tw = 0.44 Ta, R2 = 0.74)

Various studies have considered the evaluation of the treatment efficiency of

constructed wetlands as a function of temperature depending on components such

as substrate composition, degree of plant growth, seasonal changes in

evapotranspiration rates, and microbial activities (Winthrop et al., 2002). Kadlec and

Reddy (2000) studied the temperature dependence of many individual wetland

processes and wetland removal of contaminants in surface flow wetland. They

concluded that microbial mediated reactions are affected by temperature; the

treatment response was much greater to changes at the lower end of the

temperature scale (<15ºC) than at the optimal range (20 to 35 ºC). Furthermore they

observed that the processes regulating organic matter decomposition were affected

by temperature and so were all the nitrogen cycling reactions (mineralization,

nitrification and denitrification).

With caparisons the fig. of air and water temperature with the fig. of COD, BOD, NH4-

N, TN and TP reduction, it is clearly showed that 94-96% BOD, 86-88% COD is

reduced by microorganism in the period of summer (June, July, August), when water

temperature was 14-18°C. BOD (84-94%) and COD (72-89%) reduced in winter

(January, February and December), when the water temperature was on the range of

5-7°C. Similarly constructed wetlands reduced COD (20-83%), NH4-N (63-70%), and

y = 0,4387x + 6,7985R² = 0,7451

0

2

4

6

8

10

12

14

16

18

20

-5 0 5 10 15 20 25 30

Wat

er

tem

per

atu

re

°C

Air temperature ° C

Air and Water temperature corelation



TP (74-102%) in summer and COD (34-47%), NH4-N (25-48%), TP (27-47%) in

winter in the case of Berel project.

Fig 9.19: Water temperature of inflow and outflow from SP, CWs, and PP of Berel WWTP

From above data analysis, it can be concluded that temperature affected on the

organic matter (COD, BOD) decomposition and nutrients removable by

microorganism that found maximum in summer and minimum in winter. This is the

very simple way analysis comparing of monthly and seasonally BOD, COD, NH4-N

and TP reduction in percentage with the monthly and seasonally water temperature.

Nutrients reductions are strongly influenced by plants and algal uptake on a seasonal

basis. It is analyzed from above data that Microbial activity is peak in midsummer and

low in winter. These results justified the literature study mentioned above by Kadlec

and Wallace (2009). For the better understanding of temperature effects on pollutants

reduction and efficiency of CWs, it is necessary for the concrete analysis by using

modified Arrhenius equation (Kt = K20 * θ (T-20)) and by tracer method.

9.8 Energy / Power consumption at Gadenstedt and Berel WWTP

Energy is required for the development of different sector like energy consumed 44%

by industry, transportation by 3% and households by 27% and services and

commercials by 26% (AGEB, 2008). Electricity demand in Germany was increased

by 16.8% from 1990 to 2008 and decreased by 7 % from 2008 to 2009

(www.umweltbundesamt.de). Furthermore, as populations growing, more demand for

0

5

10

15

20

25

0 2 4 6 8 10 12 14

°C

Month

Water Temperature

Water temp inflow Water temp effluent of SPWater temp effluent of CWs Water temp effluent of PP

http://www.umweltbundesamt.de/



electricity and continual increases in energy costs which affect the operation and

maintenance cost in wastewater treatment plants. This gives overstress to people to

expense more money on wastewater management. So it is compelled to rethink

about the alternative system of wastewater treatment system not only in Germany but

also in the case of underdeveloped country of Asia, Africa and Latin American.

So it is analysis the data of power consumed by electric pumps, which were installed

in different parts of treatment plants like screening, grit chamber, trickling filter, and

constructed wetlands for the wastewater treatment process. It is only to find out

difference of total annual power consumed and energy cost between the

conventional and constructed wetlands system during the wastewater treatment.

Fig 9.20: Power consumed by conventional system and Constructed Wetlands

From the fig 9.20, power consumed by pumps during the operation periods in the

conventional system in every month is higher than the pumps used in constructed

wetlands. However electricity used by two pump for wastewater lifting, screening,

compressor, sand classifier, sand blower, trickling filter (2 pumps) in the conventional

system and only two pumps are used to pump out water into CWs, which are

collected in collection chamber.

The total power consumed for the wastewater treatment process is 84152 kWh. As

shown in figure 9.21, in which conventional and CWs system consumed about 65060

kWh (77%) and 19092 kWh (23%) respectively. Total annual energy cost is invested

in 14928 € in which conventional system bare 11541.64 € and 3386.92 € by CWs.


By Conventional system 8101 6542 6881 4863 4943 4087 3603 3786 4129 4845 6153 7127

By Bodenfilter 1652 1447 1134 1270 1323 1079 1152 1318 1338 1554 2912 2913

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

kWh

Power consumption at Gadenstedt WWTP



Total energy cost to be paid 5.33 € per person (4.12 € for conventional & 1.21€ for

CWs).

