Upgrading alternatives for a wastewater treatment pond … · Water and Environmental Engineering...
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__________________________________________________________________________________________ Water and Environmental Engineering Department of Chemical Engineering Upgrading alternatives for a wastewater treatment pond in Johor Bahru, Malaysia Master’s Thesis by Alexander Szabo and Oscar Engle March 2010
Transcript of Upgrading alternatives for a wastewater treatment pond … · Water and Environmental Engineering...
__________________________________________________________________________________________
Water and Environmental Engineering Department of Chemical Engineering
Upgrading alternatives for a wastewater treatment pond in Johor Bahru, Malaysia
Master’s Thesis by
Alexander Szabo and Oscar Engle
March 2010
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__________________________________________________________________ Vattenförsörjnings- och Avloppsteknik Water and Environmental Engineering Institutionen för Kemiteknik Department of Chemical Engineering Lunds Universitet Lund University, Sweden
Upgrading alternatives for a wastewater treatment pond in Johor Bahru, Malaysia
Master Thesis number: 2010-X
Alexander Szabo and Oscar Engle Water and Environmental Engineering Department of Chemical Engineering
April 2010
Supervisor: Associate Professor Dr. Karin Jönsson Co-Supervisor: Associate Professor Dr. Azmi Bin Aris
Examiner: Professor Jes la Cour Jansen
Picture on Front Page:
Inlet distribution pipe at Treatment Pond during de-sludging operation, UTM, Johor Bahru, Malaysia.
_________________________________________________________________________________
Postal address: Visiting address: Telephone:
P.O. Box 124 Getingevägen 60 +46 46-222 82 85
SE-221 00 Lund +46 46-222 00 00
Sweden Telefax:
+46 46-222 45 26
Web address: www.vateknik.lth.se
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List of abbreviations
BOD – Biological Oxygen Demand
CFU – Coliform Forming Units
COD – Chemical Oxygen Demand
DO – Dissolved Oxygen
ha – Hectares (10.000 m2)
HRT – Hydraulic Retention Time
IWK – Indah Water Konsortium
MLSS – Mixed liquor suspended solid
P.E. – Population Equivalent
UTM – Universiti Technologi Malaysia
TSS – Total Suspended Solids
WSP – Waste Stabilization Pond
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Summary Malaysia is developing fast and is striving to become a fully developed country by 2020. After
independence in 1957 from Great Britain, Malaysia has gradually set up goals for its wastewater
management, which often goes together with economical development and growth. Most of the waste
water treatment facilities built so far have been made simple and in form of treatment ponds, septic
tanks and low flushing latrines. In this project a treatment pond at UTM in Johor Bahru has been
analyzed. At present, the management of UTM is not satisfied with the treatment efficiency and is
looking for options to upgrade the pond or replace it with an activated sludge system. The objective of
this study is to propose an upgraded wastewater treatment facility to the current treatment pond.
The treatment pond consists today of two parallel lines, each line with a facultative pond followed by a
maturation pond. After treatment the water is discharged to a stream close to the treatment pond. At
two occasions in November 2009 and one occasion in January 2010 sampling and flow measurements
were performed at the treatment pond. During each occasion sampling and flow measurements were
made every second hour for 24 hours. This was made to get the characteristics and behavior of the
wastewater quality and the wastewater flow. The samples were analyzed and the amount of COD, BOD
and TSS were measured.
The analysis of the data shows that the concentration of COD, BOD and TSS is low. It seems there is a
significant infiltration into the sewer network. This was confirmed by the flow measurements done at
the inlet into the treatment pond. During rain events the influent flow is more than doubled and this is
something that must be considered when dimensioning a new treatment facility. During these peaks,
the concentration of COD is more than doubled. The high COD-values are confirmed by higher TSS
values during these rain events. The exact reason for this is unknown but one possible explanation could
be that the increased flow in the wastewater pipes will catch and carry with it deposits from the sewage
pipe. Another explanation could be that somewhere a storm water channel is connected to the sewer
pipes and the water is carrying organic material from the surface into the pipes which ends up at the
treatment pond.
At late night the COD value is low but there is still a significant influent flow. This leads to the conclusion
that the pipe is also taking in groundwater. Together with the increased influent flow during rain events
and the high flow at night, the total infiltration is estimated to 60-90% of the total influent flow.
From the data collected and analyzed three different solutions for better treatment efficiency have been
proposed. One solution is an activated sludge system; another is upgrading the current pond by
rearranging the water flow so that it flows in a series through all four treatment ponds. The third
alternative is to add aeration to the upgraded treatment pond as calculations shows that the area is not
sufficient and therefore it is overloaded.
According to assumptions and calculations the activated sludge system will give the best treatment
efficiency in terms of BOD, nitrogen and phosphorous removal. An activated sludge system will achieve
standard A requirements according to Malaysian recommendations and according to Malaysian
standard the activated-sludge system will have an footprint area of around 1 ha if the system receives
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water from more than 10.000 people. The current pond received wastewater from around 10.500
people at the time this report was written.
The treatment technology will however be comparatively expensive to build and run. An activated
sludge system is also less effective, compared to the other suggested alternatives, in removing
pathogens and there may be a need for some pathogen removal device after activated-sludge
treatment.
The second suggestion to upgrade the current treatment pond does not achieve the same treatment
efficiency as the activated sludge system. On the other hand it is less expensive to run and easier to
maintain. It will also reduce pathogens more effectively than an activated sludge system. According to
assumptions and calculations it will be wise to install oxygen generators as the upgraded treatment
pond system is overloaded and the oxygen the algae produce is not sufficient for organic breakdown. If
conservative assumptions and calculations are made the treated water will barely fulfill the
requirements for Malaysian standard A, but at a low price. If optimistic assumptions are made, the
treatment result will reach down just below standard A.
Our recommendations are for financing reasons and for simplicity to keep the old treatment plant,
improve it by installing screening, installing aeration and baffles and redirecting the flow from parallel
flow to serial flow through all four treatment ponds.
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Acknowledgements
This report is a result of a project which has been carried out both in Sweden and in Malaysia. In Sweden
we were part of the Water and Environmental Engineering at the Department of Chemical Engineering
where we started and completed our project. In Malaysia where the field study of our project was
performed we were part of the Environmental Engineering at the Department of Chemical Engineering
(IPASA).
We are proud to participate in the cooperation between LTH in Sweden and UTM in Malaysia. We are
only the “second generation” of Swedish students going away to this friendly and multicultural country.
Therefore we would like to give our sincere greetings to Prof. Dato’ Ir. Dr. Zaini bin Ujang for introducing
us to his university during his guest lectures in Sweden, spring 2009.
A warm gratification goes to our supervisor in Sweden, Ass. Pr. Karin Jönsson, for her professional
support and guidance during the whole project. Your help and feedback has made this project a lot
easier and the project would not have been possible without your co-operation between LTH and UTM
in Malaysia.
We would like to give our supervisor in Malaysia Ass. Pr. Azmi Bin Aris our sincere greetings for his
relentless help at IPASA in Malaysia. Your help and support at UTM was necessary for us in a completely
new country and environment. We hope to see you again in the future, both in Malaysia and in Sweden.
We are also very grateful to Civ. Eng. Rozlan Md Shariff for his support with maps and data of the
treatment pond. A special thanks goes to PhD student Chow Ming Fai at IPASA for his help and support
at the laboratory. We thank PhD student Mohd Noor Asyraf bin Amirruddin for his help with
precipitation data from the university area. Another special thanks goes to the staff at IPASA for your
service and helpfulness when we needed it the most.
We are grateful to our examinator Prof. Jes la Cour Jansen for his useful viewpoints during our project.
We wish to express our warm gratitude to Prof. Dr. Zulkifli Yusop for professional help and for
introducing us further into the Malaysian gastronomy with its very tasteful dishes, especially the Satay
chicken.
Finally, we would like to thank Ångpanneföreningen, Helsingkrona nation, Rotary Ängelholm and
Lundabygdens sparbanks stiftelse for your financial support. Without your help this project would never
had been possible to carry out financially.
Alexander Szabo and Oscar Engle
Lund, April 2010
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Contents 1. Introduction .............................................................................................................................................. 1
1.2 Background ......................................................................................................................................... 1
1.3 Objective ............................................................................................................................................. 4
2. Waste Water Treatment Ponds Technology ............................................................................................ 5
2.1 Introduction to Wastewater treatment ponds ................................................................................... 5
2.2 Pond Types .......................................................................................................................................... 5
Anaerobic ponds ................................................................................................................................... 5
Facultative Ponds .................................................................................................................................. 6
Maturation ponds ................................................................................................................................. 6
Mechanically aerated ponds ................................................................................................................. 7
2.3 Degradation processes ........................................................................................................................ 7
Removal of pollutants in Wastewater treatment ponds ...................................................................... 7
Aerobic degradation ............................................................................................................................. 7
Anaerobic degradation ......................................................................................................................... 8
Sedimentation ....................................................................................................................................... 8
Disinfection ........................................................................................................................................... 8
3. Pond Hydraulics ........................................................................................................................................ 9
3.1 Retention time .................................................................................................................................... 9
3.2 Complete-mix model........................................................................................................................... 9
3.3 Plug flow ............................................................................................................................................ 10
3.4 Dispersed flow .................................................................................................................................. 10
3.5 Hydraulic design ................................................................................................................................ 10
Short Circuiting ................................................................................................................................... 10
Building several ponds in series .......................................................................................................... 10
Baffles.................................................................................................................................................. 11
4. Activated sludge process technology...................................................................................................... 13
Introduction to activated sludge process technology ............................................................................ 13
Primary treatment .................................................................................................................................. 13
Biological treatment ............................................................................................................................... 14
Nitrification and denitrification .......................................................................................................... 14
Chemical treatment ................................................................................................................................ 16
Activated sludge system – arrangements ............................................................................................... 17
Sludge treatment .................................................................................................................................... 18
5. Previous studies on WSP systems .......................................................................................................... 21
5.1 Example of computer simulation of WSP geometry ......................................................................... 21
Method ............................................................................................................................................... 21
Results and conclusions ...................................................................................................................... 22
5.2 Facultative and maturation ponds in Sri Pulai, Johor Bahru, Malaysia. ........................................... 23
Method ............................................................................................................................................... 23
Results and conclusions ...................................................................................................................... 23
5.3 Previous Study on the studied treatment pond at UTM .................................................................. 24
6. Study Area .............................................................................................................................................. 25
6.1 Climate .............................................................................................................................................. 25
6.2 The wastewater treatment facilities at UTM .................................................................................... 25
6.3 Recipient ........................................................................................................................................... 26
Introduction ........................................................................................................................................ 26
Method ............................................................................................................................................... 27
Results and discussion ........................................................................................................................ 28
7. Sampling and analysis methods .............................................................................................................. 31
Sampling and flow measurements ......................................................................................................... 31
COD ......................................................................................................................................................... 31
BOD5 ........................................................................................................................................................ 32
8. Performance of the existing WSP ........................................................................................................... 35
8.1 Method ............................................................................................................................................. 35
8.2 Results and discussion ...................................................................................................................... 35
De-sludging conditions ........................................................................................................................ 35
BOD5 and COD in effluent from WSP .................................................................................................. 35
TSS in effluent ..................................................................................................................................... 36
Average effluent values ...................................................................................................................... 38
Algae in effluent .................................................................................................................................. 38
Reduction in pond system .................................................................................................................. 39
9. Wastewater flow ..................................................................................................................................... 41
9.1 Survey of wastewater producers at UTM campus ............................................................................ 41
Method ............................................................................................................................................... 41
Results and discussion ........................................................................................................................ 42
9.2 Flow measurements .......................................................................................................................... 43
Method ............................................................................................................................................... 43
Results ................................................................................................................................................. 44
Water flow .......................................................................................................................................... 48
Total flow ............................................................................................................................................ 48
Discussion ............................................................................................................................................ 49
10. Infiltration ............................................................................................................................................. 51
10.1 Calculations ..................................................................................................................................... 51
10.2 Discussion and conclusion .............................................................................................................. 52
11. Influent wastewater quality .................................................................................................................. 53
11.1 Method ........................................................................................................................................... 53
11.2 Results and discussion .................................................................................................................... 53
BOD5 and COD ......................................................................................................................................... 53
Total Suspended Solids ........................................................................................................................... 56
Dimensioning values ............................................................................................................................... 57
Degradation speed of BOD ................................................................................................................. 58
12. Proposals for upgrading of the treatment system ................................................................................ 59
Alternative 1: Upgrading of existing WSP ............................................................................................... 59
Screening device ................................................................................................................................. 60
Flow through ponds ............................................................................................................................ 60
Alternative 2: Upgrading of existing WSP – Partly aerated pond ........................................................... 62
Alternative 3: Conventional activated-sludge treatment plant .............................................................. 66
Screening device ................................................................................................................................. 66
Grit chamber ....................................................................................................................................... 66
Equalization tank ................................................................................................................................. 67
Primary settling tank ........................................................................................................................... 68
Activated sludge tank .......................................................................................................................... 70
Secondary settling tank ....................................................................................................................... 73
Sludge handling ................................................................................................................................... 74
Disinfection ......................................................................................................................................... 75
13. Discussion on the upgrading alternatives ............................................................................................. 77
14. Conclusion ............................................................................................................................................. 81
15. Future work ........................................................................................................................................... 83
15. References ............................................................................................................................................ 85
Appendix A: Studies on the present treatment pond at UTM ................................................................... 89
Result and conclusion ......................................................................................................................... 89
Appendix B: Calculation of P.E. ................................................................................................................... 93
Appendix C: Addition concerning new effluent standard ........................................................................... 95
Appendix D: Map of the sewer network connected to the pond ............................................................... 96
Appendix E: Sample values ......................................................................................................................... 99
Appendix F: Calculation of k-value by Thomas method ........................................................................... 101
Appendix G: Technical data and construction drawings........................................................................... 107
Appendix H: Reduction of pathogens in WSP systems ............................................................................. 109
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1. Introduction
1.2 Background Malaysia is developing rapidly and the government has set up goals for becoming a fully developed
country by 2020. This will put more strains on the environment and the keyword is therefore sustainable
development (Liew, 2008). With an increasing population and a more water-demanding society more
wastewater is produced. Wastewater can have a negative impact on the population, the economy and
the environment if it is not managed in a wise way. Therefore Malaysia is trying to develop a system for
wastewater handling which is both sustainable and suitable for the country’s specific conditions. The
complexities and unique environment of Malaysia prevent the adoption of a “carbon copy”
development that has been successful in other countries.
Malaysia is considered to be a good case study example for other developing countries because of its
many experiences with different wastewater solutions. The government and the authorities have tried
to implement decentralized on-site systems such as septic tanks and latrines in rural and semirural
areas. Other implemented systems have been centralized conventional treatment plants in urban areas
(Ujang & Henze, 2006). The development of institutions and financial solutions for wastewater systems
in Malaysia could also serve as a good study example for many developing countries.
The first sewerage policy in Malaysia was created during the British occupation at the end of the 19th
century. During this period the so-called Sanitary Boards were organized in Malaysia’s major cities and
provided services like water supply, latrines, irrigation etc. The Boards were however only responsible
for wastewater and sanitary problems concerning British settlers (Ujang & Henze, 2006). After
Independence in 1957, sewerage facilities were administrated by the Environmental Health and
Engineering unit. The unit belonged to the Ministry of Health created in the 1960’s (Ujang & Henze,
2006). The unit initiated a successful program in which pour-flush latrines were implemented in rural
and semirural areas. A pour-flush toilet utilize small amounts of water (around 2-3 litres) to pour down
human excreta deposit in a pit latrine (UNEP, n.d.). The excreta are poured down into a tank where the
organic material is decomposed. The sludge collected in the tank has to be emptied on a regular basis.
