milestone a final review

7/31/2019 Milestone a Final Review

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Faculty of Engineering and Industrial Sciences

Swinburne University of Technology

HES4146 Water and Environmental Engineering

Project Milestone A

Group 8

Dayang Zulena (4210581)

Muaid Abduklkareem Alnazir Ahmed (4207114)

Peerun Mohammud Irfaan (4225929)

Sharifah Nur Azureen (4224698)

Tang Sieu Wei (4239547)

Uhudhu Ahmed (4225953)


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HES4146 Water and Environmental Engineering, Semester 2, 2010

Project Milestone A i

GROUP DECLARATION

Declaration

We declare that this report contains no material which has been submitted for assessment in

any other subject at Swinburne University of Technology. To the best of our knowledge and

belief, this report contains no material that has been previously published by any other person,

except where due acknowledgement has been made.

Student

ID

Family Name Other Names Contribution Signature

4225929 Peerun Irfaan 16.67%

4207114 Ahmed Muaid 16.67%

4224698 Nur Azureen Sharifa 16.67%

4239547 Sieu Wei Tang 16.67%

4225953 Ahmed Uhudhu 16.67%

4210581 Dayang Zulina 16.67%


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Project Milestone A ii

TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................... 1

2. AERATED LAGOONS ....................................................................................................... 2

2.1. Advantages ..................................................................................................................... 3

2.2. Disadvantages ................................................................................................................. 4

3. ANAEROBIC FILTER ....................................................................................................... 5

3.1. Advantages ..................................................................................................................... 6

3.2. Disadvantages ................................................................................................................. 7

4. BIOLOGICAL WASTEWATER TREATMENT ............................................................ 8

4.1.

Preliminary Treatment .................................................................................................... 8

4.2. Primary Treatment .......................................................................................................... 8

4.3. Secondary Treatment ...................................................................................................... 8

4.4. Tertiary Treatment .......................................................................................................... 8

4.5. Sludge Treatment............................................................................................................ 9

4.6. Advantages ................................................................................................................... 10

4.7. Disadvantages ............................................................................................................... 10

4.8. Environmental Impacts ................................................................................................. 10

4.9. Prevention ..................................................................................................................... 11

5. CONSTRUCTED WETLAND ......................................................................................... 12

5.1. Design ........................................................................................................................... 12

5.2. Construction ................................................................................................................. 13

5.3. Advantages ................................................................................................................... 14

5.4. Disadvantages and Limitations..................................................................................... 14

6. GRAVEL CONTACT AERATED SYSTEM ................................................................. 15

6.1. Design ........................................................................................................................... 15

6.2. Advantages ................................................................................................................... 16

6.3. Disadvantages ............................................................................................................... 17

7. OXIDATION DITCH ....................................................................................................... 18

7.1. OD System Components .............................................................................................. 18

7.2. How does the OD work? .............................................................................................. 19

7.3. Construction ................................................................................................................. 19

7.4. Cost ............................................................................................................................... 20


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Project Milestone A iii

Construction ..................................................................................................................... 20

Operation and Maintenance ............................................................................................. 20

7.5. Advantages ................................................................................................................... 20

7.6. Disadvantage ................................................................................................................ 21

7.7. Environmental Impacts ................................................................................................. 21

Solutions ........................................................................................................................... 21

7.8. OD in Malaysia............................................................................................................. 21

8. SELECTION OF ALTERNATIVE ................................................................................. 22

9. CONCLUSION .................................................................................................................. 24

9.1. Selection and Justification ............................................................................................ 24

10. REFERENCES ............................................................................................................ 25


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HES4146 Water and Environnemental Engineering, Semester 2, 2011

Project Milestone A 1

1. INTRODUCTIONSibu is a town located near the Rajang River. It has a population of about 200 000 people. The

town is found on the bank of the river and the terrain is known to be very flat. Several septic

tanks are used to treat the black water since Sibu does not have a centralized sewage treatment

facility. The grey water is being sent directly to the streams. Due to high raise in population

and the flat terrain, a serious case of pollution has risen for the drains especially in dry

seasons (Sewerage Services Department Sarawak 2011).