Fig 9.21: Energy cost of Gadenstedt WWTP

Similarly, in the case of Berel, one small pumps of 4.5 kW was installed in the

screening to collect the screenable materials and two pumps are used as

alternatively to distribute the wastewater on the CWs as per design hydraulic loading

rate of 59 l/m2.d (average).

Fig 9.22: Power consumed and total power cost for Berel WWTP

Total power consumed by these three pumps are 11078 kWh in the year 2010 and

energy cost be 2077.00 €. Total energy cost is to be paid 3.46 € per person per year,

which is equivalent to 1.22 € / m3, which is very cheap for the wastewater treatment.

77%

23%

Energy cost camparision ,Gadenstedt

By Conventional systemBy Bodenfilter

3386.92 €

11541.64 €

19092 kWh

65060 kWh

Total power cost = 14928 . 56 €


By CWs 1835 2576 941 543 484 456 384 384 599 518 2453 538

0

500

1000

1500

2000

2500

3000

kWh

Energy consumption in Berel CWs



Similarly, in comparison to 2002, in Germany municipalities are allowed to pass on

the full cost to the consumer without and profit with average wastewater fee was 2.24

Euro/m3, which translates to an annual cost of 117 euro per person (www.eawag.ch).

According to BDEW, the federal association of the electricity and water industry,

electricity prices for private households rose by 2.1% in the first half of 2010. A

household with three people using 3,500 kWh pays about EUR 69 per month

(www.germanenergyblog.de).

So decentralized system is very fruitful to treat wastewater of small community in the

economic way and helps to preserve the environment with the ecological way also.

9.9 Efficiency of Constructed Wetlands in Germany and Nepal

Germany Nepal

Gadenstedt* Berel** Dhulikhel** Sunga**

in out rem %

in out rem %

in out rem %

in out rem %

mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l

COD 37.87 16.66 56 243.97

39.89 84 325 20 94 1188 50 96

BOD5 8.35 4.40 47 190 12.92 93 110 3 97 450 30 94

NH4-N 1.2 0.61 49 30.71 8.59 72 33 1.6 95 408.9 214.1 48

NO3-N 14.75 6.61 55 26.6 4.34 84 - - - - - -

TN 16.05 7.29 55 - - - - - - - - -

TP 2.47 1.81 26 6.23 2.92 53 8 4 50 44.3 24.3 45

TSS - - - - - - 83 2.3 97 204 28 86

Table 9.4: Summary of removal efficiency of constructed Wetlands in Germany and Nepal. (* as tertiary treatment system, ** as secondary treatment system)

In the given table 9.4, all the data are taken in average inflow and outflow values and

focused to measure the removal efficiency of constructed wetlands. Concentration of

pollutants in wastewater and removal efficiency of CWs at Gadenstedt and Berel are

already discussed in this chapter and similarly in the case of Dhulikhel and Sunga

described detail at chapter 7. But here the main objective of the results analysis is to

compare the treatment efficiency of constructed wetlands between Nepal and

Germany being the different climatic condition.

http://www.eawag.ch/



The removal efficiency of COD at Gadenstedt and at Berel is found 56% and 84%

respectively. Efficiency of COD reduction at Dhulikhel treatment plan is 94%, which is

38% higher than Gadenstedt and 10% more than Berel. Removal efficiency of COD

at Sunga is about 40 % more than Gadenstedt and 12% more than Berel. Similarly,

BOD reduction is nearly same efficiency between Sunga and Berel and only 3%

difference between Dhulikhel and Berel. 49% NH4-N is reduced by CWs at

Gadenstedt, 72% by Berel, 95% by Dhulikhel and 48% by Sunga respectively.

Similarly, TP reduction at Gadenstedt, Berel, Dhulikhel and Sunga are found 26%,

53%, 50% and 45% respectively.

This is demonstrated by removal efficiencies of BOD, COD, ammonium-nitrogen and

phosphorus given in percentage. The removal efficiency of organic compound (COD,

BOD) are high that indicates biological activity increased which is temperature

dependent. According to the Köppen Climate Classification System (1997), the global

climatic regions can be specified by the latitude ranges. Likewise, German lies under

the mid-latitude climate (Europe: 45° - 60° N) and temperate climate occurs and large

seasonal changes between summer and winter, high annual temperature range and

abundant precipitation throughout the year. Whereas, Nepal lies under low-latitude

climate (0° - 30° N and S) and partially part is under subtropical climate region. Major

climate characteristic are seasonal changes between a very wet, hot and a dry and

cooler period. High and tropical temperatures occurred during the wet season and

high precipitation during the wet season.

