Case Study Hlt234- Final

7/30/2019 Case Study Hlt234- Final

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TABLE OF CONTENT

1.0 INTRODUCTION........................................................................................................................... 11.1 Background ............................................................................................................................... 11.2 Problem Statement ................................................................................................................... 1

1.3 Objectives.................................................................................................................................. 22.0 LITERATURE REVIEW ................................................................................................................... 1

2.1 Sewage Treatment Plant ........................................................................................................... 12.1.1 Sewage Treatment Method .........................................................................................12.1.2 Classification of Sewage Treatment Plant.................................................................... 2

2.1.2.1 Attached Growth Processes.......................................................................... 22.1.2.2 Suspended Growth Processes ......................................................................32.1.2.3 Hybrid Processes - Attached Growth with Suspended Growth.................... 3

2.2 Technologies for Sewage Treatment ........................................................................................ 42.2.1 Oxidation Pond (OP)..................................................................................................... 42.2.2 Sequencing Batch Reactor (SBR) ......................................................................... ......... 52.2.3 Extended Aeration (EA)................................................................................................ 72.2.4 Oxidation Ditch (OD) .................................................................................................... 8


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2.2.5 Rotating Biological Contactor (RBC)............................................................................. 92.2.6 Membrane Bio Reactor (MBR) ..................................................................................... 9

2.3 Comparison of Sewage Treatment Technologies ................................................................... 102.4 Life Cycle Assessment ............................................................................................................. 11

3.0 METHODOLOGY ........................................................................................................................ 133.1 Site Visits ........................................ ......................................................................................... 133.2 Process Description................................................................................................................. 14

4.0 RESULTS AND DISCUSSION ........................................................................................................ 174.1 Design and Process Review..................................................................................................... 174.2 Collected Data of STP .............................................................................................................. 194.3 Kinetic Parameters .................................................................................................................. 19

4.3.1 Calculations .......................................................................................... ...................... 204.4 Analysis.............................................................................................. ...................................... 25

4.4.1 Actual Removal Efficiency .......................................................................................... 254.4.2 Operational Cost ........................................................................................................25

5.0 CONCLUSION............................................................................................................................. 276.0 REFERENCES.............................................................................................................................. 28


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1.0 INTRODUCTION

A public Sewage Treatment Plant (STP) located in Cheras has been selected for the case study. This

STP which is serving for residential and commercial areas at Taman Segar Perdana, Cheras is operated and

maintained by Indah Water Konsortium Sdn Bhd (IWK).

1.1 Background

The process type of the selected STP is Sequencing Batch Reactor (SBR) system. The system

is designed to cater for 12,000 population equivalent (PE) which is equals to 2,700 m 3/ day of

average flow. Treated effluent from the STP is discharged into nearby monsoon drain which

eventually flows into Sungai Langat.

The STP is located at the upstream of Bukit Tampoi Water Intake Point, thus the effluent

must comply with Standard A of EQ(S)R 2009 Second Schedule. However, the STP is not designed to

include nutrient removal process since it was constructed before the gazette date of EQ(S)R 2009.

1.2 Problem Statement

Sewage, also known as domestic wastewater is one of the major contributors to river pollution.

Various systems are presented nowadays, which offer sophisticated technologies for high efficiency of

treatment.

Despite the availability of the high technology for sewage treatment, there had been numerous

occasions where water intake points and its treatment facilities had to cease operation as the river

water quality was very poor at intake point. The water treatment facilities were unable to treat it to the

required drinking water quality. This happens due to the fact that the environmental need is not given

precedence in selecting an appropriate sewage treatment system for a new development. In pursuit of

economic growth, cost has always been the number one factor considered in providing sewage

treatment systems to cater for new developments.


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1.3 Objectives

The objectives of this study are;

i. To determine the efficiency of the selected STP in meeting the required effluentstandard as stipulated by EQA

ii. To review the physical design of selected STP and determine whether the design issufficient to accommodate daily flow connected to the STP.

iii. To compare the physical design of the selected STP to the requirements inGuidelines for Developers Volume IV Design of Sewage Treatment Plant.

iv. To assess whether the plant is operated in an efficient mannerv. To come out with a proposal to operate the plant efficiently, at a lower cost while

still achieving the stipulated standard


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2.0 LITERATURE REVIEW

2.1

Sewage Treatment Plant

Sewage, also known as domestic or municipal wastewater is created by residential,

institutional, commercial and industrial establishment. In simple word, sewage is defined by human

waste. It includes household liquid waste from toilets, bathrooms, showers, kitchens, sinks and

laundry. In many areas, sewage also includes liquid wastes from industrial and commercial activities.

