extended aeration: a comparative study between prefabricated
TRANSCRIPT
EXTENDED AERATION: A COMPARATIVE STUDY BETWEEN PREFABRICATED
REINFORCED FIBERGLASS AND CONCRETE CAST IN-SITU PLANTS
MOHD SHUKRI BIN ABDUL RAZIK
A project report submitted in partial fulfillment of the requirements for the award of the degree of
Master of Engineering (Wastewater)
Faculty of Civil Engineering Universiti Teknologi Malaysia
May, 2007
iii
ACKNOWLEDGEMENT
This master thesis concludes my study at Universiti Teknologi Malaysia
(UTM), for a Masters degree in Civil Engineering (Wastewater).
There are a number of persons I would like to thank. First of all, my
supervisor, Dr. Azmi Aris for indispensable guidance and for interesting discussions
regarding the work with this thesis. Thanks also to all lecturers involved with my
study for being such a source of inspiration and motivation. I would also like to
thank to my course mates, the personnel at IWK and my family for their interest in
my work.
iv
ABSTRACT
The choice of wastewater treatment plants for any application depends on the
quality of raw sewage, the required quality of treated water and the economics
resources available to pay for both capital cost and operating cost of the treatment
plants. The performance of any wastewater treatment plants does not only depend on
the construction cost but will also cover the cost and method of operation and
maintenance, quality of effluent treated, internal, external and design factors. While
potential for identifying a better type of wastewater treatment plant does exist, very
modest efforts have been attempted. This study compares and contrasts two of the
most commonly used extended aeration systems for small to medium size sewage
treatment plants, namely prefabricated reinforced fibreglass and cast in-situ systems.
The selected treatment plants are under the jurisdiction of Indah Water Konsortium
Sdn. Bhd. (IWK), Terengganu. The flow of raw sewage and the performance of the
treatment plants based on effluent quality (i.e. BOD, COD and SS) and electricity
cost were assessed. Three treatment plants from both types of systems were studied
for a period of five months. It was found that a small to medium size treatment
plants suffer high variation in term of flow and organic loading. It seemed obvious
that the cast in-situ treatment plants not only built structurally better and ease of
operation, but also giving better effluent standard and consumed lower electricity
cost.
v
ABSTRAK
Pemilihan loji pengolahan kumbahan untuk apa jua tujuan adalah bergantung
kepada kualiti air kumbahan atau sisa, kehendak kualiti air yang diolah dan
kemampuan sumber kewangan untuk membiayai kos pembinaan dan operasi loji
kumbahan tersebut. Tahap pencapaian mana-mana loji pengolahan kumbahan bukan
sahaja bergantung kepada kos pembinaannya, tetapi juga bergantung kepada kos dan
cara ianya beroperasi dan diselenggarakan, kualiti kumbahan yang telah diolah,
faktor-faktor dalaman, luaran dan rekabentuk loji pengolahan itu sendiri. Walaupun
wujudnya potensi untuk mengenal pasti jenis-jenis loji pengolahan kumbahan yang
lebih berdaya saing, namun usaha ke arah ini masih belum lagi dilaksanakan dengan
lebih menyeluruh. Kajian ini adalah untuk membuat perbandingan dan mencari
perbezaan antara dua loji pengolahan kumbahan jenis pengudaraan lanjutan yang
paling popular, iaitu prefabricated reinforced fiberglass dan cast in-situ. Loji-loji
pengolahan yang telah dipilih untuk kajian ini adalah di bawah seliaan Indah Water
Konsortium Sdn. Bhd. (IWK), Terengganu. Kuantiti air kumbahan, dan pencapaian
loji-loji pengolahan kumbahan dinilai berdasarkan kepada kualiti efluen (seperti
BOD, COD dan SS) dan kos penggunaan tenaga elektrik. Tiga loji dari dua jenis
sistem pengudaraan lanjutan telah dikaji dalam tempoh lima bulan. Adalah didapati
bahawa loji-loji yang bersaiz kecil ke sederhana mengalami gangguan perbezaan
influen yang ketara, atau pun perbezaan di antara influen dan beban pencemaran.
Dalam kajian ini, loji cast in-situ bukan sahaja mempunyai struktur yang lebih baik
dan lebih mudah untuk diselenggarakan, tetapi juga menghasilkan tahap efluen yang
lebih baik dan penggunaan tenaga elektrik yang lebih rendah.
vi
TABLE OF CONTENTS
CHAPTER TITLE
PAGE
DECLARATION ii
ACKNOWLEDGEMENT iii
ABSTRACT iv
ABSTRAK v
TABLES OF CONTENTS vi
LIST OF TABLES ix
LIST OF FIGURES xi
LIST OF APPENDICES xii
1 INTRODUCTION 1
1.1 Background 1
1.2 Importance of Study 5
1.3 Objective and Scope of Study 5
2 LITERATURE REVIEW 7
2.1 Source of Raw Sewage 7
2.2 Characteristic of Raw Sewage 8
2.2.1 Soluble and Insoluble Materials
10
2.2.2 Organic and Inorganic Materials 11
2.2.3 Suspended Solids 11
vii
2.2.4 Biochemical Oxygen Demand (BOD) 11
2.2.5 Chemical Oxygen Demand (COD) 12
2.2.6 Interrelationships between BOD and COD 12
2.2.7 Contaminants of Concern in Sewage Treatment 13
2.3 Flow Rate of Domestic Wastewater 14
2.4 Wastewater collection 17
2.4.1 Sewer line 17
2.4.2 Pumping Stations 18
2.5 Wastewater Treatment Processes 18
2.5.1 Preliminary Treatment 19
2.5.2 Equalization or Balancing Tank 20
2.5.3 Primary Treatment 21
2.5.4 Biological or Secondary Treatment 21
2.5.5 Final Clarifier or Sedimentation Tank 23
2.5.6 Sludge Treatment 23
2.5.7 Flow Measurement 23
2.6 Energy Utilization 24
2.7 Extended Aeration System 24
2.7.1 Description of Extended Aeration Process 26
2.7.2 Prefabricated Reinforce Fiberglass Extended Aeration 27
2.7.3 Cast In-Situ Extended Aeration 27
3 METHODOLOGY 28
4 RESULTS AND DISCUSSIONS 30
4.1 Flow Measurement 32
4.2 Characteristics of Raw Sewage 33
4.3 Performance of Treatment Plant 37
4.3.1 Treatment Plant Performance for 2006 41
viii
4.4 Electricity Cost 42
4.4.1 Electricity Cost for 2006 44
4.5 Operational Problems 45
5 CONCLUSIONS AND RECOMMENDATIONS 46
REFERENCES 48
Appendices A - C 50-71
ix
LIST OF TABLES
TABLE NO. TITLE
PAGE
1.1 Classification of Sewerage Treatment Plant by Size (Malaysia) 2
1.2 Treatment Plant Total by Group 3
1.3 Land Area Requirements for Mechanized Plants 4
2.1 Typical Breakdown of Residential Water Uses 8
2.2 Typical Composition of Untreated Domestic Sewage 9
2.3 Typical Value of BOD/COD in Raw Sewage 12
2.4 Contaminants of Concern in Sewage Treatment 13
2.5 Recommended Population Equivalent 14
2.6 Sewer Pipes or Conduits 17
2.7 Definition of Common Terminology Used for Biological Wastewater 22
2.8 Major Biological Treatment Processes Used for Wastewater Treatment 22
2.9 DGSS Design Parameters for Extended Aeration 26
4.1 List of Selected Extended Aeration Treatment Plants Used in the Study 31
4.2 Standard B Interim Limit 32
4.3 Flow Measurement Results 33
4.4 Characteristics of the Raw Sewage 34
4.5 BOD/COD Ratios Value for Raw Sewage 36
x
4.6 Average Effluent BOD of Prefabricated and Cast In-Situ Plants (in mg/l) 37
4.7 Average Effluent COD of Prefabricated and Cast In-Situ Plants (in mg/l) 38
4.8 BOD/COD Ratio Values for Final Effluent 40
4.9 Average Effluent SS of Prefabricated and Cast In-Situ Plants (in mg/l) 40
4.10 Standard B Compliance of the Treatment Plants 41
4.11 Average Overall 2006 Sampling Result 41
4.12 Electricity Cost (RM) of the Treatment Plants 43
4.13 Overall Electricity Cost as a Function of Aeration Time for
Prefabricated Plants 44
4.14 Overall Electricity Cost as a Function of Aeration Time for
Cast In-Situ Plants 44
4.15 Electricity Cost (RM) for 2006 45
xi
LIST OF FIGURES
FIGURE NO. TITLE
PAGE
2.1 Typical Variation in Municipal Water Demand and Wastewater Flow 15
2.2 Ratios of Extreme Flow to Average Daily Flow (Peaking Factor) for Municipal Wastewater Under Dry Weather Conditions 16
2.3 Typical Elements and Process Flow Diagram of A Sewage Treatment Plant 19
2.4 Layout of Hi-Kleen Prefabricated Plant 25
2.5 Layout of Cast In-Situ Extended Aeration Plant 25
4.1 Relationship between BOD and COD in Raw Sewage 35
4.2 Relationship between BOD and SS in Raw Sewage 35
4.3 Relationship between SS and COD in Raw Sewage 36
4.4 Relationship between BOD and COD for Final Effluent (Prefabricated Plants) 38
4.5 Relationship between BOD and COD for Final Effluent (Cast In-Situ) 39
xii
LIST OF APPENDICES
APPENDIX TITLE
PAGE
A Sampling Results 50
B Photograph of Treatment Plant 59
D Flow Measurement Data 64
1
CHAPTER 1
INTRODUCTION
1.1 Background
The most important goal of the National Sewerage Policy is to ensure that the
discarded water after it has been used is properly treated before being discharged in
order to protect the receiving environment. The evolution of fully mechanized
sewage treatment processes from primitive to primary and continued progress headed
to secondary treatment system will help us save our environment from degradation.
