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ASSESSMENT AND IMPROVEMENT OF SALASALA PRIVATE DECENTRALIZED
FAECAL SLUDGE MANAGEMENT SYSTEM
A dissertation
Submitted to the graduate faculty of Environmental Engineering of Ardhi University in partial
fulfillment of the requirements for the graduate degree of Bachelor of Science in Environmental
engineering
By
ULOTU GERALD
July 2012.
ENVIRONMENTAL ENGINEER DEPARTMENT
SCHOOL OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY (SEST)
ARDHI UNIVERSITY
P.O.BOX 35176
Dar es Salaam
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|COPYRIGHT
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COPYRIGHT
This dissertation is a copyright material protected under Berne Convention, the Copyright Act
1999 and other International and National enactments in that behalf, on intellectual property. It
may not be reproduced by any means in full or in part, except for extracts in fair dealing, for
research or private study, critical scholarly review or discourse with an acknowledgement,
without written permission of the Directorate of Undergraduate Studies, on behalf of both the
Author and the Ardhi University
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ABSTRACT
This research set out to assess the Salasala privately operated decentralized faecal sludge
management system which located at Tegeta Dar es Salaaam and to critically analyze the
improvements which are needed to make it suitable a faecal sludge management system with a
potential for citywide adoption. Currently the Salasala privately faecal sludge management
facility is the only facility that is used to manage faecal sludge from on-site sanitation facilities
of the whole area of Tegeta Boko, Bunju, Ununio, Wazo Hill, Salasala, KunduchiMtongani,
Kunduchi, Africana and part of Mikocheni neighborhoods.
Wastewater samples was taken from the sludge pond (i.e. at the inlet, middle and outlet), and
outlet of constructed wetland system. The sludge volume of the pond was measured by
configuring onsite offshore coordinate system along the breadth and span of the pond and the
sludge depth was taken with a tape at each point X, Y of orthogonal projection and volume
computation was done by using a Spot height method of Earth work computation. Sludge
samples was taken from five sampling points, two points of three samples taken vertically down
along the sludge depth and three points of single samples in the sludge pond. Analysis of
physicochemical characteristics such Color, Turbidity, Total suspended solid and ammonia
nitrogen of system wastewater was observed to be not within the minimum permissible amounts
(i.e. TBS and WHO).The parameters of effluent wastewater that observed to be far away from
the standards was Color, 900Pt-Co/L where’s TBS standards is 300Pt-Co/L, Turbidity 500NTU
(TBS standards 300) and TSS 251.5 mg/L (TBS standards 100 mg/L). Chemical parameters,
Ammonia-nitrogen (NH3-N) was 200mg/l where’s TBS standards is 6mg/L, and a phosphate
PO4 129.67 mg/L where’s TBS standards is 15 mg/L. Biological characteristic of effluent
wastewater such as COD, BOD5, Faecal coliform and total coliforms was totally not within either
TBS or WHO standards. COD and BOD5 was 636.67 mg/L and 318.33 mg/L where’s TBS
standards are 60 and 30 mg/L respectively. Faecal coliforms and Total coliforms was 16 × 106
and 22 × 106 count/100 mL where’s TBS standards are 1000 and 10000 count/100mL
respectively. For sludge volume and stability test, it was observed that the pond have a sludge
volume of 252 m3 and the sludge have not yet stabilized enough. The system looks economical,
as it makes a profit of about 51,840,000 Tsh/= per year, However the system improvements
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should be made to increase its performance in wastewater and sludge treatment as well a
profit/year as per analysis, it does not effective recovers all resources suitably obtained through
sludge treatment.
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TABLE OF CONTENTS
CERTIFICATION......................................................................................................................... i
DECLARATION........................................................................................................................... ii
COPYRIGHT............................................................................................................................... iii
DEDICATION.............................................................................................................................. iv
ACKNOWLEDGEMENTS ......................................................................................................... v
ABSTRACT.................................................................................................................................. vi
TABLE OF CONTENTS .......................................................................................................... viii
LIST OF FIGURES ................................................................................................................... xiii
LST OF TABLES....................................................................................................................... xiv
LIST OF PLATES ...................................................................................................................... xv
ACRONYMS AND ABBREVIATION.................................................................................... xvi
CHAPTER ONE ........................................................................................................................... 1
1.0 GENERAL INTRODUCTION............................................................................................. 1
1.1 Justification and Motivation.................................................................................................. 3
1.2 Research problem.................................................................................................................. 3
1.3 Objective of the Study........................................................................................................... 4
1.3.1 Specific objectives .......................................................................................................... 4
1.4 Scope ..................................................................................................................................... 4
1.5 Expected output..................................................................................................................... 4
CHAPTER TWO .......................................................................................................................... 5
LITERATURE REVIEW............................................................................................................ 5
2.1 Fecal Sludge .......................................................................................................................... 5
2.1.1 Sewage sludge ................................................................................................................ 5
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2.1.2 Faecal sludge characteristics .......................................................................................... 6
2.1.3 Nutrients in sludge.......................................................................................................... 7
2.2 Domestic wastewater............................................................................................................. 9
2.2.1 Domestic waste Water Characteristics ......................................................................... 11
2.3 Faecal Sludge Treatment..................................................................................................... 14
2.3.1 Solids/liquid separation ................................................................................................ 15
2.3.2 Gravity solids/liquid separation.................................................................................... 15
2.3.3 Mechanical solids/liquid separation ............................................................................. 16
2.3.4 Digestion....................................................................................................................... 17
2.3.5 Anaerobic Decomposition ............................................................................................ 17
2.4 Wetlands and sludge treatment ........................................................................................... 18
2.4.1 Natural wetland............................................................................................................. 18
2.4.2 Constructed wetland ..................................................................................................... 19
2.5 Biological processes in CWs............................................................................................... 27
2.6 Chemical processes ............................................................................................................. 28
2.7 Physical processes ............................................................................................................... 28
2.8 Process rates ........................................................................................................................ 28
2.9 Hydrological limitations...................................................................................................... 28
2.10 Wetland nitrogen processes............................................................................................... 29
2.11 Wetland in Phosphorus removal ....................................................................................... 30
2.12 CWs in Suspended solids removal .................................................................................... 31
2.13 CWs in Pathogen removal................................................................................................. 31
2.14 CWs in Heavy metal removal ........................................................................................... 31
2.15 Abiotic Factors and their Influence on Wetlands.............................................................. 32
2.15.1 Oxygen........................................................................................................................ 32
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2.15.2 pH ............................................................................................................................... 32
2.15.3 Temperature................................................................................................................ 32
2.16 Sludge drying .................................................................................................................... 33
2.16 Sludge composting ............................................................................................................ 34
2.16.1 Advantages of composting ......................................................................................... 35
CHAPTER THREE.................................................................................................................... 36
MATERIALS AND METHODS.............................................................................................. 36
3.0 Location of the study area ............................................................................................... 36
3.1 Climatic condition ........................................................................................................... 38
3.2 Existing situation ............................................................................................................. 38
3.2.1 System description........................................................................................................ 39
3.3 Materials.............................................................................................................................. 43
3.3.1Sludge depth measurements .......................................................................................... 43
3.3.2 Wastewater Sampling ................................................................................................... 43
3.3.3 Faecal sludge sampling................................................................................................. 44
3.3.3 Equipment’s used ......................................................................................................... 45
3.3.4 Reagents used ............................................................................................................... 45
3.4 Methods............................................................................................................................... 46
3.4.1 Site visits and interview................................................................................................ 46
3.4.2 Experimental setup for sludge stability ........................................................................ 46
3.4.3 Analysis ........................................................................................................................ 47
3.4.3.1 Physical parameters ................................................................................................... 47
3.4.3.2 Chemical parameters ................................................................................................. 47
3.4.3.3 Chemical Oxygen Demand........................................................................................ 49
3.4.3.4 Faecal and Total coliforms (FC &TC) ...................................................................... 49
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3.4.3.5 Data analysis and computations ................................................................................ 49
CHAPTER FOUR....................................................................................................................... 50
DATA RESULTS AND DISCUSSION ................................................................................... 50
4.1 Wastewater characteristics .................................................................................................. 50
4.1.1 Physical Characteristics ................................................................................................ 50
4.1.2 Chemical characteristics ............................................................................................... 57
4.1.3 Biological characteristics.............................................................................................. 59
4.2 Pond Sludge stability and volume....................................................................................... 62
4.2.1Pond Sludge stability ..................................................................................................... 62
4.2.2 Sludge volume determination ....................................................................................... 64
4.3 Economic aspect of Salasala faecal sludge management system........................................ 66
4.4 Aesthetics assessment ......................................................................................................... 68
4.4.1Solid waste management................................................................................................... 68
4.4.2 Odor and smell.............................................................................................................. 68
4.4.3 Surrounding Land Use.................................................................................................. 69
4.4.4 Insect Attraction ........................................................................................................... 69
4.4.5 Personal protective equipment’s (PPE’s) ..................................................................... 70
4.5 System improvements required........................................................................................... 71
4.5.1General improvements................................................................................................... 71
4.5.1.1 Land use round system plant. .................................................................................... 71
4.5.1.2 Solid waste management at the system plant ............................................................ 71
4.5.1.3 Unit of sludge dewatering.......................................................................................... 71
4.5.1.4 Aesthetic and beauty of the surroundings system environment ................................ 71
4.5.1.5 Improvement’s to make Salasala faecal sludge management system cost effective . 72
4.5.2 Specific improvements..................................................................................................... 73
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4.5.2.1 Constructed wetland system improvements .............................................................. 73
4.5.2.2 Sludge pond improvements ....................................................................................... 73
CHAPTER FIVE ........................................................................................................................ 75
5.0 CONCLUSION ................................................................................................................... 75
5.1 RECOMMENDATION .......................................................................................................... 76
REFERENCES............................................................................................................................ 77
REFERENCES............................................................................................................................ 78
APPENDIXES............................................................................................................................. 80
Appendix 01: AVERAGE PHYSICAL CHARACTERISTICS OF WASTEWATER........ 81
Appendix 02: AVERAGE CHEMICAL CHARACTERISTICS OF WASTEWATER...... 82
Appendix 03: AVERAGE BIOLOGICAL CHARACTERISTICS OF WASTEWATER .. 83
Appendix 04: GAS VOLUME IN mL OF SLUDGE STABILITY TEST............................. 84
Appendix 05: SALASALA POND SLUDGE DEPTH AND VOLUME RESULTS............. 85
Appendix 06: RAW DATA OF PHYSICOCHEMICAL PARAMETERS ........................... 86
Appendix 07: LONGITUDINAL SLUDGE PROFILE OF THE POND...…………….…...88
Appendix 08: CROSS SECTIONAL SLUDGE PROFILE OF THE POND……………….89
Appendix 09: PICTURES DURING WASTEWATER ANALYSIS ..................................... 90
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LIST OF FIGURES
Figure 2.1: Factors influencing FS characteristics.......................................................................... 6
Figure 2.3: Emergent macrophytes treatment system with surface flow...................................... 20
Figure 2.4: Emergent macrophytes treatment system with horizontal sub surface flow .............. 21
Figure 2.5: Section through Horizontal surface Flow Constructed Wetland................................ 25
Figure 3.0: Topographical map of the study area…………………………………………..……24
Figure 3.1 Schematic diagrams of Salasala Faecal sludge treatment system ............................... 38
Figure 3.2 Wastewater sampling points………………………………………………………….44
Figure 3.3 Faecal sludge sampling points................................................................................... 44
Figure 3.4 Schematic diagram of typical experimental setup....................................................... 46
Figure 4.1 PH variations along the treatment plant. ..................................................................... 53
Figure 4.2 Temperature variations along the treatment plant ....................................................... 53
Figure 4.3 TDS variation along the treatment plant ..................................................................... 54
Figure 4.5 Conductivity variations along the treatment plant....................................................... 55
Figure 4.6 Salinity variations along the treatment plant ............................................................... 55
Figure 4.8 Colour variations along the treatment plant ................................................................ 56
Figure 4.9 Turbidity variations along the treatment plant ............................................................ 56
Figure 4.10 Ammonia-nitrogen variations along the treatment plant........................................... 58
Figure 4.11 Phosphate variations along the treatment plant ......................................................... 58
Figure 4.12 BOD5 variations along the treatment plant ............................................................... 60
Figure 4.14 Total coliforms variations along the treatment plant................................................. 61
Figure 4.15 Faecal coliforms variations along the treatment plant............................................... 61
Figure 4.16 Sludge stability progress for different sludge sample ............................................... 63
Figure 4.17 Cumulative gas volume of the sludge sample ........................................................... 64
Figure 4.18 Pond coordinate configuration .................................................................................. 65
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LST OF TABLES
Table 2.1: Characteristics of faecal sludge’s .................................................................................. 7
Table 2.2 Human excreta per capita quantities and their resource value........................................ 8
Table 2.3 Typical composition of untreated domestic wastewater ................................................ 9
Table 2.4 Composition of human faeces and urine ...................................................................... 11
Table 2.5 Vegetation type and water column contact in constructed wetlands ............................ 21
Table 2.6 Pollutant removal mechanisms in constructed wetlands ............................................. 22
Table 2.7 Wetland zones and their associated components .......................................................... 24
Table 2.8: Overview of pollutant removal mechanisms ............................................................... 25
Table: 4.5 Economic analysis of salasala faecal sludge management system.............................. 67
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LIST OF PLATES
Plate 3.1Orthophotographic map of the case study area .............................................................. 37
Plate 3.2 Screen chamber .............................................................................................................. 39
Plate 3.3 Salasala Faecal sludge pond........................................................................................... 40
Plate 3.7 Depth measurement ....................................................................................................... 43
Plate 3.7: Spectrophotometer ........................................................................................................ 45
Plate 3.5 Laboratory Sample analysis for physical parameter ...................................................... 48
Plate 3.8 Laboratory sample dilution for of chemical parameters analysis .................................. 48
Plate 3.9 Dumped Solid waste from screen .................................................................................. 68
Plate 3.6 Area used for grazing..................................................................................................... 69
Plate 3.7: Faecal sludge disposing activity conducted by worker wears PPE .............................. 70
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ACRONYMS AND ABBREVIATION
BOD Biochemical Oxygen Demand
COD Chemical Oxygen Demand
CW Constructed Wetland
FC Faecal Coliforms
FS Faecal Sludge
M+O Maintenance and operation cost
NH3-N Ammonia Nitrogen
NH4-N Ammonium Nitrogen
SS Suspended Solids
TBS Tanzania Bureau of Standards
TDS Total dissolved solids
TKN Total Kjeldahl Nitrogen
TOC Total Organic Carbon
TS Total Solids
TSh Tanzania Shillings
TVS Total Volatile Solids
WHO World Health Organization
WSP Waste Stabilization Ponds
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER ONE
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CHAPTER ONE
1.0 GENERAL INTRODUCTION
In Dar es Salaam, it has been estimated to have a population of about 3.5 million people
of which 70% of the population lives in 40 unplanned settlements. The total number of
households is about 547,000 with an average size of 6.4 persons. Only15% of the
households is connected to the old and degenerated sewerage system which discharges to
the 8 oxidation ponds of which only 4 of the ponds are considered to be operating,
University of Dar-es- Salaam Kurasini Mikocheni and Vingunguti
The sewerage system covers only an area of City Center, parts of Sinza, Ubungo and
Vingunguti. 80% of the households in the rest of Dar es Salaam depends on-site
sanitation facilities such as septic tanks, soak-away pits or pit latrines for wastewater
treatment. With interval of 2-3 years, the faecal sludge of onsite sanitation facilities needs
to be dislodged
Fecal sludge (FS) is defined as the sludge of variable consistency collected from on-site
sanitation systems and is comprised of varying concentrations of settle able or settled
solids (Heinss et al., 1998).