Pour-flushed toilets were also installed in urban areas but in these areas the unit tried to adopt a more
conventional sewage approach found in the industrialized world. Due to a lack of finances and a well
developed national framework for wastewater management the implementation was slow. In many
cases the drawings and plans for the treatment plants remained on the bookshelves.
A significant step in Malaysia’s wastewater management was taken in 1974 when the government
established the Environmental Quality Act which was the first national legal framework for regulating
the quality of effluent water from sewage and industries (Ujang & Henze, 2006). In 1980 the Malaysian
Parliament implemented a new law where developers of new housing areas with more than 30 houses
were required to provide proper sewage treatment. It was favored to keep the new treatment facilities
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as simple as possible. In order to keep the treatment facilities simple, treatment ponds or Imhoff tanks
were usually implemented. The idea was that after one year of utilization, the responsibility for running
and maintaining the treatment facilities was transferred to the municipal authorities. However, not
every local authority had the resources to run the centralized treatment facilities and as a result
centralized treatment systems grew only from 3.5% in 1970 to 5% in 1990. This can be compared to
septic tanks coverage in urban areas which grew from 17.2% in 1970 to 37.3% in 1990 (Ujang & Henze,
2006).
In 1993 a new law called the Sewage Service Act was implemented and a new Federal agency called the
Sewage Service Department was established. The main task of the new agency was to plan, regulate
and control sewage water treatment. Since 1993 the agency has been responsible for the national
privatization project and in 1993 Indah Water Konsortium (IWK) was given the task to operate and
maintain existing treatment facilities (Ujang & Henze, 2006). The reason for privatizing was to assist the
Sewage Service Department with maintenance of existing sewage systems, refurbishment of old systems
and constructions of new sewage systems in urban areas (Ujang & Henze, 2006).
At the moment there are two standards for treated waste water quality, according to the Environmental
Quality Act from 1974. Every treatment system must comply with either standard A or standard B.
Standard A is used if the water is discharged upstream of any raw water intake and Standard B is used
when water is discharged downstream of a raw water intake (Sewerage Services Department, 1998).
The most important parameters of treated wastewater to be followed are Biochemical Oxygen Demand
over a period of 5 days (BOD5) and total suspended solids (TSS). No discharge of treated wastewater
higher than the absolute values are permitted by the law. Because of fluctuations in the quality of the
treated wastewater, the effluent wastewater quality should be designed to reach a lower “design” value
(Table 1.1). This is to ensure that the effluent wastewater quality never reach above the absolute values.
The permitted limits for Standard A and Standard B can be seen in Table 1.1 below.
Table 1.1: Malaysian Design values for BOD5 and TSS for treated effluent wastewater quality. (Re-drawn from
Sewerage Services Department, 1998)
Parameter Standard A Standard B
Absolute Design Absolute Design
BOD5 (mg/l)
TSS2 (mg/l)
20 10
50 20
50 20
100 40
During the project the effluent standard from 1974 was changed. It came to our knowledge after all the
sampling from the pond was done that a new standard was introduced in December 2009. The new
standard is similar to the one of 1974. The permitted limits for BOD5 and TSS levels are unchanged. The
main difference is the introduction of nitrogen and phosphorous removal (Department of Environment,
2009). Because no measurements of nitrogen and phosphorous was not done we will mostly use
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Standard A and Standard B from 1974 throughout the report. For more information about the new
effluent standard see Table C.1 in Appendix C.
In this project, a treatment pond built in 1985 at the Universiti Teknologi Malaysia (UTM) has been
studied. Figure 1.1 below shows where UTM is situated. The treatment pond was originally built for a
population of 8,000 PE but is currently treating wastewater from around 10,500 PE from the university
area. The treatment pond consists of two parallel lines each treating equal amounts of wastewater. The
treated water is discharged to a small stream next to the treatment pond. The current discharged
wastewater is not complying with Standard A according to Malaysian requirements. At the moment the
pond is only complying with standard B quality which is a lower quality standard for treated wastewater.
The university would like to upgrade the treatment facility so that it can comply with Malaysian
Standard A requirements as the water downstream is used for canoeing by UTM students. The idea is
that a new treatment facility could also be used for educational purposes for students from the
university. Moreover, an improved treatment facility at the university also goes hand in hand with
Malaysia’s national goals to reach a more effective and better management of wastewater.
In order to get a deeper understanding of the water quality and its flow characteristics to the current
treatment pond, sampling and different kinds of measurements have been performed. The obtained
information is important as the result of the samples and measurements will be used as a basis when
designing an improved and more effective treatment facility.
Figure 1.1: Map of Malaysia and the location of UTM, Johor Bahru. (with permission from Reuterwall &
Thorén, 2009)
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1.3 Objective The objective of this master thesis project is to propose upgraded wastewater treatment facilities which
can improve the treated effluent wastewater quality at Universiti Teknologi Malaysia. A new treatment
facility should have a footprint area of 25% compared to the present treatment pond, as the area
around the current treatment pond is planned for recreation. The upgraded treatment facilities must
also be able to perform a better treatment of the wastewater compared to the system used today. The
requirement is that the effluent can comply with an effluent of Standard A quality according to
Malaysian directives.
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2. Waste Water Treatment Ponds Technology
2.1 Introduction to Wastewater treatment ponds Wastewater treatment ponds are used around the world for treatment of municipal wastewater. They
can offer a good alternative where land prices are low and where the climate is beneficial. Since there is
a general relationship between growth rate of bacteria and algae that contribute to the treatment of
wastewater, pond systems in a warmer climate benefit from high temperatures. A pond system can be
built easily and does not require much maintenance. Since it can hold large quantities of water, it has a
good resistance to shock loads and hazardous substances that may enter the system.
A typical arrangement of wastewater treatment ponds consists of a primary facultative pond followed
by one or multiple maturation ponds. Under some conditions it is also possible to use an anaerobic pond
before the facultative pond (see Figure 2.1).
Figure 2.1: In this figure three possible arrangements for pond system are illustrated. The first two series
illustrates a primary facultative pond (F) followed by one or two maturation ponds (M). The third pond series
illustrates an anaerobic pond (A) followed by a facultative pond and finally a maturation pond.
2.2 Pond Types
Anaerobic ponds
Anaerobic ponds operate without the presence of algae or oxygen, and have an advantage over the
facultative pond since they can deal with higher organic loading. They can reduce the organic load by 40
to 70% with a retention time of only a few days (Shilton et al., 2005).
Methane (CH4) and sulphide (H2S) are gasses that are produced under anaerobic conditions. Methane
gas may be considered as a fuel resource if collected, but if not collected as a greenhouse gas,
contributing to the climate change as it escapes into the atmosphere from the pond. If sulphide is
produced and released, it is not appreciated since it is releases a bad odor. If the anaerobic pond is not
properly design, or when overloaded, the release of sulphide may be problematic for people living in the
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surroundings (Mara, 2003). This is confirmed by a study at Lee Summit WSP, Missouri, where odor
nuisance occurred after the load was increased above the pond capacity (McKinney, 1968).
Facultative Ponds
The main features of the facultative ponds are that they are horizontally divided into two layers, with
and without oxygen presence. In the top layer (down to 20 – 30 centimeters of depth) photosynthesis
makes micro-algae produce oxygen during daytime, the oxygen is then used by aerobic bacteria to
degrade organic substrate. Some of the oxygen in the top layer has its origin from surface mass transfer,
but it has been estimated that more than 80% of the oxygen is produced by algae (Shilton et al., 2005).
The depth of oxygen presence in the water is changing and depends on many factors such as sunlight,
water turbidity and organic loading (Shilton et al., 2005). In the bottom of the pond, no dissolved oxygen
is available, which gives anaerobic bacteria opportunities to degrade substrate. The retention time of
facultative ponds is relatively large, up to several weeks. The long retention time and the shallow design,
typically depth is 1.5 meter, make the ponds consume relatively large land areas (Mara, 2003).
Since the light needed for the algae arrives through the surface, facultative ponds are usually designed
by surface loading. In temperate climates, algae are more productive in terms of oxygen production and
the pond may therefore receive a higher loading of BOD. Eq. 2.1 is used to calculate the maximum
possible BOD loading per area:
= (Eq. 2.1)
T = Temperature (°C)
(Mara, 2003)
Maturation ponds
The maturation ponds usually follow facultative ponds as the last step of the treatment. Since most of
the substrate has been removed during the previous steps, they are clearer and contain more dissolved
oxygen. They are preferably built shallow in order to enhance sunlight penetration. Sunlight penetrating
through the water column will kill pathogens effectively. An example of effective pathogen removal in
maturation ponds is seen in Christchurch WSP, where the quality of the disinfection can be compared to
the disinfection capacity of an activated-sludge treatment plant using UV equipment (Masterton District
Council, 2009).
Some final polishing of BOD, up to 25 percent, is possible within the maturation pond (Shilton et al.,
2005).
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Mechanically aerated ponds
Additional oxygen can be injected into the water by surface aerators or submerged diffusion systems at
the bottom of the pond. Submerged aerators are more effective and can deliver around 3.7 to 4 kg O2
per invested KWh whereas surface aerators deliver around 1.5 to 2.1 kg O2 for the same amount of
energy (EPA, 2002). The mechanically aerated ponds are divided between partial-mix aerated systems
and complete-mix systems. In the partial-mix system, aerators just supply enough oxygen required for
biological degradation. In complete mix ponds, the aeration and mechanical stirring mixes the sludge
and keeps it in suspension, which makes the treatment effective since it gives good contact between
sludge and wastewater. The complete mix system requires about 10 times more energy than the partial-
mix system (EPA, 2002). Since the aeration in a complete mix pond keeps large quantities of suspended
solids mixed in the pond, a following post-settling pond should be installed. Partial-mix aeration may be
installed into an existing facultative pond to improve the overall treatment efficiency.
2.3 Degradation processes
Removal of pollutants in Wastewater treatment ponds
The earth is capable to degrade human wastewater when it is released into the waterways. Problems
occur when the load on our natural environment is bigger than the self-cleansing mechanisms available
in our lakes and rivers. The more populated the world becomes, the higher the stress on our
environment. The wastewater treatment ponds are cleaning the water using the same processes as in
nature. The task of the wastewater treatment ponds is to optimize and isolate the processes, so that the
cleaning has been done before the water is released in our waterways. In nature several processes are
responsible for the treatment of polluted water, and these processes should be used and optimized as
much as possible. Some of nature’s processes will be discussed in this section.
Aerobic degradation
When oxygen is present in water, aerobic microorganisms will use oxygen to oxidize organic compounds
and produce carbon dioxide (CO2), water and biomass (sludge). Since oxygen is consumed by the
degradation, the process will be limited by the presence of oxygen. If large quantities of organic material
are to be degraded, large amounts of oxygen must be supported. In the case of wastewater treatment
ponds, the algae are the main producers of oxygen (Shilton et al., 2005). Since the algae are only present
in the upper part of a pond, it is difficult to achieve aerobic decomposition through an entire pond.
There are however more advanced pond systems where algae are mixed through the water to
oxygenate larger volumes. In mechanically aerated ponds, oxygen is pumped or mixed into the water
which will achieve high dissolved oxygen levels. The disadvantage of mechanical oxygen support is that
it consumes large amounts of energy.
Aerobic degradation in wastewater treatment ponds requires larger volumes and a longer retention
time then the conventional activated sludge-systems, because the concentrations of active biomass,
containing the microorganisms, are much lower.
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Anaerobic degradation
When no oxygen is available, anaerobic degradation may occur by anaerobic microorganisms. The
benefit of anaerobic digestion is that it can deal with highly concentrated wastewater and can achieve
good purification results within short retention times. The process is temperature dependent and will, if
properly designed, reduce the BOD concentrations by 40% at 10°C, 60% at 20°C and 70% at 25°C (Shilton
et al., 2005). The anaerobic pond should be installed as the first treatment step, when the load of
wastewater is the highest. The high load of organic matter would inhibit the presence of algae. A typical
anaerobic pond receives more than 3000 kg BOD/ha/day, whereas facultative ponds should not receive
more than 400 kg BOD5 /ha/day in order to sustain a healthy algal population (Mara, 2003).
Sedimentation
Large amounts of settleable and flocculated colloidal materials that enter the pond will settle to the
bottom of the pond and create a sludge layer as the water speed declines. Independent of whether the
particles settle in an anaerobic or facultative pond, the environment, within the formed sludge layer, will
be anaerobic. Even maturation ponds, which are at the last step of the treatment, may produce a thin
anaerobic sludge layer at the bottom. The sludge layer is broken down anaerobically and thickens over
time. Gases that result from the degradation arises up though the water and escapes into the
atmosphere. It is estimated that up to 30% of the BOD load disappears as gas (Shilton et al., 2005).
Disinfection
There are several factors within a WSP that together contribute to the removal of illness-causing
bacteria, viruses, worms and protozoan parasites. It is however difficult to exactly evaluate the
contribution to the disinfection effect from a single factor, since the processes within a WSP are both
complex and dynamic. Factors that are known to contribute to disinfection are sunlight (UV) exposure,
pH, temperature, algal toxins, sedimentation and hydraulic retention time (Shilton et al., 2005). The
WSP:s are generally considered very good at removal of pathogens (Maynard et al., 1999). Research
about disinfection shows treatment results from 26 WSP:s around the world (see Table H.1, Appendix
H). The reduction performance of pathogens in WSP systems is generally better than conventional
mechanical treatment with activated sludge (George et al., 2002).
Sunlight (UV) is considered to be the most important factor for disinfection (Davies-Colley et al., 2000).
UV disinfection is complex since different wavelengths affects different species in various ways. Some
reactions with certain species required dissolved oxygen dependent photo-oxidations. In these cases,
oxygen is crucial for the performance (Davies-Colley et al., 2000).
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3. Pond Hydraulics
3.1 Retention time When dimensioning a pond, the water flow behavior is crucial. One of the key parameters is the
“retention time”, or “hydraulic retention time” HRT, which occurs as a key parameter in almost every
calculation. The retention time tells us how long the water, on average, stays within the pond. The
formula for retention time is:
(Eq. 3.1)
= Retention time (days)
V = Volume (m3)
Q = Flow (m3/day)
In most cases, the aim is to keep the water in the system as long as possible to allow maximum
degradation. In natural pond systems, long retention times created through the large volumes of the
ponds has to compensate for slow degradation, compared to advanced mechanical-chemical systems.
The retention time is a theoretical value, and the behavior of water in reality is far more complex.
There are several models which can be used when simplifying the water movements.
3.2 Complete-mix model The complete-mix model assumes that the water is becoming completely mixed when entering the
pond.
All the content of the pond is therefore assumed to be homogenous. The equation for degradation in a
complete-mix model is:
(Eq. 3.2)
(Mara, 2003)
10
3.3 Plug flow If water is transported through a pipe, the flow pattern can be simplified by a plug-flow model. The
water moves uniformly through the system without mixing.
The equation for degradation in a plug-flow model is:
(Eq. 3.3)
(Mara,2003)
3.4 Dispersed flow Another more complex equation that can be used is created for “non-ideal” dispersed flow.
It is a model that takes mixing into consideration, and it lies between the complete-mix model and the
plug-flow model. Since the equation is complicated, and many unknown factors are part of the
equation, it will not be further used in this report.
Theoretically, within a pond of a certain volume, plug-flow leads to better removal of BOD than
complete-mix flow (Mara, 2003). In the case of partly and fully aerated lagoons, the flow pattern is
assumed to be complete-mix since the aerators mixes the water. Facultative and maturation ponds
might be considered having plug-flow conditions.