This trend created new and modern equipments ranging from pumps, screens,
aeration systems, sludge process systems and other technological advancement
equipments which continuously help us to reduce pollutants entering our water
systems.
In 1998, only 4.9% population in Malaysia was served by central sewerage
systems (from 3.4% in 1970). Individual septic tanks or communal treatment
systems such as oxidation pond, trickling filter, extended aeration and imhoff tank
served 34% of the population (up from 17.2 in 1970). Pour flush latrine and other
less satisfactory systems served 52.9% of the population while 8.2% have no
facilities at all [1].
2
Based on statistic released by the Department of Environment (DOE),
domestic sewage contributed 46% of the total biological oxygen demand (BOD) load
into inland waters in 1985 and the figure has increased to 69% in 1988 [2]. It is
clearly shown that the domestic sewage is the number one BOD contributor in this
country and to remain so if no proper mitigation measures take place.
The declared aim of the Government to promote the involvement of the
private sector in the implementation, operation and management of the sewerage
infrastructure project, has resulted in 1993, the appearance of Indah Water
Konsortium Sdn. Bhd. (IWK) as the national public sewerage systems operator. The
main idea of the privatization is to synchronize and harmonize planning,
construction, maintenance and operations aspect of this industry under the Ministry
of Energy, Water and Telecommunication. Sewerage Service Department (SSD) is
the entrusted government agency to coordinates regulation, ordinance and
enforcement of the sewerage systems in Malaysia.
The number of sewage treatment plant increase tremendously after the
introduction of the National Sewerage Policy in 1994. It was found that in 2005,
about 82% of the sewerage treatment plants serving not more than 2,000 PE as
shown in Table 1.1 [2]. This increment coupled with technology improvement has
taken the sewerage industries to a greater level.
Table 1.1: Classification of Sewage Treatment Plant by Size (Malaysia)
PE Year
Less Than 150
150-2,000
2,001-5,000
5,001- 25,000
25,001- 50,000
More Than 50,001
Total No of STP
1994 276 (26.4%)
537 (33.7%)
166 (15.9%)
55 (5.3%)
7 (0.7%)
2 (0.2%) 1,043
1997 2,204 (48.6%)
1,706 (37.6%)
416 (9.2%)
191 (4.2%)
11 (0.2%)
10 (0.2%) 4,538
2005 4,163 (47.4%)
3,053 (34.7%)
922 (10.5)
573 (6.5)
42 (0.5)
29 (0.3) 8,782
Source: [2]
3
In march 2007, out of 8,537 public sewage treatment plants maintained by
IWK, 43% are communal septic tanks, 9% are imhoff tanks, 5% are oxidation ponds,
3% are mechanical plants with media and 40% are mechanical plant without media
as shown in Table 1.2 [1].
Table 1.2: Treatment plant total by group.
NO TYPE OF STP TOTAL PERCENTAGE PE 1 Communal Septic Tank 3,637 43% 432,841 2 Imhoff Tank 767 9% 563,967 3 Oxidation Ponds 460 5% 1,892,318 4 Mechanical Plants with
Media 247 3% 857,322
5 Mechanical Plant without Media 3,426 40% 11,527,075
GRAND TOTAL 8,537 100% 15,273,523 Source: [1]
The second most important goal of the National sewerage Policy is to manage
the required wastewater treatment plants as cost effective as possible as the cost of
the sewerage systems operation is being bore by the tax payer, an effective system is
essential as to save money of the tax payer or the public as a whole. With many
treatment systems currently available in the market today, proper selection of the
systems is crucial and many factors need to be considered which include cost of
construction, operation and maintenance, and performance of the systems.
The conversional extended aeration of prefabricated fiber reinforced glass
and concrete in-situ are currently considered as the most popular systems particularly
for small to medium size treatment plants. Due to the competitive edge on the
marketing strategies, the initial capital cost or construction per population equivalent
(PE) of these systems is about the same. Typical land area requirements for sitting of
small to medium size wastewater treatment plants is also about the same as shown in
Table 1.3 [3]. However, no specific study has been conducted to evaluate the
performance and the efficiency of these two systems.
4
Table 1.3: Land Area Requirements for Mechanized Plants
Standard A * Standard B * Population Equivalent (ha) (acre) (ha) (acre) 2,000 0.17 0.42 0.17 0.42 3,000 0.22 0.42 0.17 0.55 4,000 0.27 0.66 0.27 0.66 5,000 0.31 0.76 0.31 0.76
10,000 0.78 1.93 0.66 1.63 15,000 1.00 2.47 0.84 2.09 20,000 1.19 2.95 0.99 2.44 25,000 1.37 3.38 1.13 2.79 30,000 1.53 3.79 1.26 3.11 35,000 1.81 4.48 1.65 4.08 40,000 1.97 4.88 1.79 4.43 45,000 2.12 5.25 1.93 4.77 50,000 2.23 5.52 2.03 5.02 55,000 2.37 5.84 2.15 5.31 60,000 2.52 6.22 2.29 5.66 65,000 2.67 6.61 2.43 6.00 70,000 2.93 7.23 2.66 657 75,000 3.27 8.07 2.82 6.96 80,000 3.49 8.61 3.03 7.49 85,000 3.69 9.12 3.23 7.99 90,000 3.89 9.61 3.42 8.46 95,000 4.07 10.06 3.60 8.90 100,000 4.25 10.49 3.77 9.32 110,000 4.57 11.29 4.09 10.10 120,000 4.87 12.02 4.38 10.81 130,000 5.14 12.70 4.64 11.47 140,000 5.39 13.32 4.89 12.08 150,000 5.63 13.90 5.12 12.64 160,000 5.84 14.44 5.33 13.17 170,000 6.05 14.95 5.53 13.67 180,000 6.25 15.43 5.72 14.14 190,000 6.43 15.89 5.90 14.58 200,000 6.60 16.32 6.07 15.00 250,000 7.36 18.20 6.81 16.83 300,000 7.98 19.73 7.41 18.32 450,000 9.36 23.14 8.76 21.65
Source: [3]
The required area does not include any buffer zone surrounding each plant. Appropriate setbacks and access paths within the plant have been included.
5
1.2 Importance of Study
Presently the Department of Environment (DOE) governs the effluent
standards while the Sewerage Service Department (SSD) is an approving authority
for any construction of the treatment plants. It appears that no previous study has
been conducted to monitor the overall performance efficiency and energy costs to
operate any of the treatment plants in Malaysia. As the concessionaire public
sewerage systems operator, IWK has to accept all the systems approved by SSD and
to fulfill the DOE effluent requirement by baring all the operations and maintenances
costs.
It has been proven that operational improvement such as pumping system
optimization, flexible tanks release strategies for water distribution, alternative
aeration system optimization and use of low cost timer and controls has saved
millions of dollars without compromising the effluent standard requirements [4].