From early, it has been know that, the managing of faecal sludge from local community
is the municipal responsibility, however the current condition and fast expansion of Dar
es salaam metropolitan, has cause the current system of wastewater and faecal sludge
treatment to fail to satisfy the needs. Later, the circumstance has creates opportunity for
local and private entrepreneurs to make money through treatment and disposal of faecal
sludge. Most of private entrepreneurs lack knowledge of proper treatment, handling and
disposal of faecal matter. Uncontrolled and indiscriminate dumping of FS removed from
on-site or other faecal sludge treatment systems creates the potential risks for human
health through human contact with untreated FS and the potential for drinking water
contamination (Van oven, 2004).
Faecal sludge treatment pools a great demand especially in developing countries, there
are different methods used to treat Faecal sludge, each methods has its merits and
demerits.
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Whereas there are great demands of treating and disposing faecal sludge in sprawling
areas, final application or disposal challenges ascend. The widely and suitable option
used is the land application. The constraints on the land application of sludge vary
according to the treatment to which the sludge has been subjected and the crops which
are produced subsequent to the sludge application. The constraints apply particularly to
conventionally treated sludge’s where there is a greater risk of pathogens being present.
The constraints have to be more stringent the greater the risk to the consumer. For
example there is a much higher risk when fruit and vegetables are eaten raw, as with
salads, than from processed cereals from arable land. In reality, sludge would not be used
on land growing salad crops and this guidance would apply in situations where a farmer
growing, for instance, arable crops fertilized with sludge plans to change the land use to
salad crops without sludge. Evidence to justify the 10-month no-harvest recommendation
for vegetables in ground contact was presented by Carrington et al. (1998)
While the major output of the treatment system is wastewater and bio solids, Wastewater
from treatment system also can presents a source of hazards to public health and
environment. Watercourses when contaminated then utilized by man either as a source of
portable water or for washing or bathing would present potential risk of transmission of
large number of water related diseases (Horan, 1991)
Therefore in order to achieve the goal of public health prevention and environmental
protection, care must be taken while treating faecal sludge as well as wastewater before
disposing to the land or to reuse for agriculture activities.
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1.1 Justification and Motivation
Dar es Salaam is the metropolitan city with each day increases in population. It has more
than 2,500,000 populations in which large number of population depends on on-site
sanitation facilities such as septic tanks, soak-away pits or pit latrines for wastewater
treatment. In course of time, essentially 2-3 years the systems usually are emptied of
sludge for final treatment and disposal. The Salasala Private Faecal sludge management
systems receives the faecal sludge from on-site sanitation facilities of the whole area of
Tegeta Boko, Bunju, Ununio, Wazo Hill, Salasala, KunduchiMtongani, Kunduchi,
Africana and part of Mikocheni neighborhoods with hesitant from people around the
facility and organization such as NEMC and OSHA about its performance and suitability
in managing and treating faecal sludge. Uncontrolled and indiscriminate dumping of FS
removed from faecal related management systems creates the potential risks for human
health and environment’s as well.
1.2 Research problem
The performance and aptitude of Salasala decentralized faecal sludge management
system located at Tegeta Kinondoni Dar es salaam, in polishing Septic tank and pit
latrine as a pre-treated domestic wastewater basically from Tegeta, Boko, Bunju and
Kunduchi neighborhoods has been one of the big issue among the people and
organizations such as NEMC and OSHA. The grievances here are “If the system is
suitable for management of faecal sludge hauled from septic tank and pit latrine though
private cesspit emptier, and also, if the effluent comply with the required standards, i.e.
TBS and WHO for treating domestic wastewater to meet irrigation purpose which is the
current activity performed by the treatment owner with plant final effluent. Disposing of
untreated or partial treated wastewater to the Environment, threaten and cause damage to
Public health and Environments, especially if it does not comply with the required
standards.
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1.3 Objective of the Study
The general objective of this study was to assess Salasala privately operated decentralized
Faecal sludge management system and critical analyze the improvements which are
needed to make it suitable (cost effective) faecal sludge management system with a
potential for citywide adoption
1.3.1 Specific objectives
The specific objectives of this study were the following:
Technical assessment of Salasala private operated decentralized faecal sludge
management system,
Assessment of aesthetic and land scape quality of Salasala private operated
decentralized faecal sludge management system,
Economic assessment of Salasala private operated decentralized faecal sludge
management system,
Analysis of the improvements needed to make the Salasala decentralized system a
suitable faecal sludge management system,
1.4 Scope
This study is limited to assess the performance of existing private decentralized faecal
sludge management system located at, Tegeta-Dar es salaam and offer improvements
which are needed to make it suitable faecal sludge management system with a potential
for citywide adoption
1.5 Expected output
The expected output involves a well writer report with the critical improvements needed
to make Salasala private decentralized faecal sludge management system suitable faecal
sludge management system with a potential for citywide adoption.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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CHAPTER TWO
LITERATURE REVIEW
2.1 Fecal Sludge
Faecal sludge is defined by as Sludges of variable consistency collected from on-site
sanitation systems, such as latrines, non-sewered public toilets, septic tanks and aqua
privies (Heinss et al. (1998). The faecal sludge comprises varying concentrations of
settable or settled faecal solids as well as of other, non faecal matter.
Fecal Sludge is a highly variable, organic material with considerable levels of grease,
grit, hair, and debris. In addition to its variable nature, FS tends to foam upon agitation,
resists settling and dewatering and serves as a host for many disease-causing viruses,
bacteria, and parasites (USEPA, 1999).
The helminthes eggs, ammonium, and organic and solids concentrations in fecal sludge
are typically higher by a factor of ten or more than in wastewater (Montangero and
Strauss, 2002).The criteria and procedures for the treatment of fecal sludge’s, therefore,
differ from those used for domestic wastewater. As fecal sludge contains a variety of
fertilizers, including nitrogen and phosphorus and is low in chemical contaminants, it
tends to lend itself well to agricultural use. Prior to disposal of fecal sludge or land
application for agricultural use, however, it must be stabilized to reduce levels of
pathogenic organisms, lower the potential for putrefaction, and reduce odors (CWRS,
1999).
2.1.1 Sewage sludge
Common value for sewage sludge is a solids content of around 2%. Anaerobically
digested sludge generally has higher solids content, while aerobic sludge has lower solids
content (De Maeseneer, 1997). In general, the nutrient concentrations of sewage sludge
are lower than in human excreta and faecal sludge
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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2.1.2 Faecal sludge characteristics
The physical characteristics of fecal sludge (FS) vary significantly due, among other
factors, to climate, tank emptying technology and pattern, storage duration (months to
years), performance of tank, additional components of FS including grease, kitchen/solid
waste, and potential groundwater intrusion (Montangero and Strauss, 2002).Compared to
sludge’s from wastewater treatment plants or to municipal wastewaters characteristics
differ widely according to location (from household to household, from city district to
city district, from city to city).The factor’s influencing faecal sludge characteristics are
illustrated in Figure 2.1
Figure 2.1: Factors influencing FS characteristics. (Source: Heinss et al., 1998)
General Characteristics of faecal sludge characteristics are given by SANDEC (1997)
(Table 2.1).Concentrations of COD, ammonium, SS and helminth eggs in FS are much
higher than in sewage due to the lower water contents.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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Public toilet
sludge
Septage Sewage
Characterization Highly
concentrated,
mostly fresh FS;
stored for days or
weeks only
FS of low
concentration;
usually stored for
several years
;more stabilized
than public toilet
sludge
Sewage for
comparison
Tropical sewage
COD (mg/l) 20-50000 < 10000 500--2,500
COD/BOD 2:1-5:1 5:110:1 2:1
NH4-N (mg/l) 2,-5000 < 1000
TS ≥ 3.5% < 3% 30 - 70
SS (mg/l) ≥ 30,000 = 7000 < 1%
Helminth eggs
(no/litre)
20,-6000 = 4000 200 - 700
Table 2.1: Characteristics of faecal sludge’s (source: Heinss et al., 1998)
2.1.3 Nutrients in sludge
Table 2.2 contains relevant characteristics and per capita quantities of human excreta,
including its resource elements, viz. organic matter, along with phosphorus, nitrogen and
potassium as major plant nutrients. Average nutrient contents of plant matter and cattle
manure are also included for comparison’s sake. Faecal Sludges, if adequately stored or
treated otherwise, may be used in agriculture as soil conditioner to restore or maintain the
humus layer or as fertilizer.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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Faces Urine Excreta
Quality and consistence
Gram/cap. Day (wet) 250 1200 1450
Gram/cap. Day (dry) 50 60 110
Including 0.35 litres
for anal cleansing
gram/ cap. Day (wet)
1800
m3/cap.year (upon
storage and digestion
for>1 year in pits or
vault in hot climate
0.04-0.07
Water content % 50-95
Chemical
composition
% of dry solids
Organic matter 92 75 83
C 48 13 29
N 4-7 14-18 9-12
P 2 O5 4 3.7 2.7
K20 1.6 3.7 2.7
For comparison
sake
% of dry solids
N P 2 O5 K20
Human excreta 9-12 3.8 2.7
Plant matter 1-11 0.5-2.8 1.1-11
Pig manure 4-6 3-4 2.5-3
Cow manure 2.5 1.8 1.4
Table 2.2 Human excreta per capita quantities and their resource value (Strauss 1985)
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2.2 Domestic wastewater
Domestic wastewater is the water that has been used by a community and which contains
all the materials added to the water during its use. It is thus composed of human body
wastes (faeces and urine) together with the water used for flushing toilets, and sullage,
which is the wastewater resulting from personal washing, laundry, food preparation and
the cleaning of kitchen utensils. The typical composition of domestic wastewater is
presented in table 2.3 bellow.
Content(all in mg/l exceptsettle able solids)
Weak Medium Strong
Alkalinity 50 100 200
Ammonia (free) 10 25 50
BOD5 (as O2) 100 200 300
Chloride 30 50 100
COD (as O2) 250 500 1000
Total suspendedsolids (TSS)
120 210 400
Volatile (VSS) 95 160 315
Fixed 25 50 85
Settle able solidsml/L
5 10 20
Sulfates 20 30 50
Total dissolvedsolids (TDS)
200 500 1000
Total Kjeldahlnitrogen (TKN) (asN)
20 40 80
Toatal organiccarbon (TOC) (asC)
75 150 300
TotalPhosphorus(as P)
5 10 20
Table 2.3 Typical composition of untreated domestic wastewater (Metcalf and eddy2003)
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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Fresh wastewater is a grey turbid liquid that has an earthy but inoffensive odor. It
contains large floating and suspended solids (such as faeces, rags, plastic containers, and
maize cobs), smaller suspended solids (such as partially disintegrated faeces, paper, and
vegetable peel) and very small solids in colloidal (ie non-settleable) suspension, as well
as pollutants in true solution. It is objectionable in appearance and hazardous in content,
mainly because of the number of disease-causing (‘pathogenic’) organisms it contains. In
warm climates wastewater can soon lose its content of dissolved oxygen and so become
‘stale’ or ‘septic’. Septic wastewater has an offensive odor, usually of hydrogen sulphide.
The composition of human faces and urine is given in Table 2.4. The organic fraction of
both is composed principally of proteins, carbohydrates and fats. These compounds,
particularly the first two, form an excellent diet for bacteria, the microscopic organisms
whose voracious appetite for food is exploited by public health engineers in the
microbiological treatment of wastewater. In addition to these chemical compounds, faces
and, to a lesser extent, urine contains many millions of intestinal bacteria and smaller
numbers of other organisms. The majority of these are harmless – indeed some are
beneficial– but an important minority is able to cause human disease. Sullage contributes
a wide variety of chemicals: detergents, soaps, fats and greases of various kinds,
pesticides, anything in fact that goes down the kitchen sink, and this may include such
diverse items as sour milk, vegetable peelings, tea leaves, soil particles (arising from the
preparation of vegetables) and sand (used to clean cooking utensils).
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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Quantities Faces urine
Quantity (wet) per personper day
135–270 g 1.0-1.3kg
Quantity (dry solids) perperson per day
35–70 g 50-70g
Approximate composition (%)Moisture 66–80 44–55 4.5Organic matter 88–97 15-19Nitrogen 5.0–7.0 2.5-5.0Phosphorus (as P 2 O5) 1.0–2.5 3.0-4.5Carbon 44–55 11–17Calcium (as CaO) 4.5 4.5–6.0
Table 2.4 Composition of human faeces and urine (Source: Gotaas 1956)
2.2.1 Domestic waste Water Characteristics
Wastewater is mainly comprised of water (99.9%) together with relatively small
concentrations of suspended and dissolved organic and inorganic solids which are highly
hazardous in nature and may cause pollution of stream, underground water and lakes. So
it is important to know the characteristics of wastewater which will give the idea of
degree pollution and method of treatment to be adopted for safe disposal. These
characteristics are divided into three classes i.e. physical, chemical and biological.
(Chatterjee, 1973)
2.2.1.1 Physical Characteristics
i. Temperature
The temperature of wastewater is usually higher because of the addition of warm water
from domestic use. Wastewater temperature is important for two reasons.
Biological processes are temperature dependent and
Chemical reactions and reaction rates and aquatic life are all temperature
sensitive.
The best temperatures for wastewater treatment range from 15o C to 45o C
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ii. Solids
Solid materials in wastewater can consist of organic and/or inorganic materials
and organisms. The solids must be significantly reduced by treatment otherwise
they can increase BOD levels when discharged to receiving waters. Solids are
classified as;
Total solids
Suspended solids
Dissolved solids
Settable solids
Fixed solids
2.2.1.2 Chemical characteristics
i. Inorganic
Inorganic minerals, metals, and compounds, such as sodium, potassium, calcium,
phosphorus, nitrogen, magnesium, cadmium, copper, lead, nickel, and zinc are
common in domestic wastewater. Phosphorus and nitrogen are the most
environmental significant elements in wastewater for causing eutrophication. Most
of these inorganic substances are relatively stable and cannot be broken down easily
by organisms in wastewater.
ii. Phosphorus
Phosphorus exists in wastewater in many forms and includes soluble
orthophosphate ion (PO4-3), organically-bound phosphate, and other
phosphorus/oxygen forms, calcium phosphate.
Effects of Phosphorous and Nitrogen (Nutrients)
Increases algal photosynthesis (eutrophication) i.e. increased plant life on
surface, Reduces light in lower levels.