3.5 Hydraulic design
Short Circuiting
When water is entering a pond, there can be a tendency that a part of the water seeks the quickest
route to the outlet. The water that travels directly to the outlet will leave the pond much earlier than it
is designed for, hence it receives minimal time for treatment. There is evidence that water has been able
to leave the pond after only a few hours in ponds with theoretical retention times of several weeks
(Shilton et al., 2002). There are however ways to reduce the risks, or amounts, of short-circuiting water.
One obvious way is to give the pond a longer shape (length to width ratio). Another way is to use baffles
(see next page) and/or building several smaller ponds after each other will have good effect in
eliminating short-circuiting.
Building several ponds in series
When building a partly aerated pond, the flow through the pond is assumed to be complete-mix. In this
case, it is theoretically better to use several smaller ponds instead of a single large one. Using a
theoretical example from Shilton et al. (2005), where an aerated pond is given a BOD influent of 200
11
mg/l, effluent of 30 mg/l, k=0.28 d-1 and a temperature of 20°C, one can see how the demanded total
retention time changes with the number of ponds:
Table 3.1: The demanded retention time when treating wastewater BOD5 from 200 to 30 mg/l at 20° C. k-
value of 0.28 d-1
. The model assumes complete-mix condition.
Number of ponds in series
Demanded retention in each cell (days)
Total demanded retention time (days)
1 20.2 20.2 2 5.65 11.3 3 3.15 9.5 4 2.17 8.7 5 1.65 8.2 6 1.1 7.8 7 1.0 7.6
The retention time of the complete-mix system will approach the retention time of a plug-flow system
by increasing the numbers of ponds (Shilton et al., 2005). It can be observed that the reduction of
necessary retention time is greatest with the first additional ponds. Maturation ponds will also benefit
from multiple pond systems in series. Short-circuiting sewage water may result in large amounts of E.
coli bacteria in the effluent. If another following maturation pond is used, the risk that untreated short-
circuiting water from the first pond, will be part of the water that immediately gets to the outlet in the
second pond, is minimized.
In Christchurch wastewater treatment plant (New Zeeland), two series of 3 ponds each were used after
a biological trickling-filter process for treatment of domestic wastewater. In 2004, the two series were
joined to one train of 7 ponds in total (some rearrangements were done with additional baffles). The
reduction of E. coli bacteria was reduced from an average of 22.400 CFU/100 ml before down to 340
CFU/100 ml after reconstruction. The BOD5 average decreased from 25 to 14 mg/l with the new
arrangement (Masterton District Council, 1999).
Baffles
Baffles are “walls” within a pond that force the water to go through certain patterns. The baffles are
preferably built as a part of the original design. It is however possible to add “retro-fitting” baffles using
plastic-fabric sheeting, anchored in the pond bottom and connected to a floating device at the top.
12
13
4. Activated sludge process technology
Introduction to activated sludge process technology The use of activated sludge systems is a relatively new and modern treatment technology and was not
used to treat municipal wastewater in large scale until the 1950’s in the industrialized part of the world
(Alleman & Prakasam, 1983). A modern treatment facility uses a combination of mechanical, biological
and chemical treatment in order to purify wastewater. The activated sludge basin is the biological
treatment stage in which treatment is achieved by active microorganisms in wastewater. Because the
microorganisms in the activated-sludge basin use oxygen to degrade biodegradable material, the basin
must be supplied with aerators. The aeration consumes a lot of energy which is costly but at the same
time the treatment efficiency is high.
The possible reduction of nitrogen and phosphorous is dependent on which activated sludge system is
used. Figure 4.1 shows a typical arrangement of a primary treatment followed by biological treatment.
Figure 4.1: Typical arrangement of an activated sludge system (printed with permission from Kemira, 2003)
Primary treatment Before the wastewater enters the activated-sludge basin course contaminants are removed by a screen.
The gaps of the screen normally range between 3 and 20 mm in width (Kemira, 2003). The screen is
usually followed by a grit chamber in which heavier contaminants such as sand and gravel sink to the
bottom. Sometimes the grit chamber is combined with aeration to reduce courser particles and to
achieve grease removal. After the grit chamber the remaining settleable material can be collected in a
sedimentation tank.
The mechanical treatment is referred to as a primary treatment and the screen, the grit chamber and
the sedimentation tank together remove around one third of the oxygen demanding particles (BOD)
from wastewater (Kemira, 2003). According to Federal Wastewater Treatment Requirements (United
States) at least 30% of BOD must be removed in the primary treatment in order to meet the
requirements (EPA, 2009).
14
Biological treatment After mechanical treatment, wastewater is normally treated biologically and mechanical treatment is
therefore known as secondary treatment. With the help of micro-organisms, organic contaminants are
broken down to biological sludge. As wastewater contains a wide range of different contaminants there
are also a number of different microorganisms specialized in breaking down specific substances in
wastewater. The most common type of microorganism in wastewater treatment water is bacteria. The
bacteria are naturally occurring in nature and in a biological treatment basin these bacteria are brought
together in large numbers to break down unwanted substances (see chapter 2.3 - Degradation
processes). Apart from bacteria a biological treatment basin should also include other types of
microorganisms which help to improve treatment efficiency. There are for example worm-like organisms
which help to improve treatment efficiency by permeating the sludge and thus facilitate a better flow of
wastewater through the sludge.
Nitrification and denitrification
All wastewater contains nitrogen which is an important nutrient for biological growth. A small part of
the nitrogen is removed during the primary treatment. Most of the nitrogen in wastewater is in the form
of ammonium ( ) which is most easily removed in a biological twostage process called nitrification
and denitrification. This process ensures an effective removal of nitrogen in which nitrogen in form of
ammonium is finally removed from wastewater as nitrogen gas ( ). The first step in this process is
called nitrification and in two separate chemical reactions, autotrophic bacteria use oxygen in order to
convert ammonium into nitrate ( ).
The two chemical reactions can be seen below.
(Eq. 4.1)
(Eq. 4.2)
If reaction (1) and (2) are combined the total chemical equation can be written as:
(Eq. 4.3)
From the first chemical reaction (Eq. 4.1) it can be seen that acid in form of hydrogen ions ( ) is
produced. The hydrogen ions will react with the carbonate in water, if it is available. So if the amount of
carbonate is low, the pH in wastewater could drop and thus inhibit the nitrifying bacteria. If the pH
drops below 5.5 the nitrification process stops completely. But at the same time, the bacteria oxidizing
nitrite into nitrate in formula (Eq. 4.2) prefer a lower pH and so the pH cannot be kept too high.
The nitrification process is also temperature dependent. At lower temperatures, the sludge age has to
be higher in order to achieve nitrification (Figure 4.2).
15
Figure 4.2: Design curve for nitrification (Jansen, n.d)
In Eq. 4.4 below the equation for sludge age is given. The sludge age is the time the average sludge
particle spend in the activated sludge basin before it is removed.
(Eq. 4.4)
where:
SA = sludge age, days
V = volume of activated sludge basin, m3
SSa = average sludge content of aeration basin, kg SS/m3
Qex =excess sludge flow rate, m3
SSex =sludge content of excess sludge, kg SS/m3
Qef = effluent water flow rate
SSef = suspended content of effluent water, kg SS/m3
In the next step microorganisms called facultative anaerobes will reduce the nitrate into nitrogen gas.
This step is referred to as denitrification and it is a process in which bacteria is oxidizing organic matter
without dissolved oxygen. In an activated-sludge system the nitrogen gas is ventilated into the air. The
facultative anaerobes can also utilize oxygen when breaking down organic matter so it is important to
exclude oxygen during the denitrification process. Instead, the bacteria have to utilize oxygen which is
bound up as nitrate or nitrite (Kemira, 2003). The formula for the denitrification process can be seen
below.
(Eq. 4.5)
16
As can be seen in equation 4.5, facultative bacteria need a carbon source (organic matter) for the
denitrification process. Some of the carbon is taken from the wastewater but this is usually only
sufficient for denitrifying 50 % of the nitrogen (Kemira, 2003). If the wastewater does not contain
enough organic content for the denitrification process an external carbon source can be added, for
example in the form of methanol or glycol.
Chemical treatment Chemical treatment is a reliable method for removal of BOD and phosphorous. It can be used in many
parts of the treatment system where mechanical or biological treatment is not considered to be
sufficient. In chemical treatment, a coagulant is mixed with water and suspended flocs develop. The
suspended flocs are removed as sludge by sedimentation, flotation or filtration (Kemira, 2003).
The coagulants used in order to precipitate biological material, nutrients and minerals can be used
directly after the grit chamber in the primary treatment. This will give a reduction of phosphorous of
around 90% and a reduction of organic matter of around 75% (Kemira, 2003). The problem of using
chemical precipitation before the biological treatment stage is that more untreated sludge will be
produced.
Another stage where chemical coagulants can be used is during the biological activated-sludge process.
If a coagulant is added during the activated sludge process the chemical-biological sludge created there
will be removed in the subsequent sedimentation stage. By adding a coagulant in the activated-sludge
basin around 90% of the BOD, 90% of the phosphorous and 25% of the nitrogen will be removed
(Kemira, 2003). Because more sludge is created from the coagulant, the time the sludge spends in the
activated sludge basin (sludge age) will be lowered and the possibility for nitrification is reduced.
In order to maintain an effective nitrification and denitrification process in the activated-sludge basin,
coagulants can be added after the biological step. This will ensure an effective removal of phosphorous
without reducing the biological removal of nitrogen. Around 95% of the phosphorous will be removed
by this method (Kemira, 2003).
17
Activated sludge system – arrangements Practically, the activated sludge system can be arranged in a way which ensures efficient nitrification,
denitrification and organic breakdown of BOD. For example, sludge collected from the subsequent
sedimentation stage is recycled back to the activated-sludge basin in order to achieve a high
concentration of bacteria in the in sludge basin (Figure 4.3).
Figure 4.3. In this activated sludge system, sludge is recirculated back from the sub-sequent pre-settler in
order to achieve a more efficient breakdown of organic matter.
The method of recycling sludge could also serve as an extra carbon source for denitrification. If the first
basin in the activated sludge is kept anoxic, which means that no oxygen is available, the denitrification
bacteria can utilize carbon from incoming wastewater and recycled sludge. The last basins in the
activated sludge are kept aerated in order to achieve nitrification. The nitrate produced during the
nitrification stage is needed for the denitrification process and nitrate from the aerobic basin is
therefore transferred to the anoxic basin together with sludge from the aerobic zone. The amount of
nitrogen removed with this method is dependent on the degree of recirculation. This arrangement for
achieving both nitrification and denitrification with the help of recirculation of nitrate and sludge is
called pre-denitrification and is illustrated schematic by Figure 4.4.
18
Figure 4.4. In this activated-sludge arrangement both nitrification and denitrification are achieved with the
help of recirculation of nitrite and sludge to the anoxic zone. This method is called pre-denitrification.
Another solution for achieving denitrification is called post-denitrification. The wastewater will first
enter an aerobic zone where nitrification and breakdown of BOD occurs. After the aerobic zone
wastewater is transferred to a subsequent anoxic basin. Because the wastewater now contains smaller
amounts of BOD when entering the anoxic zone, an external carbon source is added (usually in the form
of hydrolyzed primary sludge or different kinds of alcohol) (Kemira, 2003). The advantage of this method
is that no recirculation of nitrate is needed. The disadvantage is that an external carbon source in form
of methanol or ethanol is expensive and large amounts may be necessary to add.
Sludge treatment Sludge created from wastewater treatment could easily become a public-health hazard if not handled
properly. What to do with the sludge is today considered as one of the main problems in wastewater
treatment. Still, there are several methods to choose from when selecting arrangements which can
process sludge. A careful selection of the sludge-treatment method has to be made, as costs for
stabilization, dewatering and disposal of sludge may be higher than the operating cost for the activated-
sludge treatment (Hammer, 1986).
In Malaysia facilities for treating sludge are limited and today most of the sludge is treated in sludge
lagoons or dried on large sludge-drying beds. Only in semirural areas are these methods seen as long
term solutions. A more long-term solution for urban areas would be to install digesters and mechanical
dewatering facilities. Then the gas produced from the digestion chamber could be captured and utilized
as fuel.
According to Malaysian standards presented in Sewerage Services Department (1998) a sludge strategy
consists of three main stages:
19
Stage 1 – Preliminary treatment and digestion
Stage 2 – Conditioning and dewatering
Stage 3 – Utilization and disposal
In stage 1, the sludge can be thickened in a centrifuge in order to increase the dry-solids content. After
the sludge has been thickened, it is sent to an aerobic or anaerobic digestion chamber.
In stage 2, the stabilized sludge is dewatered in a filter press and the dry-solids content in the sludge is
raised to more than 25% (Sewerage Services Department (1998). Sludge lagoons or drying beds can also
be used in rural areas.
In stage 3, a sludge tank which can handle sludge for more than 30 days must be provided (Sewerage
Services Department, 1998). The final step is composting or disposal of the sludge. The treated sludge
can for example be utilized as fertilizers on fields.
20
21
5. Previous studies on WSP systems
5.1 Example of computer simulation of WSP geometry
Method
In a test which was executed at Alexandria University, Egypt by Abbas et al. (2006), different
length/width ratios for a WSP were tested in a computer program in order to determine the degradation
of BOD and the amount of dissolved oxygen. In reality, there are always a lot of parameters affecting the
treatment pond which the engineers cannot control, for example temperature variations, amount of
sunlight and wind speed. In the computer model these parameters were set to a constant value.
The influent wastewater had the following characteristics: BOD concentration 300 mg/l, DO
concentration 0.0 mg/l and 150 kg/(ha*day) in surface organic loading rate of BOD. The retention time
was set to 31 days, the inflow was set to 0.18 m3/s and the pond depth to 1.5 meter (Abbas et al., 2006).
The simulation was executed for the four different length/width ratios which can be seen in Figure 5.1
below.
Figure 5.1: Different shapes of the waste stabilization pond simulated in the computer program (printed with
permission from Abbas et al., 2006).
For each shape, simulations were also executed with 2 or 4 baffles. The baffles will change parameters
such as the retention time and the flow path in the waste stabilization pond. In Figure 5.2 an example of
the 4 ponds with 2 baffles can be seen.
22
Figure 5.2: A schematic representation of each shape with two baffles (printed with permission from Abbas et
al., 2006).
Results and conclusions
The effluent amount of BOD5 was calculated for the different length/width ratios L1/L2 =1, 2, 3 and 4. In
the first case, simulations were executed for different length/width ratios with no baffles. The same
procedure was then done for each shape with two and four baffles respectively. In Table 5.1 the values
of BOD5, DO and water velocity can be seen from the simulations.
Table 5.1: The amount of BOD and DO in effluent water (re-drawn from Abbbas et al.,2006)
Without baffles
With two baffles With four baffles
Range of BOD5 concentration found in effluent water (mg/l) 235-252 22-233 13-54
Range DO found in effluent water (mg/l) 0.26-0.51 6.24-9.96 9.57-10.03
Range of minimum water velocity (x 10-3 m/s) 0.002-0.015 0.018-0.91 0.047-0.05
Range of maximum water velocity (x 10-3 m/s) 2.69-3.01 3.19-169 105-765
The analysis of the results shows that the BOD5 reduction increases significantly by introducing two or
four baffles. The best removal efficiency of BOD5 was achieved with four baffles and a value of 4:1 in
length/width ratio. Within each case it was reported that increasing the length/width ratio and
introducing baffles slightly increases the water velocity and DO in the effluent water (Abbas et al., 2006).