Figure 1.1. Map of Sibu Town (Sewerage Services Department Sarawak 2011)

The aim of this project is to find a suitable solution for the wastewater in Sibu town by

selecting a suitable wastewater management. Milestone A consists of several proposition

about wastewater treatment system such as: Anaerobic Filters, Constructed Wetland,

Biological Wastewater Treatment, Gravel Contact Aerated System, Aerated Lagoon and

Oxidation Ditch.

The most suitable system is being chosen using a matrix system where the specific

components are taken into consideration such as the construction phase, operation,

maintenance, design and environmental impacts.


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2. AERATED LAGOONSAerated lagoons are suspended-growth process treatment units which provide artificial

aeration involves biological oxidation of wastewater for a predetermined period of time. They

can deliver a discharge limit of 30mg/L, both total suspended solids (TSS) and Carbonaceous

Biological Oxygen Demand 5 (cBOD5) (Lagoon Systems in Maine, 2003).

Figure 2.1. Aerated Lagoons in Malaysia (Indah Water Konsortium, 2011)

Oxygen is supplied through mechanical or diffused aeration rather than by algal

photosynthesis. Lagoons systems consists maximum of three lagoons in sequence; initial cell

which is a complex mix unit, partial mix and settling cell, with total detention time depends

on the water temperature (Environmental Protect Agency 2002).

Table 2-1. Typical figures for Aerated Lagoons (Indah Water Konsortium 2011)

(mg/L) Raw Sewage Effluent DOE Standard B

Biological Oxygen Demand 200-400 20-80 50

Suspended Solids 200-350 40-100 100

The first lagoon is the most intense aeration, consists of surface aerators where they float on

the surface and stir the input continuously with paddle mixer. They operate to maintain

oxygen content in the sewage and prevent solids from settling. It requires high amount of

energy for an equal sized mixing the municipal waste. It is similar to the activated sludge

treatment process but excludes recycling of organic materials. Therefore, the process requires

a longer hydraulic detention time compared to activated sludge treatment (Environmental

Protect Agency 2002; Indah Water Konsortium 2011).


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Next is the second lagoon where degraded organic matter and sediments are settled to form

sludge which takes an average of one day retention time. Lastly, the effluent passes to the

final lagoon which function is to discharge to a receiving waterway that has little or no

aeration to allow settling. As for today, there are approximately 40 aerated lagoons sewagetreatment plants in Malaysia (Environmental Protect Agency 2002; Indah Water Konsortium

2011).

Figure 2.2. Aerated Lagoons diagram (Indah Water Konsortium 2011)

2.1.Advantages Lagoon systems are simple wastewater treatment plants. It can be cost-effective to

design and construct in areas where land is inexpensive. Therefore, it is rarely found in

densely urban areas (Lagoon Systems in Maine 2003).

Aerated lagoon systems use less energy compared to other wastewater treatmentsystems (National Small Flows Clearinghouse 1997).

Furthermore, sludge disposal may be necessary but the quantity will be relativelysmall compared to other secondary treatment processes (Environmental Protect

Agency 2002; Lagoon Systems in Maine 2003).

The operation and maintenance of lagoon systems are simple; mowing grass and weedgrowth control around the lagoon. Long grass and weed growths will block wind

around the lagoon and cause breeding areas for insects, trap trash, grease and scums to

prevent odours. Besides that, they also cause damage to banks and dikes around the

lagoons and increase BOD levels. Furthermore, weed growth on the surface of the

water prevent sunlight and wind from penetrating the wastewater (Lagoon Systems in

Maine 2003).


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Lagoon systems are suitable for irrigation due to its high-nutrient and low pathogencontent (Lagoon Systems in Maine 2003).

2.2.Disadvantages Odour can become unpleasant during spring when algae blooms in cold climates as air

changes the environment and microbes which process the wastewater as it reduces the

rates of biological activity. As a result, chemical reactions between various types of

microbes changes or reduces the odours produced by the lagoons (Lagoon Systems in

Maine 2003).

The site should be distanced from the homes they serve, possibly incurring extra coston pumps (Lagoon Systems in Maine 2003).

Cold climate increase sludge accumulation rates due to low temperature which inhibitsanaerobic reactions (Lagoon Systems in Maine 2003).