Hence, effort should be made to select proper treatments plants, as it will improve
the economic of the treatment plants operations.
1.3 Objective and Scope of Study
The main objective of this study was to compare and contrast two most
commonly used extended aeration systems for small to medium size sewage
treatment plants namely prefabricated reinforced fiberglass and concrete in-situ
systems.
6
This study was limited to the extended aeration systems of prefabricated fiber
reinforced glass and cast in-situ plants of the same PE size ranging from 1,000 –
3,500 PE which were currently under the operation of IWK, Terengganu. The
comparisons were based on the operational cost of the system, particularly the energy
cost, the efficiency of the process and the ease of operation of the systems.
7
CHAPTER 2
LITERATURE REVIEW
2.1 Sources of Raw Sewage
Understanding of the nature of raw sewage is a fundamental to the design and
operation of raw sewage collection, treatment and reuse facilities as water usages in
the communities vary with the different type of activities and social background
composition.
The chemical and microbiological contents of residential wastewater depend
upon the physical, chemical and biological characteristics of catchments area. A
typical residential water usage is shown in Table 2.1 [5]. A basic residential uses of
water like washing, food preparation and water closet flushing will normally provide
a relatively uniform wastewater. Variations are caused by modification of this
normal use such as inclusion of industrial effluents which can further modify the
characteristics of the wastewater. The analysis or raw sewage data involves the
determination of the flow rate and mass loading variations.
8
Table 2.1: Typical Breakdown of Residential Water Uses
Type of Water Use Neoconservative Home
Usage, Percent
Toilet flush, including toilet leakage 33
Shower and bathing 28
Wash basin 11
Kitchen 9a
Drinking (2-6%)
Dishwashing (3-5%)
Garbage disposal (0-6%)
Laundry and washing machine 16b
Lawn sprinkling and miscellaneous 3
Source: [5]
aDishwasher is 1%, and remaining is faucet use. bHigher percentage because increase use of washing machines and reduced Total demand.
2.2 Characteristics of raw sewage
A typical characteristic of the raw sewage in Malaysia is given in Table 2.2
[3]. Depending on the concentration of the constituents, the wastewater can be
classified as strong, medium and weak.
9
Table 2.2: Typical Composition of Untreated Domestic Sewage
Concentration ( mg/l ) No. Parameter
Strong Medium Weak
1 Solids, Total 1,200 720 350
2
Dissolved, Total
Fixed
Volatile
850
525
325
500
300
200
250
145
105
3
Suspended, total
Fixed
Volatile
350
75
275
220
55
165
100
20
80
4
Settle able solids, ml/l
20*
10*
5*
5 Biochemical oxygen
demand, 5-day, 20 C 400 250 110
6
Total organic carbon (TOC) 290 160 80
7 Chemical Oxygen Demand
(COD) 1,000 500 250
8 Nitrogen (total as N) 85 40 20
9 Organic 35 15 8
10 Free ammonia 50 25 12
11 Nitrites 0 0 0
12 Nitrates 0 0 0
13 Phosphorus (total as P) 15 8 4
14 Organic 5 3 1
15 Inorganic 10 5 3
16 Chlorides 100 50 30
17 Alkalinity (as CaCO3) 200 100 50
18 Grease 150 100 50 Source: [3]
* All values except settle able solids are expressed in mg/l.
10
Wastewater normally contains solids feaces, detergents, hydrocarbon oils,
common salts, clay and food particles and these must ultimately be returned to
receiving waters or to the land or reuse. Many microorganisms, such as Giardia
lamblia and Cryptosporidium Parvern and many trace compounds have been found
and may cause adverse health effects [6]. In larger sewage catchments area, the
constituents of wastewater are generally more homogenous with higher trend in SS
due to a higher infiltration of ground water especially during the wet season.
All the analysis conducted on wastewater constituents normally to group
materials in a manner relevant to treatment processes and at the same time to gain
more knowledge on the behavior of wastewater or raw sewage constituents and how
they affect process performance and effluent quality [7].
2.2.1 Soluble and Insoluble Materials
Materials can be classified according to their ability to form a solution in
water, or their insolubility and hence their tendency to settle out of water. In
wastewater treatments, insoluble particles can be removed by settlement process or
by the addition of chemicals or suitable microorganisms in proper environment in
which they will metabolize the insoluble particles and produce a large, settle able
biological mass. Completely soluble materials must be converted by chemical or
biological means into a settle able form or into gaseous product or they may be
subjected to other separation processes [7].
11
2.2.2 Organic and Inorganic Materials
Thousands of different types of organic materials can be found in the raw
sewage. Organic compound are normally a combination of carbon, hydrogen and
oxygen, or sometimes with nitrogen. In wastewater typically it consists of protein
(40-60%), carbohydrates (25-40%), oil and fat (8-12%) together with urea in some
cases [6]. They can often be biodegraded and this process is particularly important in
wastewater treatment plants. Inorganic compound such as NaCl and Ca(HCO3) are
unaffected by simple settlement and biological growth.[7].
2.2.3 Suspended Solids
The most important physical characteristics of raw sewage are suspended
solid, which is composed of floating, settle able and colloidal matters in solution [5].
Suspended solids in the raw sewage are often removed in the connection to the inlet
or preliminary processes. In Malaysia, the removal materials are disposed to
municipal solid waste dumping ground.
2.2.4 Biochemical Oxygen Demand (BOD)
The most widely used parameter of organic pollution applied to wastewater.
This is the measurement of the dissolved oxygen used by organic microorganisms in
the oxidation of organic matter. BOD test can only be completed in five days.
12
2.2.5 Chemical Oxygen Demand (COD)
Chemical oxygen demand parameter is used to determine the oxygen
equivalent of the organic material in wastewater that can be oxidized chemically.
Normally the COD test can be completed in about 2.5 hours and a rapid COD test
that takes only about 15 minutes is also available in the market today. [6]
2.2.6 Interrelationships between BOD and COD.
Typical values for BOD/COD are shown in table 2.3. For raw sewage any
value greater than 0.5, the waste can be easily removed by biological processes and if
the ratio below about 0.3, raw sewage may have some toxic components or
acclimated microorganisms may be required in the stabilization [6].
Table 2.3: Typical value of BOD/COD in raw sewage Type of wastewater BOD/COD
Raw sewage 0.3-0.8
After primary treatment 0.4-0.6
Final effluent 0.1-0.3
Source: [6]
13
2.2.7 Contaminants of Concern in Sewage Treatment.
Other than BOD and COD, pollutants normally measured and their concern
in sewage treatment plants are shown in Table 2.4 [3].
Table 2.4: Contaminants of Concern in Sewage Treatment.
Contaminants Reason for Concern Suspended solids Suspended solids can lead to the development of
sludge deposits and anaerobic conditions when untreated sewage is discharged in the aquatic environment.
Biodegradable organics Composed principally of protein, carbohydrates and fats, biodegradable organic are measured most commonly in terms of BOD (biochemical oxygen demand). If discharged untreated to the environment, their biological stabilization can lead to the depletion of natural oxygen resources and to the development of septic conditions.
Pathogens Communicable diseases can be transmitted by the pathogenic organisms in sewage.
Nutrients Both nitrogen and phosphorus, along with carbon, are essential nutrients for growth. When discharged to the aquatic environment, these nutrients can lead to the growth of undesirable aquatic life. When discharged in excessive amounts on land, they can also lead to the pollution of groundwater.
Refractory organics These organics tend to resist conventional methods of sewage treatment. Typical examples include surfactant, phenols and agricultural pesticides.
Heavy metals Heavy metals are usually added to sewage from commercial and industrial activities and may have to be removed if the sewage is to be reused.
Dissolved inorganic solids
Inorganic constituents such as calcium, sodium and sulphate are added to the original domestic water supply as a result of water use and may have to be removed if the sewage is to be reused.
Source: [3]
14
2.3 Flow Rate of Domestic Wastewater
In the design of sewer line and treatment plant, the sizing is to be based on
the hydraulic loading. This is done through the population equivalent (PE) as shown
in Table 2.5 [3]. In Malaysia one population equivalent is equal to 225 l/c/d of
sewage discharge to the sewer line or treatment plant.