Sewage treatment is the process of removing physical, chemical and biological contaminants in

sewage prior to discharge into water bodies. It involves physical, chemical and biological process with

the objective to produce treated effluent (fluid) which is considered safe to be discharged to the

environment and also treated sludge (solid) which is suitable for disposal or reuse. Physical unit

operation includes screening, mixing, flocculation, sedimentation, filtration and floatation. In chemical

unit processes, removal or conversion of contaminants is achieved by means of chemical additions or

chemical reactions. This includes precipitation, adsorption and disinfection. Biological unit process is the

method where pollutants are removed through biological activity. Biodegradable organic substances are

converted into gases released to the atmosphere while the cell tissue is removed through settling

process.

2.1.1 Sewage Treatment Method

Sewage treatment method can be categorized into preliminary treatment, primary

treatment, secondary treatment and tertiary treatment.

Preliminary and/ or primary treatment refers to the physical unit process, is the first stage of

treatment which is applied to any sewage. Preliminary treatment includes screening and grinding to

remove debris and rags, grit removal by sedimentation and oil and grease removal by floatation.

Primary treatment removes some of the suspended solids and organic matter through screening and

sedimentation. Effluent from primary treatment still contains high organic constituent.


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Secondary sewage treatment refers to biological and chemical unit processes.

Biodegradable organic and suspended solids are removed mainly using biological unit processes.

Some secondary sewage treatment also includes disinfection.

Tertiary sewage treatment refers to combination of physical, biological and chemical unit

processes. It includes removal of nutrients, toxic substances such as heavy metal, also further

removal of suspended solids and organics. Tertiary treatment produces effluent of high quality

which is suitable for reuse.

In Malaysia, the focus has been to provide a basic preliminary, primary and secondary

sewage treatment. However, current trend is moving towards providing tertiary sewage treatment

for removal of nutrients including ammonia and phosphorous since the new effluent standard for

sewage (gazetted in December 2009) has become more stringent. Thus, new sewage treatment

plant (STP) which is designed after December 2009 must include nutrient removal process.

2.1.2 Classification of Sewage Treatment PlantThe microorganisms in sewage treatment can be grown in a form of fixed film, suspension

or a combination of both. Hence, biological treatment processes for sewage treatment works can

be classified under one of the followings:

a) Attached Growth Processes

b) Suspended Growth Processes

c) Combined Processes (Hybrid)

2.1.2.1 Attached Growth ProcessesIn an attached growth process, the active microorganisms grow and attach on the

mobile or immobile medium (rock, gravel, slag, plastic or other synthetic materials) that is in

contact with sewage. The organic material and nutrients are removed from wastewater

flowing past the attached growth also known as biofilm. Attached growth process can be

operated as aerobic or anaerobic process. Types of attached growth processes include:


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a) Trickling Filter (TF)b) Fluidised Bedc) Packed Bed Reactord) Rotating Biological Contactor (RBC)e) Submerged Biological Contactor (SBC)

2.1.2.2 Suspended Growth ProcessesIn a suspended growth process, active microorganisms responsible for treatment

remain in suspension in the sewage by appropriate mixing methods. Their concentration is

usually related to mixed liquor suspended solid (MLSS) or mixed liquor volatile suspended

solid (MLVSS). This system was developed as a result of studies that showed that if sewage is

aerated over a long period of time, the organics in the sewage are removed by the active

microorganisms grow during the process. The most common suspended growth process used

for municipal wastewater treatment is the activated sludge process.

Types of suspended growth processes include:

a) Waste Stabilisation Pond Systemb) Aerated Lagoonc) Conventional Activated Sludge (CAS)d) Extended Aeration (EA)

2.1.2.3 Hybrid Processes - Attached Growth with Suspended GrowthRecent technologies in sewage treatment include combination of attached growth

and suspended growth process in order to obtain best performance and most economical

treatment. Among advantages of Hybrid Process is; it combines the stability and capability to

handle shock loads of an attached growth process and the capability of suspended growth

system in producing high quality effluent.


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Hybrid processes can be used to upgrade existing attached growth and suspended

growth process, especially in plants with high suspended solids in the final effluent due to

poor solids settlement in the final clarifier.

2.2 Technologies for Sewage Treatment

In Malaysia, primary treatment systems such as communal septic tanks and Imhoff tanks have

been widely used to treat sewage. Other common system is the unreliable low cost secondary system

like oxidation ponds. These systems only treat sewage partially, discharging treated effluent which is

still contains high organic constituent. This creates risk of public health and environmental problems,

especially in urban areas. 38% of public sewage treatment plants in Malaysia are mechanical plants.

Sewage breakdown is accelerated in mechanical plants, by means of mechanical equipments. Common

types of mechanical STP used in Malaysia are Extended Aeration, Sequencing Batch Reactor, Oxidation

Ditch and Conventional Activated Sludge.