Requires energy high input (Dawson Wastewater 2011; Environmental ProtectAgency 2002).

Lagoon systems require large hectares of stable, permafrost-free and level ground landwhere lagoon structures can be built depends on the soil conditions where the water

table and composition of soil should be considered. Otherwise, the surface of the

lagoons should be lined materials such as rubber or concrete to prevent environmentalimpact such as groundwater pollution. Therefore, this method may cause the increase

of construction costs (Lagoon Systems in Maine 2003).


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3. ANAEROBIC FILTERAn anaerobic filter is a fixed-bed biological reactor. Organic matter can be dissolved by the

filter and non-settleable solids are filtered and anaerobically digested by bacteria of the

biofilm attached to the filter materials. When wastewater flows through the filter, particles are

trapped and organic matter is degraded by the biomass. Anaerobic filters are commonly used

as secondary treatment of waste water in household blackwater or greywater treatment

systems. It also can improve the solid removal compared to septic tanks or anaerobic baffled

reactors.

Filter material normally used includes gravel, crushed rocks, cinder or specially formed

plastic pieces. Typical filter material sizes range from 12 to 55mm in diameter. Filters withtwo to three filter layers and a minimum depth of 0.8 to 1.2m are recommended. The material

will provide 90 to 300m2

of the surface area per 1m3

of reactor volume. There is increased

between the organic matter and the active biomass that effectively degrades it to providing the

large surface area for the bacterial mass.

The anaerobic filter can be functioned as up-flow or down-flow systems. The up-flow systems

are recommended because there is less risk that washed out active bacteria. On the other hand,

flushing of the filter for the purpose of cleaning is easier with the down-flow system. A

combination of the down-flow and up-flow chambers is also possible. The water level should

cover the filter media by at least 30cm to guarantee an even flow system. Filter material size

may decrease from bottom to top with the up-flow systems. As the wastewater flows through

the filter usually from the bottom to the top (up-flow), it comes into contact with the biomass

on the filter and is subjected to anaerobic filter.

Anaerobic filter are used for wastewater with a low percentages of suspended solids and

narrow COD/BOD ratio (Chemical Oxygen Demand/Biological Oxygen Demand). It is

suitable for all industrial wastewater and domestic wastewater which has a low content of

suspended solids. The anaerobic filter can be built above or below ground depending on land

availability and the hydraulic gradient of the sewer. However, most often they are below the

ground surface to save space, to reduce health risks and to provide insulation and protection

against cold climates.


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Figure 3.1 Three chamber anaerobic filter units following a septic tank. Source: SASSE (1998)

Figure 3.2 Three setting chambers followed by five anaerobic filter units. Source: SANIMAS (2005)

3.1.Advantages Resistant to organic and hydraulic shock loadings. Low reduction of nutrients, thus outflow adapter for reuse in agriculture. Low sludge yield. No electrical energy required. Can be built and repaired with locally available materials. Long life services. Moderate capital costs, moderate operating costs depending on emptying; can be

lowered depending on number of users.

High reduction of BOD and solids. Low-energy process and making it more environmentally friendly. Lower running costs as a result of the low energy inputs.
http://www.sswm.info/glossary/2/lettera#term31http://www.sswm.info/glossary/2/lettera#term31http://www.sswm.info/sites/default/files/toolbox/SANIMAS%202005%20Anaerobic%20Filter.jpghttp://www.sswm.info/sites/default/files/toolbox/SASSE%201998%20Anaerobic%20Filter.jpghttp://www.sswm.info/glossary/2/lettera#term31http://www.sswm.info/sites/default/files/toolbox/SANIMAS%202005%20Anaerobic%20Filter.jpghttp://www.sswm.info/glossary/2/lettera#term31http://www.sswm.info/sites/default/files/toolbox/SASSE%201998%20Anaerobic%20Filter.jpg


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3.2.Disadvantages Not good at removing non-organic pollution within wastewater, such as nutrients or

disease-causing micro-organisms (pathogens).

Requires constant source of water. Effluent requires secondary treatment and appropriate discharge. Low reduction of pathogens and nutrients Requires expert design and construction. Long to start up time. Only suitable for low-density housing in areas with low water table and not prone to

flooding.