Table 2.5: Recommended Population Equivalent
Type of Premises / Establishment Population Equivalent
( Recommended)
Residential 5 per house Commercial: Includes offices, shopping complex, Entertainment/recreational centers, Restaurants, cafeteria, theatres
3 per 100m² gross area
Schools/Educational Institutions: - Day schools/Institutions - Fully residential - Partial residential
0.2 per student 1 per student 0.2 per non-residential student 1 per residential student
Hospitals 4 per bed Hotels with dining and laundry facilities 4 per room Factories, excluding process water 0.3 per staff Market (wet type) 3 per stall Market (dry type) 1 per stall Petrol kiosks/Service stations 15 per toilet Bus terminal 4 per bus bay Taxi terminal 4 per taxi bay Mosque 0.2 per person Church/Temple 0.2 per person Stadium 0.2 per person Swimming pool/ Sport complex 0.5 per person Public toilet 15 per toilet Airport 0.2 per passenger bay
0.3 per machine Laundry 10 per machine Prison 1 per person Golf course 20 per hole
Source: [3]
15
The rate of flow varies within 24 hours of the days. In residential area, the
flow rate is lowest in the early morning, while the high values are normally observed
in the periods from 6 am to 8 am and 6 pm to 8 pm. Flow from industrial,
institutional and commercial areas are mostly during daylight hours. Typical
variation in municipal water demand and wastewater flow is shown in Figure 2.1 [5]
and the relationship between wastewater and water usage is ranging from 60 to
130%.
Figure 2.1: Typical variation in municipal water demand and waster water flow [5]
16
The ratios of extreme flows to average daily flow of wastewater are shown in
Figure 2.2 [5]. The higher water usage will normally reduced the contaminations
concentration due to the dilution factor and reduced the septicity or anaerobically
degraded of the raw sewage which leads to the release of hydrogen sulfide and other
odors and gives a better effluent result.
Figure 2.2: Ratios of extreme flow to average daily flow (peaking factor) for municipal wastewater under dry weather conditions [5]
17
2.4 Wastewater Collection System
2.4.1 Sewer Line
The collection of wastewater from domestic, commercial, institutional and
industrial sources via underground sewer line necessary for environmental protection
was developed in the mid nineteenth century [2]. The design of sewer line must
have a sufficient velocity to prevent deposition of solids. The flow in the sewer line
is by gravity either partly or full. It does not flow under pressure as to avoid
contaminating to the surrounding ground as a result of the sewer line bursting or
exfiltration at joints and cracks.
With the advancement of technology, new pipe materials are periodically being
offered for use in sanitary sewer constructions. The types of conduit or pipe
normally used in sewer construction today are shown in Table 2.6 [7].
Table 2.6: Sewer pipes or conduits
Type Range of diameter
(mm)
Remarks
Asbestos-cement pipe 100-900 Gravity and pressure type (autoclave-curve)
Clay (verified) pipe 100-900 Glazed and unglazed gravity type
Concrete (plain) pipe 100-600 Gravity type Concrete (reinforced) pipe
300-600 Circular, elliptical and arch types
Concrete cast in place - For special site conditions Iron (cast) pipe 100-1200 For pressure lines and
treatment works Plastic (solid wall) pipe 100-300 For service line and laterals
Source: [7]
18
Manholes are provided at certain locations to provide access from the ground
surface to sewer line for the purpose of inspection, repair and clearing blockages.
Inverted siphons are normally used when sewage need to pass below any
obstructions.
2.4.2 Pumping Stations
Pumping station is used when it is more economical for passing sewage from
low area over high ground than a tunneled gravity main. The pump sump storage
capacity is designed by avoiding excess accumulation of sludge, nuisance from odors
and septicity of the raw sewage. A standby pump is normally provided so that any
one of the pumps can be taken out for services.
Inlet pump stations must be provided by primary screens to protect the pumps
from being damage or clogged and must be equipped with sewerage application
pumps.
2.5 Wastewater Treatment Processes
Figure 2.3 gives an overview of the typical flow diagram and elements of a
sewage treatment plants. It clearly can be seemed that one facility is closely related
to another and thus has an impact upon the overall design and must be designed to
produce an effluent quality as under provisions of the Environmental Quality Act
1974 (EQA) [3].
19
Source: [3]
Figure 2.3: Typical elements and process flow diagram of a sewage treatment plant.
Methods of treatment in which the application of physical forces predominate
are known as unit operation while methods of treatment in which removal of
contaminations is brought about by chemical or biological reactions are known as
unit processes. At the present time, unit operation and processes are grouped
together to provide various levels treatment categorized as preliminary, primary, and
secondary.
2.5.1 Preliminary Treatment
A preliminary treatment normally consist of primary screen, raw sewage
pump, secondary screen, grid and grease removal and balancing tank. When the raw
sewage is unable to gravitational flow to the treatment plants, the flow must be
20
collected and screened in the pump sump before being lifted or pumped up to the
treatment plants. The pumping processes can consume a quite large energy and can
cause biological reactions within the raw sewage which normally produced
hazardous gases or odors.
The screen in the pump sump is to remove large solids and the fine screen
provided after the pumping processes, will remove the smaller solids which pass
through the first screen. The screenings bar must be cleaned to avoid clogging,
either manually or by electrical driven raking devices. The removal of large solids
and grid is necessary to avoid the damage of the equipment downstream and reduce
the interference within plants flow and performance.
2.5.2 Equalization or Balancing Tank
An equalization tank is used to overcome the flow variation of the raw
sewage in order to improve the performance of the downstream processes and to
reduce the size and cost of downstream treatment facilities. It also will enhance
biological processes, improved effluent quality and thickening performance in the
aeration tank through consistent solids loading [6].
Disadvantages of equalization tanks are requirement of large land area,
release of odor, needs of additional operation and maintenance, increase of capital
cost and higher energy consumption for extra pumping and aeration system within
the equalization tank.
21
2.5.3 Primary Treatment
For primary treatment or a physical operation, sedimentation tank is usually
used to remove a portion of suspended solids, scum and organic matter from the
wastewater. The removal of BOD in primary sedimentation tank is normally about
30-40 % and TSS removal is about 50-70% [7].
2.5.4 Biological or Secondary Treatment
For discharging the effluent to inland streams, a considerably higher quality
is necessary. Practical aerobic biological treatment processes seek to do this, within
the constraints of available land area and economic resources. The biological or
secondary treatment processes is carried out by microorganisms, mainly bacteria.
These microorganisms use waste matter as a food source in order to synthesize new
cell material. They obtained the energy for their synthesize and cell maintenance
functions by degrading some of the organic matter to simple compounds. The
degraded matter is then bound into floc particles and separated from the wastewater
by settling, thus creating sludge. Some of the floc will be recycled back to the
aeration tank from settling tank to mix with raw sewage.
The biological treatment process can be classified as either fixed film or
suspended growth processes. An outline of the main processes of each of these
classification is shown in Table 2.7 [6].
22
Table 2.7: Definition of common terminology used for biological wastewater treatment.
Treatment processes Definition Suspended-growth processes Biological treatment processes in which the microorganisms
responsible for the conversion of the organic matter or other constituents in the wastewater to gases and cell tissue are maintained in suspension within the liquid
Attached-growth processes Biological treatment processes in which the microorganisms responsible for conversion of the organic matter or other constituents in the wastewater to gases and cell tissue are attached to some inert medium, such as rocks, slag, or specially designed ceramic or plastic materials. Attached-growth treatment processes are also known as fixed-film processes
Combined processes Term used to described combined processes (e.g. combined suspended and attached growth processes)
Lagoon processes A generic term applied to treatment processes that take place in ponds or lagoons with various aspect ratios and depth
Source: [6]
Typical process application for fixed film and suspended growth biological
processes are as shown in Table 2.8. In recent years, a number of hybrids systems,
which incorporate elements of both fixed film and suspended growth systems, have
also been developed [6].
Table 2.8: Major biological treatment processes used for wastewater treatment.
Type Common Name Use Suspended growth
Activated-sludge process(es) Aerated lagoons Aerobic digestion
Carbonaceous BOD removal, nitrification Carbonaceous BOD removal, nitrification Stabilization, Carbonaceous BOD removal
Attached growth
Trickling filters Rotating biological contactors Packed-bed reactors
Carbonaceous BOD removal, nitrification Carbonaceous BOD removal, nitrification Carbonaceous BOD removal, nitrification
Hybrid (combined) suspended and attached growth processes
Trickling filter / activated sludge
Carbonaceous BOD removal, nitrification
Source: [6]
The microorganisms used in this processes need oxygen (aerobic) to survive
and to be supplied by the aeration systems. Some part of the organic matter is also
used for the growth of the microorganisms.