23
The conclusion drawn from these data simulations is that a pond should have a length/width ratio of 4:1
and at least two baffles.
5.2 Facultative and maturation ponds in Sri Pulai, Johor Bahru, Malaysia.
Method
An analysis of the performance of a wastewater stabilization pond in Sri Pulai, Johor Bahru was done in
2002. The treatment system uses a primary facultative pond followed by a maturation pond (Ujang et
al., 2002). This is the same pond arrangement as used at UTM. The system in Sri Pulai serves a
population equivalent (PE) of 10.327 from a residential area of approximately 0.7 km2. The ponds
together cover an area of 17.725 m2, with pond volumes of 16.275 m3 for the facultative pond and
10.115 m3 for the maturation pond. The volume of the facultative pond should result in a retention time
of about 30 days. Around 40 % of the incoming water is assumed to origin from infiltrating ground water
(Ujang et al., 2002).
Table 5.2: Average wastewater characteristics at Sri Pulai WSP. The influent results is based on 24 samples,
the results from the effluent facultative pond and the effluent maturation pond is based on 14 respectively 7
samples. (re-drawn from Ujang et al., 2002)
COD (mg O2 / l) SS (g/l) NH4+ (mg/l) NO3
- (mg/l)
Influent
Effluent facultative pond
Effluent maturation pond
Removal in entire pond system
Removal in facultative pond
Removal in maturation pond
446
139
114
74%
69%
18%
146
48
41
72%
67%
15%
23.1
19.7
16.8
27%
15%
15%
1.5
1.6
1.2
20%
- 7%
25%
Results and conclusions
Compared with the effluent standard for Malaysia, the treatment process was not sufficient, since the
total COD concentration of the effluent was on average 114 mg O2/l (see Table 5.2). The Malaysian
effluent standard B is set to 100 mg COD/l (Ujang et al., 2002).
The authors´ conclusion of the unexpected low treatment efficiency (the pond should be able to meet
standard B) could partly be caused by hydraulic short-circuiting. The low treatment efficiency could also
be caused by the specific growth rates of biological degrading bacteria not being so temperature
dependent as expected. The authors recommended aeration and installation of baffles to improve the
treatment.
24
5.3 Previous Study on the studied treatment pond at UTM In year 1999, an under-graduate report was produced by Zahari and Zain (Faculty of Civil Engineering,
UTM) analyzing the same WSP at UTM. The report is written in Malay language, and our focus has been
on the wastewater composition data found in this report. The measurements have been conducted
without flow measurements, hence, the results only represent average values, that is the values were
not weighted against the influent water flow. When the waterflow into the treatment pond is high, it is
likely that more BOD, COD and TSS will end up in the pond, and this is not considered in the report. The
results from Zahari and Zain can be found in appendix A.
25
6. Study Area
6.1 Climate Johor Bahru lies in a tropical region very close to the equatorial line with temperatures ranging between
21 to 32°C all year around. The climate is humid with an average relative humidity around 90%
(Richmond et al., 2007). The precipitation comes in form of short but heavy rain showers and the
average rainfall in Johur Bahru is around 2400 mm each year (World Meteorological organization, n.d.).
The rainiest periods are from March to May when Johor Bahru is influenced by the southwest monsoon
and November to December when the northeast monsoon arrives.
As Johor Bahru lies in a region with a typical tropical climate with heavy thunderstorms, the storm water
is usually not connected to the wastewater treatment systems. This is also the case at UTM where the
storm water is led through channels and ditches directly to the local rivers.
6.2 The wastewater treatment facilities at UTM Within the Universiti Teknologi Malaysia, two waste stabilization pond facilities and two mechanical-
biological treatment plants are in operation. The pond system this report will focus on is located south-
west of the UTM campus area (see Figure 6.1) and it is treating the wastewater from the western part of
the catchment area in UTM (see Appendix D). These WSP:s were built in 1985. The mechanical-biological
treatment plants were built later, as the university expanded.
Figure 6.1: Map over the UTM campus area with (1) The WSP studied in this report (2) another WSP within
UTM; (3) biological-mechanical treatment plant; (Another campus area and treatment plant is located in the
north-east, outside the map.)
26
The treatment system that this report will focus on consists of two parallel lines of facultative ponds
followed by maturation ponds (Figure 6.2). The available documents do not tell for how many persons
the ponds are dimensioned for, but according to the contractor for de-sludging operation, this pond
system was built to serve approximately a P.E. of around 8000. The pond system is a simple
construction, where the influent wastewater is divided in a chamber before it enters each treatment line
through pipes located under the water surface. The ponds have no screening and objects of many
different sizes have been seen floating in the pond. These objects have a tendency to clog the cannels
between the ponds. Since the water level of the receiving river is higher than the effluent level, a
pumping station is located between the pond and the river. The pumps are currently working
discontinuously, and during the time when the pumps are not pumping, the ponds accumulate
wastewater beyond the designed water levels. The technical data of the pond system can be found in
Appendix G.
Figure 6.2: Shape of pond system with facultative ponds (1) followed by maturation ponds (2).
6.3 Recipient
Introduction
The effluent from the WSP is released into a stream passing through the UTM area (Figure 6.3). The
stream transforms into two small lakes a few hundred meters downstream, where the main entrance to
UTM is located (see Figure 6.4). In these small lakes, canoeing activities take place which demands good
water quality. The part of water that origins from the WSP is large compared to the upstream river
water. Most of the water in the lakes is therefore considered mainly to be effluent water from the WSP.
27
Figure 6.3: The receiving river. Upstream (left) and downstream (right) of WSP.
Method
Composite samples were collected consisting of 3 samples upstream and 3 samples downstream the
WSP on the 14th of January 2010. The samples were analyzed for COD and TSS according to the
procedures described in chapter 7. The points where the three composite samples upstream and
downstream were collected can be seen in 6.4.
28
Figure 6.4: Map over recipient with upstream collection points (1) and downstream collection points (2)
Results and discussion
Figure 6.5: The water quality upstream and downstream of WSP on the 14th
of January 2010.
As expected, the COD and TSS levels are significantly higher downstream of the WSP (Figure 6.5). The
stream has not received any effluent from any kind of treatment facility before passing the WSP. The
initial COD may origin from pollution caused by living organisms such as fishes, birds and algae.
0
10
20
30
40
50
60
Upstream Downstream
mg/
l
COD
TSS
29
The high TSS increase downstream may be the result of the treated wastewater, but also from high
concentration of algae and bottom sediments stirred up in the stream.
Due to limitations in time and the cost for COD reagents, focus has been set on influent and effluent
water. These values are single analyses of composite samples and should only be considered to give an
indication of the changes of pollution levels in the river.
30
31
7. Sampling and analysis methods
Sampling and flow measurements The sampling procedure included filling plastic containers (each about 1 liter of volume) with sample
water from the influent chamber and one container with water from the effluent channel. The samples
were immediately transported to the laboratory where they were stored in a cooling room
(temperature between 10-13 °C).The following day the analyses of BOD and COD was started. TSS
analyses were usually carried out a few days after the sampling. The procedure for flow measurements
is described in Chapter 9.
COD COD analyses have been undertaken with Hach standard procedure for colorimetric determination. The
Hach reagents used were capable of “high range” (0-1500 mg COD/l). The digestions of the reagents
were done in a Hach DRB 200 for 2 hours at 150 °C (see Figure 7.1). The analysis has been done with
single samples.
The reading of the reagents was done in a Hach DR/4000 and a Hach DR/5000 (see Figure 7.1). The
average values from both machines were calculated.
Figure 7.1: Hach DRB 200 Digestor for reagents (left) and Hach DR/5000 for colorimetric
determination (right).
If the reading showed unexpected low or high values for a specific sample, a new analysis on that
sample was done the following day. If the new analysis gave the same result, the average of these values
was used. If another value, that was in the same range as the other samples from that measuring event,
was measured, that value was used instead.
32
BOD5 Influent samples from the 5-6 Nov were successfully analyzed by the incubator method. The effluent
samples from that day were analyzed by the manual method due to lack of available space in the
incubator. Samples from the other testing events failed due to technical problems, or are not used as
they are considered unreliable.
Incubator method
BOD analyzes were carried out using a BOD incubator (Hach, model 205) which is especially designed for
BOD tests. The sampling bottles are connected with a tube (for oxygen measurements) and put in a
compartment that keeps the temperature at 20 °C. A computer records the oxygen consumption over
time. The procedure was performed according to the product manual. One benefit of the BOD incubator
is that it allows reading of the oxygen consumption (BOD) continuously (instead of only a final
measurement after 5 days as the “manual” procedure described above). For calculations of the k-value
(Appendix E) readings were recorded with 0.5 days intervals (Appendix F).
One full testing event with the BOD incubator was successful. Other testing events failed due to
technical problems with the BOD incubator or lack of available storage space in the equipment.
Manual method
The “manual” measuring of BOD5 is done with the following procedure:
- Filing 300 ml airtight bottles with diluted wastewater (The purpose of diluting the samples was
to reach a DO above 7 mg O2 / liter, which may be necessary for a successful BOD reading after 5
days, as the DO must be above 2 mg O2 / liter at final reading. Dilution 1:1 with distilled water
was enough for this purpose).
- Measuring the initial DO level in the samples with a DO meter.
- Storing the bottles in a refrigerator at 20 °C for 5 days.
- Measuring the final DO with a DO meter.
The BOD5 was calculated as the decrease of DO per liter of water.
This method was considered as slightly unreliable as the reading of the DO meters was difficult. The DO
measured DO concentration was not stable over time, hence making it difficult to predict the final DO.
33
Total Suspended Solids
TSS analyses were made by filtering 100 ml of sampling through a microfilter (Whatman, GF/C glasfaser
microfilter). In order to force the sampling water through the filter, an air compressor was used to
create low pressure in the bottle receiving the filtered water (see Figure 7.2). The filters were measured
before and after filtering. To eliminate the weight contribution of water, the filters were dried in an
oven at around 110°C for one hour after filtering, but before final measuring.
Figure 7.2: Sample water was filled in the upper glass container. The air compressor (right in the picture)
created under pressure in the receiving container (containing filtered water in the picture).
34
35
8. Performance of the existing WSP
8.1 Method Effluent samples were collected every two hours at the pond outlet. Since the variation of effluent
quality does not change drastically, composite samples were created where each composite sample was
created from three effluent samples under a 6 hour period. This was done in order to reduce work and
costs in the laboratory. The analysis procedures are described in chapter 7.
8.2 Results and discussion
De-sludging conditions
The treatment efficiency is dependent on the sludge, since the sludge contains bacteria that degrade
pollutants in the wastewater. If the sludge has been removed recently, the system may operate
ineffectively due to the lack of bacteria. If however, the sludge has accumulated for a long period, the
volume of the sludge will reduce the HRT in the pond system, hence making the treatment less effective.
One can assume that the best treatment occurs somewhere in the middle between the de-sludging
operations.
The WSP (north treatment line) was de-sludged after the first measurements were done on the 5-6
November 2009. During de-sludging one treatment line at a time is closed down. The wastewater is
pumped out and the accumulated sludge from the bottom of the ponds is removed. The de-sludging
operation takes a few weeks to be completed and is done with 10 year intervals. On the 9-10 January
2010, the WSP had been in operation, after de-sludging, for about 2 weeks when the samples were
collected. The average effluent COD was 64 mg/l before and 58 mg/l after de-sludging (see Figure 8.1
and 8.2). The average BOD5 for 5-6 November was 39 mg/l BOD5 on average (Figure 8.1).
Since the samples were collected just before and after de-sludging, the results presented above may be
slightly higher than during most of the operation time. Zahari & Zain (1999) showed in their report an
average effluent of 40 mg/l COD (see Appendix A) which is approximately 30% better than the results in
this report. This could be due to the sludge conditions discussed above.
BOD5 and COD in effluent from WSP
The quality of the effluent water is relatively stable (see Figure 8.1 and 8.2). Variations may depend on
sunlight that changes the concentrations of algae in the surface layer. Another factor to consider is the
effluent pump that is working discontinuously.
36
Figure 8.1: BOD5 and COD in effluent from the northern treatment line on the 5-6 November 2009 (before
de-sludging).
Figure 8.2: COD in effluent from the northern treatment line on the 9-10 January 2010 (after de-sludging).
TSS in effluent
The TSS levels are higher and show a different pattern after the de-sludging was carried out. The
average TSS on the 5-6 November was 37 mg/l (Figure 8.3), but 22 mg/l on the 9-10 January (Figure 8.4).
The reason for lower TSS values after de-sludging may be caused by many reasons. One reason is the
fact that if the ponds had high levels of sludge, the volume of water in the ponds decreased, hence
creating less retention time and higher water flow, which disturbs the settling process. If the sludge
reaches a high level from the bottom of the pond, the distance between the top sludge layer and outlet
0
10
20
30
40
50
60
70
80
17-21.40 23-03 05-09 11-13
mg/
l
Time
COD
BOD5
0
10
20
30
40
50
60
70
80
12-16 18-22 00-04 06-10
CO
D (
mg/
l)
Time
37
channel gets narrower and more solid particles may get stirred up. The algae population may not have
developed entirely after the de-sludging, and since algae contribute to the effluent TSS values, it could
be another possible explanation.
For the composite value analyzed on the 9-10 Jan, between 00-04, it can be seen that it is significantly
lower than the other values from this date (Figure 8.4). One possible reason could be that a pump
station is located just after the outlet where the effluent samples were taken. The pumps are working
discontinuously and start when the water reaches a specific height. When the pumps start operating,
the effluent water flow increases drastically. This causes differences in the water quality and the
measured changes of effluent quality over time may therefore have been influenced by the unknown
pumping pattern.
Figure 8.3: Total Suspended Solids (TSS) in the effluent on the 5-6 November 2009.
0
5
10
15
20
25
30
35
40
45
50
17-21.40 23-03 05-09 11-13
TSS
(mg/
l)
Time
38
Figure 8.4: Total Suspended Solids (TSS) in the effluent on the 9-10 January 2010.
Average effluent values
The average weighted effluent from 5-6 Nov, 9-10 Jan and average values from Zahari & Zain (1999) give
the total average values seen in table 8.1. The values from the report by Zahari & Zain (1999) may
represent “better” sludge conditions in the pond, hence lowering the average level of pollutants (data is
available in Appendix A).
Table 8.1: Effluent average values.
BOD5 (mg/l) COD (mg/l) TSS (mg/l)
5-6 November 39 64 37 9-10 January 29 58 22 Zairi & Zain (1999) 16 40 13
Average 28 54 24
Algae in effluent
Algae are present in the effluent and are known to contribute to the effluent COD and BOD. The water
showed clear signs of microalgae in every effluent sample analyzed. In order to understand the
contribution of particles to the effluent COD, one test was carried out with filtered and unfiltered
composite effluent water from 9-10 January 2010 (see Figure 8.5).
0
5
10
15
20
25
30
35
40
45
50
12-16 18-22 00-04 06-10
TSS
(mg/
l)
Time
39
Figure 8.5: Unfiltered and filtered composite effluent water (from all 12 samples 9-10 Jan 2010).
The unfiltered effluent had a COD level of 57 mg/l and the same filtered effluent 27 mg/l. The difference
between unfiltered and filtered (suspended COD) made therefore up 30 mg/l COD. Since it has been
observed that the quantity of algae in the effluent is prominent, algae are assumed to contribute to a
major part of the 30 mg/l COD difference.
Reduction in pond system
In Tables 8.2 and 8.3 below the reduction of average COD and average TSS from the samplings made on
the 5-6 November, 2009 and on the 9-10 January, 2010 is shown.