Organic nitrogen and ammonia are converted to nitrates in water
Nitrates are converted to nitrites in digestive system
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Nitrites are assimilated into blood stream where they are converted by
respired oxygen to nitrates
May cause suffocation (blue baby syndrome)
iii. Oil and grease
Oil and grease is the term given to the combination of fats, oils, waxes, and other related
constituents found in wastewater. When large amounts of oils and greases are discharged to
receiving waters from community systems they increase BOD level.
iv. pH
The pH is the measure of the inverse concentration of hydrogen ions. The acidity or alkalinity of
wastewater affects both treatment and the environment.
v. Organic matter
Organic materials in wastewater originate from plants, animals, or synthetic organic
compounds, and may enter in wastewater through human wastes, paper products, detergents,
cosmetics, foods, and from agricultural, commercial, and industrial sources.
vi. BOD – biochemical oxygen demand
The BOD test measures the amounts of dissolved oxygen which is consumed by microorganisms
in decomposing organic matter.
Effect of BOD
Depletes dissolved oxygen from streams, lakes and oceans
May cause death of aquatic organisms
Increases anoxicity in receiving water bodies
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vii. Gases
Methane, Hydrogen sulfide, Carbon dioxide and ammonia are common gases emitted from waste
water. These gases are toxic and can cause odors. Ammonia as a dissolved gas in wastewater is
dangerous to aquatic life beyond acceptable levels
2.2.1.3 Biological characteristics
Pathogens
Possible pathogens likely to be found in wastewater include viruses, parasites, and bacteria. Total
Coliforms and Fecal Coliforms are indicators of pathogens and level of biological pollution in
wastewater
2.3 Faecal Sludge Treatment
Unlike digested sludge produced in mechanized biological wastewater treatment facilities or in
other types of wastewater treatment works (e.g. waste stabilization ponds, oxidation ditches), the
organic stability of FS attains varying levels. This variability is due to the fact that the anaerobic
degradation process, which takes place in onsite sanitation systems, depends on several factors
like ambient temperature, retention period and the presence of inhibiting substances. As the
faecal matter is not being mixed or stirred, this impairs the degradation process (Koottatep et al.,
2003). The choice of a FS treatment option depends primarily on the characteristics of the FS
generated in a particular town or cities, budget availability, land availability and the treatment
objectives (Montangero and Strauss, 2004). The widely varying quality and quantity of FS
requires a careful selection of appropriate treatment options Primary treatment may encompass
solids liquid separation or biochemical stabilization if the
FS is still fresh but has undergone partial degradation during on-plot storage and prior to
collection.
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Figure 2.2 Overview of the modest faecal treatment options ( Montangero & Strauss 2004)
2.3.1 Solids/liquid separation
Dewatering or the separation of the solids and liquids of the sludge is primarily meant to reduce
the volume of the sludge and to increase the dry matter content. Most of the processes described
in this paragraph are normally used for the treatment of (primary and secondary) sewage sludge,
except the composting and vermi-composting processes which are also used for treatment or
handling of other organic wastes.
2.3.2 Gravity solids/liquid separation
Gravity dewatering makes use of sedimentation. Also, evaporation processes increased by wind
and solar energy contribute to the reduction of the water content of the sludge.
2.3.2.1 Sedimentation tanks
Using lagoons or sedimentation basins for sewage sludge dewatering a TS contents of 10 -35%
and a volume reduction of 40 - 50% (and even more when one starts with a solids content of 2 -
5 %) can be achieved (NVA, 1994; Strauss, 1999). In sedimentation tanks sedimentation and
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flotation of solid material separate the water and sludge. Heinss et al. (1997) reported about a FS
sedimentation/thickening basin, in which a thickening concentration TS = 15% could be attained.
2.3.2.2 Drying beds without plants
Gravity dewatering can also take place in (unplanted) drying beds. Similar to lagoons, drying
beds also require much space. Dewatering is attained both by evaporation and seepage.
According to Heinss et al. (1997) 40 - 70% TS content in the dewatered faecal sludge may be
attained within 8-12 days, with loading rates of 100 - 200 kg TS/m2·yr. These loading rates are
considerably lower than, for example, the loading rates that can be applied in sedimentation
tanks, which results in a larger area per capita (0,05 m2/cap). However, the effluent of drying
beds needs less polishing than the effluent of sedimentation tanks.
Based on a questionnaire and visits to wastewater treatment plants in the USA, Kim and Smith
(1997) reported that the type of sludge influences the loading rates that can be applied on sand-
drying beds without plants. Using different drying bed criteria, the solid loading rates for open
sand-drying bed range from 64 to 113 kg/m2·yr. For anaerobic sludge, the EPA recommended
100 to 160 kg/m2·yr. as sand drying bed design criteria. These conventional unplanted sand-
drying beds are simple to operate and maintain, and are inexpensive to build. Some
disadvantages are, however, that dewatering can take 2 to 4 weeks (depending on the climate,
soil type etc.), the removal of the dried sludge requires intensive labor and there is always the
danger of clogging or low dewater ability potential with undigested or only partly dewatered
Sludges.
2.3.3 Mechanical solids/liquid separation
Mechanical dewatering methods have low area requirement and the TS content of the solid
fraction can be controlled precisely. Mechanical methods are characterized by high capital costs,
high-energy consumption (1 - 10 kWh/m3) (STORA, 1981) and the need for adding chemicals
for conditioning. Most common processes applied are:
Vacuum filtering
Filter pressing
(Chemical added) centrifuging
Belt filter pressing
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The TS content that can be achieved by mechanical dewatering processes is comparable with
natural dewatering processes: 15 - 45% (NVA, 1994).
2.3.4 Digestion
The digestion of faecal sludge is not primarily meant for solid / liquid separation. During the
digestion process the organic material is decomposed. The biogas produced during the process
can be collected and used for cooking or heating, while the effluent of the digesters can be used
for plant fertilization and soil amendment purposes. The sludge that remains in the digester has
to be removed and usually needs some further treatment e.g. drying, composting, land
application or incineration. Zhao Xihui reports about four different types of digesters that are
used in China for night soil treatment (Xihui, 1988). These digesters can achieve a high parasitic
ova reduction: > 93%.The effluent of the digesters needs a post treatment before discharging into
surface water or sewer systems. The application of biogas digesters resulted in a reduced
prevalence of infectious diseases and also the density of flies decreased remarkably. In
Guatemala dome-shaped Chinese type digesters have been tested. Latrines fed the digesters. The
experiments made clear that the low temperatures and the low air pressure had a negative effect
on the treatment process. The underground-type Chinese digester used as a latrine produced
biogas, solids and a relatively clear effluent. The solids and effluent can be used as fertilizer as
the effluent contains high concentrations of nitrogen, phosphorus and potassium. The pathogen
concentration in the effluent was acceptable for reuse in agriculture and fishponds (Estrada et al.,
1986).
2.3.5 Anaerobic Decomposition
In order to achieve anaerobic decomposition, molecular oxygen and nitrate must not be present
as terminal electron acceptors. Sulfate (S4O2), carbon dioxide, and organic compounds that can
be reduced serve as terminal electron acceptors. The reduction of sulfate results in the production
of equally odoriferous organic sulfur compounds called mercaptans and hydrogen sulfide (H2 S).
The anaerobic decomposition (fermentation) of organic matter generally is considered to be a
three-step process. In the first step, waste components are hydrolyzed. In the second step,
complex organic compounds are fermented to low molecular weight fatty acids (volatile acids)
.In the third step, the organic acids is converted to methane. Carbon dioxide serves as the
electron acceptor.
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Anaerobic decomposition yields carbon dioxide, methane, and water as the major end products.
Additional end products include ammonia, hydrogen sulfide, and mercaptans. As a consequence
of these last three compounds, anaerobic decomposition is characterized by highly objectionable
odors.
Because only small amounts of energy are released during anaerobic oxidation, the amount of
cell production is low. Thus, sludge production is low. This fact is used in wastewater treatment
to stabilize and reduce the volume of Sludges produced during aerobic and anoxic
decomposition.
Typically, direct anaerobic decomposition of wastewater is not used for dilute municipal
wastewater. The optimum growth temperature for the anaerobic bacteria is at the upper end of
the mesophilic range. Thus, to get reasonable biodegradation, the temperature of the culture must
be elevated. For dilute wastewater, this is not practical. For concentrated wastes (BOD greater
than1, 000 mg/L) and sludge treatment, anaerobic digestion is quite appropriate.
2.4 Wetlands and sludge treatment
Wetlands are parts of the earth’s surface between true terrestrial and aquatic systems. Thus
shallow lakes, marshes, swamps, bogs, dead riverbeds, borrow pits, are all wetlands irrespective
of their extent and degree of human interventions. Wetlands are generally shallow and thus
differentiated from deep water bodies. Wetlands often include three main components. These are
the presence of water, unique soils differing from those of uplands and presence of vegetation
adapted to wet conditions. Gosh (1995)
2.4.1 Natural wetland
Natural wetlands are in many developing countries in use for the treatment of domestic and even
industrial wastewater. In Tanzania, natural wetlands occupy over 7% of the country's surface
area. Most natural wetland takes the form of swamps with macrophytes vegetation typical to
such areas including reeds, bulrushes, cattails, and sedges. Some wetlands are naturally seasonal
in nature and the controlled discharge of effluent from WSP or constructed wetlands can both
maintain the natural swam through the dry season and allow it to polish the effluent before this
reaches the watercourse. Compared to other wastewater treatment technologies they are a cheap
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and appropriate solution against water pollution. However, the controlled use of natural wetlands
for water pollution may become a problem, especially when the wetlands are used for other
purposes, for example as a clean water source. So the use of natural wetlands for wastewater
treatment may conflict with important issues as wetland bio-diversity and the sustainable
development of natural resources (Denny, 1997). Constructed wetlands may be more
controllable alternatives, which are appropriate and may be cost-effective solutions.
2.4.2 Constructed wetland
Constructed Wetlands (CW) is a biological wastewater treatment technology designed to mimic
processes found in natural wetland ecosystems. These systems use wetland plants, soils and their
associated microorganisms to remove contaminants from wastewater. Application of constructed
wetlands for the treatment of municipal, industrial and agricultural wastewater as well as storm
water started in the 1950s and they have been used in different configurations, scales and
designs. CWs are receiving increasing worldwide attention for wastewater treatment and
recycling due to the following major advantages:
Use of natural processes
Simple and relatively inexpensive to construct (can be constructed with local materials)
Simple operation and easy to maintain
Cost-effectiveness (low construction and operation costs)
Process stability i.e. relatively tolerant of fluctuating hydrologic and contaminant loading
rates
Provide effective and reliable wastewater treatment
Provide indirect benefits such as green space, wildlife habitats and recreational and
educational areas.
Research studies have shown that wetland systems have great potential in controlling water
pollution from domestic, industrial and non-point source contaminants. As it has been widely
recognized as a simple, effective, reliable and economical technology compared to several other
conventional systems, it can be a useful technology for wastewater treatment. However CWs has
the following disadvantages
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The land requirements (cost and availability of suitable land)
Current imprecise design and operation criteria
Biological and hydrological complexity and our lack of understanding of important
process dynamics.
The costs of gravel or other fills, and site grading during the construction period.
Possible problems with pests. Mosquitoes and other pests could be a problem for an
improperly designed and managed SSF. The system may be used for small communities
and, therefore, may be located close to the users. The dependence of wetland community
on hydrologic patterns is most obvious in the change in species composition resulting
from alterations in water depths and flows.
There are various types of constructed wetland systems for treating wastewater based on the type
of plants used, type of media used and flow dynamics.
2.4.2.1 Types of Constructed Wetlands
Constructed wetlands for wastewater treatment can be categorized as either Free Water Surface
(FWS) or Subsurface Flow (SSF) systems. In FWS systems, the flow of water is above the
ground, and plants are rooted in the sediment layer at the base of water column (Figure 2.3) In
SSF systems, water flows through a porous media such as gravels or aggregates, in which the
plants are, rooted (Figure 2.4). Table2.5 illustrates the type of wetlands, vegetation types and
water column contacts in constructed wetlands.
Figure 2.3: Emergent macrophytes treatment system with surface flow
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Figure 2.4: Emergent macrophytes treatment system with horizontal sub surface flow
Constructed wetland type Type of vegetation Section in contact with water
column
Free water surface (FWS) Emergent Stem, limited leaf contact
Floating Root zone, some stem tubers
Submerged Photosynthetic part, possibly root zone
Sub-surface flow (SSF) Emergent Rhizome and root zone
Table 2.5 Vegetation type and water column contact in constructed wetlands
SSF systems are most appropriate for treating primary wastewater, because there is no direct
contact between the water column and the atmosphere. There is no opportunity for vermin to
breed, and the system is safer from a public health perspective. The system is particularly useful
for treating septic tank effluent or grey water, landfill leachate and other wastes that require
removal of high concentrations organic materials, suspended solids, nitrate, pathogens and other
pollutants. The environment within the SSF bed is mostly either anoxic or anaerobic Oxygen is
supplied by the roots of the emergent plants and is used up in the Biofilm growing directly on the
roots and rhizomes, being unlikely to penetrate very far into the water column itself. SSF
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systems are good for nitrate removal (denitrification), but not for ammonia oxidation
(nitrification), since oxygen availability is the limiting step in nitrification.
Constructed wetlands remove pollutants from wastewater through various physical, chemical and
biological mechanisms. Some of the main pollutant removal mechanisms in constructed wetlands
are presented in table 2.6 below:
Wastewater characteristics Removal mechanism
Suspended solids Sedimentation
Filtration
Soluble organics Aerobic microbial degradation
Anaerobic microbial degradation
Phosphorous Matrix sorption
Plant uptake
Nitrogen Ammonification followed by microbial
nitrification
Denitrification
Plant uptake,
Matrix adsorption
Ammonia volatilisation (mostly in SF system)
Metals Adsorption and cation exchange
Complexation
Precipitation
Plant uptake
Microbial oxidation/reduction
Pathogens Sedimentation
Filtration
Natural die-off
Predation
UV irradiation (SF system)
Excretion of antibiotics from roots of macrophytes
Table 2.6 Pollutant removal mechanisms in constructed wetlands (source: cooper et al., 1996)
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2.4.2.2 Configuration, Zones and components of constructed wetlands
Influents to constructed wetland can range from raw wastewater to secondary effluents. Most
constructed wetlands have the following zones: inlet zone, macrophytes zone, and littoral zone
and outlet zones. The components associated in each zones are as shown in Table 2.7 and can
include substrates with various rates of hydraulic conductivity, plants, a water column,
invertebrate and vertebrates, and an aerobic and anaerobic microbial population. The water flow
is maintained approximately 15 – 30 cm below the bed surface. Plants in wastewater systems
have been viewed as nutrient storage compartments where nutrient uptake is related to plant
growth and production. Harvesting before senescence may permanently remove nutrients from
the systems. Within the water column, the stems and roots of wetland plants significantly provide
the surface area for the attachment of microbial population. Wetland plants have the ability to
transport atmospheric oxygen and other gases down into the root to the water column. Most
media used include crushed stones, gravels, and different soils, either alone or in combination.
Most beds are underlain by impermeable materials to prevent water seepage and assure water
level control. Wastewater flows laterally, being purified during contact with media surface and
vegetation roots. The sub-surface zone is saturated and generally anaerobic, although excess DO
conveyed through the plant root system supports aerobic microsites adjacent to the root and
rhizomes.