It is also noticed that NH4-N and TP removal performance found high in the case of

Berel and Dhulikhel and low in the case of Gadenstedt and Sunga. Nutrients removal

process is largely depend upon the material chosen in bed material and types of

macrophytes used in constructed wetlands. Kadlec and Wallace et.al (2009)

indicated that especially most plant roots are found on the top soil layer at the depth

of 0-10 cm, which helps to remove nutrients with high concentration from this zone by

taking up during the cycle of growth. Phosphorus sorption is heavily influenced by

the presence of calcium carbonate, aluminum oxides and iron oxides and organic

matter in the bed aggregate (Rustige et al., 2003).

Constructed wetlands are in operation in worldwide. However, there is long tradition

in this field especially in the temperate regions like Europe, North America and



Australia, but many systems have also been constructed and tested in subtropical

and tropical areas, especially in the South Asian and Southeast Asian countries, e.g.

India, Indonesia, Nepal, South China and Thailand, but also in tropical Africa.

9.10 Constructed wetlands as a suitable technology in Nepal

Most of the centrally collected wastewater treatment plants in Nepal are not

functioning due to high cost of operation and maintenance and lack off trained human

resources. To mitigate the financial problem and minimize of water pollution, low-cost

natural treatment options like Constructed Wetlands (CWs) have been introduced in

Nepal since 1997. Due to the success of the first CWs system in Dhulikhel Hospital,

since then, the interest of people has been growing in this technology and more than

a dozen constructed wetlands have been established for various applications such as

the treatment of hospital wastewater, grey water, septage, landfill leachate,

institutional, universities and municipal wastewater.

Table 9.5: Efficiency of CWs and operation cost (UN-HABITAT, 2008 and ENPHO, 2004)

Since 1997 to 2004, there are 12 sub-surface flow constructed wetland systems in

operation for treatment of grey water, wastewater and fecal sludge in Nepal. In

general, the performance of the CWs has been excellent as shown in table 9.5. After

regular monitoring of the systems and analysis of wastewater sample which shows

high pollutant removal efficiency achieving more than 90% removal of TSS, BOD and

COD. Designed system does not need any electric energy as the wastewater is fed

hydro-mechanically into the beds.

Location

TSS Removal Rate (%)

BOD5 Removal Rate (%)

COD Removal Rate (%)

Total cost

US $

O&M cost US $ per annum

Dhulikhel Hospital

97 97 94 27,000 150

Sunga Community

98 97 96 36,111 722

Single house grey water

98 98 94 520 -

Kathmandu University

87 97 93 26,000 290

ENPHO 87 95 88 570 -

SKM hospital

97 98 94 27,000 -



The total cost of CWs at Dhulikhel hospital including the sewer lines was US$ 27,000

in 1997, while the cost of O&M per year is at US$ 150. For the single house, the

system required an investment of only about US$ 520 (NRs.36, 000) and O&M cost

is very negligible. In SKM hospital, total costs of the system including the sewer lines

were US$ 27,000. In Sunga community, the total cost of the treatment plant was US$

36,111 (NRs. 2.5 million) and average O&M cost of the wetland is about US$ 722

(NRs. 50,000) per year. These projects are an example of an approach towards the

sustainable management of water and wastewater, which has inspired people to

adopt this type of technology that can be managed by the community or institution

itself for the solution of currently mis-managed wastewater in the city.

The popularity of CWs for wastewater treatment are also increasing day by day and

innovative ideas also developed for the treatment of septage and landfill leachate in

the large scale. With this motto, the plant at Pokhara Sub-Metropolitan City was

designed to treat 35 m3 of septage and 40 m3 of landfill leachate per day. It was

estimated that the city generated 12,000 m3 of faecal sludge and 15,600 m3 of

municipal waste every year, all of which would be collected and brought to the site.

The treatment plant comprises of 7 compartmental sludge drying beds (area 1645

m2), 2 compartmental horizontal flow CWs (1180 m2) and 4 compartmental vertical

flow CWs (1500m2). The treatment plant at Pokhara is the largest constructed

wetland in Nepal and it was built at a cost of US$ 85,700 (Rs. 6 million) under the

financial support of Asian Development Bank (ADB). The effectiveness of the

treatment plant has not yet been monitored as it is still not fully operational. It is yet in

observation and however, as experiences from other countries have shown that

constructed wetlands can be used to treat faecal sludge as well landfill leachate, the

treatment plant built in Pokhara can be a model for other cities if it is operated

properly.