23
2.5.5 Final Clarifier or Sedimentation Tank
After biological treatment processes, wastewater will be transfer to the
sedimentation tanks for the removal of biological floc produced by microorganisms
by settling under gravity to give a clarified effluent. The type of final clarifier most
suitable to be used depends on the characteristics of the wastewater to be treated as
well as the final effluent requirement before discharging to the waterways.
2.5.6 Sludge Treatment
In Malaysia, for small to medium size treatment plants, sludge is either
discharge directly to sludge treatment facilities such as drying beds or filter belts
press or sludge will be kept in the sludge holding or digestion tanks before being
desludged by tanker to another sludge treatment facilities. The pumps are required to
remove the sludge between different parts and processes within the treatment plant.
2.5.7 Flow Measurement
Other than operation requirement for checking chemical or air requirement,
flow measurement is necessary because of regulatory requirement for record purpose
or user charge update. Technically it can be used to check the status of the plants
which need for expansion due to population increase or to see the effect of
infiltration during wet weather [5].
24
2.6 Energy Utilization
In general, the large wastewater treatment plants seem to consume larger
amount of electricity cost. The major energy consumers for wastewater treatment
plants are pumps, blowers (aerations) and solids handling systems. Characteristics
of raw sewage, types of plants and mode of operation for the same size of plants can
significantly vary the energy usage. However, the raw sewage pumps generally
represent 15 to 70% of the total electricity cost. All the pumps within treatment
plants can represent as much as 90% of the total energy consumption. Aeration
systems sometimes represent as much as 50%. Poor operation and maintenance and
poorly tuned control systems can be a large cost bearer [8]. It is also very difficult
to present a general guideline of how energy utilization is divided among the
consumer within wastewater treatment plants.
2.7. Extended Aeration System
The extended aeration system is the most popular treatment system currently
being employed in Malaysia particularly for small to medium size population. The
extended aeration system in Malaysia normally consists of three types of tanks.
They are aeration tank, clarifier and sludge digestion tank. While preliminary
treatment such as screening and grit removal is available, primary sedimentation tank
is normally not provided. As mentioned earlier, two types of systems normally used
are prefabricated reinforced fiberglass and concrete cast in-situ. Figures 2.4 and 2.5
illustrate the layout of the systems. The design parameter for extended aeration is
shown in Table 2.9 [9].
25
Sewage
RASScum
SludgeOverflow Holding Tank WAS
Clarifier
Effluent
Coarse Screen
Fine Screen Control Box
Aeration Tank
EqualizationTank
Figure 2.4: Layout of Hi-Kleen prefabricated plant [9]
ScreenRaw Sewage
Screened Sewage
Final EffluentReturned Activated Sludge
Ranking for Sludge forDisposal Disposal
Activated Sludge Aeration Unit
Discharge
Figure 2.5: Layout of cast in-situ extended aeration plant [9]
26
Table 2.9: DGSS design parameters for extended aeration
Description Unit Design Criteria
Minimum number of aeration tanks 2 F/M ratio 0.05-0.1 Hydraulic retention time (HRT) Hrs 18-24 Oxygen requirements kgO2/kgBOD5 1.5-2.0 Mixed liquor suspended solids (MLSS) Typical : 3,000
Mg/l 2,500-5,000
Dissolved oxygen (DO) level in tank Mg/l 2.0 Sludge yield Kg sludge
Produced/kg BOD5 consumed
0.4 (at 24 hrs HRT) 0.6 (at 18 hrs HRT)
Sludge age Day >20 Waste activated sludge (WAS) m³/d Refer to equation Return activated sludge flow, QRAS m³/d MLSS x Qave
Cu-MLSS Cu is underflow concentration
RAS pump rating Hours/day 24 Recirculation ratio, QRAS/QINFLOW 0.5-1.0 Aerator loading Kg/ m³/d 0.1-0.4 Minimum mixing requirement W/ m³ 20
Source: [3]
2.7.1 Description of Extended Aeration Process
The basic of extended aeration process is to keep in the microorganism
suspension under aerobic condition in the aeration tanks. For system without
primary treatment, the separation of contamination and liquid usually take place in
the secondary sedimentation tank. Recycle system to be provided for returning some
of the removed solids from sedimentation tanks back to the aeration tanks for mixing
with new raw sewage.
27
2.7.2 Prefabricated Reinforced Fiberglass Extended Aeration
Hi-Kleen system is one of the commonly used prefabricated reinforced
fiberglass extended aeration. Other than inlet works, other parts of the system are
prefabricated at the factory. As compared to the cast in-situ extended aeration plant,
Hi-Kleen system is equipped with an equalization tank and a flow control box.
There are four tanks altogether, namely equalization tank, aeration tank, clarifier tank
and sludge digestion tank. Raw sewage will be screened and most of the grit will be
removed in the pump sump before being pumped to the equalization tank, via flow
control box. The hydraulic retention time (HRT) within the aeration tank is about
18 hours with theoretical mixed-liquor-suspended solids (MLSS) requirement of
between 2,500-3,000 mg/l. Return activated sludge (RAS) and waste activated
sludge (WAS) and aerators in equalization tanks are pumped by using an air-lift
pumps from the aeration systems [9].
2.7.3 Cast In-Situ Extended Aeration
In cast in-situ system, raw sewage is normally screened followed by grit
removal taking place in the grit chamber or pump sump. The sewage is then pumped
directly into the aeration tank for secondary treatment. As compared to the Hi-Kleen,
the system is normally not equipped with equalization tank. Similar to the
prefabricated system, primary sedimentation tank is not included. The HRT of the
aeration tank is between 18 to 24 hours and the theoretical MLSS requirement in the
aeration tank is between 2,500 mg/l to 5,000 mg/l. The RAS from secondary
clarifier tank is between 100 - 150% of influent quantity. The wasted sludge (WAS)
is normally very low and to be kept in the sludge digestion or holding tanks [10].
28
CHAPTER 3
METHODOLOGY
At present, there are more than 250 treatment plants operating in the state of
Terengganu. Therefore, the initial stage of the study is to identify the suitable
wastewater treatment plants to be used. In order to obtain a good comparison
between the systems, one of the main criteria being considered was the value of the
PE; the treatment plant’s PE should be between 1,000 and 3,500. Additionally,
only plants having an average compliance to Environmental Quality Act (EQA),
1974 requirement of 100% in 2006 were selected. It was also assumed that majority
of the equipments in the plants were in full operation and being operated and
maintained within the acceptable requirement. The selected treatment plants were
under the jurisdiction of IWK Terengganu and as no water intake point was involved,
the plants were only required to comply with the Standard B of the EQA. The
selection of the plant was not confine to the plants of the same area but cover a few
districts within the state of Terengganu.
The performance of the treatment plants were assessed based on water quality
parameters (i.e. BOD, COD, and SS), and electricity cost. Samples and data were
collected for the period of October 2006 to March 2007. Sampling, preservation and
29
analysis were conducted according to the Standard Methods [11] by IWK Central
Laboratory, Kuala Lumpur.
During the study period, primary sampling results and flow measurement
were monitored and analyzed. Adjustments were also made to electrical and
mechanical equipments such as raw sewage, WAS and RAS pumps, aeration devices
and pumping systems that are related to electricity cost and the overall performance
of the treatment plants.
30
CHAPTER 4
RESULTS AND DISCUSSIONS
To meet the required effluent standards, it will be necessary to consider the
variability of the flow rate and characteristics of the raw sewage, variability in the
treatment processes and variability caused by mechanical and electrical equipments,
design deficiencies, and operational failures. Due to this nature, this study did not
specifically look at one prefabricated fiber reinforced glass or cast in-situ extended
aeration treatment plant but rather on a few selected treatment plants of the same
type with PE ranging from 1,000 to 3,500 PE.
Table 4.1 shows the list of the extended aeration treatment plants used in the
study. The selection of these plants was based on secondary data made available by
IWK Terengganu and located in the districts of Kuala Terengganu, Dungun and
Kemaman. Based on IWK, all treatment plant approved and constructed before 1999
is categorized as category 3 while treatment plant approved and constructed after
1999 is categorized as category 2. The prefabricated treatment plants were of Hi-
Kleen type. The general view of the selected treatment plants are shown in
Appendix B.
