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EFFICIENCY OF AERATION SYSTEM INWASTEWATER TREATMENT PLANTS.

SRI RUTHIRA KUMAR

UNIVERSITY TEKNOLOGI MALAYSIA


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UNIVERSITI TEKNOLOGI MALAYSIA

BORANG PENGESAHAN STATUS TESIS

JUDUL : EFFICIENCY OF AERATION SYSTEM IN WASTEWATER TREATMENTPLANTS

SESI PENGAJ IAN : 2006 / 2007 II

Saya

(HURUF BESAR)

mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di PerpustakaanUniversiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:

1. Tesis adalah hakmilik Universiti Teknologi Malaysia.2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan

pengajian sahaja.3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi

pengajian tinggi.4. ** Sila tanda ( )

SULIT (Mengandungi maklumat yang berdarjah keselamatan ataukepentingan Malaysia seperti yang termaktud di dalam AKTA

RAHSIA RASMI 1972)

TERHAD (Mengandungi maklumat yang TERHAD yang telah ditentukanoleh organisasi/badan di mana penyelidikan dijalankan)

TIDAK TERHAD

Disahkan oleh

(TANDATANGAN PENULIS) (TANDATANGAN PENYELIA)

Alamat Tetap: No 22 Laluan Meru Valley 1Taman Peranginan LembahMeru 30020 Ipoh, Perak

PM.Dr Fadil Bin Othman

Nama Penyelia

Tarikh: Tarikh:

CATATAN: * Potong yang tidak berkenaan.** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi

berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagaiSULIT atau TERHAD.

Tesis dimaksudkan sebagai tesis bagi ijazah Doktor Falsafah dan Sarjana secara penyelidikan,atau disertai bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan ProjekSarjana Muda (PSM).

SRI RUTHIRA KUMAR A/L AMIRTHALINGAM


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1

i

Saya/Kami* akui bahawa saya telah membaca karya ini dan pada pandangansaya/kami karya ini adalah memadai dari segi skop dan kualiti untuk tujuan

penganugerahan ijazah Sarjana Muda / Sarjana / Doktor Falsafah

..

Tandatangan : .

Nama Penyelia I: ..

Tarikh : ..

Tandatangan : .

Nama Penyelia II: ..

Tarikh : ..

Tandatangan : .

Nama Penyelia III: ..

Tarikh : ..

* Potong yang tidak berkenaan


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Saya akui karya ini adalah hasil kerja saya sendiri kecuali nukilandan ringkasan yang tiap-tiap satunya telah saya jelaskan sumbernya.

Tandatangan: ..

Nama : ..

Tarikh: ..


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BAHAGIAN A Pengesahan Kerjasama*

Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui

kerjasama antara ________________________ dengan ______________________

Disahkan oleh:

Tandatangan : Tarikh : ....

Nama :

Jawatan : (Cop Rasmi)

* J ika penyediaan tesis / projek melibatkan kerjasama

BAHAGIAN B Untuk K egunaan Pejabat Sekolah Pengajian Siswazah

Tesis ini telah diperiksa and diakui oleh:

Nama dan Alamat Pemeriksa Luar :

.

.

Nama dan Alamat Pemeriksa Dalam :

.

.

Nama Penyelia Lain (jika ada) :

.

.

Disahkan oleh Penolong Pendaftar di SPS:

Tandatangan : . Tarikh : .

Nama :


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EFFICIENCY OF AERATION SYSTEM INWASTEWATER TREATMENT PLANTS

SRI RUTHIRA KUMAR

This project is submitted as a partial requirement for the awarding of the degreeof Master of Engineering (Civil-Wastewater Engineering)

Faculty of Civil EngineeringUniversity Teknologi Malaysia

MAY 2007


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DEDICATION

I would like to dedicate this project report to my parents(V. Amirthalingam and S.Sarojini Thevi), wife ( Lily) and

my beloved daughter (Sanjana Sri) for their constant loveand encouragement


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APPRECIATION

The author would like to extend his most sincere appreciation and gratitude to

Associate Professor Dr. Fadil Othman for his guidance and encouragement

throughout the course.

Special gratitude also goes to Indah Water Konsortium Sdn. Bhd for without its

financial sponsorship and the releasing of its professional staffs as lecturers, my

colleagues and my-self would not have completed this post-graduate course in

Wastewater Engineering.

Last but not least, I would like to record my most sincere gratitude to my colleagueMiss Monica who had taken a lot of her own time to type and proof read this project

report for me.


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ABSTRACT

The most important factor in selecting aeration equipment for a specific

application is the oxygen transfer rate. Other factors that are equally important are

reliability, serviceability, capital cost, system appurtenances and cost of operation and

maintenance. Although there are many systems designed to aerate and mix the waste

water, they vary in their effectiveness in providing uniform oxygen dispersion. It is

the intention of the study to evaluate the performance of different types of aeration

devices based on dissolved oxygen (DO) readings and costing. To achieve this

objective, experimental work were carried out on five different aeration devices

namely brush aerator, tornado, surface aerator, aspirator and diffusers on five different

sewerage treatment plant with average PE of 2000. Through the experiment it was

found that aspirator was able to achieve 1 to 2 mg/l dissolved level while meeting the

regulators requirement on biochemical oxygen demand level. In the terms of

electricity, aspirator needed the lowest consumption compared to the other type of

device system. A detailed study on costing was done for the last 6 months in term of

operating and maintenance on the aeration device and was found that aspirator was

the cheapest to maintain compared to the others. While meeting the biochemical

oxygen demand standard as require by the regulators, this outcome of the study would

be a crucial factor when selecting a suitable aeration device in sewerage industry in

future.


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ABSTRAK

Kadar resapan oksigen merupakan faktor yang paling penting semasa

pemilihan peralatan untuk pengudaraan Faktor-faktor lain termasuk realiabiliti,

servisabiliti, kos pembelian, kos peralatan sampingan serta kos operasi dan

penyelenggaran. Walaupun terdapat berbagai-bagai sistem direkabentuk untuk

mengudarakan serta mengadunkan kumbahan, ia berbeza dari segi kecekapan dalam

menghasilkan oksigen yang setara. Tujuan projek ini adalah untuk menilai kecekapan

pelbagai jenis peralatan pengudaraan melalui bacaan oksigen terlarut serta

perbelanjaan penyelenggaraan dan operasi setiap loji kumbahan. Untuk mencapai

objektif ini satu kajian telah dijalankan terhadap lima jenis peralatan aeration yang

berbeza iaitu brush aerator, tornado, surface aerator, aspirator serta

diffusers yang terdapat pada lima loji kumbahan tersebut yang mempunyai penduduk

setara sekitar 2500. Melalui kajian ini, telah terbukti bahawa aspirator mampu

mencapai oksigen terlarut dissolved oksigen sebanyak antara 1 mg/L hingga 2

mg/L. Aspirator juga menggunakan kadar elektrik yang rendah berbanding dengan

peralatan pengudaraan yang lain. Satu kajian perbelanjaan terperinci telah dijalankan

selama enam bulan untuk penyelenggaran peralatan pengudaraan dan terbukti

bahawa aspirator merupakan peralatan yang paling murah untuk diselenggarakan.

Keputusan dari kajian ini merupakan faktor terpenting dalam pemilihan peralatanpengudara aeration yang sesuai dalam industri pembetungan pada masa hadapan.