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4.5.Sludge TreatmentThe sludge collected from the tank can be furthermore processed by heating it at 35 degrees

Celsius in an enclosed digester. During this process, methane gas is being produced which can

be used to produce electricity. It is a good means of reducing the use of non-renewableenergy.

The water from the sludge is being dried by natural evaporation and the dry bio-solid obtained

is used as fertilizer (SA Water 2004).

Figure 4.1 Biological Wastewater Treatment Process (SA Water 2004)


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4.6.Advantages Environment friendly reduces the use of non-renewable energy Affordable suitable for a small scale project Gas and fertilizer are obtained as residue it can produce its own electricity by using

the gas produced and the fertilizers can be sold and reduce the operational cost.

Low cost to construct and operate simple technology used, no expensive machineryrequired.

Good water quality obtained the water can be reused for several purposes such asirrigation.

Less-skilled operators can be recruited employment is being created for the peoplenearby.

Chemical-free non-toxic process.

4.7.Disadvantages Slow process since the wastewater has to be flowed at a specific rate, the production

is relatively slow.

Cultural acceptability the community people do not accept the recycled wastewaterheartily.

Unpleasant odour resulting complaints if it is located nearby a residential area. Constant maintenance required the plant has to be maintained constantly so as to

achieve a good water quality.

Requires a large piece of land the treatment plant consisting of the screening,primary settling tank, secondary settling tank, biological filters and sludge tank, hence

a big area is required for this system.

4.8.Environmental ImpactsThere will be a temporary impact while considering the construction phase of the treatment

plant such as drilling, blasting rocks, excavation works and natural habitats might be

destroyed depending on the site location. Solid waste during the construction should be

treated or reused so as not to pollute the surroundings. But all these are considered as short

term impacts.


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Since this project is to be built in an urban area, the odour from the wastewater might be a

problem and also if there is any residential area nearby, several complaints would be

imminent.

But since it does not use much energy to operate and also it can produce its own electricity bymeans of the residual gas, methane, it is considered as eco-friendly and hence reduces the use

of non-renewable energy. There is no use of toxic materials during the production.

4.9.Prevention The workers can be trained so as to reduce the wastage on site while operating or

maintaining the treatment plant.

During construction, the trucks entering and going out of the construction site shall becovered and the dust areas shall be spilled with water so as to reduce the dust.

Workers will be provided with appropriate safety mask and equipment.

The construction and operation time should not be during the night so as not to disturbpeople from any source of noise.


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5. CONSTRUCTED WETLANDConstructed wetlands are designed based on natural wetland ecosystems. Compared to natural

wetlands, constructed wetlands allow for controlled performance and higher reliability. They

use the physical, chemical and biological processes to remove contaminants and rely

primarily on natural components to maintain the major treatment operations, compared to

other alternatives which use energy intensive mechanical equipment while using natural

process such as gravity and biodegradation only to some extent. This results in constructed

wetlands requiring lower operations and maintenance requirements and comparatively lower

energy usage (Vesilind 2004)

5.1.DesignA constructed wetland is typically an artificial wetland, marsh or swamp built to treat

contaminated wastewater. There are two main categories of wetlands which are surface flow

and subsurface flow. There are four key components in all constructed wetlands, Soil and

drainage materials (such as pipes and gravel), Water, Plants (both above and below the water)

and Micro-organisms.

Figure 5.1 Surface flow and subsurface flow constructed wetlands (Vesilind 2004)

Surface flow wetlands are more common in wastewater treatment and consist of a lowpermeability material such as clay or synthetic liner to prevent groundwater contamination.


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Influent passes at elevated height into the system which consists of plant, microorganisms and

water (Vesilind, 2004). The plants has several functions including

Support for microorganisms Shade which reduces algae growth Insulate the water from heat loss Filter solids, debris and pathogens Provide dissolved oxygen

The plants will dominate the systems due to the high nutrient level. Commonly used plants

include cattails, reeds, rushes, bulrushes, arrowhead and sedges. Subsurface flow wetlands are

differentiated by the wastewater being kept below the surface of the medium consisting of

materials ranging from coarse gravel to sand type materials. This reduces mosquito and odour

problems.