2.2.1 Oxidation Pond (OP)

Oxidation Ponds (or Stabilization Ponds) are a popular sewage treatment method for small

communities because of their low construction and operating costs. New oxidation ponds can treat

sewage to Standard B effluent level but require maintenance and periodic desludging in order to

maintain this standard.

OPs may comprise one or more shallow ponds in a series. The natural processes of algal and

bacteria growth exist in a mutually dependent relationship. Oxygen is supplied from natural surface

aeration and by algal photosynthesis. Bacteria present in the wastewater use the oxygen to feed on

organic material, breaking it down into nutrients and carbon dioxide, which are used then by the

algae. Other microbes in the pond such as protozoa remove additional organic and nutrients to

polish the effluent.

Normally, at least two ponds are constructed. The first pond reduces the organic material

using aerobic digestion while the second pond polishes the effluent and reduces the pathogens


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present in sewage. Sewage enters a large pond after passing through a settling and screening

chamber. After retention for several days, the flow is often passed into a second pond for further

treatment before it is discharged into a drain. Bacteria present in sewage acts to break down

organic matter, using oxygen from the surface of the pond. Oxidation ponds need to be desludged

periodically in order to work effectively. Depending on the design, OPs must be desludged

approximately every 10 years.

OPs require large amounts of land and the degree of treatment is weather dependent. They

are incapable of achieving a good standard of effluent consistently. Nowadays, application of this

treatment system for new developments are ceasing due to the variations of performance and vast

land area requirement.

2.2.2 Sequencing Batch Reactor (SBR)The Sequencing Batch Reactor is a sequential suspended growth (activated sludge)

process, in which all major steps take place in the same tank. SBR system has been successfully

used to treat both municipal and industrial wastewater. In addition to removing TSS and BOD,

SBR can be designed and operated to enhance removal of nitrogen, phosphorous and ammonia.

There are five basic sequences in a cycle, namely;

1) Fill

Fill stage consists of adding the waste and substrate for microbial activity. The fill

phase can include many phases of operation depends on various modes of

control, termed as Static Fill, Mixed Fill and React Fill. Static fill involves waste

introduction of influent without mixing or aeration. In some applications, static fill

will be accompanied by mixed fill stage so that microorganism is exposed

sufficient substrate. In a react fill stage, both mixing and aeration are provided.

2) React (Aeration)

The react stage completes the reactions initiated during fill stage. The react stage

may be comprised of mixing or aeration, or both. The length of react phase can be

controlled by timers, by liquid level controls in a multitank system, or when the

degree of treatment has been achieved.


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3) Settle

- The separation of liquid-solid occurs during settle phase, which is similar to the

operation of a conventional final clarifier.

4) Decant

- Clarified effluent is decanted during this stage. Various apparatus are available for

decanting purpose. The most common are floating or adjustable weirs.

5) Idle

- Idle phase is the final phase and is only used in multi tanks applications. The time

spent in this phase depends on the time required for the preceding tank to

complete its fill cycle. Sludge wastage is normally done during this stage.

There are two major classifications of SBRs, the intermittently fill & intermittently

decant system and the continuous fill & intermittently decant system. The intermittently fill

system only accepts effluent at specified interval and in general, follow the five step sequence.

There are usually two IF units in parallel. Because this system is closed to influent flow during

the treatment cycle, two units may be operated in parallel, with one unit open for intake while

the other runs through the remainder of the cycles. In the continuous inflow SBR, influent flows

continuously during all phases of the treatment cycle. To reduce short-circuiting, a partition is

normally added to the tank to separate the turbulent aeration zone from the quiescent area.

Advantages and disadvantages of SBR system are summarized in Table below:

Advantages Disadvantages

Equalization, primary clarification (in most

cases), biological treatment, and secondaryclarification can be achieved in a single

reactor vessel.

A higher level of sophistication is required

(compared to conventional systems),especially for larger systems, of timing units

and controls.


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Operating flexibility and control. Higher level of maintenance (compared to

conventional systems) associated with more

sophisticated controls, automated switches,

and automated valves.

Minimal footprint. Potential of discharging floating or settled

sludge during the DRAW or decant phase with

some SBR configurations.

Potential capital cost savings by eliminating

clarifiers and other equipment.

Potential plugging of aeration devices during

selected operating cycles, depending on the

aeration system used by the manufacturer

Potential requirement for equalization after

the SBR, depending on the downstream

processes.

2.2.3 Extended Aeration (EA)

The extended aeration system is one of the modifications of activated sludge process. It is a

complete mix system and provides biological treatment for the removal of biodegradable organic

wastes under aerobic conditions. Air may be supplied by mechanical or diffused aeration to provide

the oxygen required to sustain the aerobic biological process. Mixing must be provided by aeration

to maintain the microbial organisms in contact with the dissolved organics.