31
Table 4.1: List of selected extended aeration treatment plants used in the study
No Ref No. Taman PE Category Remark
Prefabricated system
1 TDN021 Murni Perdana,
Dungun 3260 3
Low /
medium
cost
2 KTU095 Permint Perdana,
K.Trg. 2230 2
Low /
medium
cost
3 KTU084 Pangsapuri Permint,
K.Trg 1086 2
Medium
cost Apt
4 KTU082 Sri Kolam, K.Trg. 2130 3 Medium /
Low Apt
Cast in-situ system
1 TDN025 Rakyat Jaya, Dungun 3155 2
Low /
medium
cost
2 TKN044 Semarak, Kemaman 2262 2
Low /
medium
cost
3 TKN019 Samudra Timur,
Kemaman 1155 3
Medium
cost
KTU 082 was only sampled for flow and raw sewage.
The plants are categorized according to the new interim Standard B interim
limit as shown in Table 4.2 [3].
32
Table 4.2: Standard B Interim Limit
No Parameter Effluent Limit Category 2 Effluent Limit Category 3
1 BOD5 at 20°C 50 mg/l 80 mg/l
2 COD 200 mg/l 240 mg/l
3 SS 100 mg/l 120 mg/l
Source : [3]
4.1 Flow Measurement
Flow measurements were conducted by using Flo-Tote 3, produced by
Marsh-McBirney, Inc.. It measures both velocity and level in the same cross-section,
a requirement necessary for accurate flow rate measurement using the continuity
equation. The flow accuracy is based upon the accurate measures of both velocity
and level in hydraulic flow labs, as well as under actual conditions.
The duration of the flow measurement on the selected treatment plants were
conducted between three to five days period and the overall results are shown in the
Appendix C.
Due to time constraint only five flow measurements were completed, but it
anticipated not affecting the reliability of the overall result discussion in principle as
it represented all the PE range and location of the selected sewage treatment plants.
All the selected treatment plants were built based on maximum design PE. From the
data obtained, it was observed that the flow of raw sewage entering the treatment
plants were 28.78% to 47.18% of the design average flow as shown in the Table 4.3.
33
Table 4.3: Flow measurement results
MOBILE FLOW
MEASUREMENT
PE Design
ADWF
(m³/d)
Design
Peak WF
(m³/d)
ADWF
(m³/d)
Peak
WF
(m³/d)
% Actual
ADWF
Cal. ADWF
1 KTU082 2130 479 2073 226 1178 47.18%
2 KTU095 2230 502 2159 221 1160 44.02%
3 TDN025 3155 785 3217 226 944 28.78%
4 KTU084 1086 244 1138 109 549 44.67%
5 TKN044 2262 456 2016 168 1020 36.84%
Lower values of raw sewage flow entering treatment plant always coincide
with the increase of travel time or longer idling period in the pump sumps and more
anaerobic conditions developed. Normally the color of the raw sewage changes
sequentially form gray to dark gray, and ultimately to black, indicating the septicity
of the raw sewage reaching biological processes stage. Consequently odor is
produced by anaerobic microorganisms that reduce sulfate to sulfide and forming
hydrogen sulfide gas [6].
4.2 Characteristics of Raw Sewage
Due to time constraint, only 6 raw sewages from four treatment plant were
sampled. It anticipated not affecting the reliability of the overall result discussion in
principle as it represented a combination of low to medium cost houses, low to
medium cost apartments and medium cost apartment. The overall sampling results
are shown in Appendix A.
34
The characteristics of the raw sewage are given in Table 4.4. The values of
BOD during the sampling period ranged from 52 to 549 mg/l (classification range
from very weak to a very strong raw sewage) with an average of 252 mg/l. The
values of COD ranged from 136 to 1163 mg/l (classification from very weak to a
very strong domestic sewage) with an average of 551 mg/l.. The concentration of SS
ranged from 69 to 394 mg/l (classification range from very weak to very strong raw
sewage) with an average value of 187 mg/l. The average values of BOD and COD
were higher than medium concentration of typical untreated domestic sewage.
Table 4.4: Characteristics of the raw sewage
No. Ref No. Date BOD (mg/l) COD (mg/l) SS (mg/L)
1 TKN044 18/12/06
12/3/07
52
458
136
830
69
293
2 KTU095 12/2/07
26/2/07
164
159
433
394
165
99
3 KTU084 5/2/07 128 348 100
4 KTU082 26/2/07 549 1163 394
Average 252 551 187
As can be depicted from Table 4.4, the characteristics of the wastewater
highly varied from time to time. This is one of the main characteristics of small and
medium size treatment plant; a slight change in the discharge from the households
will affect the quality and quantity of the wastewater. Furthermore, release of illegal
backyard or industrial wastewater into the domestic sewer could increase the strength
of the wastewater. Based on IWK’s experience, the higher strength of wastewater
normally occurs during school holidays and festivals.
The higher value of BOD appeared to occur at the same time with the value of
COD. The relationship between the BOD and COD values is shown in Figure 4.1
with an R-squared value of 0.9726. The higher value of BOD also appeared to occur
35
at the same time with the value of SS. As shown in Figure 4.2, the BOD and SS
values show a good relationship with R-squared value of 0.973. Similarly, as shown
in Figure 4.3, the higher value of COD appeared to occur about at the same time with
the value of SS. This indicates the possible significant contribution of the organic
content originating from the suspended solids in the wastewater.
y = 1.8398x + 87.657R2 = 0.9726
0
200
400
600
800
1000
1200
1400
0 100 200 300 400 500 600BOD (mg/l)
COD
(mg/
l)
Figure 4.1: Relationship between BOD and COD in raw sewage
y = 1.5831x - 53.074R2 = 0.973
0
100
200
300
400
500
600
0 100 200 300 400 500
Suspended Solids (mg/l)
BO
D (m
g/l)
Figure 4.2: Relationship between SS and BOD in raw sewage
36
y = 2.9177x - 4.0173R2 = 0.9719
0
200
400
600
800
1000
1200
1400
0 100 200 300 400 500
Suspended solids (mg/l)
CO
D (m
g/l)
Figure 4.3: Relationship between SS and COD in raw sewage
Based on Table 4.5, the ratio of BOD/COD ranged from 0.38 to 0.55
indicating that the waste is treatable by biological processes. It can also be assumed
that no toxic components were presence in the raw sewage.
Table 4.5: BOD/COD ratios value for raw sewage
No. Ref No. Date BOD / COD
1 TKN044 18/12/06
12/3/07
0.38
0.55
2 KTU095 12/2/07
26/2/07
0.38
0.40
3 KTU084 5/2/07 0.38
4 KTU082 26/2/07 0.47
Average 0.42
In general, there is no relationship between suspended solids in the raw
sewage and turbidity [6]. However, turbidity is expected to increase with the strength
of raw sewage [5].
37
4.3 Performance of Treatment Plant
During the study period, 23 effluent samples were taken from prefabricated
treatment plants while 19 effluent samples were taken from cast in-situ treatment
plants. The overall sampling results are shown in appendix A.
The BOD effluent as shown in Table 4.6, ranged from 6 to 106 mg/l (average
of 28.98 mg/l) for prefabricated treatment plants as compared to 7 to 116 mg/l
(average 27.45 mg/l) for cast in-situ treatment plants. On average, the latter shows a
better effluent quality with a difference of about 18%.
Table 4.6: Average effluent BOD of prefabricated and cast in-situ plants (in mg/l)
Prefabricated Plant Cast In-Situ Plant No Month
TDN021 KTU095 KTU084 TDN025 TKN044 TKN019
1 Oct 06 35.0 116.0 6.0 43.0 47 12
2 Nov 06 106.0 21.0 11.0 40.5 41 -
3 Dec 06 25.0 27.0 - 23.0 42 -
4 Jan 07 8.0 17.5 6.0 15.0 34 7
5 Feb 07 19.0 24.0 6.0 - 41 14
Average 38.6 41.1 7.25 30.37 41.0 11.0
Overall Average 28.98 27.45
As shown in Table 4.7, the effluent COD for prefabricated plant ranged from
26 to 296.0 mg/l with an average of 104 mg/l. The COD for cast in-situ ranged from
46 to 161 mg/l with an average of about 100 mg/l. On average, the latter gave a
better effluent COD quality. The smallest plant, served only medium cost residential
type, KTU 084 of fabricated plant and TKN 019 of cast in-situ plants seems to give
better effluent BOD and COD than any other plants.