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TABLE OF CONTENTS

CHAPTER TITLE PAGEDECLARATION i

DEDICATION ii

APPRECIATION iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENTS vi

LIST OF TABLES vii

LIST OF FIGURES viii

LIST OF APPENDICES ix

CHAPTER 1 - INTRODUCTION

1.1. MALAYSIAN SEWERAGE SYSTEM 1

1.2. IMPORTANCE OF A SEWERAGE SYSTEM 1

1.3. SEWERAGE SYSTEM 2

1.4. UNCONNECTED SEWERAGE SYSTEMS 4(TRADITIONAL TOILET)

1.5. CONNECTED SEWERAGE SYSTEMS 4

1.6. MECHANICAL PLANTS 4

1.7. MONITORING EFFLUENT 4

1.8. OBJECTIVE 6

1.9. SCOPE OF STUDY 6

CHAPTER II - LITERATURE REVIEW

2.1. INTRODUCTION 7

2.2. OXYGEN TRANSFER 7

2.3. FACTORS AFFECTING OXYGEN REQUIREMENTS 92.4. AERATION 10

2.4.1. DIFFUSED-AIR AERATION 13

DIFFUSES 13

POROUS DIFFUSES 15

NON-POROUS DIFFUSES 16

OTHER AIR-DIFFUSION 17

DIFFUSER PERFORMANCE 17

BLOWERS 20

AIR PIPING 22

2.4.2. MECHANICAL AERATORS 22

AERATOR PERFORMANCE 23

MECHANICAL AERATION 23

2.5. OXYGEN DIPERSION EFFICIENCY AND MIXING 24


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CHAPTER II I - METHODOLOGY

3.1. INTRODUCTION 26

3.2. MEASURING AERATION DISSOLVED OXYGEN 273.2.1 WINKLER TITRATION METHOD

3.2.2 MEMBRANE ELECTRODE METHOD

3.3. AERATION BASIN DISSOLVED OXYGEN

PROFILES 28

CHAPTER IV - RESULTS & DISCUSSION

4.1. DISSOLVED OXYGEN 29

4.2. COSTING 34

OPERATIONAL AND MAINTENANCE COSTING /

CAPITAL COST 36

4.3. ELECTRICITY CONSUMTPTION 37

CHAPTER V - CONCLUSION AND SUGGESTION

5.1. CONCLUSION 40

5.2. SUGGESTION 41

REFERENCES 42

APPENDICES 43


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LIST OF TABLES

TABLES TITLES PAGES

1.1. EFFLUENT STANDARD BY ENVIRONMENT 5QUALITY ACT (1974)

2.1. EFFICIENCY OF VARIOUS AERATION SYSTEM 11IN KWH/KG

2.2. DESCRIPTION OF COMMONLY USED DEVICES 12

FOR WASTEWATER AERATION

2.3. DESCRIPTION OF COMMONLY USED AIR 14DIFFUSION DEVICES

3.1. TYPE OF AERATION 26

4.1. DISSOLVED OXYGEN READINGS 31AT TAMAN GERMUDA

4.2. DISSOLVED OXYGEN READINGS AT 31TAMAN PAKATAN JAYA

4.3. DISSOLVED OXYGEN READINGS AT 31TAMAN ANDA

4.4. DISSOLVED OXYGEN READINGS AT 32TAMAN DESA KEBUDAYAAN

4.5. DISSOLVED OXYGEN READINGS AT 32TAMAN MEDAN PENGKALAN IMPIAN

4.6. CHART & SUMMARY OF AVERAGE 33DISSOLVED OXYGEN FOR DIFFERENT PLANTS

4.7. CAPITAL COST OF DIFFERENT TYPE OF AERATION 35DEVICES

4.8. SUMMARY OF OPERATIONAL AND MAINTENANCE 36COSTING FROM NOV06-APRIL06

4.9. SUMMARY OF ELECTRICITY CONSUMPTION 38

FROM NOV06-APRIL06


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LIST OF FIGURES

FIGURES TITLES PAGES

1.1. WHAT ENTERS THE SEWERAGE SYSTEM 3FROM HOUSEHOLDS

1.2. MECHANICAL PLANTS 4

2.1. PICTURES OF BLOWERS 19

4.1. GRAPH DISSOLVED OXYGEN AT EACH TAMAN 33

4.2. GRAPH CAPITAL COST OF AERATION DEVICE 35

GRAPH SUMMARY OF OPERATIONAL 36

AND MAINTENANCE COSTING

4.4 GRAPH SUMMARY OF ELECTRICITY 38

CONSUMPTION

4.5 RESULTS OF MIXING CAPABILITIES AND 39

FLOW PATTERN


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LIST OF APPENDICES

APPENDICES TITLES PAGES

A. SUMMARY OF SAMPLING RESULTS

FOR SEWERAGE PLANTS 43

B. PHOTOGRAPH OF VARIOUS AERATIONDEVICE 44


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CHAPTER 1

INTRODUCTION

1.1 MALAYSIAN SEWERAGE SYSTEM

An effective sewerage system ensures sewage being treated and disposed in a

safe manner. Sewage includes human waste, urine and wastewater from kitchens,

bathrooms and laundries. Sewerage systems are designed to collect, transfer, treat and

dispose of human waste and wastewater. The system serves government, domestic,

commercial and industrial properties in economical and environmentally responsible

manner.

In some countries the sewerage systems are designed to treat commercial and

industrial sewage, toxic waste and manufacturing waste. However Malaysias

sewerage system treats only human waste and household wastewater. Industrial and

trade waste is treated separately by on site industrial waste treatment plant. None of

the industrial waste or trade effluent is allowed to be discharged into existingsewerage system.

1.2 IMPORTANCE OF A SEWERAGE SYSTEM

In certain places in Malaysia, where there are no sewerage systems, sewage

ends up in waterways. This is usually due to toilets discharging straight into the

waterways or sewer pipes discharging into the sea. Irrespective of the manner, in

which the sewage ends up in our waterways, it can have detrimental effects on public

health and the environment. Untreated human waste may carry infectious pathogenic

organisms into our rivers. Such polluted rivers cause the spread of diseases like

cholera, typhoid and hepatitis A. polluted rivers will contaminate sea life, particularly

fish, cockles and prawns. People who eat this contaminated seafood can become

seriously ill. Incidents of waterborne diseases such as these are not uncommon in

Malaysia and have often been traced to sewage contaminated waters.


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Other than the tremendous public health risk that untreated sewage poses, it

also pollutes our environment. This is because sewage is able to consume oxygen

normally found dissolved in river water, for example, will mean that eventually the

river will lack sufficient oxygen to allow aquatic life and plants to survive.

As a result of this, there will be drop in supply of seafood and aquatic plants.

Aquatic plants produce oxygen, which keep the river alive. This vicious cycle will

eventually result in the river being dead. A dead river emits an unpleasant odor, is

unsightly, poses a health risk and does not support any plant or animal life.

Sadly enough, today 72% of the rivers in Malaysia are polluted and 65% of all

pollution loads has been identified as raw sewage. A step towards keeping our rivers

clean is to treat all the sewage that is generated by the community.

1.3 SEWERAGE SYSTEM

A modern and efficient sewerage system is vital of a developing nation such

as ours if we are to successfully move towards Vision 2020. A reliable system will not

only ensure that our increasing population is kept away from unnecessary health risks

but also that our water resources are preserved for future generations.

Sewage comprises of various pollutants that enter the sewerage system from

domestic, commercial and industrial premises. It is more than just what goes down a

toilet as it also includes wastewater from kitchen, bathrooms and laundries.

Many of our activities at home generate pollutants that find their way into the

sewerage system. Unless treated at a sewage treatment plant, raw sewage and

pollutants can end up in our drains, rivers and coastal water. It risks public health,

contaminating water resources and polluting the environment.

In Malaysia, sewerage systems range from simple toilets providing little or no

treatment to sewage to modern sewage treatment plants that employ mechanical

means to treat large volumes of sewage to acceptable environmental standards.


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WHAT ENTERS THE SEWERAGE SYSTEM FROM HOUSEHOLDS

Figure : 1.1: - Source : Indah Water Konsortium 1998

There are various sewerage systems that produce effluent of differentstandards. There are simple toilets, where sewage undergoes no treatment causing it to

be highly damaging to our environment, to the more modern mechanical plants that

are able to produce Standard A effluent. Sewerage systems can be categorized into

two board categories that are unconnected sewerage systems and connected sewerage

system.

TOILET

Faeces, toilet paper,

Urine,Sanitary goods,

medicine,Bacteria + viruses

Disposable nappies,Toys

BATHROOM

Shower/ bath waterSoapHair

Nail Clippings

Toothpaste tubesToothbrushes

Blood

KITCHEN

Sink Water

Leftover foodFat + grease

Cutlery + GlassTea leaves

Coffee Grinds

LAUNDRY

Clothes Washing

DetergentsLint

HouseholdCleaning bleach

SEWERAGE LINE


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1.4. UNCONNECTED SEWERAGE SYSTEMS (TRADITIONAL TOILETS)

Simple toilets come under this category. These toilets were very popular

before the modern day toilets came into the scene. Depending on its make, there are

two types of traditional toilets. Firstly, toilets that do not treat the sewerage and

secondly, toilets that partially treat the sewage.

1.5. CONNECTED SEWERAGE SYSTEMS

In connected sewerage systems, sewage outlets from a number of premises are

connected to a sewage treatment plant via a network of underground sewer pipes.

Modern and efficient sewage treatment plants are the best way to treat sewage.

Connected sewerage system generally comprise of a network of underground sewer

pipes, pump stations, sewage treatment plants and sludge treatment facilities.

Connected sewerage system generally operates by gravity so sewage treatment plants

should be located at the outlet of drainage catchments to capture all the sewage from

the catchments without the need for costly pumping.

1.6. MECHANICAL PLANTS

In Malaysia, 11% of treatment plants are made up of various types of

mechanical plants. These plants run on mechanical equipment that accelerates the

breakdown of sewage. In the long term it is hoped that Malaysias sewerage system

will be made more efficient by standardising the types of plants used.

The diagram below shows an extended aeration plant where air is bubbled

through sewage to accelerate the breakdown of sewage by bacteria.

Figure : 1.2.: - Source : I ndah Water Konsortium 1998


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1.7. MONITORING EFFLUENT

Various pollutants in sewage are analyzed in order to understand how sewage

should be treated and to examine the effect of treated sewage (effluent) on the

environment.

Effluent from all sewage treatment plants is sampled at regular intervals and

analyzed in modern laboratories to ensure it complys the required standards. These

tests are carried out as part of a monitoring programmed to ensure that Indah Water

meets its operational license conditions and that its treatment processes are operating

efficiently. This provides for a cleaner and safer environment that improves the living

conditions of Malaysia.