Since there is complete stabilization occurs in the aeration tanks, there is no need for

separate sludge digester. Primary settling tank is also not required since the settleable organic solid

is allowed to settle in aeration tank due to long hour of retention time i.e. 18 to 24 hours.

EA is one of the most common systems used in municipal wastewater treatment in Malaysia

since it is easy to operate, capable to handle organic loading and flow fluctuation, also the system

have relatively low sludge yield due to long residence time and sludge age.


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2.2.4 Oxidation Ditch (OD)

Oxidation ditch system is an extended aeration activated sludge process. It consists of a

"ring or oval shaped channel" equipped mechanical aeration devices, commonly brush aerators.

Screened wastewater enter the ditch is circulated through the channel and aerated. The tank

configuration and aeration and mixing devices promote unidirectional flow in channel, so that the

energy used for aeration is sufficient to provide mixing in a system, with relatively long hydraulic

retention time. High degree of nitrification can be achieved if the basin is sized using appropriate

SRT.

The ditch is built on the surface of the ground and is lined with an impermeable lining. This

allows the wastewater to have plenty of exposure to the open air for the diffusion of oxygen. The

liquid depth in the ditches is very shallow, 0.9 to 1.5 m, which helps to prevent anaerobic

conditions from occurring at the bottom of the ditch. The oxidation ditch effluent is clarified in a

secondary clarifier and the settled sludge is returned to maintain a desirable MLSS concentration.

As in the extended aeration system, OD system also produces low sludge volume due to

long residence time in the ditch. However, this system requires relatively larger land area than

other types of activated sludge process.


Long hydraulic retention time and complete

mixing minimize the impact of a shock load or

hydraulic surge.

Effluent suspended solids concentrations are

relatively high compared to other

modifications of the activated sludge process.

Produces less sludge than other biological

treatment processes owing to extended

biological activity during the activated sludge

process.

Requires a larger land area than other

activated sludge treatment options. It makes

this system less feasible in urban areas where

land acquisition cost is relatively high.

Energy efficient operations result in reduced

energy costs compared with other biological

treatment processes.


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2.2.5 Rotating Biological Contactor (RBC)

Rotating Biological Contactors (RBCs) are mechanical secondary treatment systems. The

system comprises of a series of closely spaced circular discs, normally made from plastic material.

The disks are partially submerged and slowly rotated in sewage. Organic pollutants are breakdown

and stabilized by the bacteria and microorganisms present in sewage that grows on the rotating

disks.

As the disks rotate, the micro-organisms obtain oxygen from the atmosphere. As the micro-

organisms grow, they build up on the media until they are strip off due to shear forces provided by

the rotating disks in sewage. Effluent from the RBC is then passed through final clarifiers, where the

micro-organisms in suspension settle as sludge. The sludge is withdrawn from the clarifier for

further treatment.

RBC units are suitable where land area is restricted. They are quite and consistently produce

a high quality effluent. Because they are modular they are also suitable for a staged development.

Operations and maintenance costs are lower than other forms of mechanical treatment.

2.2.6 Membrane Bio Reactor (MBR)

Membrane Bioreactors combine conventional biological treatment processes with

membrane filtration to provide an advanced level of organic and suspended solids removal. This

system can also provide an advanced level of nutrient removal when designed accordingly.

In MBR system, the membranes are submerged in an aerated biological reactor. The

porosities of the membranes range from 0.035 microns to 0.4 microns, depending on the

manufacturer. This level of filtration produces high quality of effluent to be drawn through the

membranes while eliminating the typically used sedimentation and filtration processes in other

types of system. Because the need of sedimentation is eliminated, the biological process can be

operated at a higher mixed liquor concentration. This significantly reduces the number and size of

tankage required, thus allowing many existing plant to be upgraded without adding new tanks.


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The distinct advantages of MBR over EA and SBR system make the system a favourable

option especially where land area is limited and plant located in environmentally sensitive area.

However, due to high cost of equipments, it is not the appropriate technology for every

application.

Other benefits of MBRs include:

Hydraulic Retention Time (HRT) of 4-8 hours vs 16-24 hours Solids Retention Time (SRT) of 15-365 days, can vary based on flow without negative

process impact

MLSS of 10,000-15,000 mg/L Sludge Yield of 20-40% less than conventional Footprint of 25% Conventional Plant Modular expandability Highest quality effluent Capable of meeting new standards for nutrient removal Less susceptible to upsets due to flow variations Less odour Simple, yet sophisticated

2.3 Comparison of Sewage Treatment Technologies

Factors considered in selecting an appropriate system for a proposed new development are

capital cost, treatment efficiency, sizing of the system which is related to land area requirement, ease

of operation and maintenance, as well as the O&M cost.