38
Table 4.7: Average effluent COD of prefabricated and cast in-situ plants (in mg/l)
Prefabricated Plant Cast In-Situ Plant No Month
TDN021 KTU095 KTU084 TDN025 TKN044 TKN019
1 Oct 06 133.0 265.0 36.0 142.5 161.0 62
2 Nov 06 296.0 143.0 66.5 104.0 124.0 -
3 Dec 06 81.0 86.0 - 77.0 151.0 -
4 Jan 07 48.0 68.5 26.0 77.0 129.0 46
5 Feb 07 82.0 147.0 40.0 - 141.5 74
Average 128.0 141.9 42.12 100.1 141.3 60.6
Overall
Average 104.06 100.7
The higher values of COD appear to occur at the same time with the values of
BOD for prefabricated treatment plants as shown in Figure 4.4. The R square value
of the relationship is 0.9961 and is given by
CODe = 2.8595 x BODe + 21.13 (4.1)
y = 2.8595x + 21.13R2 = 0.9961
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50BOD (mg/l)
COD
(mg/
l)
Figure 4.4: Relationship between BOD and COD for final effluent (prefabricated plants)
39
Similarly, the higher values of COD appear to occur at the same time with the
values of BOD for cast in-situ treatment plants as shown in Figure 4.5. The R square
value of the relationship is 0.9693 and is given by
CODe = 2.613 x BODe + 28.983 (4.2)
y = 2.613x + 28.983R2 = 0.9693
020406080
100120140160
0 10 20 30 40 50BOD (mg/l)
CO
D (m
g/l)
Figure 4.5: Relationship between BOD and COD for final effluent (Cast In-situ)
The overall average of BOD/COD ranged from 0.15 to 0.44 for prefabricated
plants and 0.15 to 0.38 for cast in-situ plants as shown in Table 4.8. As discussed in
section 2.2.6, the theoretical values of treated effluent are ranging from 0.1 to 0.3 for
treated or final effluent and 0.4 to 0.6 values for after primary settling processes.
The value of 0.44 was happened in the month of October, 2006 for KTU 095 and
during this time, the plant (prefabricated) has failed to meet the effluent standard
requirement. In another words, if the ratio of BOD/COD of treated effluent is greater
than 0.4, it indicate the untreatable nature of the sewage. Longer hydraulic retention
time for aeration is therefore required.
40
Table 4.8: BOD/COD ratio values for final effluent
Prefabricated Plant Cast In-Situ Plant No Month
TDN021 KTU095 KTU084 TDN025 TKN044 TKN019
1 Okt06 0.26 0.44 0.17 0.30 0.29 0.19
2 Nov06 0.36 0.15 0.16 0.38 0.33 -
3 Dec06 0.31 0.30 - 0.29 0.28 -
4 Jan07 0.39 0.25 0.23 0.19 0.26 0.15
5 Feb07 0.23 0.16 0.15 - 0.29 0.19
Average 0.31 0.23 0.18 0.29 0.29 0.18
Overall
Average 0.24 0.25
For SS removal as shown in Table 4.9, the prefabricated plants were found to
give better effluent than the cast in-situ plants. The average effluent SS of the former
was 37.08 mg/l while the latter was 42.14 mg/l. The SS of the effluent for
prefabricated plants and cast in-situ plants ranged from 4 to 105 mg/l and 10 to
74 mg/l. For an unknown reason (other than medium cost residential type), the
effluent SS for KTU084 (prefabricated plant) was extremely low (i.e. between 4 to 9
mg/l).
Table 4.9: Average effluent SS of prefabricated and cast in-situ plants (in mg/l)
Prefabricated Plant Cast In-Situ Plant No Month
TDN021 KTU095 KTU084 TDN025 TKN044 TKN019
1 Okt06 57.0 105.0 5.0 48.0 74.0 16.0
2 Nov06 95.0 34.5 9.0 45.5 58.0 -
3 Dec06 18.0 44.0 - 31.0 85.0 -
4 Jan07 34.0 47.0 5.0 29.0 61.0 10.0
5 Feb07 17.0 76.0 4.0 - 60.0 38.0
Average 44.2 61.30 5.75 38.4 67.6 21.33
Overall Average 37.08 42.14
41
The Standard B compliance of the treatment plants are shown in Table 4.10.
In term of BOD, COD and SS, cast in-situ plants complied better than cast
prefabricated plants. Compliance of 100% was achieved by the cast in-situ plants
while compliance between about 86 to 93% was achieved by prefabricated plants.
Table 4.10: Standard B compliance of the treatment plants
% of Compliance
No. Plant Type BOD COD SS 1 Prefabricated Plants 85.7 92.8 92.8 2 Cast In-Situ Plants 100.0 100.0 100.0
4.3.1 Treatment Plant Performance for 2006.
Based on IWK Terengganu, the average effluent BOD, COD and SS for 2006
is shown in Table 4.11. For BOD and SS removal, it clearly shown that the cast in-
situ plants were found to give better effluent than the prefabricated plants. For SS
removal, both plants achieved the same average.
Table 4.11: Average Overall 2006 Sampling Result (mg/l)
Prefabricated Plant STP BOD COD SS
TDN021 30 131 56 KTU095 26 82 29 KTU084 24 82 36 Average 26.67 100.3 40.3
Cast In-situ Plant TDN025 15 71 30 TKN044 22 98 44 TKN019 16 69 47 Average 17.6 79.3 40.3
Source: [1]
42
4.4 Electricity Cost
In Malaysia, typical electricity costs include consumption charge (kWh) and
demand charge (kW or KVA) and in some cases, a power factor penalty. As the
current practice, the electricity cost is charged at a basic flat rate; hence, time of use
has no impact on the cost. For extended aeration, 45 to 60% of the total energy
consumption is due to the aeration system [12]. Previous study has also shown that
the use of Variable Frequency Drives (VFDs), an electronic controller that adjusts
the speed of an electric motor (soft start capability, gradually ramping up a motor to
operating speed) can have significant effect on energy saving. With this device, it
will lessen mechanical and electrical stress on the motor system reduces maintenance
and repair costs. It was observed that a small reduction in motor speed will contribute
to a substantial energy saving. From the observation made, a 20% reduction in
motor speed can reduce the energy requirement by 50%. Additionally, other savings
can be achieved from reduced maintenance cost and longer equipment life [13].
The electricity cost of the treatment plants are shown in Table 4.12. For
prefabricated plants, the cost per month ranged from RM 546 to RM 2975 while for
cast in-situ plants, costs are in the range of RM 149 to RM 2161. On average, the
cost per PE for cast in-situ plants (i.e. RM 0.49/PE) is lower than the cost for
prefabricated plants (i.e. RM 0.74/PE). Higher electricity cost for prefabricated plant
could be resulted from the use of air-lift systems for RAS, WAS, and aerator in the
equalization tanks which run concurrently by using the same pumps systems with the
blower in the aeration tanks. This definitely required bigger pumps size and an extra
pumps are also needed in the equalization tanks.
43
Table 4.12: Electricity cost (RM) of the treatment plants
Prefabricated plant Cast in-situ plant
Date TDN021
(PE 3260)
KTU095
(PE 2230)
KTU084
(PE 1086)
TDN025
(PE 3155)
TKN044
(PE 2262)
TKN019
(PE 1155)
Oct 06 2047 1300 546 2006 904 335
Nov 06 1708 2975 630 1983 1063 394
Dec 06 2013 1806 610 1802 1118 230
Jan 07 1798 2050 1020 1482 1022 149
Feb 07 1910 2690 1377 2161 1172 332
Ave
Cost 1895 2164 837 1887 1056 288
Cost/PE 0.58 0.97 0.77 0.60 0.47 0.25
Av.
Cost/PE RM 0.74 / PE RM 0.49 / PE
It was also observed that the electricity cost of the plants does not necessarily
have direct relationship with the aeration period. As shown in Tables 4.13 and 4.14,
there were many occasions where higher costs of electricity were incurred despite the
use of lower aeration period. It is possible that for a small sewage treatment plant,
other costs such as raw sewage pumps also play a major part in determining the total
electricity cost. As mentioned earlier in section 2.6, that it is difficult to determine
how energy utilization is divided among the consumer within the wastewater
treatment plants. Sometimes all the pumps within treatment plants can represent as
much as 90% of the total energy consumption [8].