The two most important parameters measured are biological oxygen demand

(BOD) and suspended solids (SS). BOD is a measurement of the amount of oxygen

sewage will consume over a given time. High BOD means that sewage will rapidly

consume all the oxygen naturally dissolved in streams, rivers and lakes killing all

aquatic life and turn the water septic and smelly. SS is a measurement of the

undissolved material in sewage. High SS leads to sludge deposit in the waterways

causing significant environmental degradation.

Table 1.1.: Effluent Standard by Environmental Quality Act (1974)

Biochemical

Oxygen

Demand (BOD)

Suspended

Solids (SS) Oil &

Grease

COD

STANDARD A 20 mg/L 50 mg/L 0 mg/L 50 mg/L

STANDARD B 50 mg/L 100 mg/L 10 mg/L 100 mg/L

If the effluent is discharged upstream of a water supply intake point, it should

meet Standard A. For effluent that is discharged downstream, it should meet Standard

B. These standards are set by the Environmental Quality Act (1974).


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1.8. OBJ ECTIVE

The objective of this study is to determine the most effective aeration device

in wastewater industry by monitoring their oxygen transfer and costing which

includes operational and maintenance cost, the capital cost and electricity

consumption of each and every aeration device.

1.9. SCOPE OF STUDY

The study consists of a thorough experimental work at five sewerage treatment

plants using five sewerage treatment plants with five different aeration devices. The

five sewerage treatment plants were observed based on their oxygen transfer level. It

was carried out by using dissolved oxygen meter on a daily basis for one week.

During the experiment, five sewerage treatment plants sampling were carried out in

order to monitor the BOD level. These would enable to verify the most efficient

aeration device while meeting the Standard as required by the regulators.

There was also a study on the energy saving of different type of aeration

device. It was carried out by monitoring the electricity consumption of aeration

device for a period of six months. Capital cost and the operation and maintenance cost

were also taken into consideration as factors before deciding the most effective

aeration device.


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CHAPTER II

LITERATURE REVIEW

2.1. INTRODUCTION

In the treatment of wastewater, an aeration system is ineffective in providing a

completed and uniform transfer of oxygen without the capability to disperse oxygenthroughout the entire process/basin. Although many systems are designed to aerate

wastewater, they vary in their effectiveness in providing uniform oxygen dispersion.

In this literature review, the importance of oxygen transfer and types of

aeration system that normally being practiced in Malaysian sewerage system were

discussed.

2.2. OXYGEN TRANSFER

Oxygen is supplied to the mixed liquor in an aeration tank by dispersing airbubbles through sub-merged diffusers or by entraining air into the liquid by

mechanical means. Air diffusers are porous plates, tubes or nozzles attached either to

air piping on the bottom of the tank or to pipe headers that can be lifted out of the

tank. Centrifugal blowers provide compressed air to the diffusers. Coarse-bubble

devices are orifices or nozzles designed so that the discharged air is broken up into

bubbles and dispersed in the surrounding liquid. Fine-bubble devices are porous

materials that release air as fine bubble. Although each kind of diffuser has individual

features, coarse-bubble nozzles are noted for maintenance-free operation, but fine-bubble diffusers have been the advantage of higher oxygen-transfer efficiency.

Mechanical aerators are horizontal paddle, vertical turbine, and vertical-turbine draft

tube. A horizontal rotor rotates partially submerged in an aeration channel. A vertical

turbine may be surface unit or completely submerged with compressed air supplied

under the rotating blade. For deep mixing, a vertical turbine may be in a draft tube so

that liquid from the bottom of the tank is drawn up through the tube and discharged at

the surface.


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Oxygen transfer is a two-phase process. First, gaseous oxygen is dissolved in

the wastewater by diffused or mechanical aeration. Then the dissolved oxygen is

taken up by the microorganisms in metabolism of the waste organic matter. If the rate

of oxygen utilization exceeds the rate of dissolution, the dissolved oxygen in the

mixed liquor is depleted. The oxygen transfer from the air bubbles into solution.

The K-factor depends on wastewater characteristics and more important on the

physical features of knowledge of the basic concepts of oxygen transfer and uptake, is

helpful in understanding operational problems generally associated with aeration

processes. An oxygen deficiency in an aerating basin is possible if the rate of

biological utilization exceeds the capabilities of the equipment. For example, organic

overloading of an extended aeration system that is equipped with coarse-bubble

diffusers set a shallow depth can result in a dissolved oxygen level of less than 0.5

mg/l even though the tank contents are being vigorously mixed by air bubbles

emitting form diffusers. Perhaps a situation that occurs more frequently in practice isuneconomical operation from over aeration, producing a dissolved oxygen level

greater than is necessary in the mixed liquor. Since biological activity is just as great

at low levels and the transfer rate from air to dissolved oxygen increases with

decreasing concentration, it is logical to operate a system as close to critical minimum

dissolved oxygen as possible. Operation of the air compressors at reduced capacity, or

even turning off one blower on weekends may be feasible to conserve electrical

energy with no adverse effects to the biological process. Automatic control of blowers

using dissolved oxygen probes has increased with improvements in control systems

and the reliability of dissolved oxygen meters. (Metcalf and Eddy. 1991)


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2.2. FACTORS AFFECTING OXYGEN REQUIREMENTS

There are many factors that affect oxygen requirements of the bacteria in the

aeration basin. But in this chapter, the discussion or explanation is only on two

factors. The first factor is the direct relationship between the influent BOD

concentration and the aeration basin dissolved oxygen. As the concentration of BOD

entering the aeration basin rises, the amount of oxygen required to maintain DO levels

rises also. If you dont respond to increase influent BOD levels by increasing aeration

rates, the level of dissolved oxygen in the aeration basin will drop.

Some operators mistakenly assume that if dissolved oxygen drops, a toxic

material has entered the aeration basin and killed or inhibited the bacteria. Actually,

the opposite happens. Healthy bacteria are the agents that use the oxygen in the mixed

liquor. If you kill or slow them down, the aeration basin dissolved oxygen will

increase (Tim Hobson. 1992)

There is another relationship concerning dissolved oxygen and the amount of

bacteria in the aeration basin that you should be aware of. The amount of aeration

required to maintain a given level of dissolved oxygen is directly proportional to the

amount of bacteria you have in the aeration basin. As the concentration of bacteria in

the basin goes up, aeration rates must be increased to maintain a given level of

dissolved oxygen.

If you are having trouble-maintaining dissolved oxygen and your solids level

in the aeration basin is high, you can increase dissolved oxygen by washing more

sludge to bring solids levels down. (Tim Hobson. 1992).


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2.4. AERATION

Aeration is the process by which the area of contact between water and air is

increased, either by natural or mechanical means, resulting in air being suspended in

air. Aeration is the most important operation in the treatment process, to provide

oxygenation and mixing. The aeration facilities are designed to meet the calculated

oxygen demand of the process while maintaining in the aeration tank minimum

Dissolved oxygen of about 1-2 mg/l which is necessary for proper development of

biological sludge.

In addition to supplying dissolved oxygen, the aeration devices have also to

provide adequate mixing ad agitation so that the mixed liquor suspended solids do not

settle down. This way aeration increases the contact opportunity between the floc and

sewerage.

To summarize aeration serves the following three functions:

(i) Oxygenation of the mixed liquor

(ii) Flocculation of the colloids in sewage influent and

(iii) Suspension of activated sludge floc.

Following are the three methods, which are usually employed for the purpose of

aeration in activated sludge process:

(i) Diffused air aeration

(ii) Mechanical aeration

(iii) Combined diffused air and mechanical aeration

One of the pollutants of water is organic matters. The reason why organic

matters are considered water pollutants is that microorganism feed on them and in the

process used up the dissolved oxygen needed for aquatic life. If the organic matters

are in sufficient quantity, this can lead to nearly all the dissolved oxygen being used

up, aquatic life killed, and to anaerobic conditions in which anaerobic microorganism

produces hydrogen sulfite and other odorous constituents are produced.


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The purpose of aeration is to improve their physical and chemical

characteristics, to remove or reduction of objectionable taste and odor and to

precipitate inorganic contaminants such as iron and manganese. In wastewater

treatment, the purpose of aeration is to ensure continued aerobic conditions for the

microorganism to degrade the organic matters. The efficiency of aeration systems can

be measured in different ways. Different aeration systems have different efficiency.

(Metcalf and Eddy. 2004)

The exact efficiency of an aeration system is veries, depending on

circumstances under which it is measured such as liquid depth, density of diffuser,

energy level in the tank, etc.. The following Table 2.1 is a table of the efficiency of

various aeration systems adapted to give values in kilowatt-hour per kilogram of

oxygen. It is adapted from the table given by Environmental Dynamics.