Zones Components Functions
Inlet zone Inlet structure, splitter box
Flow distribution across the full width at a
minimum of 3 – 5 m interval
Macrophyte zone
Porous bed/substrate, open
water, vegetation, island,
mixing baffles, flow diversion
To provide the substrate with high hydraulic
conductivity; to provide surface for the
growth of Biofilm; to aid in the removal of
fine particles by sedimentation or filtration; to
provide suitable support for the development
of extensive root and rhizome system for
emergent plants.
Reduce short circuiting by re-orienting flow
path; reduce stagnant areas by allowing for
mixing by wind; enable UV disinfections of
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Deep water zone Usually deeper, non-vegetated bacteria and other pathogens; provide habitat
for waterfowl.
Littoral zone Littoral area
Littoral vegetation protects embankment from
erosion; littoral vegetation serves to break up
wave action.
Outlet zone Collection devices, spillway,
weir, outlet structures
Control the depth of the water in the wetland;
collect the effluent water without creating of
dead zones in the wetlands; provide access for
sampling and flow monitoring.
Table 2.7 Wetland zones and their associated components
2.4.2.3 Processes in Sub-surface Flow Constructed Wetlands (SSFCW)
Wetland can effectively remove or convert large quantities of pollutants from point sources
(municipal, industrial and agricultural wastewater) and non-point sources (mines, agriculture and
urban runoff), including organic matter, suspended solids, metals and nutrients. The focus on
wastewater treatment by constructed wetlands is to optimize the contact of microbial species
with substrate, the final objective being the bioconversion to carbon dioxide, biomass and water.
Wetlands are characterized by a range of properties that make them attractive for managing
pollutants in water. These properties include high plant productivity, large adsorptive capacity of
the sediments, high rates of oxidation by micro flora associated with plant biomass, and a large
buffering capacity for nutrients and pollutants (Cooper, 1990). Table 2.8 provides an overview of
pollutant removal mechanisms in constructed wetlands.
Pollutant Removal Processes
Organic material (measured as BOD) Biological degradation, sedimentation,
microbial uptake
Organic contaminants (e.g., pesticides) Adsorption, volatilization, photolysis, and
biotic/abiotic degradation
Suspended solids Sedimentation, filtration
Nitrogen Sedimentation, nitrification/denitrification,
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microbial uptake, volatilization
Phosphorous Sedimentation, filtration, adsorption, plant and
microbial uptake
Pathogens Natural die-off, sedimentation, filtration,
predation, UV degradation, adsorption
Heavy metals Sedimentation, adsorption, plant uptake
Table 2.8: Overview of pollutant removal mechanisms
2.4.2.4 Horizontal surface Flow Constructed Wetland (SFCW)
A Horizontal surface Flow Constructed Wetland is large gravel and sand-filled channel that is
planted with aquatic vegetation. As wastewater flows horizontally through the channel, the filter
material filters out particles and microorganisms degrade organics.
The water level in a Horizontal surface Flow Constructed Wetland is maintained at 5 to 15cm
below the surface to ensure subsurface flow. The bed should be wide and shallow so that the
flow path of the water is maximized (figure 2.5). A wide inlet zone should be used to evenly
distribute the flow. Pre-treatment is essential to prevent clogging and ensure efficient treatment.
Figure 2.5: Section through Horizontal surface Flow Constructed Wetland
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The bed should be lined with an impermeable liner (clay or geotextile) to prevent leaching.
Small, round, evenly sized gravel (3–32mm in diameter) is most commonly used to fill the bed to
a depth of 0.5 to 1m. To limit clogging, the gravel should be clean and free of fines. Sand is also
acceptable, but is more prone to clogging. In recent years, alternative filter materials such as PET
have been successfully used.
The removal efficiency of the wetland is a function of the surface area (length multiplied by
width), while the cross-sectional area (width multiplied by depth) determines the maximum
possible flow. A well-designed inlet that allows for even distribution is important to prevent
short-circuiting. The outlet should be variable so that the water surface can be adjusted to
optimize treatment performance.
The filter media acts as both a filter for removing solids, a fixed surface upon which bacteria can
attach, and a base for the vegetation. Although facultative and anaerobic bacteria degrade most
organics, the vegetation transfers a small amount of oxygen to the root zone so that aerobic
bacteria can colonize the area and degrade organics as well. The plant roots play an important
role in maintaining the permeability of the filter.
Any plant with deep, wide roots that can grow in the wet, nutrient-rich environment is
appropriate.
2.4.2.4.1 Adequacy of surface flow constructed wetlands
Clogging is a common problem and therefore the influent should be well settled with primary
treatment before flowing into the wetland. This technology is not appropriate for untreated
domestic waste water (i.e. blackwater). This is a good treatment for communities that have
primary treatment (e.g. Septic Tanks or WSPs) but are looking to achieve a higher quality
effluent. This is a good option where land is cheap and available, although the wetland will
require maintenance for the duration of its life.
Depending on the volume of water, and therefore the size, this type of wetland can be
appropriate for small sections of urban areas, peri-urban and rural communities. They can also be
designed for single households.
Horizontal Subsurface Flow Constructed Wetlands are best suited for warm climates but they
can be designed to tolerate some freezing and periods of low biological activity.
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2.4.2.4.2 Health Aspects/Acceptance
The risk of mosquito breeding is reduced since there is no standing water compared to the risk
associated with Free-Water Surface Constructed Wetlands. The wetland is aesthetically pleasing
and can be integrated into wild areas or parklands.
2.4.2.4.3 Maintenance of surface flow constructed wetlands
With time, the gravel will clog with accumulated solids and bacterial film. The filter material
will require replacement every 8 to 15 or more years. Maintenance activities should focus on
ensuring that primary treatment is effective at reducing the concentration of solids in the
wastewater before it enters the wetland. Maintenance should also ensure that trees do not grow in
the area as the roots can harm the liner.
2.5 Biological processes in CWs
There are six major biological reactions involved in the performance of constructed wetlands,
including photosynthesis, respiration, fermentation, nitrification, denitrification and microbial
phosphorus removal (Cooper, 1990). Photosynthesis is performed by wetland plants and algae,
with the process adding carbon and oxygen to the wetland. Both carbon and oxygen drive the
nitrification process. Plants transfer oxygen to their roots, where it passes to the root zones
(rhizosphere). Respiration is the oxidation of organic carbon, and is performed by all living
organisms, leading to the formation of carbon dioxide and water. The common microorganisms
in the CW are bacteria, fungi, algae and protozoa. The maintenance of optimal conditions in the
system is required for the proper functioning of wetland organisms. Fermentation is the
decomposition of organic carbon in the absence of oxygen, producing energy-rich compounds
(e.g., methane, alcohol, volatile fatty acids). This process is often undertaken by microbial
activity. Nitrogen removal by nitrification/denitrification is the process mediated by
microorganisms. The physical process of volatilization also is important in nitrogen removal.
Plants take up the dissolved nutrients and other pollutants from the water, using them to produce
additional plant biomass.
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2.6 Chemical processes
Metals can precipitate from the water column as insoluble compounds. Exposure to light and
atmospheric gases can break down organic pesticides, or kill disease-producing organisms (EPA,
1995). The pH of water and soils in wetlands exerts a strong influence on the direction of many
reactions and processes, including biological transformation, partitioning of ionized and un-
ionized forms of acids and bases, cation exchange, solid and gases solubility.
2.7 Physical processes
Sedimentation and filtration are the main physical processes leading to the removal of
wastewater pollutants. The effectiveness of all processes (biological, chemical, physical) varies
with the water residence time (i.e., the length of time the water stays in the wetland). Longer
retention times accelerate the remove of more contaminants, although too-long retention times
can have detrimental effects.
2.8 Process rates
The chemical and biological processes occur at a rate dependent on environmental factors,
including temperature, oxygen and pH. Metabolic activities are decreased by low temperature,
reducing the effectiveness of pollutant uptake processes relying on biological activity. Low
oxygen concentrations limit the processes involving aerobic respiration within the water column,
and may enhance anaerobic processes, which can cause further degradation of water quality.
Many metabolic activities are pH-dependent, being less effective if the pH is too high or low.
2.9 Hydrological limitations
The capacity of wetlands to treat wastewater is limited, both in terms of the quantity of water,
and the total quantity of the pollutants. Hydraulic overloading occurs when the water flow
exceeds the design capacity, causing a reduction in water retention time that affects the rate of
pollutant removal. Pollutant overloading occurs when the pollutant input exceeds the process
removal rates within the wetland (Metacalf., 1991). Hydraulic overloading may be compensated
for by using surcharge mechanisms, or the design may be based on a flush principle, whereby
large water flows bypass the wetland when used for storm water treatment Mashauri, 1993).
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Inflow variations are typically less extreme for wetlands treating municipal wastewaters, with
incoming pollutant loads also being more defined and uniform.
2.10 Wetland nitrogen processes
The most important nitrogen species in wetlands are dissolved ammonia (NH+
4), nitrite (NO
-
2),
and nitrate (NO-
3). Other forms include nitrous oxide gas (N
2O), nitrogen gas (N
2), urea
(organic), amino acids and amine (Kadlec & Knight, 1996). Total nitrogen in any system is
referred to as the sum of organic nitrogen, ammonia, nitrate and nitrous gas (Organic-N + NH+
4+
NO-
3+ N
2O). The various nitrogen forms are continually involved in transformations from
inorganic to organic compounds, and vice-versa.
NH+
4,+ O
2
+NitrosomonasH
++ NO
-
2+ H
2O
The nitrite produced is oxidized aerobically by nitrobacteria bacteria, forming nitrate as follows:
NO-
2+ O
2
NitrobacterNO
-
3
The first reaction produces hydroxonium ions (acid pH), which react with natural carbonate to
decrease the alkalinity (Metcalf, 1991). In order to perform nitrification, the nitrosomonas must
compete with heterotrophic bacteria for oxygen. The BOD of the water must be less than 20 mg/l
before significant nitrification can occur (Reed et al., 1995). Temperatures and water retention
times also may affect the rate of nitrification in the wetland. Denitrification is the process in
which nitrate is reduced in anaerobic conditions by the benthos to a gaseous form. The reaction
is catalyzed by the denitrifying bacteria Pseudomonas spp. and other bacteria, as follows:
NO-
3+ Organic-C
Denitrifying BacteriaN
2(NO &N
2O)
(G)+ CO
2(G)+ H
2O (3.4)
Denitrification requires nitrate, anoxic conditions and carbon sources (readily biodegradable).
Nitrification must precede denitrification, since nitrate is one of the prerequisites. The process of
denitrification is slower under acidic condition. At a pH between 5-6, N20 is produced. For a pH
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below 5, N2
is the main nitrogenous product (Nuttall et al., 1995). NH+
4is the dominant form of
ammonia-nitrogen at a pH of 7, while NH3
(present as a dissolved gas) predominates at a pH of
12. Nitrogen cycling within, and removal from, the wetlands generally involves both the
translocation and transformation of nitrogen in the wetlands, including sedimentation
(resuspension), diffusion of the dissolved form, litter fall, adsorption/desorption of soluble
nitrogen to soil particles, organism migration, assimilation by wetland biota, seed release,
ammonification (mineralisation) (Orga-N – NH+
4), ammonia volatilization (NH
+
4– NH
3(gas)),
bacterially-mediated nitrification/denitrification reactions, nitrogen fixation (N2, N
2O (gases –
organic-N)), and nitrogen assimilation by wetland biota (NH+
4, Nox organic – N, with NO
x
usually as NO-
3). Precipitation is not a significant process due to the high solubility of nitrogen,
even in inorganic form. Organic nitrogen comprises a significant fraction of wetland biota,
detritus, soils, sediments and dissolved solids (Kadlec , 1996).
2.11 Wetland in Phosphorus removal
Phosphorus is an essential requirement for biological growth. An excess of phosphorus can have
secondary effects by triggering eutrophication within a wetland, and leading to algal blooms and
other water quality problems. Phosphorus may enter a wetland in dissolved and particulate
forms. It exits wetlands in outflows, by leaching into the sub-soil, and by removal by plant and
animals. Phosphorus removal in wetlands is based on the phosphorous cycle, and can
Involve a number of processes. Primary phosphorus removal mechanisms include adsorption,
filtration and sedimentation. Other processes include complexation/precipitation and
assimilation/uptake. Particulate phosphorus is removed by sedimentation, along with suspended
solids. The configuration of constructed wetlands should provide extensive uptake by Biofilm
and plant growth, as well as by sedimentation and filtration of suspended materials. Phosphorus
is stored in the sediments, biota, (plants, Biofilm and fauna), detritus and in the water. The
interactions between compartments depend on environmental conditions such as redox
chemistry, pH and temperature. The redox status of the sediments (related to oxygen content)
and litter/peat compartment is a major factor in determining which phosphorus cycling processes
will occur. Under low oxygen conditions (low redox potential), phosphorus is liberated from the
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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sediments and soils back into the water column, and can leave the wetland if the anaerobic
condition is not reversed (Okun 1979).
2.12 CWs in Suspended solids removal
Solids may be derived from outside a wetland (e.g., inflows and atmospheric inputs), and from
within a wetland from plankton (zooplankton and phytoplankton), and plant and animal detritus.
With low wetland water velocities and appropriate composition of influent solids, suspended
solids will settle from the water column within the wetland. Sediment resuspension not only
releases pollutants from the sediments, it increases the turbidity and reduces light penetration.
The physical processes responsible for removing suspended solids include sedimentation,
filtration, adsorption onto Biofilm and flocculation/precipitation. Wetland plants increase the
area of substrate available for development of the Biofilm. The surface area of the plant stems
also traps fine materials within its rough structure.
2.13 CWs in Pathogen removal
Pathogens are disease-causing organisms (e.g., bacteria, viruses, fungi, protozoa, helminthes).
Wetlands are very effective at removing pathogens, typically reducing pathogen number by up to
five orders of magnitude from wetland inflows (Reed at al., 1995). The processes that may
remove pathogens in wetlands include natural die-off, sedimentation, filtration, ultra-violet light
ionization, unfavorable water chemistry, temperature effects, predation by other organisms and
pH (Kadlec & knight 1996).They showed that vegetated wetlands seem more effective in
pathogen removal, since they allow a variety of microorganisms to grow which may be predators
to pathogens.
2.14 CWs in Heavy metal removal
Heavy metals is a collective name given to all metals above calcium in the Periodic Table of
Elements, which can be highly toxic, and which have densities greater that 5g/cm3
(Skidmore ,
1983). The main heavy metals of concern in freshwater include lead, copper, zinc, chromium,
mercury, cadmium and arsenic. There are three main wetland processes that remove heavy
metals; namely, binding to soils, sedimentation and particulate matter, precipitation as insoluble
salts, and uptake by bacteria, algae and plants (Kadlec, 1996). These processes are very effective,
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
32
with removal rates reported up to 99% (Reed et al., 1995). A range of heavy metals, pathogens,
inorganic and organic compounds present in wetlands can be toxic to biota. The response of
biota depends on the toxin concentration and the tolerance of organisms to a particular toxin.
Wetlands have a buffering capacity for toxins, and various processes dilute and break down the
toxins to some degree.