As water flows through the system, the velocity is reduced and the suspended solids are

trapped by vegetation and settles. Nutrients, such as nitrogen and phosphorous, are deposited

into wetlands from storm water runoff, from areas where fertilizers or manure have been

applied and from leaking septic fields (Davis, 1998). These excess nutrients are oftenabsorbed by wetland soils and taken up by plants and microorganisms. Other pollutants are

transformed to less soluble forms or rendered inactive while the microorganisms also remove

the pollutants from the water.

A typical design criterion includes a detention time of 7 days and a hydraulic loading 200 m3

/ha-d. Water depths in surface flow wetlands have been 100 to 450mm while bed depths for

subsurface flow wetlands have been 0.45 to 1m. The system can achieve effluent of 5 to 10

mg/L BOD and total nitrogen and 5 to 15 mg/L total suspended solids (TSS).

5.2.ConstructionWetlands are usually constructed on uplands and outside floodplains in order to avoid the

impact on natural wetlands and other aquatic resources. The construction consists of

excavating, backfilling, grading, and diking. Water control structures are installed at the

design levels to establish hydraulic flow patterns. Wetland vegetation is then planted or

allowed to establish naturally.


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5.3.Advantages Wetlands are biologically diverse and productive. When artificially replicated it can be

a sustainable alternative for the treatment of wastewater. They are an environmentally-

sensitive approach that is viewed with favour by the general public (Vesilind 2004).

Constructed wetlands require low construction and maintenance cost as use ofmechanical instruments are limited and the system depends mostly on natural

processes.

Operation and maintenance require only periodic, rather than continuous, on-sitelabour.

The approach of using wetlands is technically feasible in most areas where space isavailable.

The scale of the wetland can be adjusted to the required needs and as such, the usageis flexible.

Wetlands can tolerate fluctuations in flow. Wetlands are aesthetically pleasing compared to other alternatives to water treatment.

It can reduce or in some cases eliminate odour associated with wastewater.

They can be built to fit harmoniously into the landscape

5.4.Disadvantages and Limitations They generally require larger land areas than do conventional wastewater treatment

systems. Wetland treatment may be economical relative to other options only where

land is available and affordable.

Performance may be less consistent than in conventional treatment. Wetland treatmentefficiencies may vary seasonally in response to changing environmental conditions,

including rainfall and drought. Wetland treatment cannot be relied upon if effluentquality must meet stringent discharge standards at all times.

The biological components are sensitive to toxic chemicals, such as ammonia andpesticides (Vesilind 2004).

Flushes of pollutants or surges in water flow may temporarily reduce treatmenteffectiveness.

They require a minimum amount of water to survive. They can tolerate temporarydrawdown but cannot withstand complete drying.


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6. GRAVEL CONTACT AERATED SYSTEMIn Japan, their Ministry of Land, Infrastructures, Transport and Tourism using gravel contact

aeration system to clean water in the rivers, process in which the pollutants are broken down

and removed by the microorganisms growing on the surface of the gravel. Besides that, the

waters have been cleaned through removal of Nitrogen and Phosphorus by aquatic plants such

as reeds and others plants.

The gravel contact aeration system is a simple structurally process and it is can be designed

for different size of population with a vary site conditions. This system is a low maintenance

cost because it gives out a little sludge. This system is agreed for rural areas and it is

decentralized treatment system.

6.1.DesignA gravel contact oxidation treatment system is a kind of packed-bed reactor with the packed

medium of gravels as biofilm carriers. It might be classified as one type of natural and

ecological treatment techniques for the improvement of river water quality. When the system

is applied to treat the polluted river water, two installation ways are always seen (Crite et

al. 2000; Reed 2000; Kivaisi 2001; Zhen 2002; Tsai 2007). First one is installing the

treatment system beside the river, and the other one is installing it inside the river. For the

first way, the river water should be pumped or directed by gravity to the gravel contact

oxidation treatment system located beside the river. However, for the second way, the river

water normally flows by gravity through the gravel-packed-bed reactor. No matter which way

is selected, biofilm will grow on the surface of gravels and utilize the organic pollutants in the

river water. Some researchers reported that the biofilm growing on the gravels will be thicker

for an open channel with lower flow velocity (Lau, 1990; Lau and Liu, 1993). The whole

treatment system included a compound section of inlet channel, two bar screens, one grit

chamber, three influent distribution channels, three effluent collection channels, and three

gravel-packed contact oxidation tanks with the backwash air pipes and sludge collection

channel installed at their bottoms. The sludge must be removed once or twice a year and it is

then recycled as a fertilizers.