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Table 1 : Comparison of Technologies for the Wastewater

Average Removal Efficiency

Treatment System BOD

(%)

COD

(%)

SS

(%)

Ammonia

(%)

Total N

(%)

Total P

(%)

Oxidation Pond 75 - 85 65 - 80 70 - 80 < 50 < 60 < 35

Sequencing Batch

Reactor (SBR)

85 - 95 80 - 90 93 - 97 > 80 < 60 < 35

Extended aeration (EA) 90 - 97 83 - 93 87 - 93 > 80 < 60 < 35

Membrane Bio Reactor

(MBR)

99 99 99.9 99.2 99 96.6

Conventional Activated

Sludge (CAS)

85 - 93 80 - 90 87 - 93 > 80 < 60 < 35

Rotating Biological

Contactor (RBC)

88 - 95 83 - 90 87 - 93 65 - 85 < 60 < 35

High Rate Trickling Filter 80 - 90 70 - 87 87 - 93 < 50 < 60 < 35

2.4 Life Cycle Assessment

Life cycle assessment (LCA) is an appropriate methodology for assessing the sustainability of a

sewage treatment plant design. ISO 14040:2006 describes the principles and framework for life cycle

assessment (LCA). Environmental costs and benefits of different sewage treatment technologies and

standards can be compared quantitatively using the LCA method.

Factors considered in comparing the technologies are:

Potential Negative Impact Factors Contributing to the ImpactNonrenewable energy High sludge production, High energy consumption, Land use

Global warming impact High sludge production, CO2 produced (directly related to the energy

consumption)

Acidification NOx produced

Eutrophication NOx produced


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High Medium Low

Sludge production CAS SBR MBR, EA, OD

Energy consumption MBR, CAS, EA SBR OP

Land use OP, OD, CAS EA MBR, SBR

CO2 produced MBR, CAS, EA SBR OP

NOx produced CAS, EA, OD SBR MBR

Potential Negative Impact Nonrenewable

energy

Global warming

impact

Acidification Eutrophication

Type of System

Oxidation Pond (OP) ++ +++ + +

Sequencing Batch Reactor

(SBR)

++ ++ ++ ++

Extended Aeration (EA) ++ + + +

Oxidation Ditch (OD) + + ++ ++

Membrane Bio Reactor

(MBR)

++ + +++ +++

Note:

+++ - Most favourable/ least negative impact

++ - Intermediate grade

+ - Least favourable/ most negative impact


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3.0 METHODOLOGY3.1 Site Visits

Site visit has been conducted on 26th January 2011. During site visits, dimensions of key

process units from inlet pump stations to the SBR tank were measured. Layout plan of the SBR

plant is shown in drawing in Appendix A.

The plant has been designed to treat flow equivalent to 12,000PE and the current PE loading

is 11,305PE (94%). Based on MS1228, 1PE is equals to 0.225m3/day/capita, thus the plant receives

flow equivalent to 2,544m3/day at average. Peak flow is calculated using following equation from

MS1228:

Qpeak = PFF x Qave

Where PFF = 4.7 PE x (PE / 1000)-0.11

= 3.58

Thus, Qpeak = 3.58 x 2,700m3/day

= 9,655m3/day

Since the STP is located in water catchment area, the design was designed to meet Standard

A effluent based on Guidelines for Developers Volume IV (Sewage Treatment Plant). It is important

to note that the STP was designed in year 2002, before the gazette date of Environmental Quality

(Sewage) Regulation: 2009. Thus, design of this plant does not include for tertiary treatment to

remove nutrient and further removal of suspended solids and organics.


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3.2 Process Description

Raw sewage from the last manhole of Taman Segar Perdana enters the inlet works via two (2)

mechanical coarse screen of 25mm clear opening to collect the rubbish. The primary screen is controlled

by one (1) unit of manual penstock. After screening process, the raw sewage flows into a pump sump

and periodically pumped by two (2) raw sewage pumps (1 duty, 1 standby). These pumps transfer the

raw sewage via 350mm DI pipe to the next process unit.

Before reaching the single grit removal chamber, the sewage will flow through the secondary

screen chamber which comprises of two (2) units of mechanical fine screens of 12mm bar spacing. The

collected rubbish is then transferred down to the collection bin via 500mm wide conveyor system.

Concurrently, sewage flows from the top level and undergoes aeration at the grit chamber. At selected

intervals, the airlift pump will pump up the settled grit to a collection sump. Then, the pre-treated

sewage flows out to the grease chamber whereby the floating grease is removed by the surface grease

scrapper conveyor. Finally, the pre-treated sewage flows into the distribution chamber at the head of

the reactor tanks. The flow of the pre-treated sewage into the reactor tanks is controlled by two (2)

numbers of motorised penstocks. Periodically, the flow will be released out into the SBR tank.