Table 2.1.: - Efficiency of various aeration system in kWH/kg

Aeration system kWh/kgMechanical aeration systemsBrush aerators surface aeration

Slow speed surface

High speed splash surface aeration

Induced surface aeration

0.47-0.66

0.47-0.55

0.51-0.66

1.10-1.64

Combination systemsSubmerged turbine

Jets (pumps with compressors)

0.66-1.10

0.47-0.82

Diffused Aeration, Coarse BubbleStatic tubes

Wide band grid

Misc. coarse bubble

0.47-0.82

0.47-0.66

0.47-0.82

Diffused Aeration, Fine PoreCeramic disc or ceramic dome grid

Flexible membrane disc

Advanced technology membrane

0.23-0.33

0.23-0.41

0.14


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Table 2.2.: - Description of commonly used devices for wastewater aeration

Classification Description Use or application

Submerged:

Fine-bubble

(fine-pore)

system

Bubbles generated with ceramic, plastic, or

flexible membranes (domes, tubes, disks,

plates, or panel configuration)

All types of activated-sludge

processes

Coarse bubble

(nonporous)

system

Bubbles generated with orifices, injectors

and nozzles, or shear plates


processes, channel and grit

chamber aeration and aerobic

digestion

Sparger turbine Low-speed turbine and compressed-air

injection


processes and aerobic digestion

Static tube mixer Short tubes with internal baffles designed

to retain air injected at bottom of tube in

contact with liquid

Aerated lagoons and activated-

sludge processes

Jet Compressed air injected into mixed liquid

as it pumped under pressure through jet

device


processes, equalization tank

mixing and aeration, and deep

tank aeration

Surface:

Low-speed

turbine aerator

Large-diameter turbine used to expose

liquid droplets to the atmosphere

Conventional activated-sludge

processes, aeration lagoons, and

aerobic digestion

High-speed

floating aerator

Small-diameter propeller used to expose

liquid droplets to the atmosphere

Aerated lagoons and aerobic

digestion

Aspirating Inclined propeller assembly Aerated lagoons

Rotor-brush or

rotating-disk

assembly

Blades or disks mounted on a horizontal

central shaft are rotated through the liquid.

Oxygen is induced into the liquid by the

splashing action of the rotor and by

exposure of liquid droplets to the

atmosphere

Oxidation ditch, channel

aeration and aerated lagoons


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2.4.1. DIFFUSED-AIR AERATION

The two basic methods of aerating wastewater are (1) injection of air or pure

oxygen into the wastewater with submerged diffusers or other aeration devices or (2)

to agitation of the wastewater mechanically so as to promote solution of air from the

atmosphere. A diffused-air system consists of diffuses that are submerged in the

wastewater, header pipes, air mains and the blowers and appurtenances through which

the air passes. The following discussion covers the selection of diffusers, the designs

of blowers and air piping.

Diffuses

In the past, the various diffusion devices have been classified as either fine

bubble or coarse bubble, with the connotation that fine bubbles were more efficient in

transferring oxygen. The definition of terms and the demarcation between fine and

coarse bubbles, however, have not been clear, but they continue to be used. The

current preference is to categorize the diffused aeration systems by the physical

characteristics of the equipment.


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Three categories are defined: (1) porous or fine-pore diffusers, (2) nonporous

diffusers, and (3) other diffusion devices such as jet aerators, aspirating aerators and

U-tube aerators. The various types of diffused-air devices are described in Table 2.3

Table 2.3.: - Description of commonly used air diffusion devices

Type of diffuser ordevice

Transfer efficiency Description

Porous

Disk High Rigid ceramic disks mounted on air-distribution pipes near the tank floor.

Dome High Dome-shaped ceramic diffusers mountedon air-distribution pipes near the tankfloor.

Membrane High Flexible porous membrane supported ondisk mounted on air-distribution grid

Panel Very High Rectangular panel with a flexible plasticperforated membrane

NonPorous

Fixed orifice

Orifice Low Devices usually constructed of moldedplastic and mounted in air-distributionpipes.

Slotted tube Low Stainless-steel tubing containingperforations and slots to provide a wide

band of diffused air

Static Tube Low Stationary vertical tube mounted on basinbottom and functions like an air-liftpump


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Porous Diffuses

Porous diffuses are made in many shapes, the most common being domes,

disks and membrane. Tubes are also used. Plates were once the most popular but are

costly to install and difficult to maintain. Porous domes disks and membrane has

largely supplanted plates in new installations. Domes, disks, or tube diffuses are

mounted on or screwed into air manifold, which may run the length of the tank close

to the bottom and along one or two sides, or short manifold headers may be mounted

on movable drop pipes on one side of the tank. Dome and disk diffusers may also be

installed in a grid pattern on the bottom of the aeration tank to provide uniform

aeration throughout the tank.

Numerous materials have been used in the manufacture of porous diffusers.

These materials generally fall into the categories of rigid ceramic and plastic materials

and flexible plastic, rubber or cloth sheaths. The ceramic materials consist of rounded

passageways through which compressed air flows. As the air emerges from the

surface pores, pore size, surface tension and air flow rate interact to produce the

bubble size. Porous plastic materials are newer developments. Similar to the ceramic

materials, the plastics contain a number of interconnecting channels or pores through

which the compressed air can pass. Thin, flexible sheaths made from soft plastic or

synthetic rubber have also been developed and adapted to disks and tubes.

Air passages are created by punching minute holes in the sheath material.

When the air is turned on, the sheath expands and each slot acts as variable aperture

opening; the higher the air flow rate, the greater the opening.Rectangular panels that use a flexible polyurethane sheet are also used in

activated-sludge aeration. The panels are constructed with a stainless steel frame and

are placed on or close to the bottom of the tank and anchored.


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Advantages cited for aeration panels are:

(1)Ultra-fine bubbles are produced that significantly improve oxygen transfer and

system energy efficiency

(2)Large areas of the tank floor can be covered, which facilities mixing and oxygen

transfer, and

(3)Foul ants can be dislodged by bumping, i.e. increasing the airflow to flex the

membrane.

Disadvantages cited for aeration panels are:

(1)The panel is a proprietary design and thus lacks competitive bidding,

(2)The membrane has a higher head loss, which may affect blower performance in

retrofit applications, and

(3)Increased blower air filtration is required to prevent internal fouling.

With all porous diffusers, it is essential that the air supplied be clean and free

of dust particles that might clog the diffusers. Air filters, often consisting of viscous

impingement and dry-barrier type, are commonly used. Precoated bag filters and

electrostatic filters have also been used. The filters should be installed on the blower

inlet. (S.K. Gang, 2004)

Nonporous Diffuses

Several types of nonporous diffusers are available. Nonporous diffusers

produce larger bubbles than porous diffusers and consequently have lower aeration

efficiency; but the advantages of lower cost, less maintenance and the absence of

stringent air-purity requirements may offset the lower oxygen transfer efficiency and

energy cost. Typical system layouts for orifice diffusers closely parallel the layouts

for porous dome and disk diffusers; however single and dual roll spiral patterns using

narrow or wide-band diffuser placement are the most common. Application for orifice

and tube diffuser includes aerated grit chambers, channel aeration, flocculation basin

mixing, aerobic digestion and industrial waste treatment.


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In the static tube aerator air is introduced at the bottom of a circular tube that

can vary in height from 0.5 to 1.25 m (1.5 to 4.0 ft). Internally, the tubes are fitted

with alternately placed deflection plates to increase the contact of the air with the

wastewater. Mixing is accomplished because the tube aerator acts as an airlift pump.

Static tubes are normally installed in a grid-type floor coverage pattern.

Other Air-Diffusion

Devices Jet aeration combines liquid pumping with air diffusion. The pumping

system re-circulates liquid in the aeration basin, ejecting it with compressed air

through a nozzle assembly. This system is particularly suited for deep (>8 m) tanks.

Aspirating aeration consists of a motor-driven aspirator pump. The pump draws air in

through a hollow tube and injects it underwater where both high velocity and

propeller action creates turbulence and diffuses the air bubbles. The aspirating device

can be mounted on a fixed structure oron pontoons. U-tube aeration consists of a deep

shaft that is divided into two zones. Air is added to the influent wastewater in the

down comer under high pressure; the mixture travels to the bottom of the tube and

then backs to the surface.

The great depth to which the air-water mixture is subjected results in high

oxygen transfer efficiencies because the high pressure forces all the oxygen into

solution. U-tube aeration has particular application for high-strength wastes.

Diffuser PerformanceThe efficiency of oxygen transfer depends on many factors, including the type,

size, and shape of the diffuser; the air flow rate; the depth of submersion; tank

geometry including the header and diffuser location; and wastewater characteristics.

Aeration devices are conventionally evaluated in clean water and the results adjusted

to process operating conditions through widely used conversion factors. Typical clean

water transfer efficiencies and air flow rates for various diffused-air devices.


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Typically, the standard oxygen transfer efficiency (SOTE) increases with

depth; the transfer efficiencies for the 4.5-m (15-ft) depth, the most common depth of

submergence. Data on the variation of SOTE with water depth for various diffuser

types can be found in WPCF (1988).

The variation of oxygen transfer efficiencies with the type of diffuser and

diffuser arrangements. Additional data on the effects of diffuser arrangement on

transfer efficiency are reported in V.S. EPA (1989).

Oxygen transfer efficiency (OTE) of porous diffusers may also decrease with

use due to internal clogging or exterior fouling. Internal clogging may be due to

impurities in the compressed air that have not been removed by the air filters.

External fouling may be due to the formation of biological slimes or inorganicprecipitants. The effect of fouling on OTE is described by the term F. The rate at

which F decreases with time is designated F which is expressed as the decimal

fraction of OTE lost per unit time. The rate of foul will depend on the operating

conditions, changes in wastewater characteristics, and the time in service.