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Figure 6.1 The flow of the gravel contact aeration process and gravel contact aeration process.

The design flow rate of this system was 10,000 CMD (m3/day), and it flew through the whole

system by gravity. During clear days, the polluted river water will flow through inlet channel,

pass through two bar screens, then enter the grit chamber. At the end of grit chamber, three

distribution weirs and three distribution channels are used to evenly distribute river water into

three gravel-packed contact oxidation tanks. The treated water of each contact oxidation tank

will flow through a collection channel and then back to the downstream of the river. During

wet days, if the river flow rate is higher than the design flow rate, the superfluous flow will

directly pass through the treatment system to the downstream of the river. The sludge

assembly about 15 to 25 percentages if compared to activated sludge process or oxidation

ditch process. This is very much lower than activated sludge process and low maintenance

cost is required.

6.2.AdvantagesRural areas, which are less densely populated than urban areas, require a decentralized

sewage treatment system to cover a relatively highly populated area rather than a large-scale

centralized sewage treatment system as seen in urban areas. In view of the economic situation

of rural areas, systems that have low construction, maintenance, and operation costs are

required.

The environmental impact of this system is low because it is produce less sludge thanactivated sludge process and it require a small land.

Low construction, low maintenance, low operation cost


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The improvement of hygienic conditions in rural areas and the reduction of effects onwatersheds.

No odours-topped with soil. Less sludge produces than activated sludge process. No power consumed in the whole treatment process. It is buried underground.

Figure 6.2 The construction status of the low cost facility.

6.3.Disadvantages There is less information available on domestic wastewater discharge conditions in

rural areas than on those in urban areas.

Unable to cater for increase in wastewater volume. Decentralized sewage treatment- each residential area required one or two system.


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7. OXIDATION DITCHAccording to United States Environmental Protection Agency EPA (2010) Oxidation ditch

(OD) is a modified form of activated sludge system which utilizes long solids retention time

(SRTs) in order to remove biodegradable organics. The treatment or detention process via OD

takes long time and is capable of removing 75%-95% of Biological Oxygen Demand (BOD)

based on Indah Water Consortium Corporate (n.d).

Figure 7.1 Oxidation ditch overview (The Water Treatments 2011)

7.1.OD System ComponentsOD system comprises of a single or multiple channel that has a ring or elliptical basin.

Besides that, the channel is equipped with aqua rotor to circulate and aerates the waste water

in the channel therefore OD can be considered as a mechanical system. Also, the OD system

needs a clarifier to remove the suspended solids (Japanese Advanced Environment Equipment

2002).


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7.2.How does the OD work?

Figure 7.2 Typical oxidation ditch (United States Environmental Protection Agency EPA 2010 cited in Parsons

Engineering Science Inc. 2000)

General design of the OD process includes two separate aeration basin, the first is anoxic and

the second is aerobic (United States Environmental Protection Agency EPA 2010). The waste

water is diverted to the ditch after the primary treatment to mix with the return activated

sludge from a secondary clarifier. The mixture enters the anoxic zone. Then a rotor works to

mix the liquor to increase the amount of the Oxygen and foster the microbial growth to start

the biological process to treat the raw water from the organic waste. The waste water in the

ditch has to maintain a depth of 0.9-1.5 m to prevent any anaerobic condition at the bottom of

the basin (The Water Treatments 2011). When the treatment is completed in the ditch, thewater is taken to a secondary clarifier to clean it from the suspended solids before proceeding

to the disinfection stage to make the effluent ready to dispose.

7.3.ConstructionNormally the channel is constructed from a reinforced concrete. Other materials such as

gunite, asphalt, clay or even butyl rubber can also be used (United States Environmental

Protection Agency EPA 2010).