Table 8.2: Influent (weighted COD average, see chapter 10.2) and Effluent COD values.
Date Influent COD (mg/l) Effluent COD (mg/l) Reduction
5-6 Nov, 2009 122 64 48%
9-10 Jan, 2010 113 58 49%
Table 8.3: Influent (weighted TSS average, see chapter 10.2) and Effluent TSS values.
Date Influent TSS (mg/l) Effluent TSS (mg/l) Reduction
5-6 Nov, 2009 63 37 41%
9-10 Jan, 2010 47 22 53%
0
10
20
30
40
50
60
Unfiltered effluent
Filtered effluent
mg/
l
40
41
9. Wastewater flow
9.1 Survey of wastewater producers at UTM campus
Method
Construction drawings over the area were used to identify the sewage pipes connected to the WSP. The
chief engineer at UTM helped to identify the outer borders of the catchment. The amounts of students
and staff living and studying/working within the catchment were identified by consulting housing and
university offices. Some assumptions have been made where no information could be found about the
number of people living and working in buildings connected to the treatment pond (for more
information of the estimation of P.E., see Appendix B).
The number of students and staff working within the faculties at UTM were given a P.E. of 0.2 instead of
1 (Guidelines for developers) as they do not consume as much water at the faculties as they would have
done at home, thus lowering the PE value.
Outside UTM campus there are private family houses where the sewerpipes are connected to the
studied treatment pond. The number of people living in each household is not exactly known so it was
estimated that each household consists of 5 family members.
Other buildings connected to the treatment pond where no information of the number of residents
could be given were the UTM Main Office and the Mosque. The number of staff in the UTM Main Office
was assumed to be 500 and the number of people visiting the Mosque could be up to 3000 people. The
P.E. for the people working and visiting the buildings was set to 0.2 in both cases (Guidelines for
developers).
The water consumption for UTM’s students is based on a value collected from a report by Katimon and
Demun (2004). The report concludes that the average water consumption for UTM is 260
litres/(person*day). This value is higher than the average value of 208 liter/(person*day) for the rest of
Malaysia (Ithnin, 2007).
The reason for the higher consumption according to our proposition could be:
1. Students and staff at UTM have a more water consuming behavior, such as more showering and more
use of laundry facilities.
2. Leakage of fresh water from delivery pipes.
A third proposition by Katimon and Demun (2004) for the higher water consumption at UTM is:
3. Water intensive faculties at UTM, such as the Environmental Engineering Laboratory and Marine
Engineering Laboratory, consume large quantities of water.
42
When estimating the water consumption behavior of UTM the value from Katimon and Demun (2004) of
260 litres/(person*day) is initially used. The water consumption and waste water production is normally
of equal amount if no irrigation occurs. At UTM it was observed that washing machines, cooking
facilities and students’ laundry in some cases were not connected to the sewer network so the final
waste water production behavior of UTM will be lower than 260 litres/(person*day).
Results and discussion
The pond receives wastewater from around 10.500 persons according to the survey (see Appendix B).
No factories or other similar activities are present within the catchment. Hence, the wastewater is pure
domestic.
If the value of 260 litres/(person*day) from Katimon and Demun (2004) is used the wastewater flow into
the pond can be calculated:
(Eq. 9.1)
However, all the freshwater consumed will not end up as wastewater due to losses. For example, it has
been observed that the public dinner facilities do not drain their kitchen wastewater into the sewer
system, but into the storm water channels. These facilities support the majority of the students with
food since students usually do not have access to kitchens.
It has also been observed that washing machines for the students’ laundry in some cases are connected
to the storm water drain. Washing machines generally consumes much water and therefore some losses
also from laundry take place.
According to the household water consumption in Sweden around 20 percent of the total water
consumption is used for cooking and laundry. If the same value is applied to Malaysian circumstances
the consumed fresh water going into the sewer system at UTM will be:
(Eq. 9.2)
or if calculating water consumption per capita at UTM:
(Eq. 9.3)
The value of will be used in Chapter 9 when estimating the infiltration of
water into the sewer pipes.
43
9.2 Flow measurements
Method
The inlet water velocity has been measured during three 24h-events. Water speed was measured with a
current meter (model SWOFFER 2100) in one of the two inlet concrete chambers (see Figure 9.1 for
point of measurement) every two hours. The propeller was placed so that it measured the water
velocity in the centre of the inlet pipe.
Figure 9.1. The flow measurements were made in a concrete chamber illustrated from above in the drawing.
Before the wastewater is sent to the two different treatment lines, the waterflow is split in the water divider
chamber. The pipes seen in the figure are placed beneath the surface and have a diameter of 18 inches (45.7
cm) each.
The diameter of the two inlet pipes is 18 inches (45.7 cm). The water velocity was measured at a point
where the pipe ends and releases the water into the inlet chamber. If one assumes that the measured
water velocity is the average water velocity in the pipe, the flow can be calculated by equation 9.4:
Q (Flow of wastewater) (m3/s) = Area of pipe (m2) * Water velocity (m/s) (Eq. 9.4)
Calculations of the flow are done on two hours basis. This means that the flow measured at one event is
assumed to be valid for two hours (3600 seconds). Since the measurements on the 5-6 November are
not complete (9 measurements instead of 12 due to technical problem), the first three flow values from
17:30 to 22:00 on the 5th of November is estimated with “designed” values. The designed values are
designed similar to the flow measurements made on the 18-19 November where rain occurred in the
afternoon around the same time as on 5-6 November (see Figure 9.5 on page 48).
44
In the case 5-6 November the following equations below are used:
(Eq. 9.5)
(rain-peak-flow at 14:15 is excluded) (Eq. 9.6)
In the case 18-19 November the following equations below are used:
(Eq. 9.7)
(rain-peak-flow at 16:15 is excluded) (Eq. 9.8)
In the equations, Q is the measured flow values from each sample day. In the data from 5-6 November
the total water flow is also calculated without the rain-peak- flow at 14:15 with Eq. 9.6. The same
procedure is made with the data from 18-19 November where the total water flow is calculated without
the rain-peak- flow at 16:15 with Eq. 9.7. This is made in order to estimate the amount of infiltrating
water into the sewer pipes (see Chapter 10).
Results
Measurements 5-6 Nov 2009
“Thursday-Friday under school period”
The first measurements were made from the 5th of November to the 6th of November. This was the week
before the examination week. During this period no lectures at the university were held and most
students were assumed to stay at home at campus. The sampling period started at 17:30 on the 5th of
November but unfortunately there were no flow measurements made from the first three sample
occasions that day due to technical problems. The first flow measurement started at 23:00 which can be
seen in Figure 9.2 below. The flow decreased at night and increased slightly in the morning. From 13:00
to 16:00 a rainstorm started which can be seen in Figure 9.2 in the precipitation data from UTM’s own
rain gauge. In connection to the rainstorm there was a significant increase of the flow.
45
Figure 9.2: Above: The water velocity in the inlet chamber for the northern treatment line of the WSP system
during 5-6 November. Below: Precipitation data at site (UTM weather station data)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
23:00 01:00 03:00 05:00 07:00 09:00 11:00 13:00 14:15
Ve
loci
ty (
m/s
)
Time
0
5
10
15
20
23 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Pre
cip
itat
ion
(m
m/h
)
Time
46
Measurements 18-19 November 2009
“Holiday period”
The second measurement period was from the 18th to the 19th of November. During this period it is
estimated that approximately two third of the population had left the UTM campus for vacation. The
monsoon had arrived and there was rainfall almost every day from the beginning of November to the
beginning of January. The measurements started at 12:30 on the 18th of November and continued every
second hour until 10:00 the next day. A rainstorm started at around 15:00 on the 18th of November and
continued more than one hour. During this period there is a huge increase in the influent flow. When
the rain stops the influent flow decreasing rapidly. The flow continues decreasing until late night and
starts increasing in the morning. The behavior of the influent flow and precipitation data can be seen in
Figure 9.3 below. During this measurement, only one line of the WSP was in operation, hence the
velocity is the double compared to the flow measurements from 5-6 November.
Figure 9.3 (above): The water velocity in the inlet chamber for the southern treatment line of the WSP during
18-19 November 2009. Below: Precipitation data at site (UTM weather station data).
0
0.2
0.4
0.6
0.8
1
1.2
1.4
12:30 14:00 16:00 18:00 20:00 22:00 00:00 02:00 04:00 06:00 08:00 10:00
Ve
loci
ty (
m/s
)
Time
0
5
10
15
20
25
30
35
12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8 9 10
Pre
cip
itat
ion
(m
m/h
)
Time
47
Measurements 9-10 January 2010
Weekend
The last flow measurements were made from the 9th of January to the 10th of January 2010, during the
weekend from Saturday to Sunday. The first measurements started at 12:00 a.m. on the 9th of January
and continued every second hour to 10:00 a.m. on the 10th of January. This was the first flow
measurement period with no rain and thus no significant flow peak connected to a rain event. From the
afternoon on the 9th of January the flow decreases gradually and in the evening the flow goes up
distinctly. The influent flow reaches a maximum at 20:00 and goes thereafter down during the night.
During the morning on the 10th of January the flow increases again. The behavior of the flow
characteristics from this period can be seen in Figure 9.4 below.
Figure 9.4: The water velocity in the inlet chamber for northern treatment line of the WSP system 9-10
January 2010. No rainfall occurred during the measurements 9-10 January 2010.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
12:00 14:00 16:00 18:00 20:00 22:00 00:00 02:00 04:00 06:00 08:00 10:00
Ve
loci
ty (
m/s
)
Time
48
Water flow
Figure 9.5: The inlet wastewater flow to the WSP system. The designed flow is made to fill the gap between
the measurements during 5-6 Nov.
* On the 5-6 of November and 9-10 of January, the total flow is assumed to be twice the flow in one
inlet, since there are two inlets with equal amounts of water.
* On the 18-19 of November, there was only one line and one chamber in use. However, some leakage
to the closed line occurred except at the last measurement at 10 a.m., when workers managed to stop
the leakage. The leakage was measured to 9 l/s and is considered when calculating the flow from 18-19
November.
Total flow
The total inflow for 5-6 November has been calculated with Eq. 9.5 where the peak-flow during the rain
is included and Eq. 9.6 where the peak-flow during the rain is excluded. The total inflow for 18-19
November has been calculated with Eq.9.7 where the peak-flow during the rain is included and Eq. 9.8
where the peak-flow during the rain is excluded. The total inflow for 9-10 January has been calculated
with Eq. 9.5 and since there was no precipitation during this measuring period no rain peaks have been
considered. Average inflow quantity to the pond each day will be based on Qtot with rain from 5-6
November, 18-19 November and Qtot without rain from 9-10 January. The results can be seen in Table
9.1.
0
0.05
0.1
0.15
0.2
Wat
er
Flo
w (
m3
/s)
designed flow 5-6 Nov5 Nov (Thursday)
6 Nov (Friday)
18-19 Nov (holiday)
9-10 Jan (weekend)
49
Table 9.1: Calculated total influent waterflow into the pondsystem for one day. *Partly using designed values.
** Rainfall peaks excluded (on the 5-6 November designed values are used).
Date
Qtot
With rain
(m3/day)
Qtot
Without rain
(m3/day)
Q max
(m3/s)
Q min
(m3/s)
Q Average
With rain
(m3/s)
Q Average
Without rain
(m3/s)
5-6 Nov
18-19 Nov
9-10 Jan
6346*
7527
No rainfall
5428**
6617**
5526
0.190
0.203
0.085
0.039
0.059
0.049
0.073*
0.087
No rainfall
0.058**
0.077**
0.064
Discussion
It is obvious that the rain influences the wastewater flow significantly. It can be seen on the velocity
measurements that soon after the rainfall occur, the flow speed increases rapidly. As the rainfall ends,
the flow tends to go down quickly. On the 18-19 of November, most students left UTM for holiday.
Approximately one half to two thirds of all students were not at the University during these
measurements. Despite this, both Qmax and Qmin were higher during the holiday than during the school
period. This could be explained by that the monsoon period started just after the measurements on the
5-6 November, but before the 18th of November. More or less every day received heavy rainfalls which
could have raised the groundwater level, thus creating more infiltration into the sewer system (see
chapter 10).
50
51
10. Infiltration High infiltration of groundwater into the sewer pipes is a common problem. Sewers may leak
wastewater out of the pipes or infiltrate groundwater into the sewer pipes, depending on the
surrounding soil water content. It has been observed during our measurements that there is a flow of
wastewater even in late night or early morning time even during vacation periods. The wastewater flow
drastically increases during rain events, and the wastewater strength is weak (diluted). This is clear
evidence of infiltration into the pipes. The extra infiltrating water is mostly unwanted since it demands
bigger tanks, or ponds, and to some degree will make the treatment less effective. However, one benefit
is that since the water is already diluted, it may be easier to meet the requirements for discharging the
water.
Three different approaches have been used to find the amounts of infiltrating water.
10.1 Calculations Method 1: Estimation of domestic water consumption If one assumes that the average contribution of wastewater per capita is 208 l/day, and the number of
people is known to be 10.500, the infiltration may be calculated (see Table 10.1).
Table 10.1: Estimation of infiltrating water, taking total water flow and assumed domestic water
consumption into consideration. **Assumes all inhabitants present. *Assumes only 1/3 of students and staff
present due to holiday.
Date Measured total
inlet water during
24h (m3)
Assumed
Domestic water
consumption (m3)
Infiltration (Total
– Domestic)
(m3)
Amount of
infiltration in
pipes
5 – 6 Nov 6346 2184** 4162 66%
18 – 19 Nov 7527 728* 6799 90%
9 – 10 Jan 5526 2184** 3342 60%
Method 2: Calculating base flow and rain peaks
The lowest flow measured during night times is considered as base flow. At this time (lowest flow
usually occurred between 04:00 a.m. and 06:00 a.m.) the water is considered to be purely infiltrated
water. The contribution from rainfall has been excluded according to Eq. 9.5 and Eq. 9.6 respectively.
52
Table 10.2: Calculations of infiltration by using baseflow and peak flow.
Date Measured total
inlet water during
24h (m3)
Total inlet water
without base-flow
and rain peak
(m3)
Infiltration
(Base
flow+Rainpeak)
(m3)
Amount of
infiltration in
pipes
5 – 6 Nov 6346 2028 4318 68%
18 – 19 Nov 7527 1559 5968 79%
9 – 10 Jan 5526 1275 4251 77%
Method 3: Calculating the COD dilution in wastewater
The load per capita is assumed to be 120 g COD per day (Kemira, 2004). With assumed fresh water
consumption it is possible to estimate the theoretical concentration of COD in the wastewater.
(eq. 10.1)
Since the concentration of COD in the measured samples is lower than the theoretical value, one
explanation may be infiltrating water. This model assumes that the infiltrating water is clean and does
not contribute with any pollution.
Table 10.3: Amount of infiltrating water through theoretical dilution of COD concentration.
Date Average
weighted COD in
inlet (mg/l)
Theoretical COD
(mg/l)
Amounts of
infiltration in pipes
5 – 6 Nov 122 577 79%
18 – 19 Nov 112 577 81%
9 – 10 Jan 113 577 80%
10.2 Discussion and conclusion The methods in chapter 10.1 show that infiltration and possible misconnections with storm water
channels contributes with 60-90% of the total incoming water to the WSP. Since the storm water
channels are built to receive all the storm water, no additional water should enter the sewage network.
If the infiltrated water could be reduced, the HRT in the WSP would increase, hence improving the
treatment efficiency. An unavoidable effect of reducing the infiltration is the increase in concentrations
of pollutants in the wastewater. These both aspects must be considered against each other.