The fouling rates are important in determining the loss of OTE and the

expected frequency of diffuser cleaning. Fouling and the rate of fouling can be

estimated by (1) conducting full-scale OTE tests over a period of time, (2) monitoring

aeration system efficiency and (3) conducting OTE tests of fouled and new diffusers.

Factors commonly used to convert the oxygen transfer required for clean

water to wastewater are the alpha, beta, and theta factors.The alpha factor, the ratio

of the KLa of wastewater to the KLa of clean water, is especially important because

alpha factor varies with the physical features of the diffuser system, the geometry of

the reactor, and the characteristics of the wastewater. Wastewater-constituents may

affect porous diffuser oxygen transfer efficiencies to a greater extent than other

aeration devices, resulting in lower alpha factors. The presence of constituents such as

detergents, dissolved solids, and suspended solids can affect the bubble shape and size

and result in diminished oxygen transfer capability.


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Values of alpha varying from 0.4 to 0.9 have been reported for fine-bubble

diffuser systems (Hwang and Stenstrom, 1985). Therefore, considerable care must be

exercised in the selection of the appropriate alpha factors.

Another measure of the performance of porous diffusers is the combination of

the alpha and fouling factors, designated by the term F In a number of in-process

studies, the values ofF have ranged widely, from 0.11 to 0.79 with a mean of< 0.5,

and were significantly lower than anticipated (U.S. EPA, 1989).

The variability ofF was found to be site-specific, and demonstrated the need

for the designer to investigate and evaluate carefully the environmental factors that

may affect porous diffuser performance in selecting an appropriate orF factor.

Because the amount of air used per kilogram (pound) of BOD removed varies

greatly from one plant to another, and there is risk in comparing the air use at

different plants, not only because of the factors mentioned above but also because of

different loading rates, control criteria, and operating procedures. Extra-high air flow

rates applied along one side of a tank reduce the efficiency of oxygen transfer andmay even reduce the net oxygen transfer by increasing circulating velocities. The

result is a shorter residence time of air bubbles as well as larger bubbles with less

transfer surface. (Metcalf and Eddy. 2004)

Methods of cleaning porous diffusers may consist of refining of ceramic

plates, high-pressure water sprays, brushing, or chemical treatment with acid or

caustic baths. Additional details on cleaning methods may be found in U.S. EPA

(1989). .

Figure 2.1 - Picture of blowers


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Blowers

There are three types of blowers commonly used for aeration: centrifugal,

rotary lobe positive displacement and inlet guide vane-variable diffuser. Centrifugal

blowers (see Figure 2.1) are almost universally used where the unit capacity is greater

than 425 m3/min (15,000 ft3/min) of free air. Rated discharge pressures range

normally from 48 to 62 kN/m2. Centrifugal blowers have operating

characteristics similar to a low-specific-speed centrifugal pump. The discharge

pressure rises from shutoff to a maximum at about 50 percent of capacity and

then drops off.

The operating point of the blower is determined, similar to a centrifugal

pump, by the intersection of the head-capacity curve and the system curve.

In wastewater-treatment plants, the blowers must supply a wide range of

airflows with a relatively narrow pressure range under varied environmental

conditions. A blower usually can only meet one particular set of operating conditions

efficiently. Because it is necessary to meet a wide range of airflows and pressures at a

wastewater treatment plant, provisions have to be included in the blower system

design to regulate or turn down the blowers.

Methods to achieve regulation or turndown are:

(1) Flow blow off or bypassing,

(2) Inlet throttling

(3) Adjustable discharge diffuser

(4) Variable speed driver, and

(5) Parallel operation of multiple units. Inlet throttling and an adjustable discharge

diffuser are applicable only to centrifugal blowers; variable-speed drivers are

more commonly used on positive-displacement blowers. Flow blow off and

bypassing is also an effective method of controlling surging of a centrifugal

blower, a phenomenon that occurs when the blower operates alternately at zero

capacity and full capacity, resulting in vibration and overheating. Surging occurs

when the blower operates in a low volumetric range.


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For higher discharge pressure applications [> 55 kN/m2] and for capacities

smaller than 425 m3/min (15,000 ft3/min) of free air per unit, rotary-lobe positive

displacement blowers are commonly used. The positive-displacement blower is a

machine of constant capacity with variable pressure. The units can throttle, but

capacity control can be obtained by the use of multiple units or a variable speed drive.

Rugged inlet and discharge silencers are essential.

A relatively new blower design, the inlet guide vane-variable diffuser that

developed in Europe, mitigates some of the problems and considerations associated

with standard centrifugal and positive-displacement aeration blowers. The design

based on a single-stage centrifugal operation that incorporates actuators to position

inlet guide vane and variable diffusers to vary blower flow rate and optimize

efficiency

The blowers are especially well suited to applications with medium to high

fluctuations in inlet temperature, discharge pressure, and flow rate. Blower capacities

range from to 1700 m3/min (3000 to 60,000 ft3/min) at pressures up to 170 kN/m2.

Turndown rates of up to 40 percent of maximum capacity are possible without

significant reduction in operating efficiency over the range of operation. Principal

disadvantages are high initial cost and a sophisticated computer control system to

ensure efficient operation.

The performance curve for a centrifugal blower is a plot of pressure versus

inlet volume and resembles the performance curve for a centrifugal pump. The

performance curve typically is a falling-head curve where the pressure decreases as

the inlet volume increases. Blowers are rated at standard air conditions, defined as atemperature of 20C (68F), a pressure of 760 mm Hg, and a relative humidity of 36

pen Standard airs has a specific weight of 1.20 kg/m3. The air density aft the

performance of a centrifugal blower; any change in the inlet air temperature

barometric pressure will change the density of the compressed air.


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The greater the density, the higher the pressure will rise. As a result, greater

power is needed for compression process. Blowers must be selected to have adequate

capacity for a hot summer day, and be provided with a driver with adequate power for

the cold set winter weather.

Air Piping

Air piping consists of mains, valves, meters, and other fittings that port

compressed air from the blowers to the air diffusers. Because the pressure [less than

70 kN/m2 J, lightweight piping can be used.

The piping should be sized so that losses in air headers and diffuser manifolds

small in comparison to the losses in the diffusers. Typically, if head losses in the air

piping between the last flow-split device and the farthest diffuser are less than 10

percent of the head loss across the diffusers, good air distribution through the aeration

basin can be maintained. Valves and control orifices are an important consideration in

design (WEF, 1998b).

2.4.2. Mechanical Aerators

Mechanical aerators are commonly divided into two groups based on major

design and operating features: aerators with vertical axis and aerators with horizontal

axis. Both groups are further subdivided into surface and submerged aerators. In

surface aerators, oxygen is entrained from the atmosphere; in submerged aerators,

oxygen is entrained from the atmosphere and, for some types, from air or pure oxygenintroduced in the tank bottom. In either case, the pumping or agitating action of the

aerators helps to keep the contents of the aeration tank or basin mixed. In the

following discussion, the various types of aerators will be described, along with

aerator performance and the energy requirement for mixing. (D.Lal. 2004)


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Aerator Performance

Mechanical aerators are rated in terms of their oxygen transfer rate expressed

as kilograms of oxygen per kilowatt-hour (pounds of oxygen per horsepower-hour) at

standard conditions. Standard conditions exist when the temperature is 20C, the

dissolved oxygen is 0.0 mg/L, and the test liquid is tap water. Testing and rating are

normally done under non-steady-state conditions using fresh water, deaerated with

sodium sulfite. Commercial-size surface aerators efficiency ranges from 1.20 to 2.4

kg 02kWh.

Oxygen transfer data for various types of mechanical aerators. Design

engineer should accept efficiency claim for aerator performance only when they are

supported by actual test date for actual model and size of aerator under consideration.

Mechanical Aeration

Two major types of mechanical aeration equipment are commonly used for

post-aeration systems: low-speed surface aerators and submerged turbine aerators.

Low-speed surface aerators are preferred because they are usually the most

economical, except where high oxygen transfer rates are required. For high oxygen

transfer rates, submerged turbine units are preferred. Most installations consist of two

or more aerators in rectangular basins. Detention times for post-aeration using either

mechanical or diffused-air aeration is usually 10 to 20 min at peak flow rates.


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Aeration rates in mechanically aerated tanks center controlled in several ways:

Changing aerator speed

Changing the amount of bite that the aerator makes in the mixed liquor. This

increases of decreases the amount of energy transferred to the water (and the

amount of aeration)

Changing the numbers of aerators in services

Changing the amount of time the aerators are ON in a given period. When using

this type of aeration control, be careful to keep OFF times under an hour in

duration. An OFF time of 10 15 minutes is even better because it is not

advisable for the bacteria to spend much time in an anaerobic environment and

unaerated mixed liquor organisms or it will start to active aneraobically.

2.5. OXYGEN DISPERSION EFFICIENCY AND MIXINGIn the treatment of wastewater, an aeration system is ineffective in providing a

complete and uniform transfer of oxygen throughout the entire basin. Although many

systems are designed to aerate wastewater, they vary in their effectiveness in

providing uniform oxygen dispersion.