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7.4.CostConstruction

A large area is needed to build the OD treatment system. Therefore this system is not

advisable for the urban areas where the land is expensive.

Operation and Maintenance

The system requires little maintenance, minimal operator attention, low energy, no chemicals

are used in the system, and limited staff needed to operate the system, all together, contributes

to the saving costs of the OD system compared to other secondary system used.

7.5.AdvantagesJapanese Advanced Environment Equipment (2002) and United States Environmental

Protection Agency EPA (2010) highlighted both advantages and disadvantages of the OD

system.

The main advantage of the method is the ability to achieve performance objective with low

operational and maintenance requirements and costs. More specified advantages include:

OD system is a measure of reliability and performance owning to a constant waterlevel and continues discharge that lowers the weir overflow rate and prevents the

periodic effluent surge which is common to other secondary processes.

The system is energy efficient as little energy required which results in saving costs. The sludge resulted is little compared to other biological methods due to extended

biological activity during the activated sludge treatment.

The ease of operating OD process which helps on minimizing the number of staffrequired to operate the process.

The system minimizes the impact of a shock load or hydraulic surge due to longhydraulic retention time (HTT) and complete mixing using the rotor.


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7.6.Disadvantage OD needs a large land area compared to other biological systems. The basin area

depends on the capacity size, design effluent limitations, land and construction costs

and others.

The suspended solids concentration is quite high compared to other sludgemodification activated processes.

7.7.Environmental ImpactsAs mentioned earlier the system requires a large piece of land, therefore, clearing the land,

cutting the trees, noise and displacement of animals during the construction period areconsidered as negative impacts. While the long term impacts can include the sludge that is

resulted from the treatment if it is being disposed direct without further treatment that will

definitely harms the surrounding. Moreover, the unpleasant odours cannot be avoided in the

treatment plant.

Solutions

The surrounding of the treatment area has to be planted to replace the trees that were cut

during the construction. Also, the sludge has to be taken to further treatment to be used as

source energy and fertilizers in agriculture.

7.8.OD in MalaysiaCurrently there are approximately 30 OD systems in Malaysia. The system is graded to be A

standard in waste water treatment according to Indah Water Consortium Corporate (n.d).

Table 7-1 Typical figures for ODs (Indah Water Consortium Corporate n.d)

(mg/L) Raw Sewage Effluent DOE Standard A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50


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8. SELECTION OF ALTERNATIVEThe factors that were considered in the selection of the alternatives (American Water Works

Association, 1999) included:

(1) Source water quality,

(2) Regulatory compliance and contaminant removal requirements,

(3) Process reliability and flexibility,

(4) Initial construction and annual operating and maintenance costs,

(5) Environmental impacts,

(6) Utility preferences and capabilities,

(7) Available site space, and

(8) Residuals handling requirements and site constraints.

Factors such as source water quality and regulatory compliance and contaminant removal

requirements and available site space were site dependent and thus common to all the

alternatives. The above mentioned factors were evaluated and scored on a matrix to

determine the best alternatives. Weightage was based on the importance of that particular

factor in the selection of alternative.


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Table 8-1 Matrix

Alternative

Construction Operation MaintenanceEnvironmental

Impacts

Su

stainability

Design

O

verallScore

Cost

Difficu

lty

Cost

LevelofFle

xibility

ProcessReliability

ExpansionC

apacity

Regular/Periodical

Cost

WaterQu

ality

Contamin

ation

Possibility

UtilityRequirements

SpaceRequired

ResidualHandling

Centralized

Weightage 5 5 4 2 3 3 2 4 5 4 5 2 3 1 3

1) Aerated Lagoons I I I 1 3 1 P I III B III A 1 Y 1332) Anaerobic Filter III I I 2 1 3 P III II A II A 3 N 1073) Biological Wastewater

TreatmentIII II II 1 1 3 R I III A II C 2 Y 108

4) Constructed Wetland I I II 3 3 3 P II I C III A 1 Y 1025) Gravel Contact I II I 2 3 3 P I II A II B 3 N 1126) Oxidation Ditch II I I 2 2 2 P I III A III A 1 Y 129