2.15 Abiotic Factors and their Influence on Wetlands
2.15.1 Oxygen
Oxygen in wetland systems is important for heterotrophic bacterial oxidation and growth. It is an
essential component for many wetland pollutant removal processes, especially nitrification,
decomposition of organic matter, and other biological mediated processes. It enters wetlands via
water inflows or by diffusion on the water surface when the surface is turbulent. Oxygen also is
produced photosyntheticcally by algae. Plants also release oxygen into the water by root
exudation into the root zone of the sediments. Many emergent plants have hollow stems to allow
for the passage of oxygen to their root tissues. The oxygen-demand processes in wetlands
include sediment-litter oxygen demand (decomposition of detritus), respiration (plants/animals),
dissolved carbonaceous BOD, and dissolved nitrogen that utilizes oxygen through nitrification
processes (Kadlec & Knight, 1996). The oxygen concentration decreases with depth and distance
from the water inflow into the wetland. It is typically high at the surface, grading to very low in
the sediment –water interface.
2.15.2 pH
The pH of wetlands is correlated with the calcium content of water (pH 7 = 20 mg Ca/L).
Wetland waters usually have a pH of around 6-8 (Kadlec and Knight, 1996). The biota of
wetlands especially can be impaired by sudden changes in pH.
2.15.3 Temperature
Temperature is a widely-fluctuating abiotic factor that can vary both diurnally and seasonally.
Temperature exerts a strong influence on the rate of chemical and biological processes in
wetlands, including BOD decomposition, nitrification and denitrification.
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2.16 Sludge drying
All types of emergent macrophytes systems contain at least one species of rooted emergent
aquatic macrophytes planted in some type of medium (usually soil, grave, or sand).Many plant
systems e.g. Typha, Phragmites,and Scirpus (Schoenoplectus), are capable of not only becoming
readily established in the various materials but also grow efficiently and assist in the treatment of
the various systems. (Alexander & Wood (1987)
Emergent macrophytes systems are, amongst other systems, in use for the dewatering of Sludges.
The main reason for dewatering of the sludge is that it will decrease the transport and handling
costs. Other reasons are that the high water content will be a problem when sludge is used for
(co)-composting and also when the sludge is incinerated or disposed of to a landfill. Reed beds
are used for dewatering and mineralization purposes as reed is expected to improve the treatment
performance. The sludge is dried and together with the reed finally turned into compost, which
can, for example, be applied as soil amendment or as landfill cover. The reed bed for the
dewatering of sludge is composed of selected media supporting emergent vegetation and the
flow path for liquid is vertical. The sludge is spread over the system and accumulates there for a
period of considerable period of time - up to 8-10 years (depending on the loading rate, the
capacity of the system and the mineralization rate).The pollutants are removed through a
combination of physical, chemical, and biological processes including sedimentation,
precipitation, adsorption to soil particles, assimilation by the plant issue, and microbial
transformations (Brix, 1994).The penetration of the stems of the plants (reed) through the
different layers of sludge maintains adequate drainage pathways; evaporation takes place over
the whole reed bed area and the plant contributes directly to dewatering through
evapotranspiration. The root system of the vegetation absorbs water from the sludge, which is
then lost to the atmosphere via evapotranspiration. For European and US conditions it is
estimated that during the warm season the evapotranspiration can account for up to 40 percent of
the liquid applied to the bed.
Aerobic conditions in the soil or filter medium are maintained through the combination of root
rhizome penetration, oxygen transfer which boosts the population and activity of naturally
occurring micro-organisms and the mechanical effect of the tall reeds rocking in the wind. This
will result in aerobic conditions on or near the root surfaces in an otherwise anaerobic
environment which will enable different complementary microbiological processes to take place
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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in the soil of the reed bed (Reed et al., 1994). The reeds fed with wastewater or sludge grows
rapidly in the nutrient-rich medium and absorbs some of the minerals and water. Heinss et al.
(1998) assumes that reed beds are a feasible treatment option for faecal sludge treatment.
Compared to unplanted sludge drying beds, from which require dewatered of dried sludge
removal every few weeks or months, the sludge and reeds may have to be removed after several
years, as the root rhizome maintains the permeability of the filter and the increasing sludge layer.
Not much is known about the application of reed bed systems for the treatment and resource
recovery of the nutrients, organic matter and water present in faecal sludge. There is, however,
quite some experience with macrophytes systems used for the mineralization of sewage sludge
from activated sludge plants. Sewage sludge is to some extent comparable with faecal sludge as
argued in chapter 2. Therefore, examples of sewage sludge treatment may also represent the
possibilities for faecal sludge treatment.
Most popular for application in dewatering beds is the common reed (Phragmites) which is
usually planted in centres of 30 cm. Reed et al. (1994) mention that reed beds are not suitable for
the application of raw sludge (and thus not for FS as well) due to the high organic content which
will overwhelm the oxygen-transfer capacity of the plants. Strauss et al. (1999a), however, report
that the treatment of faecal sludge is possible when a ventilation system is installed, which
increases the oxygen input into the filter bed. A design criterion of 2.5 m2/p.e. for a minimal
planted surface is given by Boutin (1987) based on one population equivalent of 40g of BOD,
100g of COD and 150 litres (what means that it has a sewage character). Usually an area of 4 -
10 m systems for wastewater treatment.52/p.e is used for macrophytes
2.16 Sludge composting
The objective of sludge composting is to biologically stabilize putrescible organics, destroy
pathogenic organisms, and reduce the volume of waste (Tim Evance 2003). During composting
organic material undergoes biological degradation, resulting in a 20 to 30 percent reduction of
volatile solids (Imhoff Karl et al 1971).
In composting, aerobic microorganisms convert much of the organic matter into carbon dioxide
leaving a relatively stable odor free substance which has some value as a fertilizer (J.Jeffrey
pierce.et al 1998). Eccentric micro-organisms are also destroyed due to the rise in temperature of
the compost.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER TWO
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Composting includes the following operation:
a. Mixing dewatered sludge with a bulking agent.
b. Aerating the compost pile by mechanical turning or the addition of air.
c. Recovery of the bulking agent.
d. Further curing and storage.
e. Final disposal.
The resulting end product is stable and may be used as a soil conditioner in agricultural
applications. Aerobic composting is more commonly used than anaerobic composting (Tim
Evance 2003) the aerobic composting process is exothermic and has been used at the household
level as a means of producing hot water for home heating. The major advantage of this is
compost is a very good fertilizer but it is not much used yet (J.Jeffrey pierce.et al 1998)
2.16.1 Advantages of compostingComposting is an important treatment process for many organic wastes and residues, including
animal manure, municipal and industrial sludge, and solid or semisolid crop residues.
Major Advantages of Composting
• It produces a biochemically stable product that has low odor and good physical properties, and
it attracts few flies.
• It significantly reduces the volume of material that must be stored, transported, disposed of, or
used.
• It is a forgiving, robust and simple process that can be done on-site without a tremendous
investment in heavy infrastructure.
The improved physical properties of compost include low moisture content (usually below 35
percent by mass), more uniform particle size, friable texture, reduced volume and reduced
weight. These propertieslower the hauling costs per unit of active ingredient and make it easier to
spread the material uniformly. Aerobic, thermophilic composting also inactivates or kills most
pathogens and weed seeds.Phosphorus, potassium and other mineral elements are retained in
composted material. While ammonia nitrogen may be volatilized, or lost to the atmosphere as a
gas, total nitrogen usually remains stable as a proportion of total dry matter. Because of those
advantages, there is greater market potential for compost than for un-stabilized organic wastes.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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CHAPTER THREE
MATERIALS AND METHODS
Abstract
This chapter gives detail information on materials and methods used in the accomplishment of
this study. This includes Laboratory analysis of Wastewater for Physicochemical and biological
parameters which conducted at Ardhi university laboratory, Field activity of sludge depth
measurement and experiment study of Sludge stability test which was carried out at Ardhi
university research center.
3.0 Location of the study area
The Salasala faecal sludge management system is located at coordinates 6°40ʹ58.16ʺS, 39°
11ʹ30.11ʺE, Tegeta ward, Kinondoni municipal, Dar es Salaam-Tanzania, and is elevated about
47m above the sea level. The area is bounded by Mtongani in east, Mbopo in west, Manyema in
south and Wazo in North. The case study area can be accessed via Bagamoyo, Scansca and
Upendo roads.
Figure 3.0: Topographical map of the study area
Salasala Treatment
Bagamoyo road
Scansca road
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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Plate 3.1 Orthophotographic map of the case study area (source: Google earth)
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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3.1 Climatic condition
The climate of Salasala as other part of Dar es Salaam is characterized as hot and humid coastal
tropical climate with high day and night temperatures with an annual mean maximum of 30.5 0C
and annual average of 250C. Additionally it is characterized by high humidity range in between
60 – 73% and heavy rainfall of above 1000mm per year, the long rainy season spines from
March to May and short season from November to December.
3.2 Existing situation
Salasala faecal sludge management system was established by the private owner Mr. Macha on
June 2007.The treatment system receive only domestic wastewater from pit latrine and septic
tank systems by means of his private two cesspit emptier of 5000 liters volume capacity each for
discharge fee of 60000=/Tsh per track . The treatment system comprises a screen chamber, one
Pond and one horizontal surface water flow constructed wetland. Wastewater flow through the
system is by gravity, the vacuum truck discharge the effluents though the plastic pipe of about
12cm diameter to the screen where’s start to flow through the system by gravity (Ref Figure3.1
below). The system effluent is collected and pumped to irrigate two plots of banana farm of
about 2023m2 in size, one is located near the treatment system and another is contiguous the
owner house.
From vacuum track
Low lift pump
Figure 3.1 Schematic diagrams of Salasala Faecal sludge treatment system
Screen Sludge Pond Constructed wetland
Storagetank
Banana farm
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
39
3.2.1 System description.
3.2.1.1 Screen chamber
The Salasala faecal sludge management system is consisting of a one hand cleaned course
screen. A screen chamber have the size of (2.5 m×2m) in dimension and consist of a bar racks of
10mm diameter with 45mm clear spacing between the bars. The screen removes coarse materials
from the influents that could cause damage and blockage of the sysytem and also from setteld
sludge that will inhibit the beneficial reuse of biosoil. From the screen chamber, the sludge
flows by gravity to the pond.
Plate 3.2 Screen chamber
3.2.1.2 Sludge pond
The Faecal sludge systems have only one faecal sludge pond of length to width ratio (Aspect
ratio) of 2.The effective pond dimension is 31.8 m length, 16 .2m width and 1m depth, is used to
retain faecal sludge and its contents to allow physical separation and biological treatment of
pretreated faecal sludge and wastewater to occurs and later, wastewater enters the constructed
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
40
wetland system where auxiliary treatments proceed. According to the owner of the faecal
sludge management system, since the system was constructed year 2007, the sludge pond has not
dislodged.
Plate 3.3 Salasala Faecal sludge pond
3.2.1.3 Constructed wetland system
Salasala faecal sludge system also comprises a constructed wetland system of 56m length, 1.1m
width and 0.6 m depth. The constructed wetland system which used for additional treatment of
wastewater from sludge pond is located adjacently into the pond system. During research
investigation it was found that, the wetlands system does not contain aquatic plants
(macrophytes) and during interview with facility owner, he said that he was about to plant
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
41
aquatic plants to his wetland system but he have not clear acquaintance of what type of aquatic
plant are implanted on constructed wetlands.
Plate 3.4 Constructed wetland system
Plate 3.5 Banana farm irrigated with final effluent
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Plate 3.6 Farm irrigated with final effluent (source: Site survey)
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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3.3 Materials
3.3.1Sludge depth measurements
Plate 3.7 Depth measurement Plate 3.8 A tape measurer fixed on a rod
3.3.2 Wastewater Sampling
Four wastewater sample points were established at various point of the Treatment system, at the
inlet of the pond, at nearly middle of the pond, at the outlet of the pond (also inlet of the
constructed wetland) and at the outlet of wetland system. The samples were collected in 1000ml
bottles for analysis at Ardhi University Laboratory. A total number of 16 representative samples
were collected during research investigation.
The sludge depths of the pond system were measured by configuring offshore coordinate system
along the breadth and span bank of the pond. At each point X, Y of orthogonal projection, the
depth of the sludge were taken with a white tape measure fixed to adjacent end of the rod.
The white tape measure was allowed to stay for a while in the sludge at a specific point to give
clearand visible reading
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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Figure 3.2 Wastewater sampling points
3.3.3 Faecal sludge sampling
Five sampling points of faecal sludge were established. Two points of triple samples vertically
down is within sludge zone locality (i.e. sample of upper, nearly middle and bottom sludge
layer), two points of single sample at Water zone locality and one point at the middle of the pond
(Ref Figure 3.2 below).The number of samples that taken were selected based to the profile and
accumulation of the faecal sludge in the sludge pond. Point of higher accumulation and high
sludge depth, three samples were taken.
Figure 3.3 Faecal sludge sampling points
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
45
3.3.3 Equipment’s used
Physical parameters such as pH and Temperature were measured using pH C101 probe
connected to pH meter (HQ30d) HACH product, HACH Sension 6 - DO meter, HACH
Sension156 conduct meter capable of measuring specific conductivity, TDS and Salinity.
Chemical parameters N-NH3, PO4 were measured using HACH DR/2010 Data logging
spectrophotometer and Calorimetric with test strip methods respectively. Biological parameters
such as COD and BOD5, were measured using EMDC1 1173: Part 4 Dichromate Digestion
Method, Ratio method i.e. (COD: BOD=2:1) and Membrane filtration method using nutrient
agar and MacConkey for Faecal coliform FS and Total coliform measurements. Sludge stability
experimental setup equipment’s such as syringe, rubber stoppers, plastic pipes, 1000mls and 350
mls bottles for wastewater and faecal sludge collection and setup. Other equipment includes
beakers, petri-dish, test tubes, pipette, measuring cylinders and aluminum foil.
Plate 3.7: Spectrophotometer Plate 3.8 Membrane filtration system
3.3.4 Reagents used
Reagents and chemicals for COD determinations and physicochemical parameters used include
Sulphuric acid (H2SO4) and Potassium dichromate, Ammonia salcylicate, ammonia cynurate,
reagent Distilled water for sample dilution and minimization of sample concentration during
analysis, the known concentrations of the samples used for spectrophotometer calibration; For
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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sludge stability experimental setup only sodium hydroxide (NaOH) was used. For other
parameters, only distilled water was used to rinse the probes of the equipment’s and for solutions
preparation.