Nonetheless, one of the conventional treatment system plant at Guheshwori, the

operation and maintenance cost is estimated NRs 12.5 million per year (US $

167,000 /year) (Richards, 2003). This cost is really very big difference than the

constructed and operation cost of constructed wetlands. So, Constructed wetlands

(CWs) are less expensive for construction, operation & maintenance as compare to

conventional expensive technology as well as higher removal efficiency of pollutants



and utilization of treated effluent for multiple purposes. Therefore, CWs are an

alternative and suitable technology in Nepal, which are considered as effective,

economic and environmentally friendly and sustainable systems for wastewater

treatment.

9.11 Wildlife habitat at Gadenstedt WWTP

Constructed Wetlands and Combined biotopes (Lagoon) at Gadenstedt has been a

new destination to many wildlife habits. Some of the macro invertebrate groups can

be seen in the wetland area, such as Mollusca and insects but there are no

comprehensive lists of even the most common species in these groups. Especially

focus to bird species, about 70 species have been recorded from the Gadenstedt

WWTP and more than 1380 individuals have been caught and ringed. Reed Warbler,

Reed Bunting, Mallard, Greylag Goose and Tufted Duck are dominating bird in the

wetlands area. These are the high bird density (33 – 48 BP/ha.). Some of 27 species

birds are found migrants from the different places of Germany and as well as from

other country during the early spring and summer seasons. Some of them have been

achieved remarkable of long distant migrants from Ibiza, Southern Spain and France.

Fig 9.23: (a) Mr. Matthias Meyer with a Kingfisher in the station. (b) Snails

(invertebrates) on bed, (c) Tufted Ducks swimming at combined biotopes (Lagoon) The water bodies are enriched by nutrients and organic matter from wastewater and

stormwater discharge, which are suitable food chain supply for Tufted Duck and

macroinvertebrate are the main food of other birds in the wetlands area. There is no

hunting but consequent bird protection system. Some of artificial nest are provided

for the breeding process focus to Weißstorch birds. The diversity and abundance of

birds in and around wetlands attract the many birds watcher. So, constructed

wetlands are providing benefits beyond effective water treatment, such as wildlife

enhancement and recreational opportunity.

http://animals.about.com/od/i/g/invertebrate.htm

125 Chapter 10: Conclusion and Recommendation


10 Conclusion and Recommendation

Constructed wetlands have been evolved during the last five decades into a reliable

treatment technology which can be applied to all types of wastewater including

domestic, industrial and agricultural wastewaters, landfill leachate and stormwater

runoff. Pollution is removed through the processes which are under more controlled

conditions.

These treatment systems are very favorable for use in rural community and semi-

urban areas of low population density, where land is easily available with low price

and can usually be constructed from local materials. Constructed wetlands are very

effective in removing organics and suspended solids, whereas removal of nitrogen is

lower but could be enhanced by using a combination of various types of CWs.

Removal of phosphorus is usually low unless special media with high sorption

capacity are used.

Constructed wetlands require very low or zero energy input and, therefore, the

operation and maintenance costs are much lower compared to conventional

treatment systems. In addition to treatment, constructed wetlands are often designed

as dual- or multipurpose ecosystems which may provide food and habitat for wildlife

and create pleasant landscapes. So Gadenstedt WWTP is one of the tourist

attraction places for many visitors from different country as well as lot of flora and

fauna can be seen.

At Gadenstedt, constructed wetlands are used as tertiary treatment only for polishing

purpose which helps further reduction of organic matter and nutrients from the

wastewater to ensure better surrounding environment of receiving water course. And

the final effluent of CWs can be used for the multipurpose such as irrigation crops,

aquaculture products. However these practices are not in use and directly discharge

to small river Fuhse but it alternatively helps to recharging the ground water. The

concentration of organic matter and nutrients are very less than legal limit of Federal

law and specific limit of Gadenstedt WWTP.

As per trial experiment from December 2001 to April 2002, CWs used as secondary

treatment and removal efficient of COD, BOD5 was found more than 90 % and

126 Chapter 10: Conclusion and Recommendation


nutrients reduction 50% and 30% respectively. So it is recommended that CWs can

be used as secondary treatment to make more sense fulfilling its objective instead of

tertiary treatment and energy cost can be saved. The operation of trickling filter

would be better to close.

At Berel, wastewater is treated with the combination of CWs and pond system. The

treatment process achieves high effective in the reduction of organic matter and

nutrients. Final effluent values of polishing pond are increased than effluent of CWs.

So it is better to divert the effluent of CWs directly into the small river Sangebach

instead of pond 3.

CWs are also very suitable for the application in developing countries where most of

the problems with inadequate sanitation occur. A crucial step for the implementation

of CWs in developing countries is proper technology transfer.

Constructed wetlands (CWs) are an alternative and suitable technology in Nepal,

which are considered as effective, economic and environmentally friendly and

decentralized sustainable systems for wastewater treatment.

127 References


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