53
11. Influent wastewater quality
11.1 Method The influent water was collected every two hours during the measurement periods. Samples were
withdrawn from the inlet chamber and immediately taken to the laboratory and stored in a refrigerator.
The first sampling started 5th November at 17:30 and continued every second hour until 14:15 the next
day. The second sampling started at 12:30 a.m. on the 18th of November and continued every second
hour until 10:00 a.m. the next day. The third sampling started at 12:00 a.m. on the 9th of January and
continued every second hour to 10:00 a.m. the 10th of January.
From all these samplings days COD, BOD5 and TSS were analyzed according to the methods described in
chapter 7. From the samples 5-6 November k-values were analyzed. Since the measurements during 5-6
November lacks flow data between 17:30 and 22:00, a designed imaginary flow was created and used in
order to get complete measuring data and to calculate weighted parameters (see Figure 9.5). For more
information about how the imaginary designed curve was created see Chapter 9.
11.2 Results and discussion
BOD5 and COD The inlet COD concentrations show a tendency to follow the typical pattern where the concentration
rises when people use water consuming facilities at most, usually in the morning and late afternoon.
When water flow increases due to rainfall, the COD values peaks and reaches levels much higher than
during normal flow. At late night or early morning (04:00-06:00) all three sampling periods reach their
lowest values (12 mg/l – 33 mg/l) (Figure 11.1). The pattern of COD concentrations is lower during the
holiday period, which is explained by the lower load due to absence of students in combination with
infiltration. According to Mara (2003), a COD concentration of less than 400 mg/l is considered as “weak
strength”. This water is therefore placed into this category.
From the first sampling period 5-6 November, BOD5 from all 12 measurements were analyzed. For all 12
measurements that period, COD was also analyzed. This was done in order to get a ratio between BOD5
and COD for the wastewater entering the pond. In Figure 11.2 below COD and BOD5-values have been
plotted.
54
Figure 11.1: The inlet COD during three 24-hours measurements.
Figure 11.2: BOD5 and COD values in inlet to the WSP during 5-6 November 2009.
0
50
100
150
200
250
17:00 19:00 22:00 23:00 01:00 03:00 05:00 07:00 09:00 11:00 13:00 14:15
mg/
l
Time
BOD5
COD
55
Ratio BOD5/COD in Inlet
By using the samples from the 5-6 November, the average ratio between the BOD5 and COD values are
0.5 (see Table 11.1 below). This value will be used to estimate BOD5 when only COD values are available.
Table 11.1: Measured BOD5 and COD on the 5-6 Nov 2009. Relationship BOD5/COD is
calculated from average values.
Time:
COD (mg/l) BOD5 (mg/l) Ratio BOD5/COD
17:00
120
58 0.48
19:00
77
35 0.45
22:00
62
36 0.58
23:00
79
41 0.52
01:00
72
54 0.75
03:00
48
29 0.60
05:00
23
26 1.13
07:00
46
39 0.85
09:00
126
76 0.60
11:00
222
63 0.28
13:00
148
66 0.45
14:15
195
89 0.46
Average: 102
51
Ratio = 0.5
56
Total Suspended Solids
Figure 11.3: Above: TSS concentrations from all three measurements periods from influent wastewater to the
WSP. Below: Rain data collected from UTMs weather station. It can be observed that the TSS on the 5-6
November and 18-19 November are directly affected by the precipitation.
The TSS trend tends to be highly affected by rainfall (see Figure 11.3). The peak at 08:00 on the 9-10 Jan
is not related to any rainfall and the cause is unknown. The cause is unknown but the same sample
showed an unusual high COD-value as well the TSS result is considered as valid.
0
50
100
150
200
250
12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8 9 10 11
TSS
(mg
/ l)
Time
5-6 Nov
18-19 Nov
9-10 Jan
0
5
10
15
20
25
30
35
12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8 9 10 11
Pre
cip
itat
ion
(m
m/h
)
5-6 Nov
18-19 Nov
57
Dimensioning values
TSS
For all 12 wastewater samples collected on 5-6 November 2009, 18-19 November 2009 and 9-10
January the maximum and minimum TSS-value has been tabulated in Table 11.2 below. From the flow
data collected an average weighted TSS value and total load per day has been calculated.
Table 11.2: Measured TSS-values on 5-6 November 2009, 18-19 November 2009 and 9-10 January
2010.
* Partly based on designed flow
Maximum (mg/l)
Minimum (mg/l)
Weighted average (mg/l)
Total load per day (kg)
5-6 Nov 18-19 Nov 9-10 Jan Average value
150 210 193
11 1 2
63* 52 47 54
401* 389 261 350
COD
For all 12 wastewater samples collected on 5-6 November 2009, 18-19 November 2009 and 9-10
January the maximum and minimum TSS-value has been tabulated in Table 11.3 below. From the flow
data collected an average weighted COD value and total load per day has been calculated.
Table 11.3: Measured COD on 5-6 November 2009, 18-19 November 2009 and on 9-10 January 2010.
*Partly based on designed flow
Maximum (mg/l) Minimum (mg/l) Weighted average (mg/l)
Total load per day (kg)
5-6 Nov 18-19 Nov 9-10 Jan Average value
222 381 390
23 12 23
122* 112 113 116
775* 841 626 747
BOD5
For all 12 wastewater samples collected on 5-6 November the maximum and minimum BOD5-values has
been tabulated below. Because there is no data for BOD5 on 9-10 November 2009 and on 9-10 January
2010 the BOD5 from these measurements are estimated by using the BOD5/COD-ratio from 5-6
November 2009. From the flow data collected an average weighted BOD5 value has been calculated in
order to calculate the total BOD5 load per day. The values can be seen in Table 11.4 on the next page.
58
Table 11.4: Measured BOD5 on 5-6 Nov 2009 and estimated BOD5 on 18-19 Nov 2009 and 9-10 Jan 2010.
* Partly based on designed flow
** Based on estimated BOD5-value
Maximum (mg/l) Minimum (mg/l) Weighted average (mg/l)
Total load per day (kg)
5-6 Nov 18-19 Nov 9-10 Jan Average
89 191** 195**
26 6** 12**
59* 56** 57** 57
371* 421** 314** 369
Degradation speed of BOD
K-value used in this report indicates the speed of the BOD degradation. The k-value, in this report used
for degradation of BOD, is calculated by the increase of oxygen consumption over time. Results of the k-
value are listed in Table 11.5 below. The k-value data can be found in Appendix F. For more information
about the k-value see Appendix E.
Table 11.5: k20-values calculated with Thomas method;
Influent wastewater from 5-6 November 2009.
Time: k-value (d-1)
17:00 19:00 22:00 23:00 01:00 03:00 05:00 07:00 09:00 11:00 13:00 14:15
0.235 0.144 0.254 0.282 0.256 0.294 0.179 0.289 0.274 0.190 0.255 0.222
Average k-value (d-1)
0.24
59
12. Proposals for upgrading of the treatment system
Alternative 1: Upgrading of existing WSP
Introduction
The existing WSP has advantages since it does not consume any energy and the required maintenance is
low. With some, relatively inexpensive adjustments the pond system could operate more efficiently.
Proposed new design
Installing screening device
Rearranging the water flow
Installing baffles in two ponds
Figure 12.1: Overview over current pond arrangement (left) and upgraded alternative 1 (right).
The purpose of rearranging the water flow to one long train of 4 ponds, instead of two parallel lines with
two ponds in each (Figure 12.1), is both theoretically and practically motivated. The theoretical benefit is
due to the enhanced plug-flow behavior of water when more ponds are used after each other (see
chapter 3.5 and 2.3 - Disinfection). The practical evidence was seen in Christchurch (NZ), where a similar
rearrangement was done and significant reduction of pathogens, BOD and TSS (Masterton District
Council, 2009) took place. The benefits of installing baffles are discussed in chapter 5.1.
60
Screening device
The task of the screening device is to separate larger particles from the wastewater and protect the
following treatment steps. The treatment ponds today have no screening device and large floating
objects have been seen in the pond. Except from being an unpleasant sight at the pond (and especially
in the receiving river) the larger objects have been observed to clog channels.
According to the Sewerage Services Department (1998) the screening device should have a maximum
clear spacing of 25 mm and be automatically raked, since it serves over 10.000 P.E.
Flow through ponds
Design values:
(TheWeatherChannel)
(Table 9.1)
(Table 9.1)
(Table 9.1)
(See Appendix G)
Calculations
The volume of one singe pond is 5548 m3. The measured daily inflow was in the range of 5526-7527
m3/day. This gives an HRT of:
(Eq. 12.1)
61
(Eq. 12.2; see Eq. 2.1)
(Eq. 12.3)
Results and discussion
The Pond system will have the equal total retention time independently of how the water is divided.
With this arrangement the HRT in each pond will be on average 0.87 days with a total HRT of 3.5 days.
The designed surface loading should be 370 kg BOD5 / (ha * day) but in reality the pond receives 607 kg
BOD5 / (ha * day). The first pond is therefore overloaded.
Estimated treatment results
It is difficult to predict the future treatment result, but estimation can be based on the equation in
chapter 3.5 (Building several ponds in series) where the demanded HRT for certain BOD5 degradation
decreased from 11.3 to 8.7 days, when 4 ponds are used instead of 2 (see table 3.1). The conditions
differ, but if one assumes the relationship in valid in this case, the improvement can be estimated by eq.
12.4:
(Eq. 12.4)
The BOD5 average in Christchurch WWTP was reduced from 25 mg/l to 14 mg/l after the 3 pond in series
were connected to one long train, together with a baffle installation (Masterton District Council, 2009).
This resulted in a reduction of
(Eq. 12.5)
However, an aeration cascade (with unknown DO contribution) was installed which should contribute to
the improvement as well.
62
The average TSS reduction was
(Eq. 12.6)
As shown in chapter 5.1, the installation of baffles will improve the result as well.
It may be, with great uncertainties, estimated that the reduction of BOD5 and COD is in the range of 20-
40% with improvements mentioned above. If a value of 30% is assumed, the future BOD5 and COD
effluent will be:
(Eq. 12.7)
(Eq. 12.8)
The future TSS is hard to estimate since it is difficult to predict the future algae concentrations in the last
pond, but the TSS should be reduced rather than increased.
Alternative 2: Upgrading of existing WSP – Partly aerated pond
Introduction
As described in Alternative 1, the current pond system can be upgraded to perform better with minor
rearrangements. Since the first ponds are (according to Eq. 12.2 and Eq. 12.3) overloaded, mechanical
aeration is necessary to supply the demanded oxygen for optimal degradation.
Since BOD is degraded through the system the load will decrease with every pond. The overloading is
highest in the first pond, therefore the aeration should be installed in the beginning of the treatment
line. Aeration is chosen for pond No.1 and No.2. This will decrease the load on pond No.3, which should
operate as a facultative pond, so that it receives an adequate loading.
New design
Installing screening device
Rearranging the water flow
Installing baffles in two ponds
Installing aeration
63
Figure 12.2: Overview over current pond arrangement (left) and upgraded arrangement (right). “A”
indicates possible location of mechanical aeration devices.
Design values
(See Eq. 12.1)
(See Table 11.5)
(See Table 9.1)
(Zairi & Zain, 1999)
(EPA, 2002)
(Sewerage Services Dep., 1998)
64
Calculations
Temperature dependent constant k:
It has been measured and calculated that the inlet water has a BOD degradation speed (k-value) of 0.24
day-1 at 20 °C (see Table 11.1). After the first pond the value is unknown but may be assumed to be 0.1
day-1 (See Appendix E). These values must be converted for actual site conditions of 29 degrees Celsius,
using equation 6 from Mara, D. (2003):
(Eq. 12.9) (Mara, 2003)
(Eq. 12.10)
(Eq. 12.11)
Effluent BOD from Pond No.2:
The first ponds (No.1 and No.2) will operate as mechanical aerated ponds:
(Eq. 12.12, see Eq. 3.2)
Surface loading on Pond No.3:
Pond No.3 will receive water with 33 BOD5 mg/l (according to equation Eq. 12.11), which will result in a
surface loading in Pond No.3:
(Eq. 12.13)
65
Degradation in Pond No. 3 and No.4:
After pond No.1 and No.2 the two following ponds will have no mechanical oxygen supply, and are
considered as secondary facultative ponds. Two k-values are tested in order to see the range of possible
treatment:
K-value=0.16
(Eq. 12.14)
(Eq. 12.15)
K-value=0.37
(Eq. 12.16)
(Eq. 12.17)
Oxygen Supply - Demanded Oxygen for Pond No. 1 and 2:
(Eq. 12.18)
(Eq. 12.19)
(Eq. 12.20)
(Eq. 12.21)
Results and discussion
The calculations show that two mechanical aerated ponds (ponds No.1 and No.2), with a total surface
aeration capacity of 5 kW, are able to remove enough BOD5 (from 57 to 33 mg/l) so that pond No.3
receives a loading of 352 kg BOD5 / (ha*day) (should be below 400 kg BOD5 / (ha*day) for facultative
ponds according to Mara (2003)).
66
The final effluent is difficult to predict since the k-value may decrease along the process. If a
conservative k-value of 0.16 is used, the final calculated BOD5 effluent is 25 mg/l. If the k-value is
assumed not to decrease, the effluent is lowered to 19 mg/l. These values are in the same range as in
alternative 1, where no aeration is used. It may therefore be assumed that the effluent in reality may be
even lower, or, if a conservative view is desired, that alternative 1 is to optimistic and therefore the
values should be estimated to be higher in alternative 1.
Alternative 3: Conventional activated-sludge treatment plant
Introduction
In order to achieve efficient water treatment which can comply with the standard A requirements and at
the same time significantly reduce the land area requirements, a conventional activated sludge
treatment plant is a convenient alternative. Conventional activated sludge is one of the most expensive
alternatives but on the other hand it can guarantee an effective water treatment when operated
properly. As the new activated-sludge treatment plan will receive wastewater from more than 10.500 PE
the total footprint area will be around 1 ha (Sewerage Services Department, 1998). This is according to
Malaysian requirements for how much area is needed for activated-sludge system if PE is considered.
One important thing to consider is that an activated-sludge system is less effective in removing
pathogens than a treatment pond and because of that disinfection is needed after treatment.
Screening device
Screening device should be the same as described in Alternative 1.
Grit chamber
The purpose of the grit chamber is to remove heavy particles (sand, eggshells, coffee grounds etc.) by
reducing the flow of the water slightly. Grease is removed from the surface of the tank.
Design
According to Sewerage Services Department (1998), the grit camber should be of aerated mechanical
conveyor type since it serves over 10.000 P.E.
Design values
(Table 9.1)
HRT at Q peak = 3 min (Sewerage Services Department, 1998)
Flow through velocity= max 0.2 m/s (Sewerage Services Department, 1998)
= 0.5 (Sewerage Services Department, 1998)
= 2 (Sewerage Services Department, 1998)
67
Calculations
Tested dimensions: length=6.6 m; width=3.3 m; depth=1.7 m
V required = * 3 min = 0.203 * 60 sec * 3 min = 37 m3
V Grit Chamber = length * width * depth = 6.6 m* 3.3 m* 1.7 m = 37 m3
= = 0.5
= = 2
Footprint area= Length*Width=6.6 * 3.3 = 22 m2
Flow through velocity = = = 0.04 m/s (Eq. 12.22)
Result
A grit camber with the dimensions 6.6 x 3.3 x 1.7 fulfills the design criteria. The footprint area of this
installation is around 22 m2.
Equalization tank
First and foremost the activated sludge plant must be able to handle peak flows. The highest peak flows
has been measured during rainfall. The cause of high water flow during rainfall is discussed in chapter
10. High peak flow into a conventional treatment plant will not only disturb the treatment efficiency but
could also flush and remove the activated-sludge cultures.