Typical aeration systems such as diffused air, surface splashers, and rotor have

limited areas of influence, causing short-circuiting, dead zones, and only partial

aeration. Because the Triton aeration/mixer technology procedures a horizontal and

circular flow pattern, the equipment provides whole basin circulation.

Conventional splashing type system, pump water upward and throws it into the

air, creating a high aerosol environment. Overcoming gravity also consumes large

amounts of energy. The area of influence is confined. Short-circuiting and dead spots

may occur due to inadequate basin mixing. Sludge deposits typically accumulate at

corners and between units in the basin, creating and even greater oxygen demand.


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Blower/diffuser systems introduce compressed air through diffusers into the

water from the bottom of the basin. More horsepower (higher energy consumption) is

required to overcome the water head resistance. The mixing pattern is a limited

vertical column as air rises from the diffuser heads to the waters surface. Over time,

the systems diffuser heads clog as solids and biofilm accumulated. This reduces

oxygen transfer efficiency.

Rotor system proper water into the air creating an aerosol environment that

releases offending odour into the air. These systems are expensive to operate both in

electrical consumption and maintenance. Rotors are inefficient in suspending solids

uniformly, having similar mixing constraints of splasher type aerator.

The aspirator a horizontal circular flow pattern is created and controlled for

maximum treatment efficiency. (Mark J. Hammer. 2004)


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CHAPTER II I

METHODOLOGY

3.1. INTRODUCTION

The study was carried out by choosing five different sewerage treatment plants

(STP) with five different aeration devices. The STP and type of aeration specification

is stated in Table 3.1.

Table 3.1. Type of Aeration

STP Type PE Aeration Devices HP

Taman Germuda Oxidation Ditch 1465 Brush aerator 2 nos x 5.5kw

Taman Anda Aerated Lagoon 2300 Tornado 2 nos x 5.5kw

Depa Kebudayaan Aerated Lagoon 1420 Surface aerator 2 nos x 5.5kw

Taman PakatanJaya Oxidation Ditch 2465 Aspirator 2 nos x 3.7kw

Taman Pengkalan

Idaman

Extented Aeration 1050 Diffusers(Blowers)

2 nos x 5.5kw

All the above Sewerage Treatment Plants which are operating with different

aeration device operates 16 hours daily except Taman Pakatan Jaya operates only 8

hours were monitored by using membrane electrode dissolved oxygen meter on a

daily basis for a week to determine the device efficiency. Samplings were also done

on each Sewerage Treatment Plant while the above study was being carried out. The

samples were then sent to Taiping Indah Water Konsortium laboratory to determine

the effluent results mainly on BOD. Subsequently the dissolved oxygen readings were

compared with the sampling result to determine the most efficient aeration system.


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3.2. MEASURING AERATION DISSOLVED OXYGEN

There are two common methods for measuring aeration basin dissolved

oxygen, the Winkler Titration Method and the Membrane Electrode Method. As for

this study case I used the membrane electrode method at difficult Sewerage Treatment

Plants

3.2.1. WINKLER TITRATION METHOD

This method is commonly used when the Dissolved Oxygen meter cannot be

obtained. If you use this method, be sure that you use the modification specifically

designed for measurement of aeration basin of dissolved oxygen.

In the standard Winkler procedure for measuring of dissolved oxygen, aerobic

bacteria in the mixed liquor sample continue to remove dissolved oxygen from the

sample even while you are preparing to run the test. This causes measured dissolved

oxygen levels to be lower than true levels. In the dissolved oxygen procedure

modified for measuring aeration basin dissolved oxygen, the technician adds a

solution containing copper sulfate and sulfuric acid to the sample container before

collecting the mixed liquor sample. As the sample is collected the copper sulfate-

sulfuric acid solution kills aerobic organisms and prevents them from using dissolved

oxygen during the test. The procedure for the Winkler method is readily available in

most texts and lab manuals for wastewater treatment plant operation.

3.2.2. MEMBRANE ELETRODE METHOD

This is other common way of determining aeration basin dissolved oxygen. Iused this method because of it reliability speed and also easier to handle. The

equipment consists of a meter, probe and cable and is available at any major scientific

equipment supplier.

After calibration, I measured the dissolved oxygen in the aeration basin on all

the five Sewerage Treatment Plants by directly placing the probe where I want a

dissolved oxygen reading. I attached the probe to a light-weight pole so it can be

positioned exactly where they want it. The probe is often attached to the pole upside

down (membrane end up).


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This prevents air bubbles from getting trapped against the membrane and

causing high readings. After positioning the probe in the mixed liquor, switch the

meter to get a temperature reading. I recorded the temperature of the mixed liquor for

later reference. Now switch the meter and read the dissolved oxygen. It may take as

much as a minute for the meter to stabilize around a specific dissolved oxygen

reading.

3.3. AERATION BASIN DISSOLVED OXYGEN PROFILES

Most aeration basins wont have dissolved oxygen concentration that is the

same all through the tank. Since the dissolved oxygen reading is high and low, I

took few readings with a minimum of 0.5mg/l. The bacteria in the basin failed to

perform properly when the dissolved oxygen drops below that level for more than a

few minutes. Therefore, a reading at the location, of the lowest dissolved oxygen

concentration is the most important factor. To find this location, you need to have a

dissolved oxygenprofile in thebasin. To perform an aeration basin dissolved oxygen

profile, you will need a dissolved oxygen meter with a 4.5m cord on the probe.

Mark the probe cord in one meter intervals and attach to a long pole so I can position

it precisely where I want it.

Testing of Dissolved oxygen concentrations should be done at selected points

across the length and width of the tank. Measure the Dissolved oxygen at designated

depths (intervals of 2-3 meters) for each selected sampling point. Plot the cross

sectional measurements along the length of the tank that results from plotting the

Dissolved oxygen results. As you can see the Dissolved oxygen in the example tank,

varied a great deal from one location to another. The location for taking regular

Dissolved oxygen measurement, in this case, should be in the center, near the bottom

of the tank where the region of lowest Dissolved oxygen is located. Adjust aeration

rates to maintain dissolved oxygen of around 1.0 mg/L here and you can be

reasonable certain there is enough Dissolved oxygen in the rest of the aeration basin.

There was a comparison on costing in terms of energy saving of the aeration device

while maintaining the required Dissolved oxygen level. Wastewater treatment

facilities must meet strict effluent discharge permit standards to stay in compliance

with government regulations.


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CHAPTER IV

RESULTS & DISCUSSION

4.1. DISSOLVED OXYGEN

From the case study the below data were collected for further analysis in order to

achieve the objective of this study. The date collected for all five sewerage treatment

plants are attached as Table 4.1, Table 4.2, Table 4.3, Table 4.4 & Table 4.5.

Tab le 4.1 . D IS S O LVE D O XY G E N R E ADIN G S AT TM N G E R MU DA

L O C A T IO N T M N G E R M U D A

T Y P E O D

S A M PL IN G DA T E 8 .3 .0 7

D E P T H O F 3 M

T IM E

LE NG TH 0.5m 1.5m 0.5m 1.5m 0.5m 1.5m

06-03-07 DO R E ADING 4.6 4.2 4.5 4.2 5 4.307-03-07 DO R E ADING 4.9 4.4 3.9 3.7 5.3 4.5

08-03-07 DO R E ADING 3.8 3.5 3.7 3.1 4.2 3.8

09-03-07 DO R E ADING 5.2 4.8 5.7 5.1 4.9 4.6

10-03-07 DO R E ADING 5 4.7 4.8 4.3 5.2 4.7

Tab le 4.2 . D IS S O LVE D O XY G E N R E ADIN G S AT TM N P AK ATAN J AY A

L O C A T IO N T A M A N P A K A T A N J A Y A

T Y P E O D

S A M PL IN G D A TE 2 8.2 .0 7

D E P T H O F 3 M

T IM E

LE NG TH 0.5m 1.5m 0.5m 1.5m 0.5m 1.5m

24-02-07 DO R E ADING 1.9 1.7 2.1 1.9 2.1 225-02-07 DO R E ADING 2 1.8 1.9 1.8 1.8 1.6

26-02-07 DO R E ADING 5.1 1.9 2.36 2.1 2.3 2

27-02-07 DO R E ADING 2.1 2 2.3 2.1 2.3 2.1

28-02-07 DO R E ADING 1.8 1.6 2 1.8 2.1 2

Tab le 4.3 . D IS S O LVE D O XY G E N R E ADIN G S AT TM N ANDA

L O C A T IO N T M N A N D A

T Y P E A L

S A M PL IN G DA T E 5 .3 .0 7

D E P T H O F 3 M

T IM E

LE NG TH 0.5m 1.5m 0.5m 1.5m 0.5m 1.5m

03-03-07 DO R E ADING 5 4.6 5.3 5.1 5.3 5.2

04-03-07 DO R E ADING 4.8 4.4 5 4.8 4.9 4.7

05-03-07 DO R E ADING 5.4 5.6 5.1 4.6 5.3 5.1

06-03-07 DO R E ADING 5.3 5 4.9 4.4 5 4.8

07-03-07 DO R E ADING 5 5.1 4.9 4.6 4.8 4.6

8.30AM 1.00P M 4.30P M

DISSO LVED OXYG EN IN MG/L AT G IVEN D ISTANCE IN FR ONT OF

AERAT ION DEV ICE (BRUSH AERATOR )