3.4 Methods
3.4.1 Site visits and interview
Site visiting was conducted to have a visual inspection of the real situation of Salasala faecal
sludge treatment system. These also include interview of the facility owner Mr Macha and the
household nearby treatment system to get their views upon Salasala faecal sludge management
system and identify the major problems caused by having treatment system nearly their house
vicinity. Six households were interviewed
3.4.2 Experimental setup for sludge stability
Figure 3.4 Schematic diagram of typical experimental setup
NaOH + H2O
Experiment was conducted to determine sludge pond stability .The sludge samples were
collected from Salasala faecal sludge pond and experimental setup was done at Ardhi University
Research center. According to the sample taken, nine set of sludge stability test experiment were
established. Single set of sludge stability test experiment system was comprises three reactors
[Figure 3.3 demonstrates]; The first is the substrate reactor which contain a one liter of a sample
sludge, Second is the gas collector reactor which contain a solution of 15% sodium hydroxide
(NaOH) and distilled water and third a water collector reactor. The monitoring was done
by measuring the volume of water displaced in 24 hours interval for 14days duration to
determinethe amount of water displaced.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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Plate 3.9 Experimental setup of sludge stability test
3.4.3 Analysis
3.4.3.1 Physical parameters
Conductivity, Total Dissolved Solids (TDS) and Salinity were measured by a calibrated Hach
Sension156 conduct meter in Micro Siemens per centimeter, µS/cm or mS/cm, mg/L and ‰
respectively. Temperature and pH were measured using HANNA meter HI 8424 with pH and
temperature probes.
3.4.3.2 Chemical parameters
Chemical parameters NH3-N and PO4 were measured by using Portable Data logging HACH
DR/2010 spectrophotometer instrument and Calometric method with test strips in milligrams per
liter respectively.
Substrate reactors
Gas collector reactors
Watercollectorreactors
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Plate 3.5 Laboratory Sample analysis for physical parameter
Plate 3.8 Laboratory sample dilution for of chemical parameters analysis
So1
So2 So3
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER THREE
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3.4.3.3 Chemical Oxygen Demand
1.5 ml of potassium dichromate mixed with 3.5 concentrated Sulphuric acids was prepared in the
test tube. 2.5 mls of sample was added in a test tube containing strong oxidizing agents, followed
by thorough mixing, these processes were carried out in the fume chamber. The solutions were
digested in the hot oven for 2 hrs at 150 oC and kept to cool at room temperature. Then using
Spectrophotometer (Portable Data Logging Spectrophotometer) at wavelength of 600 nm COD
was measured in mg/L, by first putting the blank solution into cuvert (containing only strong
oxidizing agent and distilled water) for zeroing to calibrate the machine followed by reading the
solutions containing the samples
3.4.3.4 Faecal and Total coliforms (FC &TC)
1 ml of Wastewater sample was measured using a sterile measuring cylinder, then diluted with
99ml of sterile distilled water to make a total dilution of 100ml. Another 1 ml from 100mls
diluted was taken and mixed with 99mls of sterile distilled water. Another dilution was done to
make a dilution factor of (×106 ).The vacuum pump was assembled, the filtration funnel was
rinsed by using hot water for the purpose of sterilization and the filter paper was placed just
below the filter funnel, 100ml of diluted sample was sucked through the filter paper using
vacuum pump. Then the filtration apparatus was disassembled and carefully by using sterile
forceps, the filter paper was transferred onto a petri dish containing nutrient agar for fecal
Coliform test and mackonkey for Total coliform. Both petri dishes of faecal coliform and total
coliform test were bind together, labeled and incubated at 440C and 340C respectively for 24
hours.
3.4.3.5 Data analysis and computationsThe data from laboratory, experimental setup and from site measurements were analyzed and
computed by using computer programs such as Microsoft Office Excel 2010 and AutoCAD
2012. Descriptive statistics tool in Microsoft Office Excel 2010 was mainly used to determine
various statistics of interest.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER FOUR
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CHAPTER FOUR
DATA RESULTS AND DISCUSSION
Abstract
4.1 Wastewater characteristics
PH
The highest mediocre pH value was 6.7 observed in two samples S02 & S04; these were the
samples from middle of the pond (S02) and outlet of constructed wetland (S04). pH is a
measurement of the concentration of hydrogen ions (H+) in solution. Lower and higher pH
reaching alkaline and Acidity, hamper biological treatability of sewage, it also makes irrigated
soil to be acidity and alkalinity depends on amount of water used to irrigate. For irrigation, pH
has no direct effect on plant growth; however, it does affect the form/availability of nutrient
elements in irrigation water, fertilizer solutions and the growing medium. The wastewater pH of
Salasala plant for different localities of the treatment facility varies slightly throughout the
system (indicated in Fig 4.1).However the effluent pH is within the standards, the pH range
recommended by TBS is 6.5-8.5.
Temperature
Figure 4.2 shows the variations of temperature along the treatment system. It was noticed that the
temperature variation along Salasala faecal sludge treatment system increases slightly from 27.6
This chapter gives results and discussions of physicochemical and biological properties of
Wastewater, sludge stability test, various assessments such as Economic and aesthetics
assessment. It also outlines the essential improvements of Salasala Feacal sludge treatment
facility.
4.1.1 Physical Characteristics
The requisite of determine Physical characteristics of wastewater are to assess both condition of
waste water in treatment facility as well as its effect caused on reuse for irrigation. The physical
characteristic of wastewater of Salasala faecal sludge management system is tabulated in
Appendix 01.
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at inlet of the pond (sample S01) to 28.2 at outlet of constructed wetland (S04) which implies that
wastewater treatment plant is not effective enough as it tend to influence temperature along the
system. However temperature is within the standards; the TBS range for Temperature is 20-35 °.
Total dissolved solids (TDS) and Total suspended solids (TSS)
The Total dissolved and suspended solid variation throughout the treatment system is indicated
in Fig 4.3 and 4.4 respectively. As figures indicate, both TSS and TDS decreases throughout the
system: TSS decreases from 1325 to 251.5 mg/l and TDS from 1616.5 to 1167.25 mg/l, which
infers sewage stabilization occurs nevertheless the effluent TSS is not in the standards and TDS
is still strong, the TBS standards for TSS is 100mg/l and the typical domestic wastewater have
TDS of range from 200-week, 500 medium, 1000-stong (Metcalf and Eddy 2003) .This is
implies that the efficiency of Salasala faecal sludge system in wastewater treatment is not
sufficient enough.
Conductivity and Salinity
Conductivity and salinity are used to acquaint the presence of soluble ions such as salt ions in
wastewater. Eminent levels of salt can have detrimental effects on production system and the
environments. Throughout the treatment system [indicated in Figures 4.5 and 4.6], Conductivity
decreases from 3.13 to 2.41 mS/cm and Salinity from 1.5 to 1.03 ‰ .Though the system reduced
Conductivity and salinity but it does not reach the required permissible amount.
Color and turbidity
Colour and turbidity are used to assess aesthetical value of wastewater. Turbidity in water is
caused by suspended and colloidal matter such as clay, silt, finely divided organic and inorganic
matter, and plankton and other microscopic organisms. In wastewater reuse for irrigation, highly
turbid wastewater may choke irrigation system. Color and Turbidity of wastewater of Salasala
system plant, decreases from inlet to final effluent along system [indicated in figures 4.8 and
4.9]. Turbidity decreases from 1124.5 NTU to 500 NTU and Colour from 3175 to 900 mg Pt-
co/l. This shows treatment of wastewater occurs and mostly with constructed wetland as gradual
change observed between inlet and outlet of constructed wetland for both Color and turbidity.
However the wastewater effluent for both color and turbidity does not reaches the required
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER FOUR
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permissible amount. TBS standards for color and turbidity effluent from wastewater treatment
system are 300 NTU and 300 mg Pt-co/L respectively.
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Figure 4.1 PH variations along the treatment plant.
Figure 4.2 Temperature variations along the treatment plant
6.60
6.73
6.65
6.73
6.526.546.566.586.606.626.646.666.686.706.726.74
S 01 S 02 S 03 S 04
PH
PH
27.6727.60
28.15
28.27
27.20
27.40
27.60
27.80
28.00
28.20
28.40
S 01 S 02 S 03 S 04
Temperature (°c)
Temperature (°c)
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Figure 4.3 TDS variation along the treatment plant
Figure 4.4 Total suspended solid variations along the treatment plant
S 01 S 02 S 03 S 04TDS (mg/l) 1616.50 1203.25 1220.25 1167.25
0.00
200.00
400.00
600.00
800.00
1000.00
1200.00
1400.00
1600.00
1800.00
TDS
(mg/
l)TDS (mg/l)
S 01
S 02
S 03
S 04
1325.00
407.50
407.50
251.50
Total suspended solid TSS, (mg/l)Total suspended solid TSS, (mg/l)
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER FOUR
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Figure 4.5 Conductivity variations along the treatment plant
Figure 4.6 Salinity variations along the treatment plant
3.13
2.05 2.11
2.41
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
S 01 S 02 S 03 S 04
Conductivity (ms/cm)
Conductivity (ms/cm)
Con
duct
ivit
y (m
s/cm
)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
S 01 S 02 S 03 S 04Salinity (%) 1.50 1.23 1.13 1.03
Salin
ity
Salinity (‰)
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Figure 4.8 Colour variations along the treatment plant
Figure 4.9 Turbidity variations along the treatment plant
3175.00
2325.002275.00
900.00
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
S 01 S 02 S 03 S 04
Colour (mg Pt-co/l)
Colour (mg Pt-co/l)
Col
our
(mg
Pt-
co/l)
S 01 S 02 S 03 S 04
1124.50
725.00825.00
500.00
Turbidity (NTU)
Turbidity (NTU)
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER FOUR
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4.1.2 Chemical characteristics
The Chemical characteristics of wastewater have been obtained though analysis of a toxic
pollutant Ammonia-nitrogen NH3-N (mg/l) and a nutrient phosphate in terms of PO4 (mg/l).
Chemical characteristics of wastewater are presented in Appendix 02:
Ammonia-nitrogen (NH3-N)
Ammonia nitrogen (NH3-N) is a measure of the amount of ammonia, a toxic pollutant often
found in sewage, waste products, liquid manure and other liquid organic waste products.
Ammonia can directly poison humans and upset the equilibrium of water systems. In Salasala
treatment plant, the percentage of ammonia reduction from inlet to outlet of the system plant is
about 41.93%, the other 58.07% which is more than half of inlet amount is disposed to the
environment through irrigation.
Although ammonia reduction occurs along the system plant as figure 4.10 indicates, but the final
effluent doesn’t grasp the wastewater effluents permissible amount. A TBS standard for total
nitrogen concentration is 15mg/l contrary to 129.67mg/l of final effluent. Thus, the above
signposts efficiency shows that Salasala plant is not efficient enough in ammonia nitrogen
reduction from wastewater.
Phosphate (PO4)
Phosphate (PO4) is one of the important chemical nutrients in wastewater used for irrigation as it
provides nutrient (phosphorous) which is the one of the essentials plants nutrients. While its
important wastewater parameter for agriculture and which its excess in the receiving
environments cannot easily physically observed, effluent limit must be adhered. TBS effluent
standard of phosphate is 6 mg/l .Though treatment reduction happens [As Figure 4.11 spectacle]
but efficiency of treatment is not ample. From inlet to outlet the percentage of phosphate
removed is about 42.85%, the other 57.15% is not removed.
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Figure 4.10 Ammonia-nitrogen variations along the treatment plant
Figure 4.11 Phosphate variations along the treatment plant
Sample 01 Sample 02 Sample 03 Sample 04NH3-N (mg/l) 223.33 151.00 155.33 129.67
0.00
50.00
100.00
150.00
200.00
250.00
NH3
-N (m
g/l)
NH3-N (mg/l)
500.00
200.00
150.00200.00
0.00
100.00
200.00
300.00
400.00
500.00
600.00
Sample 01 Sample 02 Sample 03 Sample 04
PO4(mg/l)
PO4 (mg/l)
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4.1.3 Biological characteristics
The biological characteristic of Wastewater of Salasala faecal sludge treatment plant system was
measured in term of COD, Faecal coliforms and Total coliforms bacterial. BOD5 in 20°C was
calculated from assumption ratio of COD: BOD = 2:1.
COD test is used to determine the oxygen equivalent of the organic matter that can be oxidized
by a strong chemical oxidizing agent (potassium dichromate) in an acid medium. On other side
the BOD5 is the important parameters because it determines the amount of oxygen required to
stabilize waste biologically. Other parameters such as faecal coliforms and Total coliforms
bacterial are used to assess and to identify presence of pathogens and’ specific organisms in
connection with plant operation and effluent re-use. The biological characteristics of Salasala
plant wastewater is tabulated in Appendix 03:
COD (mg/l)
Chemical oxygen demand in the system, measures the total amount of Oxygen needed to oxidize
organic carbon present in wastewater .A higher value of COD signifies that wastewater has large
amount of organic matters. Faecal sludge treatment plant efficient on organic matter reduction is
not utterly sufficient comparing to the recognized minimum allowable standards of wastewater
effluents from wastewater treatment facilities. Though the treatment plant removes COD with
satisfactory efficiency of about 85% from inlet to outlet as fig 4.13 stipulates, but effluent
concentration of 636.67mg/l is far away from 60 and 50 mg/l a TBS and WHO standards. This
signifies that Salasala faecal sludge treatment system is not efficient enough in COD remove.
BOD5 (mg/l)
This is the important parameter in wastewater treatment and disposal because it articulates to
which extent wastewater will pollute the receiving water bodies. BOD5 gives the amount of
Oxygen needed to oxidize organic waste biologically. The Salasala plant efficient in BOD
remove as calculated is not enough as per recognized minimum allowable standards of
wastewater effluents from wastewater treatment facilities. As Figure 4.12 bellow demonstration,
BOD removed from wastewater along the system plant is about 1935mg/l which is 85.88% of the
BOD at the inlet point of the system. Though system reduces BOD with good efficiency,
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nonetheless the final effluent BOD concentration doesn’t grasp the required standard. TBS
standard for BOD5 in 20°C is 30(mg/l).
Figure 4.12 BOD5 variations along the treatment plant
Figure 4.13 COD variations along the treatment plant
0
500
1000
1500
2000
2500
Sample 01Sample 02
Sample 03Sample 04
2253
10401015
318
BO
D5(m
g/L
)
BOD5 (mg/l) at 20 °C
BOD5 (mg/l) at 20 °C
Sample 01 Sample 02 Sample 03 Sample 04
4507
2080 2030
637
COD (mg/l)COD (mg/l)
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Total and faecal coliforms
Figure 4.14 Total coliforms variations along the treatment plant
Figure 4.15 Faecal coliforms variations along the treatment plant
58,000,000
37,666,667 35,333,333
22,333,333
0
10,000,000
20,000,000
30,000,000
40,000,000
50,000,000
60,000,000
70,000,000
Sample 01 Sample 02 Sample 03 Sample 04
Total coliform (Count/100ml)
Total coliform (Count/100ml)
24,066,667 23,333,33321,000,000
16,000,000
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
Sample 01 Sample 02 Sample 03 Sample 04
Faecal coliform (count/100ml)
Faecal coliform(count/100ml)
Total and feacal coliform bacteria variation along the system plant is presented in figures 4.14
and 4.15 respectively. As figures indicated both total and faecal coliform decreases along the
system .The System plant removes 33.52% of the faecal bacteria of inlet point and 61.49% of the
Total coliforms of inlet point. However the effluent does not reach the required effluent
standards as tabulated in Appendix 03.
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4.2 Pond Sludge stability and volume
The sludge pond stability was determined through analysis of data from sludge stability
experiment. Both stability and volume of the sludge pond were determined so as to gives the
efficiency of the system in stabilizing faecal sludge and sludge accumulation rates which later
will lead to proper suggestion of improvement ideas and scaling up the decentralized faecal
sludge management system to achieve better economies of scale, volume of the sludge present.