There are two (2) SBR tanks in this plant. SBR is an activated sludge system whereby the

biological reaction, solid-liquid removal and surface liquid (effluent) removal are all carried out in a

single tank by setting specific sequences. The SBR tanks operate in the following sequences:

1) Fill and aerate Sewage is intermittently filled in the tanks and aerated for two (2) hours2) Settle Aeration stops and suspended solids settle leaving a clear liquid at the top of the

sludge blanket

3) Decant Clear liquid (effluent) is decanted with a maximum of 30% of the total tankvolume. Decant depth for the reactors are 1.2 m from top water level.

4) Idle Sludge is pumped out at the end of the cycle


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The above four (4) cycles are known as one (1) cycle which takes four hours (Fill & aerate - 2

hours, settle - 1 hour, decant & idle - 1 hour) to complete. Thus, six (6) cycles are performed in a reactor

tank per day. The waste activated sludge (WAS) pumped from the SBR tank is transferred into a circular

gravity sludge thickener tank. Sludge is expected to thicken to about 1% dry solid content in the gravity

thickener tank before it is transferred out to the drum thickener. Polymer is added prior to entering the

drum thickener to aid the flocculation of the sludge.

The dryness of the produced cake from drum thickener is typically from 8 10% and further

treated at the sludge drying beds. So far, the mechanical sludge facilities at this plant are not fully

utilized due to small amount of sludge generated by the SBR reactor. Thus, the WAS pumped out during

idle phase is bypassed to sludge drying bed and dried for 28 days. Filtrate from the drying beds is

returned to the inlet works for treatment. Every 28 days, the sludge drying beds will be cleared out and

the sludge cake is sent to an approved site for disposal as solid waste.

Meanwhile, effluent extracted from the SBR tanks is transferred to a disinfection chamber. A

flow measurement facility complete with a non-contact ultrasonic level meter is provided for the

effluent.

Flow diagram of the SBR plant is shown in Figure 1.


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Figure 1 : Flow Diagram of SBR System

Inlet Pump

Station

Incoming Sewage

Secondary

Screen Chamber

Grit Removal

Chamber

Grease Removal

Chamber

Sludge Thickening

Tank

Mechanical Sludge

Dewatering

Sludge Drying

Bed

Final Effluent

Chamber

Treated Effluent

Screened Raw

Sewage

WAS WAS

Thickened

Sludge

Filtrate

Sludge Cake for

Disposal as Solid

Waste

Stabilized Sludge

SBRTank 1

SBRTank 2


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4.0 RESULTS AND DISCUSSION

4.1 Design and Process Review

Design and process review are conducted in order to determine whether each of the key

process units at the plant has been designed sufficiently in order to meet the stipulated standard. Based

on the Guidelines for Developers Volume IV (Sewage Treatment Plant), the design influent and effluent

values adopted in the design of a Standard A plant are tabulated in Table below:

Table 2 : Design Influent and Effluent Values

Effluent Value (mg/l)Parameter Design Influent

Value (mg/l) Design Absolute**

Biochemical Oxygen Demand (BOD5) 250 10 20

Suspended Solids (SS) 300 20 50

Chemical Oxygen Demand (COD) 500 60 120

Ammoniacal Nitrogen (AMN) 30 5 50

Oil and Grease (O&G) 50 2 20

Total Nitrogen (TN) 50 n/a n/a

Total Phosphorous (TP) 10 n/a n/a

** Absolute value is the stipulated effluent standard that the plant must comply at all times.

Based on measurement and information provided by IWK, dimensions of main process units

are shown in Table 3.


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Table 3 : Dimension of Main Process Units

Tank Nos Dimension Volume

(m3)

HRT @

Qave

HRT @

Qpeak

Limits in

Guidelines

a. Wet Well 1 6.5m (l) x 2.2m (w) x

4.3m (d)

*Effective depth = 0.9m

12.87 7 min - Max. 30min @

Qave

b. Grit Removal

Chamber

1 V1 + V2 + V3 = 9.53m3 +

10.72m3

+ 0.40m3

**

20.65 11 min 3 min Min. 3min @

Qpeak

c. Grease Removal

Chamber

2 5.0m (l) x 1.0m (w) x

2.2m (d)

22 12 min 3 min Min. 3min @

Qpeak

d. Reactor Tank 2 27.5m (l) x 10.7m (w) x

4.0m (d)

2,354 20.9 hr - 18 24 hr @ Qave

* Effective depth is the difference between start and stop level of pumps

** Grit removal chamber of rotary type as shown in figure below

From the table above, it is found that the provided tank volumes of key process units are sufficient to cater

for the hydraulic load at which the plant has been designed to.