AERAT ION DEV ICE (ASP IRATOR)

8.30AM 1.00P M 4.30P M


AERAT ION DEV ICE (TORNADO)

8.30AM 1.00P M 4.30P M


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Table 4.4. DISSOLVED OXYGEN READINGS AT TMN DESA KEBUDAYAAN

LOCATION TMN DESA KEBUDAYAAN

TYPE AL

SAMPLING DATE 21.3.07

DEPTH OF 3M

TIME

LENGTH 0.5m 1.5m 0.5m 1.5m 0.5m 1.5m19-03-07 DO READING 5.6 5.1 5.8 5 5.9 5.1

20-03-07 DO READING 5.8 5 6.1 5.5 5.8 5

21-03-07 DO READING 4.6 4 5.2 4.6 6 5.1

22-03-07 DO READING 5.2 4.6 5.6 4.9 6.1 5.2

23-03-07 DO READING 4.9 4.4 5.9 5.2 6 5.3

Table 4.5. DISSOLVED OXYGEN READINGS AT MEDAN PENGKALAN IMPIAN

LOCATION MEDAN PENGKALAN IMPIAN

TYPE EA

SAMPLING DATE

DEPTH OF 3M

TIME

LENGTH 0.5m 1.5m 0.5m 1.5m 0.5m 1.5m

19-03-07 DO READING 4.8 5.1 6.2 5 5.6 5.1

20-03-07 DO READING 5.2 4.7 5.6 5.5 5.8 5

21-03-07 DO READING 4.6 6 5.2 4 6 5.1

22-03-07 DO READING 5.2 4.6 4 4.9 5.9 5.6

23-03-07 DO READING 4.9 4.4 5.9 5 6.1 5.3

DISSOLVED OXYGEN IN MG/L AT GIVEN DISTANCE IN FRONT OF

AERATION DEVICE (SURFACE AERATOR)

8.30AM 1.00PM 4.30PM

DISSOLVED OXYGEN IN MG/L AT GIVEN DISTANCE IN FRONT OFAERATION DEVICE (DIFFUSER WITH BLOWERS)

8.30AM 1.00PM 4.30PM


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TABLE 4.6: CHART & SUMMARY OF AVERAGE DISSOLVED OXYGEN FOR 5 DIFFERENT PLANTS

TMN TMN PAKATANJAYA (ASPIRATOR)

TMN GERMUDA

(BRUSH

AERATOR)

TMN DESA

KEBUDAYAAN(SURFACE

AERATOR)

TMN ANDA(TORNADO)

MEDAN

PENGKALAN

IMPIANA

(DIFFUSER

WITH BLOWER)

AVE.DO (MG/L) 1.9 4.5 5.3 4.9 5.3

FIGURE 4.1 : GRAPH DISSOLVED OXYGEN AT EACH TAMAN

BCOD~25 MG/L (REFER TO SAMPLING DATA)

0

1

2

3

4

5

6

TMN PAKATAN

JAYA

(ASPIRATOR)

TMN GERMUDA

(BRUSH

AERATOR)

TMN DESA

KEBUDAYAAN

(SURFACE

AERATOR)

TMN ANDA

(TORNADO)

MEDAN

PENGKALAN

IMPIANA

(DIFFUSER WITH

BLOWER)

TAMAN

DISSOLVED

OXYG

EN

(MG/L)

AVE.DO (MG/L)


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Dissolved oxygen readings were collected for each and every STP on different

week so it was easier on the sampling purpose. This is because it takes 3 to 4 days for

the sampling results to be analysed. The sampling results from Indah Water

Konsortium Sdn. Bhd. (IWK) were sent to Taiping laboratory so that a comparison

can be done on each and every aeration device. In actual fact air was added to an

aeration basin to keep the wastewater and activated sludge mixed. In these way

bacteria was exposed to fresh food all the time.

The other important reason for adding air to the aeration basin was to provide

dissolved oxygen which is actually oxygen which has been dissolved in water. In real

fact, oxygen is not very soluble in water. At 20 degrees Celsius only 9.2 mg/l of

oxygen can be dissolved into water.

We need to add to the aeration basin to provide an environment in the aeration

basin that will encourage the growth of many bacteria. The Dissolved oxygen test

was very crucial because it measures the amount of oxygen available to the facultative

activated sludge organisms. In general aeration rates that provided dissolved oxygen

of between 1.0 and 2.0 mg/l were adequate for maintaining efficient, healthy activated

sludge organisms.


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If the Dissolved oxygen drops below 1.0 and especially below 0.5 mg/l , the

treatment efficiency was begin to suffer because the activated sludge organisms was

starting to function anaerobically. On the other hand, if the dissolved oxygen was

maintained above 2.0 mg/l, it would be wasting power (that power providing

dissolved oxygen to the aeration basin) dissolved oxygen. Therefore, careful

measurement and control of dissolved oxygen in the aeration basin were necessary to

provide efficient treatment without wasted energy.

This was evident with the sampling result that was done on all type of aeration

devices that was discussed earlier. It was actually inter-related between sampling

results, dissolved oxygen and electricity consumption. From the result it was evident

that 2 numbers 3.7kw aspirator operating only 8 hours a day in Taman Pakatan Jaya

could achieve dissolved oxygen of 1.9 mg/l compared to the other, achieving higher

dissolved oxygen while operating on 16 hours daily. The brush aerator at Taman

Germuda was recorded at 4.5 mg/l dissolved oxygen. The aerator at Taman Desa

Kebudayaan was recorded at 5.3 mg/l dissolved oxygen while the tornado at Taman

Anda and the diffusers with blowers at Medan Pengkalan Impiana were recorded at

4.9 mg/l and 5.3 mg/l respectively.


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4.3. COSTING

Capital cost and comparison of each and every aeration system in RM is shown

in Table 4.7 and Figure 4.2. It may differ from time to time due to financial

constraints. Only 5 models are captured that mainly being operated in the waste water

industry:-

TABLE 4.7 : CAPITAL COST OF DIFFERENT TYPE OF AERATION DEVICEModel (kw) 3.7kw 5.5kw 7.0kw

Type

Brush Aerator OBSELETE OBSELETE OBSELETE

Tornado c/w set 30,000 43,000 50,000

Aspirator c/w set 25,000 40,000 45,000

Surface Aerator c/w set 15,000 20,000 25,000

Diffuser (blowers cost) 10,000 15,000 20,000

FIGURE 4.2 : GRAPH CAPITAL COST AERATION DEVICE

CAPITAL COST OF AERATION DEVICE

0

10,000

20,000

30,000

40,000

50,000

60,000

Tornado c/w set Aspirator c/w set Surface Aerator

c/w set

Diffuser (blowers

cost)

TYPE OF AERATION DEVICE

TOTAL

3.7kw

5.5kw

7.0kw


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Long term expenditure that a wastewater treatment plant endures becomes

extremely expensive for those choosing to select knockoff equipment. Original

equipment was designed to operate with very little maintenance and few parts

replacement for extended periods of time. Typical knockoff equipment is lucky if it

ever reaches a five-year lifetime. Although the knockoff equipment might be as little

as 50 per cent the cost of the original product and attractive to the customer/contractor

during the bidding process, when factor in its failure ratio, frequent parts failure andits inability to perform, the decision is quite easy.

TABL E 4.8 : SUMMARY OF OPERATIONAL AND MAINTENANCE COSTING FROM NOV'06 - APRIL'07

MONTH NOV'06 DEC'06 J AN'07 FEB'07 MAC'07 AP R'07

TAMANTOTAL (IN

RM)

TMN PAKATAN JAYA (ASPIRATOR) 594 1,220 515 714 3,043

TMN GERMUDA (BRUSH AERATOR) 6,880 8,580 3,485 18,945

TMN DESA KEBUDAYAAN (SURFACE

AERATOR)1,260 1,500 650 573 3,983

TMN ANDA (TORNADO) 1,890 780 600 3,270

MEDAN PENGKALAN IMPIANA

(DIFFUSER WITH BLOWER) 870 2,560 200 1,800 300 5,730

FIGURE 4.3 : GRAPH SUMMARY OF A OPERATIONAL & MAINTENANCE COSTING

SUMMARY OF OPERATIONAL & MAINTENANCE COSTING

500

2,500

4,500

6,500

8,500

10,500

12,500

14,500

16,500

18,500

20,500

TMN PAKATAN

J AYA

(ASPIRATOR)

TMN GERMUDA

(BRUSH

AERATOR)

TMN DESA

KEBUDAYAAN

(SURFACE

AERATOR)

TMN ANDA

(TORNADO)

MEDAN

PENGKALAN

IMPIANA

(DIFFUSER WITH

BLOWER)

TAMAN

COSTING(RM)

TOTAL (IN RM)


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This high cost of operation endured by selecting the knockoffs ends up causing

the client to pay sometimes over double the amount in operation expenditures over a

10 year period of time. The decision to choose the cheapest knockoff to save a small

portion of investment usually ended up creating numerous headaches and costing

them (and the public taxpayers) a heap of cash.