4.2.1Pond Sludge stability
The stable sludge can be defined as the sludge which has been treated to reduce volatile organic
matter, vector attraction and to reduce the potential of putrefaction and offensive odor. The more
organic the greater the gas produced and vice versa.
The vector attractiveness (frequently associated with odors and unsightliness) of sludge is an
important parameter in protecting public health and the public’s acceptance of bio solids land
application. Odor is the most common complaint. This is the currently accepted methods for
assessing vector attractiveness of anaerobically digested sludge.
4.2.1.1 Experimental results
Experimental results for stability test (i.e. the gas volume mL produced per day interval for
14days duration are summarized and tabulated in Appendix 04:
The fallouts shows that, the sludge on the pond has not yet stabilized enough as still it produces
methane gas though decreases in time [Figures 4.17 and 4.18 indicates] this indicates that the
sludge have either highly variable depending on the influent sludge characteristics or require an
exorbitant amount of time to complete. Therefore, the pond system is not performing well in
faecal sludge stabilization process and a need exists for establishing a more efficient and reliable
method to complete sludge stabilization so as to minimize the vector attractiveness of anaerobic
digested sludge
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Figure 4.16 Sludge stability progress for different sludge sample
5536
25
4
70
10
70
35
75
0
300
0
100
15
75
36
90
50
0
100
200
300
400
500
600
700
800
900
1000
DAY01
DAY02
DAY03
DAY04
DAY05
DAY06
DAY07
DAY08
DAY09
DAY10
DAY11
DAY12
DAY13
DAY14
Gas v
olum
e (m
l)Volume of gas VS Days
S9
S8
S7
S6
S5
S4
S3
S2
S1
SAMPLE NAME DESCRIPTION
S1 Upper sludge sample from sampling point 01
S2 Middle sludge sample from sampling point 01
S3 Bottom sludge sample from sampling point 01
S4 Water zone sludge sample from South side of the pond
S5 Water zone sludge sample from North side of the pond
S6 Sludge sample from middle point of the pond
S7 Upper sludge sample from sampling point 02
S8 Middle sludge sample from sampling point 02
S9 Bottom sludge sample from sampling point 02
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Figure 4.17: Cumulative gas volume of sludge samples
4.2.2 Sludge volume determination
Since the sides and base of the sludge pond are planes, the sludge volume was computed by
using a Spot height method of earth work volume estimation
The coordinates was configured onsite by interval of 2m along the span and breadth of the sludge
pond and sludge depth was taken at each intersection of x,y coordinates. [Figure 4.18 bellow
shows]
830
185
540
650
294
761.5
447
786
928
0
100
200
300
400
500
600
700
800
900
1000
S1 S2 S3 S4 S5 S6 S7 S8 S9
Cum
ulat
ive
gas v
olum
e (m
Ls)
Sampling points
Cumulative Gas volume vs Sampling points
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65
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
2
4
6
8
10
12
14
16
Figure 4.18 Pond coordinate configuration
From Spot height method
Volume = plan area × mean height
Plan Area of one square = 2×2, A = 4m2
Therefore, volume for one square is given by
= 4 × 14 [h (0, 0) + h (2,0) + h(0,2) + h(2,2)]Where h(x,y) = sludge depth at x,y coordinates
The result is tabulated in Appendix 05:
The total sludge volume is 252.52 m3 equivalents to 55,546.6 gallons
Y (m)
X (m)
Inlet
Exit
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4.3 Economic aspect of Salasala faecal sludge management system
Salasala private decentralized faecal sludge management system receives faecal sludge from the
community by means of two hauling private vacuum tracks of capacity of 5000 liters each, with
a total charge of 60000/= Tsh per trip. This total charge includes fee for, sanction, transportation
and dumping of faecal sludge. The table 4.5 summarizes the economic assessment of Salasala
faecal sludge management system.
As the Table 4.5 indicates, the Salasala Faecal sludge management facility makes a profit of
about 51,840,000 Tsh/= per year. The system looks economical, as it makes a profit of about
34.5% of the investment cost, however it does not recovers effectively all resources suitably
obtained through sludge management and treatment.
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Plant size and sludgeload
Plant capacity 63.13 m3 FS/yTotal surface area 582 m2COD Loading 6100 mg/lBOD Loading 3050 mg/lPond capacity 512m3
Amount received peryear
Total charge /Trip/truck 60000.00Average trip/day/truck 3.50Amount received/day pertruck 210,000 (Tsh)Amount received permonth per truck 6,300,000 (Tsh)Amount received permonth for 2 trucks 12,600,000(Tsh)
Total (Tsh) 151,200,000.0Operation and
Maintenance cost (O+M)
Item Amount per dayAmount per
monthAmount per
yearLabour Salary and Fuelcost 250000.00 7,500,000.0 90,000,000.0
Car services and plantrepairing cost 150,000 1,800,000.00
Total (Tsh) 91,800,000.0Annual cost
Life time of the plant 4 yearsinterest rate [%] 0.05
Investment Cost (Tsh) 150,000,000.0
Profit per year
Profit per year = [Amount received per year-interest rate -(O+M)]Profit per year = [151200000-(150000000×5%) -91800000]
Profit per year = 51,840,000Total profit per year (Tsh/year) 51,840,000
Table: 4.5 Economic analysis of salasala faecal sludge management system
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4.4 Aesthetics assessment
4.4.1Solid waste management
In any faecal sludge or wastewater treatment plant, solid matter and wastes from influent is
unavoidable. These wastes are mostly from pit latrine and other latrine types; these are simply
because latrines can be one of the local disposing points of domestic solid wastes. In Salasala
faecal sludge treatment plant, it was observed that solid waste exists mostly at the screen more
than any part of the system and other small part of solid waste is generated by surrounding plants
and human being, Also it was observed , there were no solid waste management activity taking
place.
Plate 3.9 Dumped Solid waste from screen
4.4.2 Odor and smell
From oral interview of plant nearby residents, complaints have been raised concerning odor and
smell especially during disposing of faecal sludge when the truck arrived. In one way or another
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it has been source of arguments about the system performance and suitability on treating faecal
sludge. However they said that, few moments after disposing the smell disappears.
4.4.3 Surrounding Land Use
The Salasala surrounding land is mainly used for cultivating fruit crops such as Banana, okra,
African eggplants, salad, pawpaw’s, overdoes, mangoes etc. and grazing domestic livestock’s.
Waste water from the treatment system is used to irrigate adjoining farm, and small area
surrounding the system (on west side of the pond) is adjoin the resident houses.
Plate 3.6 Area used for grazing
4.4.4 Insect Attraction
It is quite common for insects to live and breed at faecal sludge treatment plants. Insects at
faecal sludge treatment plants become a problem when there are large populations of them, and
they create a nuisance for residents of neighboring properties.
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However according to physical observation and interview of people surrounding the plant area,
no large populations of insects have been observed at the Home bush of Salasala pond in recent
years and there have been no complaints about insect nuisance associated with the Treatment
system.
4.4.5 Personal protective equipment’s (PPE’s)
Personal protective is one of the worth concern in any associated physical activity of which risk
can be Physical, Mental or personal health. In wastewater and faecal sludge treatment plants,
there are many risks which are associated with daily activities: In Salasala Faecal sludge
treatment plant it was observed that, workers wears Personal protective equipment’s during
activities.
Plate 3.7: Faecal sludge disposing activity conducted by worker wears PPE
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4.5 System improvements required
The following are the system improvements required to make Salasala faecal sludge
management system suitable as well as efficient in faecal sludge management and treatment
4.5.1General improvements
4.5.1.1 Land use round system plant.As it was observed, the land use nearby Salasala treatment plant is for domestic livestock’s
keeping such as goats, chickens, pig and other agriculture activity, improvements attention of
isolating the system plant from such activity should be taken so as to minimize risk of human
and animal health against wastewater and faecal sludge vulnerabilities.
4.5.1.2 Solid waste management at the system plantOne of the prevalent grumbles of residents contiguous Salasala Faecal sludge system was
obnoxious odor from the system plant, as observed this is mainly caused by improper disposal of
plant solid waste specifically from screen and pond outlet. Therefore the system should have
solid waste treatment and disposal facility such as Incinerator.
4.5.1.3 Unit of sludge dewateringAny sludge treatment facility must have at least a single unit for sludge dewatering so as to
achieve a complete sludge treatment, unfortunately there was no any Sludge dewatering unit at
Salasala faecal sludge treatment system, Thus the system should have at least one sludge
dewatering unit.
4.5.1.4 Aesthetic and beauty of the surroundings system environmentThe faecal sludge and wastewater treatment facilities is supposed to have a beautifully, clean and
attractive environments. The Salasala surroundings environments are dirty, it is uninfluenced
area to stay even for a single minute which perhaps swaying people to argue about it suitability
on managing faecal sludge. The beauty can be achieved through different methods; one can
create a pleasant area though paving some important areas, creating gardens of beautifully
flowers with aroma smell and on top of that regular cleaners of the surroundings. Therefore this
should be taken into consideration.
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4.5.1.5 Improvement’s to make Salasala faecal sludge management system cost effective
The cost effective system can be attained by increasing the system profit per year through
earn/recovery and selling more recourses from faecal sludge and its components i.e. More water
for irrigation through faecal sludge treatment, organic manure through composting of dislodged
faecal sludge and energy as biogas , the followings are improvements which required;
More water through sludge treatment
More water can be recovered principally by preventing water loss from the system typically
through underground and side wall seepage by minimize the system leakages through
lining/coating the walls of system units especially the pond with a cement materials so as to
minimize both underground side wall infiltrations
Energy recovery as biogas
As sludge stability test shows in Appendix 04: The average amount of gas generated in 14 days
by 1L of a sludge sample is about 602.3889 m3 or 43.0278m3/day .Each cubic meter (m3) of
biogas contains the equivalent of 6 kWh of calorific energy. However, when biogas is converted
to electricity, in a biogas powered electric generator, only 2 kWh of useable electricity is
obtained, the rest turns into heat which can also be used for heating applications.
For sludge volume of 252.52m3, more than 10,876,036.4 m3 of gas can be generated per day
which is about 21,752.07 mWh. Therefore there is a need of modifying the system pond (to be
biogas reactor) so as to capture the biogas produced and hence economic system.
Organic manure through composting
The sludge can be composted with organic solid waste and organic fertilizer can be
wholesaled and another used to raise plants and thus the profit can be made through selling
the organic manure as well as plant sprouts of different species
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4.5.2 Specific improvements
4.5.2.1 Constructed wetland system improvementsThrough physical observation and interview it was observed that a Constructed wetland system
is not properly designed and it does not contain any biological macrophytes plants. A constructed
wetland is a system that utilizes natural processes involving wetland vegetation, soils, and their
associated microbial assemblages to assist, at least partially, in treating an effluent or other water
source. It comprise plants species such as Typha, Cyperus latifolius, cyperus papyrus,
hydrocotyle, hydrocleis etc, in general, these systems should be engineered and constructed
outside naturally occurring flood plains. The degree of wildlife habitat provided by a constructed
wetland, or sections of such wetlands, varies broadly across a spectrum. At one end of the
spectrum are those systems that are intended only to provide treatment for an effluent or other
water source, in order to meet the requirements of treating the wastewater, and that provide little
to no wildlife habitat.
Therefore this can be taken as the major improvements that’s must be considered particularly to
improve pollutants removal efficiency, as per laboratory chemical analysis results a constructed
wetland system have little efficiency in Ammonia-Nitrogen reduction and virtually negative
efficiency in nutrient phosphorous removal Ref (Fig 4.10 and 4.11)
The other improvement consideration is redesigning of a constructed wetland system or perhaps
goes to another type of constructed wetland system.
4.5.2.2 Sludge pond improvementsThe following are the improvement required to surge up pond performance as well as to make it
suitable sludge management entity.
Pond Geometry
The optimal pond geometry is that which minimizes hydraulic short-circuit. Preventing flow
short-circuiting through a pond will maximize retention time and improve final effluent quality.
In general, rectangular anaerobic ponds have length-to-breadth ratio of 2-3 to 1 so as to avoid
sludge banks forming near the inlet, unfortunately the location of inlet and outlet of Salasala
system pond was observed to be on the same side of the pond. Therefore the inlet and outlet is
required to be located in diagonally opposite corners of the pond.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER FOUR
74
Inlet and Outlet Structures
The inlets to anaerobic ponds typically discharge well below the liquid level to minimize short
circuiting and to make easily for the new incoming sludge’s be readily contact with presentbiological sludge and hence maximize sludge pond stabilization efficiency and odor reduction
which are primary objective of sludge ponds. For recommendation of inlet structure, see
Figure4.20 for anaerobic pond
Figure 4.20 Inlet arrangement of anaerobic pond
Pond sides walls
Like any other open water retain structures, side wall protection trough lining and inclination
is important as it reduces side erosion and increases side stability against water surge and
pressure and hence the structure will operate safely thought its design life. This also is the
improvements which should be taken to improve salasala pond performance as it was
observed the side walls of the pond is not lined/coated with a cement materials and is
orthodox vertical.
Dislodge of the sludge pond
From sludge volume measurements a sludge pond have found to have about 252m3 of sludge
volume which is almost 50% of the volume of pond 512m3and have not been dislodged since
the system was started to operate 4years ago. Therefore the sludge should be dislodged from
sludge pond as also it depreciates its performance, sludge stability test reveal this.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|CHAPTER FIVE
75
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.0 CONCLUSION
The primary objective of this study was to assess Salasala privately operated decentralized faecal
sludge management system and critically to analyze the improvements which are needed to make
it suitable (cost effective) faecal sludge management system with a potential for citywide
adoption.
The physicochemical and biological characteristics of system wastewater for essential
parameters such as Color, Turbidity, total suspended solids, Ammonia nitrogen, COD, BOD5,
faecal coliform and total coliform was observed to be not within minimum permissible amount
[i.e. TBS and WHO]. Additionally, sludge stability test has shown that, the system is not
performing well in sludge stabilization process and the pond system of a volume of 512m3 have
the sludge volume of about 252m3 which is almost 50% of the volume of pond and have not been
dislodged since the system was started to operate 4years ago.
Furthermore the system surrounding’s was observed to be unpleasant, dirty and dull and there
was no solid waste handling activity from treatment facility. However the system was found to
be economical, as it makes a profit of about 51,840,000=/T.sh per year and has a benefit
economic ratio (BCR) of about 1.6
From these observations it can be concluded that, Salasala Faecal sludge treatment system is not
effective enough in Feacal sludge and wastewater treatment activity for final effluent to be used
for irrigation and agriculture activities and also it does not effectively recover all resources
suitably obtained through sludge management and treatment.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald |5.1RECOMMENDATION
76
5.1 RECOMMENDATION
From the results obtained in this research, the following are recommendation
Since the treatment plant is not work efficiently, there is the need of system owner to act
upon stated improvements and hence to bring the effluent quality to the acceptable
standards of irrigation as well as to make the system to be suitable faecal sludge
management system.
A need exists for establishing a more efficient and reliable method of treating faecal
sludge to complete sludge stabilization and thus minimizes the vector attractiveness from
anaerobic digested sludge.