V2

V1

V3


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4.2 Collected Data of STP

Data collected during site visit to the STP are tabulated in Table 4 below.

Table 4 : Influent and Effluent Sampling Result

Parameter Concentration (mg/l)

BOD5in 159

BOD5eff 12

CODin 338

CODeff 36

SSin 138

SSeff 14

O&Gin 32

O&Geff 7

NH3Nin 30

NH3Neff 17

MLSS 3,300

MLVSS ~ 0.7 X 3,300 = 2,310

4.3 Kinetic Parameters

Equations used are:

aveQ

VHRT ====

XV

SQ=M/F

0

rw

cXQ

VX ====

d

c

K

1 ++++====

V

QS=V

0

L


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Assumptions are made based typical value of kinetic coefficient for the activated sludge process from

Metcalf & Eddy, 1991, as per tabulated in Table 5.

Table 5 : Typical kinetic coefficients for activated sludge type of process for domestic wastewater

ValueCoefficient Basis

Range Typical

K d-1

2 - 10 5

Ks mg/L BOD5

mg/L COD

25 100

15 - 70

60

40

Y mg VSS/mg BOD5 0.4 - 0.8 0.6

kd d-1 0.025 0.075 0.06

fd unitless 0.06 0.20 0.12

Yn g VSS/ g NH4-N 0.10 0.15 0.12

kdn g VSS/ g VSS.d 0.05 0.15 0.08

4.3.1 Calculations

Calculation of HRT

Provided volume of aeration tank = 2,354 m3

Average Flow = 2,700m3/ day

hr21hr9.20day1

hr24

day/m2700

m2354HRT

3

3

========

Calculation of SRT

MLSS, X = 3,300 mg/l

Underflow concentration, Xr = 10,000 mg/l

Volume of Sludge Wastage, Qw = 43.2 m3/ day (based on WAS pump capacity, 8 l/s,

runs 15 minutes per cycle, thus 1.5 hour per day)

days18l/mg000,10day/m2.43

l/mg300,3m354,2

3

3

c ====

====


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21

Calculation of sludge yield

Sludge wastage/ produced, Qw = 43.2m3/day

Sludge concentration, Xw = 10,0000 mg/l

kg Sludge Produced /day = 432 kg/ day

kg BOD Removed / day = day/kg6481000

day/m700,2l/mg)10250(3

====

Thus, Y = 67.0day/kg648

day/kg432==== kg sludge produced/ kg BOD5 removed

Calculation of oxygen requirement

Ro = Q (S0 S) 1.42 PX, VSS + 4.33 Q (NOx)

PX ,VSS =QY S0 S

1 + Kd SRT+

fd

kd QY S0 S SRT

1 + Kd SRT+

QYn NOx

1 + Kdn SRT

Assumefd = 0.15 g/ g

kd = 0.06 d-1

Yn = 0.12 g VSS/ g NH4-N

kdn = 0.08 g VSS/ g VSS.d

NOx = (30 5) mg/l = 25mg/l

PX,VSS = 208.73 + 33.81 + 3.32 = 245.85 kg/day

Thus,

Ro = [(2,700m3/day) (250 10)mg/l (1kg / 10

3g)] [1.42 (245.85kg/day)]

+ [4.33 Q (NOx)]

= (648 344.41 + 292. 28) kg O2/ day

= 595.87 kg O2/ day

Aeration tank/ tank

Aeration time / cycle = 2.0 hr

No. of cycles/ day = 6


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Total aeration time = 12 hr/ day

Average oxygen transfer rate = hr/kg65.49=12hr/day

day/Okg595.872

Air weight = 1.201 kg/m3

% of oxygen = 0.232

O2 transfer efficiency of Unifflex diffuser = 0.15

Air volume required = 49.65 kg/hr / (1.201 kg/m3

x 0.232 x 0.15)

= 1,188 m3/ hr or 19.8 m3/min

Based on Guidelines for Developers Volume IV,

Oxygen requirement for SBR = Cycle TimeAeration Time 2.0kgO2 per kg BOD removed

BOD to remove = 648 kg/day

Air volume required = (4 hr / 2 hr) x (2.0 kg O2 x 648 kg/day)

= 2,592 kg/day or 108 kg/hr

= 108 kg/hr / (1.201 kg/m3 x 0.232 x 0.15)