There are two ways of dealing with this problem. One is to dimension the activated sludge to operate
under high flows. This is costly since the expensive part of the system must be dimensioned for a higher
capacity. Another option is to build an equalization tank or pond before the activated sludge plant to
eliminate fluctuations in water flow. In that case, the activated sludge tank will receive the daily average
flow, without high fluctuations and maximum flow. This will benefit the operation on the following
treatment steps.
Design
The size of the equalization pond should be enough to dampen the fluctuations into the treatment plant
so the equalization pond will be designed after the measured peak flow into the pond. The highest flow
was measured during a heavy thunderstorm on the 19th of November at 14:15 (see chapter 8.2). As
heavy thunderstorms in Malaysia normally last between 1-2 hours the detention time has to be set to at
least 2 hours.
68
In Figure 12.3 below a schematic picture of the equalization pond is shown.
Figure 12.3: Equalization tank
Design values:
(Table 9.1)
Calculations:
Tested dimensions: length = 50 m, depth = 2m
(Eq. 12.23)
(Eq. 12.24)
(Eq. 12.25)
Result
The equalization tank will have a total footprint area of 0.11 ha and will be large enough to handle a
peak flow during 3 hours of heavy rain. The tank will have a depth of 2 meter, a length of 50 meter and a
width of 25 meter. This will allow the activated sludge tank to receive the highest average flow per day
which is 0.087 m3/s (see Table 9.1).
Primary settling tank
The main purpose of the primary sedimentation tank is to reduce the settleable solids and remove as
much pollutants as possible in an economical way. The sedimentation occurs when the water flow is
reduced and particles are able to settle before entering the next treatment step.
69
Design
Two parallel primary settlers are recommended since it allows maintenance in one line with the other
one still in operation. The total inflow will therefore be divided to two tanks. The shapes of the tanks are
rectangular to allow maximum area usage. The maximum overflow rate is a measurement of the
maximum possible water velocity before the sedimentation basin cannot remove the smallest particle.
In this case the maximum overflow rate is set to 30 m3/m2*day according to Malaysian standard.
Design values:
(Typical value from Degrémont, 1991)
(See Table 9.1)
(Sewerage Services Department, 1998)
Reduction capacity at 2h HRT = 30% (Kemira, 2003)
(Sewerage Services Department, 1998)
(Sewerage Services Department, 1998)
Reduction of TSS = 55% (Kemira, 2003)
TSS load per day = 350 kg / day (see Chapter 11.2)
Calculations:
(Eq. 12.26)
(Eq. 12.27)
(Eq. 12.28)
(Eq. 12.29)
BOD5 effluent from primary settler = (1-0.3) * BOD5 in = 0.7 *57 mg/l = 40 mg/l (Eq. 12.30)
TSS load per treatment line = total TSS load / 2 = 350 kg TSS / 2= 175 kg TSS/day (Eq. 12.31)
70
Sludge production = TSS load per day * Reduction of TSS = 175 kg TSS/day *0.55 = 96 kg TSS/day
(Eq. 12.32)
Result
According to calculations above, two clarifiers with dimension 20 x 6.5 x 1.5 meters fulfills the design
values. The effluent from this stage will be around 50 mg BOD5/l. The settled solids are expected to
reach around 96 kg per line every day (total settleable TSS for both lines are therefore 192 kg).
Activated sludge tank
Within the activated sludge tank biological activities breaks down the impurities of the wastewater. The
activated sludge tank with its processes is described in chapter 4.
Design
Two parallel primary settlers are recommended since it allows maintenance on one line with the other
one still in operation. The total inflow will therefore be divided into two tanks. Since the system is run in
warm climate, it is considered enough to have a sludge age of 5 days. The nitrogen concentrations that
the plant will receive is unknown, but may be estimated from chapter 5.2 (Table 5.2) where the HN4+ -N
is 23.1 mg/l on average in the influent water. The water in Taman Sri Pulai has a COD-value of 446 mg/l
whereas the water at UTM only reaches 116 mg/l on average. If the same relationship between COD and
HN4+ -N is assumed to exist at UTM, the HN4
+ -N should theoretically reach ca 6 mg/l at UTM.
Design values:
(Sewerage Services Department, 1998)
(Sewerage Services Department, 1998)
(See Table 9.1 in Chapter 9)
(Sewerage Services Department, 1998)
(Sewerage Services Department, 1998)
(Sewerage Services Department, 1998)
(EPA, 2002)
(Kemira, 2003)
(Kemira, 2003)
Designed effluent BOD5 = 10 mg/l (Sewerage Services Department, 1998)
Minimum retention time in tank = 1 hour (Kemira, 2003)
71
NH4+ -N in = 5.9 mg/l
Specific Oxygen Consumption for endogenous
Respiration = 0.1 kg O2 per kg MLSS (Jansen, n.d)
Calculations:
Tank volume based on sludge loading:
(Eq. 12.33)
Tank volume based on sludge age:
(Eq. 12.34)
Tank volume based on retention time:
Q (m3/hour) * HRT (hour) = * 1 h = 157 m3 (Eq. 12.35)
(Eq. 12.36)
(Eq. 12.37)
72
(Eq. 12.38)
(Eq. 12.39)
Volume of tank * MLSS * Specific oxygen consumption = 157 m3 * 2500 mg/l * 0.1 = 39 kg/day =
= 1.6 kg O2/h
(Eq. 12.40)
Total Oxygen Demand = 7 + 4.2 + 1.6 = 13 kg O2/h
Total Energy Demand:
= 3.4 kW
(Eq. 12.41)
(Eq. 12.42)
73
(Eq. 12.43)
Result
The volume of the tank can be designed by several factors but the limiting factor is according to these
calculations the retention time, which demands two reactors with each a volume of 157 m3. Around 3
kW is needed per line for the oxygen delivery through a diffused supply system. The sludge produced is
in the range of 73 kg per day (146 kg for both lines). With this system the effluent should be able to
reach 10 mg BOD5 /l which is suggested since the absolute standard is 20 mg BOD5 /l.
Secondary settling tank
After the biological step another settling tank must be installed to separate the biological sludge from
the treated water. The Settlers will have more or less the same properties as the primary settlers, but
with a different settling velocity, which will demand smaller tanks.
Design
Two parallel primary settlers are recommended since it allows maintenance on one line with the other
one still in operation. The total inflow will therefore be divided to two tanks. The shapes of the tanks are
rectangular to allow maximum area usage.
Design values:
(Degrémont, 1991)
(See Table 9.1 in Chapter 9)
(Sewerage Services Department, 1998)
(Sewerage Services Department, 1998)
(Sewerage Services Department, 1998)
74
Calculations:
(Eq. 12.44)
(Eq. 12.45)
(Eq. 12.46)
Length / Width ratio = 23 / 8 = 2.9
Result
According to the calculations above, two clarifiers with the dimensions 23 x 8 x 2 metres fulfills the
design values.
Sludge handling
Sludge will be produced from the primary clarifiers and from the activated sludge tank. The sludge
should be dealt with according to the procedure described in chapter 4.
Design values
Sludge from primary settler = 192 kg TSS / day
Sludge from activated sludge tank = 146 kg TSS / day
TSS content in primary sludge = 5 % (Kemira, 2003)
TSS content in activated sludge = 1 % (Hammer, 1986)
Density of sludge = 1000 kg / m3
Calculations
Sludge volume from primary settler = = = 3.8 m3
/ day
(Eq. 12.47)
75
Sludge volume from activated sludge = = =
= 14.6 m3/day (Eq. 12.48)
Total sludge production = 3.8 m3+ 14.6 m3 = 18.4 m3/day
Disinfection
Since an activated-sludge treatment plant is less effective in removing pathogens than a pond system
disinfection will be needed after treatment. Disinfection can either remove or disable pathogens so it
posses less risk to infect the human community. One of the most used method for disinfection is
chlorination, this method however produce some unwanted substances, for example different types of
acids which are harmful to the environment (Jacangelo & Trussell, 2002).
In Malaysia there is a trend toward monitoring of Giardia and Cryptosporidium. As UV-disinfection has
proven effective against these harmful micro organisms we will propose UV-radiation as the disinfection
method used after activated-sludge treatment. It is also projected that UV-disinfection will improve in
terms of efficiency, cost and maintenance as the technology continues to develop (Jasangelo & Trussell,
2002).
76
77
13. Discussion on the upgrading alternatives The initial purpose of upgrading the treatment system was to reduce the area to around 25% of the
existing area. The smallest proposed system, which is alternative 3 (activated-sludge system), will
demand around 1 ha which will decrease the existing area with about 50%. The desired reduction is
therefore not possible to reach with the evaluated alternatives. If the area must be reduced even
though the goal of 25% of the existing area is not possible, the activated-sludge system is the only
proposed option allowing some reduction in area. By repairing the sewer network and reducing the total
water flow, the area of the activated-sludge system could be reduced further. The measures concerning
the sewage network could also improve the treatment efficiency of the pond system. The activated-
sludge system is the only alternative that can give reliable nitrogen reduction if the concentrations are
above effluent standard A. The nitrogen concentrations today are unknown but probably lower than the
new effluent standard from 2009 due to the dilution with infiltrating water. The treatment of nitrogen
may therefore not be necessary under current conditions with high amounts of infiltrating water. With
regards to footprint area and nitrogen reduction capacity, the activated-sludge is the most appropriate
alternative. The effluent concentrations (BOD5 and nitrogen) will be lowest with the activated-sludge
system but on the other hand the system will have the highest energy consumption.
From a holistic viewpoint, the consequences of the increased energy consumption should be
considered. As the electricity produced in Malaysia origins from around 90% fossil fuels (Al-Amin et al.,
n.d) the increase of energy consumption consumed by the activated-sludge system will therefore
eventually increase the air pollution. The amounts of sludge produced from the activated sludge (18 m3
/day) must be handled continuously which is both expensive and demands a qualified labor. With one of
the proposed pond systems (alternative 1 or 2), the de-sludging operations should take place when the
sludge layer has reached the highest thickness according to the design. In the future, the sludge layer
should be measured and recorded on a regular basis in order to plan de-sludging operations effectively.
Considering the good possible treatment, the low costs and low energy consumption alternative 2
offers, it is a highly recommended option. Since alternative 2 is an “upgraded pond” version of
alternative 1, it could be possible to first re-construct the treatment ponds according to the plan of
alternative 1. The effluent quality could then be monitored over a period of time to see the outcome.
The sewer network could at the same time be inspected to see if there are easy measures to conduct
against the infiltrating water. If there are locations where storm water has direct access to the sewer
network, minor modifications could have significant impact on the treatment efficiency. Depending on
the demands and outcome, it is then possible to continue and install aerators according to alternative 2.
Alternative 2 will solve the problem concerning overloading and therefore improve the treatment
efficiency further. The aerators could then be allowed to operate under normal conditions and be partly
shut down under vacation periods to save energy.
The surface aerators are simple machinery and should be able to operate without disturbing
breakdowns. If however the aerators would break down (electricity blackouts or technical problems) the
pond system designed as alternative 2 will then automatically operate as alternative 1 instead, with
78
reliable operation. If however alternative 3 (activated-sludge system) faces failures, the consequences
are more serious, and the discharge of polluted wastewater may follow instantly.
Another drawback of the activated sludge is that it does not reduce the amounts of pathogens in an
effective way. Therefore it should be considered to install some kind of disinfection device before the
effluent is released into the recipient. Chlorination is not recommended since it will disturb the aquatic
life in the recipient. UV-Disinfection can fulfill the task without causing negative impact on the recipient.
The question the decision makers should ask is whether the better treatment result the activated-sludge
plant gives is justified by the high extra costs and energy demand. In Table 13.1 on page 79 the general
advantages and disadvantages of the proposed systems are shown.
79
Table 13.1: Advantages and disadvantages of the suggested upgrading alternatives.
Advantages Disadvantages
Alternative 1 : Upgrading of existing WSP
+ No energy consumption
+ Low maintenance
demand
+ No risk of mechanical failure, reliable operation
+ High pathogen
removal
+ Easy to re-construct
- No possibility to control process
- No reduction of
footprint area
- Low treatment of BOD and nutrients
Alternative 2 : Upgrading of
existing WSP – Partly Aerated Pond
+ Low energy consumption
+ Possible to control the oxygen supply (to some extent)
+ high pathogen
removal
+ Easy to re-construct
- No reduction of footprint area
- Effluent may
exceed the effluent limit A
Alternative 3 : Conventional
Activated Sludge Treatment Plant
+ Good possible reduction of BOD5
and nitrogen, within standard A
+ Reduction of footprint area
+ Possible to control and adjust process
- High energy demand
- Costly to construct
- Low pathogen
reduction
- Qualified staff and high maintenance
demand
- High sludge production
80
81
14. Conclusion The treatment pond does not comply with standard A under current conditions. The pond receives large
quantities of extra water that has its origin from infiltration and possible misconnections with
stormwater cannels. The infiltrating water together with possible misconnected storm water contributes
with between 60-90% of the total inflowing water to the ponds. During rain events, the flow increases
multiple times and the concentration of measured pollutants increases during the high flow peaks. The
pollutant concentration is weak during normal flow due to dilution of infiltrating water.
The pond receives wastewater from around 10.500 P.E. The surface loading of the pond is higher than
its capacity. The pond is currently reducing the levels of pollutants with around 50% for COD and 30%
for TSS. With this reduction, the pond reaches Standard B but not Standard A.
With upgrading Alternative 1, the water flow is rearranged in one long train of 4 ponds, instead of the
current situation with two parallel lines with two ponds in each line. In two of the ponds, baffles will be
installed and before the wastewater enters the first pond a screening device is also installed. The pond
system may operate more efficiently without consuming any energy (except from the automatic
screening device). The effluent concentration of BOD is expected to be lowered with about 20-40%
compared to the current situation.
Alternative 2 will use the same design as Alternative 1 but with additional mechanical aeration that will
solve the problem concerning overloading. The effluent quality is theoretically expected to be lowered
to between 19-26 mg/l BOD5 (50-70% total reduction). In reality, the concentration may be lowered
even more due to the positive effect of many ponds in series and baffles. The effluent may therefore
reach the BOD5 limit of 20 mg/l, but the final outcome is difficult to predict due to the complexity.
Alternative 3 suggests an activated sludge system. This system is the most advanced alternative and
demands several tanks, including an equalization tank to protect the system from high peak flows. The
activated-sludge system can guarantee a good treatment concerning COD, BOD and TSS, however, the
disinfection capacity is expected to be lower than the other alternatives. This system requires
approximately 1 ha, i.e. half the footprint area in comparison with the pond system.
The sludge produced from Alternative 3 is equal to 18 m3 sludge per day. These amounts of sludge will
demand further handling which will be costly. Alternative 1 and 2 will have similar sludge handling as
today, where the ponds are de-sludged every 10 years.
The recommendations are to upgrade the system to Alternative 2 and to conduct investigations on how
to reduce the infiltration and stormwater flow into the sewer network.
82
83
15. Future work The most important future work is to do inventory on the sewer network in order to find possible
unwanted connections with storm water. If it is not possible to find obvious misconnections along the
sewer pipes, flow measurements can be done in manholes to see if there are local points where
infiltration takes place. If a pipe section shows high flow between 04:00-06:00 a.m., it should be studied
further and possible repair work may be considered. If the flow from storm water and infiltration is
reduced, the calculations regarding the proposed systems should be recalculated.
More influent wastewater should be analyzed according to nitrogen and phosphorous, to see if, or how
much, that has to be treated in order to meet the new regulations (see Appendix C - New regulations).