Soon after mentioned improvements are implemented there should be a regular checkup
of the performance of the treatment plant so as to assess its performance.
Forward-thinking on the study may be made on the investigation of presence of heavy
metals in the system wastewater which will be from utilization of personal beauty
products, maquillages, Antibiotic’s and other home use medicines
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|REFERENCES
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REFERENCES
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|REFERENCES
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Institute for Environmental Science (EAWAG), SANDEC.
Montangero, A., Strauss, M. (eds) (2004), Faecal Sludge Treatment, Swiss Federal
Institute of Environmental Science and Technology (EAWAG)/SANDEC, Dubendorf,
Switzerland
NVA, Slibwijzer 1994, Treatment of faecal sludge, NVA publication.
SANDEC, 1997, Faecal sludge quantities and characteristics, unpublished.
Shrestha R R (1999) Application of Constructed Wetlands for Wastewater Treatment in
Nepal, Ph.D. Dissertation, Department of Sanitary Engineering and Water Pollution
Control, University of Agricultural Sciences Vienna, Austria
Van Hoven, D. (2004). “Septage in Jamaica: An Assessment of the Situation and an
Evaluation of Treatment Alternatives”, Report for the Ministry of Health.
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|APPENDIXES
80
APPENDIXES
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 01: AVERAGE PHYSICAL CHARACTERISTICS OF WASTEWATER
OF SALASALA SYSTEM ALONG THE TREATMENT PLANT
81
Appendix 01: AVERAGE PHYSICAL CHARACTERISTICS OF WASTEWATER OF SALASALA SYSTEM ALONG THETREATMENT PLANT
Sample
Number
Temperature
(°c)
TDS
(mg/l)
PH Conductivity
(ms/cm)
Salinity
(‰)
Colour
(mg Pt-co/l)
Turbidity
(NTU)
Total
suspended
solid TSS,
( mg/l)
S 01 27.67± 12.44 1616.5 ± 744.96 6.6 ± 0.36 3.13 ± 0.49 1.5 ± 0.67 3175± 1431.08 1124.5±150.56 1325 ± 598.33
S 02 27.68± 12.43 1203.25 ± 565.19 6.73 ± 0.26 2.053 ±0.65 1.23 ± 0.56 2325 ±1071.45 725 ± 150.00 407.5 ± 182.29
S 03 28.15± 12.61 1220.25 ± 563.45 6.65 ± 0.31 2.12 ± 0.49 1.13 ± 0.51 2275 ±1035.37 825 ± 150.00 407.5 ± 182.70
S 04 28.27± 14.14 1167.25 ± 549.54 6.73 ± 0.35 2.41 ± 0.49 1.03 ± 0.46 900 ± 432.43 500 ± 81.65 251.5 ± 118.31
TBS
Standards 20-35 6.5-8.5 300 300 100
Key:
S01-Sample from inlet of the pond,
S02-Sample from middle of the pond,
S03-Sample from outlet of the pond or Inlet of the constructed wetland,
S 04-Sample from outlet of constructed wetland
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 02: AVERAGE CHEMICAL CHARACTERISTICS OF WASTEWATER
OF SALASALA SYSTEM ALONG THE TREATMENT PLANT
82
Appendix 02: AVERAGE CHEMICAL CHARACTERISTICS OF WASTEWATER OFSALASALA SYSTEM ALONG THE TREATMENT PLANT
NH3-N (mg/l) PO4(mg/l)
Sample 01 223.33 ± 20.82 500 ± 0.00
Sample 02 151 ± 10.15 200 ± 86.60
Sample 03 155.33 ± 6.43 150 ± 86.60
Sample 04 129.67 ± 5.03 200 ± 86.60
TBS Standard 15 6
Key:
S01-Sample from inlet of the pond,
S02-Sample from middle of the pond,
S03-Sample from outlet of the pond or Inlet of the constructed wetland,
S 04-Sample from outlet of constructed wetland
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 03: AVERAGE BIOLOGICAL CHARACTERISTICS OF
WASTEWATER OF SALASALA SYSTEM ALONG THE TREATMENT PLANT
83
Appendix 03: AVERAGE BIOLOGICAL CHARACTERISTICS OF WASTEWATER OFSALASALA SYSTEM ALONG THE TREATMENT PLANT
BOD5 (mg/l)
at 20 °C
COD (mg/l) Faecal coliform
(count/100ml)
Total coliform
(Count/100ml)
Sample 01 2253.33± 245.1 4506.67 ± 490.03 24,066,667 58,000,000
Sample 02 1040 ± 79.37 2080 ± 158.75 23,333,333 37,666,667
Sample 03 1015 ± 58.95 2030 ± 117.90 21,000,000 35,333,333
Sample 04 318.33 ± 17.56 636.67 ± 35.12 16,000,000 22,333,333
TBS standard 30 60 1000 10000
WHO
standards
25 50 1,000 -
Key:
S01-Sample from inlet of the pond,
S02-Sample from middle of the pond,
S03-Sample from outlet of the pond or Inlet of the constructed wetland,
S 04-Sample from outlet of constructed wetland
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 04: GAS VOLUME IN mL OF SLUDGE STABILITY TEST FOR
FOURTEEN DAY DURATION
84
Appendix 04: GAS VOLUME IN mL OF SLUDGE STABILITY TEST FOR FOURTEEN DAY DURATION
SAMPLENAME
DAY01
DAY02
DAY03
DAY04
DAY05
DAY06
DAY07
DAY08
DAY09
DAY10
DAY11
DAY12
DAY13
DAY14
SubTotal
S1 55 110 130 70 80 70 50 40 40 38 38 35 38 36 830
S2 25 20 20 15 30 20 10 10 8 5 5 5 8 4 185
S3 70 60 50 50 50 50 50 45 30 20 25 15 15 10 540
S4 70 55 40 45 60 48 52 50 40 40 42 35 38 35 650
S5 75 65 30 25 20 32 35 5 2 2 1 1 1 0 294
S6 300 280 100 50 20 8 2 1.5 0 0 0 0 0 0 761.5
S7 100 80 50 10 10 50 3 30 20 20 22 22 15 15 447
S8 75 70 60 50 100 70 55 55 55 40 45 40 35 36 786
S9 90 75 65 60 80 70 70 70 68 60 60 55 55 50 928
Total 5421.5
Average 602.3889
SAMPLE NAME DESCRIPTION
S1 Upper sludge sample from sampling point 01
S2 Middle sludge sample from sampling point 01
S3 Bottom sludge sample from sampling point 01
S4 Water zone sludge sample from South side of the pond
S5 Water zone sludge sample from North side of the pond
S6 Sludge sample from middle point of the pond
S7 Upper sludge sample from sampling point 02
S8 Middle sludge sample from sampling point 02
S9 Bottom sludge sample from sampling point 02
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 05: SALASALA POND SLUDGE DEPTH AND VOLUME RESULTS
85
Appendix 05: SALASALA POND SLUDGE DEPTH AND VOLUME RESULTS
X,Y Z(m)Volume
(m3) X,Y Z (m)Volume
(m3) X,Y Z (m)Volume
(m3) X,Y Z (m)Volume
(m3)2,2 0.2 0.2 10,2 0.15 0.39 18,2 0.56 1.11 26,2 0.7 1.42,4 0.21 0.41 10,4 0.3 0.94 18,4 0.58 2.2 26,4 0.75 2.952,6 0.22 0.43 10,6 0.21 1 18,6 0.56 2.15 26,6 0.89 3.312,8 0.21 0.43 10,8 0.33 0.99 18,8 0.59 2.19 26,8 1 3.67
2,10 0.3 0.51 10,10 0.36 1.13 18,10 0.6 2.26 26,10 0.9 3.712,12 0.32 0.62 10,12 0.35 1.19 18,12 0.61 2.26 26,12 1 3.82,14 0.2 0.52 10,14 0.42 1.37 18,14 0.61 2.31 26,14 0.88 3.882,16 0.31 0.51 10,16 0.43 1.56 18,16 0.6 2.34 26,16 0.87 3.654,2 0.32 0.52 12,2 0.33 0.48 20,2 0.61 1.17 28,2 0.75 1.454,4 0.22 0.95 12,4 0.23 1.01 20,4 0.6 2.35 28,4 0.88 3.084,6 0.21 0.86 12,6 0.22 0.96 20,6 0.65 2.39 28,6 0.89 3.414,8 0.25 0.89 12,8 0.27 1.03 20,8 0.65 2.45 28,8 0.9 3.68
4,10 0.23 0.99 12,10 0.32 1.28 20,10 0.67 2.51 28,10 0.89 3.694,12 0.15 1 12,12 0.33 1.36 20,12 0.69 2.57 28,12 0.86 3.654,14 0.17 0.84 12,14 0.36 1.46 20,14 0.66 2.57 28,14 0.91 3.654,16 0.22 0.9 12,16 0.36 1.57 20,16 0.68 2.55 28,16 0.91 3.576,2 0.21 0.53 14,2 0.38 0.71 22,2 0.72 1.33 30,2 0.66 1.416,4 0.21 0.96 14,4 0.44 1.38 22,4 0.72 2.65 30,4 0.78 3.076,6 0.22 0.86 14,6 0.41 1.3 22,6 0.7 2.67 30,6 0.8 3.356,8 0.23 0.91 14,8 0.4 1.3 22,8 0.73 2.73 30,8 0.87 3.46
6,10 0.17 0.88 14,10 0.47 1.46 22,10 0.76 2.81 30,10 0.88 3.546,12 0.33 0.88 14,12 0.48 1.6 22,12 0.79 2.91 30,12 0.89 3.52 KEY6,14 0.34 0.99 14,14 0.54 1.71 22,14 0.8 2.94 30,14 0.9 3.56
X,Y-COORDINATESZ-SLUDGE DEPTH
6,16 0.33 1.06 14,16 0.53 1.79 22,16 0.81 2.95 30,16 0.9 3.628,2 0.24 0.45 16,2 0.55 0.93 24,2 0.7 1.42 32,2 0.55 1.218,4 0.25 0.91 16,4 0.51 1.88 24,4 0.8 2.94 32,4 0.59 2.588,6 0.24 0.92 16,6 0.5 1.86 24,6 0.87 3.09 32,6 0.8 2.978,8 0.21 0.9 16,8 0.54 1.85 24,8 0.91 3.21 32,8 0.86 3.33
8,10 0.23 0.84 16,10 0.53 1.94 24,10 0.9 3.3 32,10 0.9 3.51 NOTE8,12 0.25 0.98 16,12 0.52 2 24,12 1 3.45 32,12 0.93 3.6 All coordinates are in
meters (m)8,14 0.35 1.27 16,14 0.57 2.11 24,14 1 3.59 32,14 0.94 3.668,16 0.36 1.38 16,16 0.56 2.2 24,16 0.9 3.51 32,16 0.92 3.66
Total volume(m3) 252.52
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 06: RAW DATA OF PHYSICOCHEMICAL PARAMETERS FOR
WASTEWATER OF SALASALA FAECAL SLUDGE MANAGEMENT SYSTEM
86
Appendix 06: RAW DATA OF PHYSICOCHEMICAL PARAMETERS FORWASTEWATER OF SALASALA FAECAL SLUDGE MANAGEMENT SYSTEM
a) Physical parameters
1)Temperature
(°c)
TDS(mg/l
)PH
Conductivity(ms/cm)
Salinity(%)
Turbidity(NTU)
Totalsuspendedsolid TS,
(mg/l)
Colour(mg Pt-
co/l)
S 01 29.8 1918 6.9 3.85 1.4 1200 1400 3000
S 02 29.9 1422 7.1 2.78 1.2 600 410 2400
S 03 29 1426 7 2.8 1 900 400 2200
S 04 28.9 1374 7.1 2.74 1 600 300 700
2)Temperature
(°c)
TDS(mg/l
)PH
Conductivity(ms/cm)
Salinity(%)
Turbidity(NTU)
Totalsuspendedsolid TS,
(mg/l)
Colour(mg Pt-
co/l)
S 01 26.8 1590 5.8. 2.78 1.6 998 1300 3400
S 02 27.4 1006 6.5 2.12 1.2 600 410 2700
S 03 27.2 1128 6.8 1.72 1.1 1000 430 2500
S 04 27..6 1300 6.9 2 1 500 270 1000
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 06: RAW DATA OF PHYSICOCHEMICAL PARAMETERS FOR
WASTEWATER OF SALASALA FAECAL SLUDGE MANAGEMENT SYSTEM
87
3)Temperature
(°c)TDS
(mg/l) PHConductivity
(ms/cm)Salinity
(%)Turbidity
(NTU)
Totalsuspendedsolid TS,
(mg/l)
Colour(mgPt-
co/l)
S 01 27.1 1478 6.2 2.89 1.5 1000 1200 3300
S 02 27.2 1065 6.7 2.11 1.1 800 400 2000
S 03 27.5 1267 6.3 2.12 1.1 700 400 2000
S 04 27.9 995 6.3 1.98 1 400 203 1100
4)Temperature
(°c)TDS
(mg/l) PHConductivity
(ms/cm)Salinity
(%)Turbidity
(NTU)
Totalsuspendedsolid TS,
(mg/l)
Colour(mgPt-
co/l)
S 01 27 1480 6.7 3 1.5 1300 1400 3000
S 02 25.9 1320 6.6 1.2 1.4 900 410 2200
S 03 28.9 1060 6.5 1.81 1.3 700 400 2400
S 04 28 1000 6.6 2.91 1.1 500 233 800
b) Chemical parameters
1)NH3-
N(mg/l)
PO4(mg/l) 2)NH3-
N(mg/l)
PO4(mg/l) 3)NH3-
N(mg/l)
PO4(mg/l)
Sample01
230 500Sample01
200 500Sample01
240 500
Sample02
160 250Sample02
140 100Sample02
153 250
Sample03
148 100Sample03
160 250Sample03
158 100
Sample04
135 250Sample04
125 100Sample04
129 250
ARDHI UNIVERSITY Dissertation by Ulotu Gerald|Appendix 06: RAW DATA OF PHYSICOCHEMICAL PARAMETERS FOR
WASTEWATER OF SALASALA FAECAL SLUDGE MANAGEMENT SYSTEM
88
c) Biological parameters
1) BOD5 (mg/l) at20 °C
COD(mg/l)
Faecal coliform(count/100ml)
Total coliform(Count/100ml)
Sample01 2250 4500 25200000 57000000Sample02 1100 2200 22000000 35000000Sample03 950 1900 20000000 38000000Sample04 320 640 17000000 18000000
2)BOD5 (mg/l) at20 °C
COD(mg/l)
Faecal coliform(count/100ml)
Total coliform(Count/100ml)
Sample01 2500 5000 22000000 67000000Sample02 950 1900 25000000 41000000Sample03 1065 2130 22000000 33000000Sample04 335 670 15000000 23000000
3)BOD5 (mg/l) at20 °C
COD(mg/l)
Faecal coliform(count/100ml)
Total coliform(Count/100ml)
Sample01 2010 4020 25000000 50000000Sample02 1070 2140 23000000 37000000Sample03 1030 2060 21000000 35000000Sample04 300 600 16000000 26000000