44
Table 4.13: Overall electricity cost as a function of aeration time for Prefabricated Plants
Table 4.14: Overall electricity cost as a function of aeration time for Cast In-Situ Plants
4.4.1 Electricity Cost for 2006
Based on IWK Terengganu, the electricity cost of the treatment plants were
shown in Table 4.15. For prefabricated plants, the average cost/PE (i.e. RM 0.75/PE)
is higher than the cost for cast in-situ plants (i.e. RM 0.44/PE)
TDN021 KTU095 KTU084 Date Elect. Cost
(RM) Blower hours
Elect. Cost (RM)
Blower hours
Elect. Cost (RM)
Blower hours
10/06 2047.5 12 1299.8 4 545.5 4 11/06 1707.9 10 2974.8 8 630.2 4 12/06 2013.0 10 1805.8 6 609.9 4 01/07 1797.6 10 2050.1 6 1020.4 6 02/07 1910.0 10 2689.8 6 1377.0 6
TKN025 TKN044 TKN019 Date Elect. Cost
(RM) Blower hours
Elect. Cost (RM)
Blower hours
Elect. Cost (RM)
Blower hours
10/06 2006.4 6 903.8 4 335.4 4 11/06 1982.8 6 1062.6 5 394.3 4 12/06 1801.9 5.5 1118.3 5 230.4 4 01/07 1482.1 5 1022.4 5 149.4 6 02/07 2160.6 5 1172.0 5 332.3 6
45
Table 4.15: Electricity Cost (RM) for 2006 Prefabricated plant Cast in-situ plant
TDN021
(PE 3260)
KTU095
(PE 2230)
KTU084
(PE 1086)
TDN025
(PE 3155)
TKN044
(PE 2262)
TKN019
(PE 1155)
2006 Cost 24,672.25 27.880.15 7452.94 20,520.98 14,503.18 5320.66
Cost/ Month 2,056.02 2,323.34 621.08 1,710.08 1,208.60 443.38
Cost/PE 0.63/PE 1.04/PE 0.57/PE 0.54/PE 0.53/PE 0.38/PE
Overall
Cost/PE RM 0.75 / PE RM 0.44 / PE
Source: [1]
4.5 Operational problems
Based on experience of IWK, operation and maintenance for prefabricated
plants and cast in-situ plants are about the same. However, prefabricated plants have
a higher tendency to tilt and flow short-circuiting especially from aeration tank to
clarifier due to minor land movement or settlement. Due to the structure of tank,
complete emptying of the prefabricated tank during maintenance period is almost
impossible. Normally 1/3 of the liquid in the tank need to be maintained to avoid the
tanks from floating or broken. The durability of UPVC piping system is another set
back for prefabricated fiber compared to D.I. or C.I. pipe for cast in-situ tank.
In cases of piping or power supply problems, the quantity of oxygen supplied
by the aeration is not enough for biological processes and raw sewage become septic
due to longer idling period in the pump sump. The broken and blockage of the
piping systems due to floating materials or rubbish has great effects on the overall
performance for the both treatment plants such as septicity of activated sludge in the
clarifiers, release of odors and lower F/M or MLSS. These phenomena normally
will result in among others things are rising and bulking of sludge and contributed to
the inefficiency of the process.
46
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
Based on the results of this study, several conclusions could be made. They
are as follows:
Small to medium size treatment plants suffered from influent variability in
term of flow and organic loading
The characteristics of the influent show linear relationship between the COD
BOD, and SS values
On average, the cast in-situ plants have better effluent quality as compared to
the prefabricated plants. The former also has better percentage of DOE’s
Standard B compliance as compared to the latter
The Cast in-situ treatment plants are built better structurally and are more
durable than the prefabricated plants
The cast in-situ treatment plants consumed less energy or electricity cost as
compared prefabricated treatment plants.
47
The followings are the recommendations for future works from this study:
Further study is needed to understand the distribution of the electricity costs
before a general guideline of how energy utilization is divided among the
consumer within the treatment plants
Further study will also provide better design values and other factors that
affect the overall performance of the sewerage system, not only to meet the
effluent standard but also in term of the economics and ease of operations
48
REFERENCE
[1] IWK (2007). Asset Management File. unpublished.
[2] IWK (2007). Sewerage Local Plan for Pulau Redang, Terenggnau.
unpublished.
[3] Ministry of Housing and Local Government (1998). Guideline for Developer.
Vol.4. Kuala Lumpur: Digi Master Sdn. Bhd.
[4] Process Energy Services (2006). Energy Project for Water and Wastewater
Facilities. California: Project Profile.
[5] Qassim, S.R. (1999). Wastewater Treatment. Half Day Talk on Theory and
Design to IWK Staff. December 14. Lancaster, PA: Technomic Publishing Co.,
Inc, 20-33.
[6] Metcalf and Eddy (2004). Wastewater Engineering (Treatment and Reuse). 4th
ed. New York: McGraw Hill.
[7] Barnes, D., Bliss, P.J., Gould, B.W., and Vallentine, H.R. (1981). Water and
Wastewater Engineering System. Great Britain: Pitman Publishing Limited.
[8] Anderson, R. and Holmberg, M. (2006). Energy Conservation in Wastewater
Treatment Operation. Lund University, Sweden: Master Thesis.
[9] IWK (2005). Latihan Operator Loji Pembetungan. unpublished.
[10] IWK (1996). Training Course on Design of Small & Medium Treatment Works.
unpublished.
49
[11] American Public Health Association(APHA) (1995). Standard Methods for
Water and Wastewater Examinations. 19th ed. USA.
[12] Process Energy Services (2006). Modeling Wastewater Aeration System to
Discover Energy Saving Opportunities. California: Newsletter.
[13] Department of Environment Protection Bureau of Land and Water Quality
(2002). Energy Conservation in Wastewater Treatment Facilities. Maine:
O&M Newsletter.
50
APPENDIX A
SAMPLING RESULTS
Company No. 211763-P MONTHLY ANALYTICAL REPORT Central Laboratory Services Loji Rawatan Kumbahan Sg. Besi Lot 33519 Bukit Jalil 56000 Kuala Lumpur
Unit Manager : En. Mohd ShukriUnit : Kuala Terengganu
Following tests were conducted according to standard methods published by American Public Health Association (APHA) 19th edition, 1995BOD - APHA 5210 B & APHA 4500 - OG COD - APHA 5220 B Ammonia - APHA 4500-NH3FpH - APHA 4500-H SS - APHA 2540 D
INDAH LOCATION SAMPLING STP SPL REF DATE TYPE TYPE BOD, mg/l COD, mg/l NH3, mg/l pH O&G, mg/l SS, mg/l
TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN09-Oct-06 HK FE 35 133 32 7.3 57TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN09-Oct-06 HK ML 6.8 1199TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN06-Nov-06 HK FE 106 296 38 6.9 95TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN06-Nov-06 HK ML 6.7 1259TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN11-Dec-06 HK FE 25 81 40 7.1 18TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN11-Dec-06 HK ML 7.5 96TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN08-Jan-07 HK FE 8 44 10 7.4 23TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN15-Jan-07 HK FE 8 48 13 6.7 34TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN29-Jan-07 HK FE 14 37 36 7.4 22TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN12-Feb-07 HK FE 19 82 36 7.4 17TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN05-Mar-07 HK FE 10 44 28 7.6 9TDN021 TAMAN MURNI PERDANA (FASA 1A) , DUNGUN05-Mar-07 HK ML 7.4 2516
Blank - Test not required * - Questionable test result deleted0 - Not detected
RESULTS
59
APPENDIX B
PHOTOGRAPH OF TREATMENT PLANT
TDN021 (PE:3260) Taman Murni Perdana, Dgn – Prefabricated EA
KTU095 (PE:2230) Taman Permint Perdana, K.Trg – Prefabricated EA
KTU084 (PE:1056) Pangsapuri Permint Harmoni, K.Trg – Prefabricated EA
TDN025 (PE:3155) Taman Rakyat Jaya, Dgn – Cast-In-Situ
TKN044 (PE:2262) Taman Semarak, Kmn – Cast-In-Situ EA
TKN019 (PE:1155) Taman Samudera Timur, Kmn – Cast-In-Situ
KTU082 (PE:2130) Taman Sri Kolam, K.Trg – Prebaricated EA
64
APPENDIX C
FLOW MEASUREMENT DATA