Estimated capital cost of each and every aeration system in this study is stated

in below table. It may vary from time to time due to financial stability. Although it

appears that diffusers are the cheapest among the devices but this is only the

cost of blower. The costing of diffusers is not included because each aeration tank

that uses this device are different size thus making the costing vary. Each diffusers

cost are around RM 100.00. Usually an aeration tank would be using around 50

numbers of diffusers. Surface aerators would be costing around RM 15,000.00 (3.7

kw) to RM 25,000.00 (7.0 kw). Aspirators will be costing slightly cheaper compare totornado. Aspirators costing are from RM 25,000.00 (3.7 kw) to RM 45,000.00 (7.0

kw). Tornado costing are from RM 30,000.00 (3.7 kw) to RM 50,000.00 (7.0

kw).There are no costing on brush aerators because it is an obsolete product which

is no more in the market. Even-though the costing varies, but in terms of operational

and maintenance, diffusers is the most difficult to be maintained due to frequent

choking.

Aspirators are the cheapest and the easiest to maintain compared to others as

shown in Table 4.7 and Table 4.8. This is due to aspirators are the latest product in the

market.


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4.3. ELECTRICITY CONSUMPTION

Summary of TNB bill for each STP for a period of six months are stated in the table

4.9 and the comparison of electricity consumption in Figure 4.4.

TABLE 4.9: SUMMARY OF ELECTRICITY CONSUMPTION FROM NOV'06 - APRIL'07

MONTH

TAMAN kw RM kw RM kw RM kw RM kw RM kw RM kw RM

TMN PAKATAN JAYA

(ASPIRATOR)2,338 678 2,050 594 2,066 599 1,736 503 1,003 290 na na 1,839 533

TMN GERMUDA (BRUSH

AERATOR)590 171 1,295 375 na na 728 211 1,505 436 437 126 911 264

TMN DESA KEBUDAYAAN

(SURFACE AERATOR)2,753 798 588 170 4,612 1,337 1,990 577 2,730 731 1,865 540 2,423 702

TMN ANDA (TORNADO) 4,808 1,394 4,060 1,177 3,302 957 2,932 850 3,465 1,004 3,306 958 3,646 1,056

MEDAN PENGKALAN IMPIANA

(DIFFUSER WITH BLOWER)3,884 1,126 3,980 1,154 4,870 1,412 4,948 1,434 4,364 1,265 3,872 1,122 4,320 1,252

FIGURE 4.4 : GRAPH SUMMARY OF ELECTRICAL CONSUMPTION

NOV'06 DEC'06 AverageJ AN'07 FEB'07 MAC'07 APR'07

SUMMARY OF ELECTRICITY CONSUMPTION

100

200300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

TMN PAKATAN

J AYA (ASPIRATOR)

TMN GERMUDA

(BRUSH AERATOR)

TMN DESA

KEBUDAYAAN

(SURFACE

AERATOR)

TMN ANDA

(TORNADO)

MEDAN

PENGKALAN

IMPIANA (DIFFUSER

WITH BLOWER)

TAMAN

COSTING(RM)

Average


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The operational requirement for wastewater system differs according to

variation flow and strength of wastewater. The peak energy demand usually occurred

from midday to early evening hours when other peak demands for electricity occurs in

the community. As the wastewater load changes during the course of the day the

requirements for aeration, pumping and solid processing change accordingly. Some

sewerage treatment plants modified schedules for equipment operation to meet the

load condition while others operate their devices such as aeration devices

continuously at full capacity regardless of the electricity consumption. Sewerage

treatment plant that has biological treatment for nutrient removal used 30 to 50

percent more electricity for aeration, pumping and solid processing. With introduction

of new technologies for wastewater treatment, the energy requirements will change.

The impacts can either reduce in electricity or increase due to higher level of

treatment. Refer to the electricity data collected for the five different aeration system

if appears that Taman Pakatan Jaya (aspirator) needed an average of 1,839kw per

month while meeting the biological oxygen demand of Standard B requirement.

Although Taman Germuda (Brush Aerator) recorded a mere 911kw per

month, it was found that the brush aerator was unable to function efficiently due some

mechanical problem that continued for three months. Apparently this caused the

electricity consumption to be very low compared to the others which recorded

between 2423 kw till 4320 kw per month.


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To further prove that aspirator performed well by providing effective aeration

Auburn University in United Kingdom conducted an experiment on mixing capability

and flow pattern. The results were as below:-

(1) Aspirator: Utilizing units, a circular horizontal flow pattern was created,

covering the whole lagoon area, thus preventing short circuiting and

maximizing lagoon volume. The results was a highly oxygenated flow pattern

that provides complete mixing of the lagoon, keeps solids suspended in any

climate and maintain optimum temperatures year round.

(2) Surface aerators: The area of influence for surface splashers was limited and

has the additional negative affect of cooling the aeration basin through

evaporation.

(3) Blower/Diffusers System: As seen in the photograph, the diameter of

influence for a diffuser system was very limited, requiring a large quantity of

diffusers to cover the area needed. Much of the area was still snow covered

from lack of aeration and mixing, giving the lagoon a pincushion looks.

FIGURE 4.5 : RESULTS OF MIXING CAPABIL ITIES


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CHAPTER V

CONCLUSION AND SUGGESTION

5.1. CONCLUSION

When selecting aeration equipment to use for a specific application, issues it

address include reliability, serviceability, capital cost, system appurtenances and cost

of operation and maintenance. Another important consideration is oxygen transfer rate

using equipment with high oxygen transfer rate values would obviously increase the

electricity consumption.

As conclusion an effective aeration system designed for wastewater treatment

process must be adequate and comply with the biochemical oxygen demand (BOD)

Standard required by the regulators satisfy the oxygen demand of nitrification,

provide adequate mixing, maintain a minimum dissolved oxygen (1 to 3 mg/l)

throughout the aeration basin and efficient in energy saving.

Thus, from the experiment and evaluation conducted from this study case,

aspirator performed extremely well in order to provide the most effective aeration in

wastewater. It was also a very cost effective device compared to other aeration

devices.


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5.2. SUGGESTION

Since this study only concentrated on an average Population Equivalent

of 2500, further studies or experiments should be carried out on higher Population

Equivalent with different kind of STP (sewerage treatment plants) such as sequence

batch reactors, rotating biological contacted, activated sludge and others . This

would be an indicator whether different population equivalent plants reacts

differently in terms of oxygen transfer rate.

It should concentrate on different age of plants because it may produce

different results. New plants or aeration devices most probably would perform

without any hiccups compared to the aged equipment or devices.

Another factor that should be taken into consideration is the location of

the sewerage treatment plant whether it is on highland or lowland such as

Cameron Highland because low temperature would produce different results

compared to high temperature.


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REFERENCES

Indah Water Konsortium. 2002. Operation and Maintenance . Kuala Lumpur,

Tim Hobson. 1992. Activated sludge, Evaluating and Controlling Process, 2nd Ed.Mckenna

Metcalf and Eddy. 1991. Wastewater Engineering. 3rd Ed. McGraw Hill,

S.K.Gang. 2004. Sewage Disposal and Air Pollution Engineering. Khanna Publishers,

Mark J.Hammer, Mark J.Hammer,Jr. 2004. Water and Waste Water Technology 5th

Ed. Pearson Prentice Hall

D.Lal.A.K. Upadhyay. 2004. Water Supply and Waste Water Engineering. Revised

Edition. Sanjeer Kataria.

Sewerage Services Department (1999). Guidelines for Developers, Sewerage Policy

for New Developments.Malaysia, Volume I..

Sewerage Services Department (1998). Guidelines for Developers, Sewerage

Treatment Plants. Malaysia, Volume IV.


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APPENDIX A

SUMMARY OF SAMPLING RESULTS FOR SEWERAGE PLANTS

SAMPLING RESULTS

INDAH LOCATION SAMPLING EFF. SPL PURPOSE BOD COD NH3 NO3 pH O&G SS

REF DATE STD TYPE CODE mg/l mg/l mg/l mg/l mg/l mg/l

IPH240 TMN PAKATAN

J AYA, FASA 1

28-Feb-07 B FE O 20 62 6 n.a 7.1 1 47

IPH052 TMN ANDA 5-Mac-07 B FE O 26 77 26 1 8.5 2 46

IPH145 TMN DESAKEBUDAYAAN

21-Mac-07 B FE O 57 155 3 n.a 8.8 n.a 81

IPH005 TMN GERMUDA 8-Mac-07 B FE O 21 66 10 n.a 7.2 2 52

IPH346 MEDANPENGKALANIMPIAN

23-Mac-07 B FE O 28 66 21 n.a 7.4 n.a 22


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APPENDIX B

PHOTOGRAPH OF VARIOUS AERATION DEVICE

TAMAN ANDA

( TORNADO)

TAMAN PAKATAN J AYA

(ASPIRATOR)


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MEDAN PENGKALAN IMPIAN(DIFFUSERS AND BLOWERS)

TAMAN GERMUDA

(BRUSH AERATOR)

TAMAN DESA KEBUDAYAAN

(SURFACE AERATOR)

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