Regardless of which future treatment facility chosen, the effluent water should be monitored regularly
to see seasonal variations and to optimize the processes. The effluent pathogen quality should be
monitored to see if it satisfies the quality decided for recreational activities.
84
85
15. References Abbas, H., Nasr, R. & Seif, H. (2006) Study of waste stabilization pond geometry for the wastewater
treatment efficiency. Published by: Elsevier B.V.
Al-Amin., Siwar, C., Hamid, A. & Huda, N. (n.d) Pollution implications of electricity generation in
Malaysian economy: An input-output approach.
Available at: https://editorialexpress.com/cgi-
bin/conference/download.cgi?db_name=SERC2007&paper_id=117
[Accessed: 10 April 2010]
Alleman, E. & Prakasam, T. B. S. (1983) Reflections on Seven Decades of Activated Sludge History.
Journal (Water Pollution Control Federation), Vol. 55, No. 5, pp. 436-443. Published by: Water
Environment Federation.
Barnstable County Department of Health and Environment, Basics of Wastewater treatment.
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88
89
Appendix A: Studies on the present treatment pond at UTM
Result and conclusion
The authors Zahari and Zain (1999) made the measurements of BOD5, COD, TSS, NO3- and phosphorous
during the morning, mid-day and evening in one line of the treatment-pond system. The sampling for
these parts of the day was made on three different dates the values for morning, mid-day and evening
used in the tables below are based on an average value from the three samples.
COD
Table A.1: COD concentrations at WSP in UTM (Zahari & Zain, 1999)
Unit: mg/l Morning Mid-day Evening Average
Influent 66.32 70.22 115.73 84.09
Effluent
facultative pond
57.63 54.59 95.28 69.17
Effluent
maturation pond
38.99 31.64 47.86 39.50
Table A.2: Reduction of COD in the entire pondsystem,
in the facultative pond and in the maturation pond
Reduction in entire Pond
system
53%
Reduction in Facultative Pond 18%
Reduction in Maturation Pond 43%
BOD 5
Table A.2: BOD5 concentrations at WSP in UTM (Zahari & Zain, 1999)
Unit: mg O2/l Morning Mid-day Evening Average
Influent 39.83 32 41.2 37.68
Effluent
facultative pond
17.4 19.25 23.67 20.11
Effluent
maturation pond
15.7 16.75 16.17 16.21
90
Table A.3: Reduction of COD in the entire pondsystem,
in the facultative pond and in the maturation pond
Reduction in entire Pond system 57%
Reduction in Facultative Pond 47%
Reduction in Maturation Pond 19%
Suspended Solids
Table A.4: TSS concentrations at WSP in UTM (Zahari & Zain, 1999)
Unit: mg/l Morning Mid-day Evening Average
Influent 20.8 19.2 17.3 19.1
Effluent
facultative pond
12.6 17 12.6 14.1
Effluent
maturation pond
22.2 7.7 9.9 13.3
Table A.5: Reduction of TSS in the entire pondsystem,
in the facultative pond and in the maturation pond.
Reduction in entire Pond system 30%
Reduction in Facultative Pond 26%
Reduction in Maturation Pond 6%
Nitrate (NO3-)
Table A.6: NO3- concentrations at WSP in UTM (Zahari & Zain, 1999)
Unit: mg/l Morning Mid-day Evening Average
Influent 0.5 0.68 0.63 0.60
Effluent
facultative pond
0.27 0.5 0.5 0.42
Effluent
maturation pond
0.27 0.53 0.4 0.40
91
Table A.6: Reduction of NO3- in the entire pondsystem,
in the facultative pond and in the maturation pond.
Reduction in entire Pond system 33%
Reduction in Facultative Pond 30%
Reduction in Maturation Pond 5%
Phosphorus
Table A.7: Phosphorus concentrations at WSP in UTM (Zahari & Zain, 1999)
Unit: mg/l Morning Mid-day Evening Average
Influent 1.9 2.64 2.89 2.48
Effluent
facultative pond
1.59 2.29 2.66 2.18
Effluent
maturation pond
1.32 1.72 1.59 1.54
Table A.8: Reduction of phosphorous in the entire pondsystem,
in the facultative pond and in the maturation pond.
Reduction in entire Pond system 38%
Reduction in Facultative Pond 12%
Reduction in Maturation Pond 29%
92
93
Appendix B: Calculation of P.E.
Number of P.E. within Catchment
Number of residents within UTM’s College houses: Housing Area: Students:
KRP 1628 KTF 1456 KTR 1552 KTHO 1588 Kolej 12 & 13 1468
Total Residents: 7692
Total: 7692
P.E Factor: 1
P.E 7692
Number of Students and Staff within UTM’s faculties:
Faculty:
Students: Staff: Faculty of Engineering
1446 145
and Science Geoinformation Building: C1,C2,C3,C4,C5,C6, B8
Faculty of Science Building:
C8,C10,C18,C19,C17,C20,C21,C22 1800 312
Faculty of build environment 1338 170 Building: B2,B4,B5,B7,B9,B10
Total: 4584 627
Total: 5211
P.E Factor: 0,2
P.E 1042
94
Other Offices:
Students/Staff:
Centre for teaching and learning 32 CTL
Research Management Centre 61 RMC
School of graduate studies
70
UTM Property Maintanance Office 300
Total: 463
Total: 463
P.E. Factor 0,2
P.E 93
Private family houses outside UTM:
Family houses
50
Total: 1000
(50 houses * 4 families * 5 family members)
P.E. Factor 1
P.E 1000
Other buildings:
UTM Main Office (assumed value) 500
Mosque (design, maximum visitors) 3000
Total: 3500
Total: 3500
P.E. Factor 0,2
P.E 700
Total P.E. within catchment: 10527
95
Appendix C: Addition concerning new effluent standard
During the project the effluent standard from 1974 has been set as the limit to reach. It came to our
knowledge, after all measuring was performed, that a new standard has been decided in December
2009. The new standard is similar to the one of 1974. The BOD5 levels are unchanged. The main
difference is the introduction of Nitrogen and Phosphorous removal (Department of Environment, 2009)
(see Table C.1 below)
Table C.1: The Malaysian effluent standard from December 2009.
(Department of Environment, 2009)
Parameter* A B
pH 6-9 5.5-9
BOD5 at 20 d.C 20 50
COD 120 200
TSS 50 100
O&G 5 10
NH4-N (Closed water body) 5 5
NH4-N (river) 10 20
NO3 (river) 20 50
NO3 (closed water body) 10 10
Phosphorus (closed water body) 5 10
* in mg/L except for pH
Comments:
Since the inlet water is weak due to the dilution of ground water, it is likely that the water at site is well
below the introduced limit for Nitrogen and Phosphorous. Measurements should be conducted to verify
this. If Nitrogen levels are high, the activated-sludge system is the most effective system compared to
the pond systems (see Chapter 4 – Nitrification and denitrification). For Phosphorous removal, chemical
precipitation may be added all three alternatives.
96
97
Appendix D: Map of the sewer network connected to the pond
Figure D.1: Sewer network over UTM. The buildings inside the thick line are connected to the studied pond.
98
99
Appendix E: Sample values
Biological oxygen demand (BOD)
Biological oxygen demand (BOD) is a common value of the amount of oxygen needed in wastewater
treatment technology in order degrade organic material. In waste water there are particles which
bacteria can degrade if oxygen is available. These particles originate example from feces, detergents,
different kinds of fat and particles from food (Barnstable County Department, n.d.).
These different particles in wastewater will be degraded into smaller molecules by bacteria using oxygen
and in the end there is also water and carbon dioxide produced.
In order to find a value of BOD for a specific wastewater sample it is possible to measure the amount of
oxygen consumed during a certain period of time. The amount of oxygen consumed by bacteria for a
water sample during 5 days is called BOD5 and if the oxygen is consumed during 7 days it is called BOD7.
Degradation speed of BOD – k-value
One important parameter when designing the treatment facility is the reaction rate constant k. The
choice of reaction constant will have significant impact on the calculated treatment results. K-value used
in this report indicates the speed of the BOD degradation, whereas the BOD5 only holds information
about the total oxygen consumed during 5 days. The k-value, in this report used for degradation of BOD,
is calculated by the increase of oxygen consumption over time. Cutrera et al. (1999) analyzed several
methods that can be used for calculating the k-value. Their research shows that the accuracy of the
different methods varies significantly. In this report the k-value has been calculate by Thomas method
(Thomas, 1950) since it is easy and reliable to use. The method used for calculating the k-value can be
found in Hammer, J. (1986). According to Mara, D. (2003), if the k-value is unknown it can be assumed to
0.3 for primary facultative ponds treating domestic wastewater, and 0.1 for secondary facultative ponds.
Chemical oxygen demand (COD)
Some of the organic material is difficult to oxidize biologically, for example lignin (Crites et al., 1998). By
using a chemical oxidant such as dichromate which can oxidize lignin and other difficult organic
substances it is possible to measure the chemical oxygen demand (COD). Usually this will result in a
COD-value which is higher than the BOD-value. One of the main benefits of COD is that it can be
completed within 3 hours instead of 5 days compared to BOD.
100
Total suspended solids (TSS)
The value of TSS is found by filtering water through a pre-weighted filter. The filter is adjusted to
suspended material. In most cases 0.1 liters of water is poured through the filter and the amount of
captured suspended solids is dried up in an oven before weighted again. By subtracting the pre-
weighted filter with the weight of the dried solid sample and then divide it with the amount of water
poured through the filter the amount of TSS in the unit mg/l is calculated.
101
Appendix F: Calculation of k-value by Thomas method
k20-Values According to Method of Thomas (Thomas, 1950)
Time 17:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 15 0.322
1 26 0.338 1.5 37 0.344 2 44 0.357 2.5 49 0.371 3 51 0.389 3.5 52 0.407 4 56 0.415 4.5 57 0.429 5 57 0.444
A=0,3059 B/A= 0.090
B=0,0275 (B/A)2,61 0.235
Time 19:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 6 0.437 1 13 0.425
1.5 21 0.415 2 22 0.450 2.5 26 0.458 3 31 0.459 3.5 31 0.483 4 34 0.490 4.5 34 0.510 5 35 0.523
A= 0.4036 B/A= 0.055
B= 0.0223 (B/A)2,61 0.144
y = 0,0275x + 0,3059R² = 0,9943
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
y = 0.0223x + 0.4036R² = 0.8946
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
102
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 12 0.347
1 15 0.405 1.5 22 0.409 2 28 0.415 2.5 31 0.432 3 33 0.450 3.5 35 0.464 4 34 0.490 4.5 35 0.505 5 36 0.518
A= 0.3498 B/A= 0.097
B= 0.034 (B/A)2,61 0.254
Time 23:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 14 0.329
1 20 0.368 1.5 25 0.391 2 30 0.405 2.5 33 0.423 3 37 0.433 3.5 37 0.456 4 36 0.481 4.5 39 0.487 5 41 0.496
A= 0.3292 B/A= 0.108
B= 0.0356 (B/A)2,61 0.282
y = 0,034x + 0,3498R² = 0,9598
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
y = 0.0356x + 0.3292R² = 0.9744
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
103
Time 00:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0 0.5 18 0.303
1 23 0.352 1.5 32 0.361 2 39 0.372 2.5 44 0.384 3 46 0.403 3.5 48 0.418 4 51 0.428 4.5 50 0.448 5 55 0.450
A= 0.3087 B/A= 0.098
B= 0.0302 (B/A)2,61 0.255
Time 03:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 11 0.357
1 14 0.415 1.5 18 0.437 2 21 0.457 2.5 23 0.477 3 28 0.475 3.5 27 0.506 4 26 0.536 4.5 26 0.557 5 30 0.550
A= 0.3641 B/A= 0.113
B= 0.041 (B/A)2,61 0.294
y = 0,0302x + 0,3087R² = 0,9598
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
y = 0.041x + 0.3641R² = 0.9492
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
104
Time 05:00 Time (days):
BOD (mg/l):
(Time/BOD)^(1/3)
0 0
0.5 5 0.464 1 10 0.464 1.5 12 0.500 2 18 0.481 2.5 18 0.518 3 20 0.531 3.5 21 0.550 4 21 0.575 4.5 23 0.581 5 25 0.585
A= 0.4416 B/A= 0.069
B= 0.0303 (B/A)2,61 0.179
Time 07:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0 0.5 14 0.329
1 20 0.368 1.5 22 0.409 2 26 0.425 2.5 30 0.437 3 32 0.454 3.5 34 0.469 4 35 0.485 4.5 36 0.500 5 38 0.509
A= 0.3363 B/A= 0.111
B= 0.0372 (B/A)2,61 0.289
y = 0.0303x + 0.4416R² = 0.9505
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
y = 0,0372x + 0,3363R² = 0,9511
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
105
Time 09:00 Time (days):
BOD (mg/l):
(Time/BOD)^(1/3)
0 0
0.5 25 0.271
1 38 0.297 1.5 48 0.315 2 54 0.333 2.5 59 0.349 3 66 0.357 3.5 69 0.370 4 72 0.382 4.5 72 0.397 5 76 0.404
A= 0.2696 B/A= 0.105
B= 0.0283 (B/A)2,61 0.274
Time 11:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 15 0.322 1 23 0.352 1.5 35 0.350 2 42 0.362 2.5 49 0.371 3 51 0.389 3.5 55 0.399 4 56 0.415 4.5 60 0.422 5 63 0.430
A= 0.3173 B/A= 0.073
B= 0.0232 (B/A)2,61 0.191
y = 0,0283x + 0,2696R² = 0,9797
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
y = 0,0232x + 0,3173R² = 0,9789
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
106
Time 13:00
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 19 0.297 1 30 0.322 1.5 41 0.332 2 45 0.354 2.5 52 0.364 3 55 0.379 3.5 58 0.392 4 60 0.405 4.5 60 0.422 5 65 0.425
A= 0.2911 B/A= 0.098
B= 0.0284 (B/A)2,61 0.255
Time 14:15
Time (days): BOD (mg/l): (Time/BOD)^(1/3)
0 0
0.5 25 0.271 1 37 0.300 1.5 53 0.305 2 60 0.322 2.5 72 0.326 3 77 0.339 3.5 80 0.352 4 83 0.364 4.5 86 0.374 5 91 0.380
A= 0.2702 B/A= 0.085
B= 0.023 (B/A)2,61 0.222
y = 0.0284x + 0.2911R² = 0.9885
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
y = 0,023x + 0,2702R² = 0,9804
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6
(Tim
e/B
OD
)^(1
/3)
Days
107
Appendix G: Technical data and construction drawings
Table G.1: Data of pond area, depth of impermeable layer at the bottom of the pond, designed sludge layer
and designed waterlevel of the pond.
Area Depth impermeable layer at bottom
Sludge layer (designed)
Water level (at sludge layer 0.46 m)
Facultative Ponds (each)
6070 m2 0.61 m 0.46 m 0.91 m
Maturation Ponds (each)
6070 m2 0.61 m 0.46 m 0.91 m
Table G.2: Designed volume of sludge and water in each facultative pond and
maturation pond
Volume of sludge Volume of water
Facultative Ponds (each)
2792 m3 5524 m3
Maturation Ponds (each)
2792 m3 5524 m3
Area of the entire facility ≈ 24.500 m2
Figure G.1: Cross section of the first (facultative) pond with inlet distribution pipe.
108
Figure G.2: Overview over the studied pond system at UTM.
109
Appendix H: Reduction of pathogens in WSP systems
Table H.1: Removal efficiency of pathogens in WSP systems. (with permission from H.E Maynard et al 1999)