Legends

I Low 1 Large A Minor SIMPLE R Regular Y Centralized 3 pointsWeightage Scale from

1 (low importance) to

5 (high importance)II Medium 2 Medium B Moderate MODERATE P Periodical N Decentralized 2 points

III High 3 Small C Major COMPLEX 1 point


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9. CONCLUSIONIn conclusion the report highlights six different alternatives for the wastewater treatment plant

project for Sibu town. The six options are aerated lagoons, anaerobic filter, biological

wastewater treatment, constructed wetland, gravel contact aerated system and oxidation ditch.

Each one of the alternative was discussed and then graded based on six criteria the team

decided to use in the matrix. The chosen option is the one which has the highest overall score

namely the aerated Lagoons with 133 points.

9.1.Selection and JustificationThe aerated lagoons are the best systems which can be used for the waste water treatment for

Sibu town as the system successfully fulfil the requirements of the client about the cost,sustainability and environmental impacts.

The aerated lagoons have a disadvantage in terms of reliability. However, aerated lagoons are

being extensively used here in Malaysia as there are forty of them which indicate how the

system can be relied upon. Therefore, aerated lagoons are the most suitable solution for Sibu

town waste water treatment plant over the other treatment options.


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10.REFERENCESAmerican Water Works Association 1999, Water Quality and Treatmenet: A Handbook of Community Water

Supplies, 5th Edition edn., McGraw-Hill, New York.

Davis, L 1998, A Handbook of Constructed Wetlands, USDA-Natural Resources Conservation Service, US

Environmental Protection Agency-Region III, Pennsylvania

Dawson Wastewater. (2011). Aerated Lagoon. Viewed on 18 September 2011,

D. F. Juang, et.(1 June 2008), Treatment of polluted river water by a gravel contact oxidation system constructed

under riverbed Viewed on 18 September 2011,

EPA 2011, 'Constructed Wetlands', Constructed Treatment Wetlands, United States Environmental Protection

Agency, viewed 19 September 2011.

Environmental Protect Agency. (2002). Wastewater Technology Fact Sheet. Viewed: 17 September 2011,

HakanModin, (2008), Decentralized Domestic Wastewater Treatment in Rural Areas in ChinaEfforts of the

Japan-China Water Environment Partnership Project, Viewed on 17 September 2011,

Introduction to Environemnetal Engineering 2004, Second Edition, P.Aarne Vesilind, Susan M. Morgan,

Thomson Books/Cole

Indah Water Consortium Corporate (n.d), Sewerage Facts, viewed 20 September 2011,

Indah Water Konsortium. (2011). Sewage Treatment Plant: Package Plant. Viewed: 17 September 2011 ,

Lagoon Systems in Maine. (2003). Aerated Lagoons Wastewater Treatment, Viewed on 17th September 2011,

Malaysia Travel site, 2007, Sibu City Map, viewed on 18 September 2011,.

METCALF & EDDY, Fourth Edition, Wastewater Engineering Treatment and Reuse

Motoyuki Mizuochi, (2008), Small-Scale Domestic Wastewater Treatment Technology in Japan, and the

Possibility of Technological Transfer, Viewed on 18

th

September 2011,

National Small Flows Clearinghouse. (1997). Lagoon System Can Provide Low-Cost Wastewater Treatment,

Viewed on 17th September 2011

SA Water, 2004, Wastewater Treatment Process, viewed on 19 September 2011.

Sewerage Services Department Sarawak, 14th Septembre 2011, Ninth Malaysia Plan

Project, viewed on 18 September


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2011

SSWM (sustainable sanitation and water management), Anaerobic Filter, Viewed on 19 September 2011,

The Water Treatments 2011, Oxidation ditch, viewed on 20 September 2011,

United States Environmental Protection Agency EPA 2000, Wastewater technology fact sheet, viewed 20

September 2011,

UKAnaerobic Filter, Viewed on 18 September 2011,,.

WELLAnaerobic treatment of municipal wastewater: How appropriate is it for low-income countries, Water,

Engineering and Development Centre, viewed 19 September 2011,

.

milestone a final review

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