= 2,584 m3/ hr or 43.07 m

3/min

Calculation of F/M ratio

1

3

30 day09.0

l/mg3300m354,2

l/mg250day/m700,2

XV

SQM/F

====

====

====

Calculation of specific growth rate

Assume kd = 0.06 d-1

11 d12.0=d06.0+days18

1=

Calculation of BOD volumetric loading

VL = day/m/kg29.0=)kg/g10)(day/m2354(

)l/mg250)(day/m700,2( 333

3


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23

Calculation of Nutrient Requirement

BOD : N : P = 100 : 5 : 1

Based on Table 2,

BOD = 250 mg/l

TN = 50 mg/l

TP = 10 mg/l

Based on concentrations above, BOD : N : P is 25 : 5 : 1, which indicates that sufficient nutrient is

available in the influent


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24

Table6:Comparisonof

HLT234toDesignGuidelines

Guidelines

M

etcalf&Eddy

HLT234

MLSS,mg/l

3,0004,5

00

2,0005,000

3,300mg/l

MLVSS,mg/l

-

-

0.7x3,300mg/l=

2,310mg/l

F/MR

atio,

kgBOD/kg

MLVSSd-1

0.050.3

0

0.040.10

0.09

BODvolumetricloading

kgBOD/m3.d

-

0.10.3

0.29

HRT,

hr

18-24

15-40

21

SRT,days

1030da

ys

1030days

18days

SludgeYield,

kgSludge/

Kg

BOD5

load

0.751.1

0

0.40.8

0.66

CycleTime,

hr

48hrs

-

4

Decantdepth,m

Max1.0

-

1.2m

Decanttime,

hr

-

-

1

DecantVolume,%

30%

30%

30%

OxygenVolumeRequire

d,

kg/hr

CycleTime

AerationTime

2.0

kgO2p

erkgBODremoved

=108kg/hr

Q(S0S)

1.42PX,VSS+4.33Q(NOx

)

=49.65kg/hr

n/a

OxygenVolumeRequire

d,

m3/min

43.06m3/m

in

19.8m3/min

45m3/min


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4.4 Analysis

4.4.1

Actual Removal Efficiency

BOD removal = [(So - S) / So]*100%BOD removal = [(159 - 12)mg/l /159]*100%

= 92.4 %.

4.4.2 Operational Cost

Electricity cost is the highest contributor to the total O&M cost of a STP. Electricity

cost per month for HLT234 is estimated based on M&E equipments data as shown below in

Table 7.

Table 7 : List of Mechanical Equipments in HLT234

Equipments Nos Capacity Total

Capacity

Power

(kW)

Head

(m)

RSP 2 (1 duty, 1 standby) 117.5 l/s 117.5 l/s 14.0 10.0

Air Blower 4 (3 duty, 1 standby) 15.0 m3/min 45.0 m

3/min 15.0 n/a

WAS pump 2 (1 duty, 1 standby) 8.0 l/s 8.0 l/s 1.3 6.0

Primary Mechanical Screen 2 - 1.1 n/a

Secondary Mechanical

Screen

2 - 0.75 n/a


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Calculation of Electricity Consumptions

i) Raw Sewage Pump1 unit x 14.0 kWh x 24hr x 30 day = 10,080 kW/ month

ii) Air Blower3 units x 15.0 kWh x 12 hr x 30 day = 16,200 kW/ month

iii) WAS Pump1 unit x 1.3 kWh x 1.5 hr x 30 day = 58.5 kW/ month

iv) Primary Mechanical Screen2 units x 1.1 kWh x 2hr x 30 day = 132 kW/ month

v) Secondary Mechanical Screen2 units x 0.75 kWh x 2hr x 30 day = 90 kW/ month

Total kW usage per month = 27,280.5 kW/ month

TNB Tariff = RM 0.366 (Industrial)

Total electricity cost = RM 9,984.66


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5.0 CONCLUSION

It is concluded that the design of HLT234, a sequencing batch reactor plant at Taman Segar Perdana

is sufficient to treat sewage influent of 2,700 m3 per day to meet EQ(S)R. The plant is operated at an

operational cost of approximately RM 10,000 per month.


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6.0 REFERENCESMetcalf & Eddy, Inc. Wastewater Engineering: Treatment, Disposal, Reuse. 3

rdedition. New York: McGraw

Hill.

U.S. EPA. EPA Design Manual, Summary Report. Sequencing Batch Reactors. EPA/625/8-86/011, August

1986.

U.S. EPA. Wastewater Technology Fact Sheet. Sequencing Batch Reactors. EPA 932-F-99-073 September

1999.

L. K. Wang, N. K. Shammas, and Y. T. Hung. Handbook of Environmental Engineering Volume 9:Advanced

Biological Treatment Processes. New York: Humana Press

Ministry of Housing and Local Government. Guidelines for Developers Volume IV : Sewage Treatment Plant

https://www.iwk.com.my

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