SEWAGE TREATMENT PROCESS

INTRODUCTION

First of all, IWK officer Mr. Ishak give us some brief explanation about the

operation of the Sewage Treatment Plant. The Sewage Treatment Plant number at Taman

Desa Tebrau is JBT 154 and basically the process are preliminary treatment, primary

treatment, secondary treatment and the treatment and disposal of sludge. The raw sewage

are from the housing area, industrial area and shopping centre at Tebrau City.

BACKGROUND OF IWK

Indah Water Konsortium, a wholly-owned company of the Minister of Finance

Incorporated, is Malaysia's national sewerage company which has been entrusted with the

task of developing and maintaining a modern and efficient sewerage system for all

Malaysians.

In 1994, the Federal Government awarded the company the concession for

nationwide sewerage services which prior to that, was under the responsibility of local

authorities.

Since then, Indah Water has taken over the sewerage services from local

authorities in all areas except the States of Kelantan, Sabah, Sarawak and the Majlis

Perbandaran Johor Baru.

A modern and efficient sewerage system is vital for the country so as to ensure

that wastewater is treated before being discharged into our rivers. This will help preserve

the country's waste resources, protect public health and provide a cleaner and safer

environment.

In June 2000, as testimony of the Government's seriousness in ensuring that a

proper and efficient sewerage system will be successfully put in place and maintained,

the Government, through the Minister of Finance Incorporated, took over the entire

equity in Indah Water from its previous private owners.

Indah Water is now well-positioned to undertake the vital task of ensuring that

Malaysians today and in the future will be able to enjoy a clean and healthy environment

through a proper and well-maintained sewerage system.

In Malaysia extensive use has been made of primary treatment systems such as

communal septic tanks and imhoff tanks and unreliable low cost secondary systems such

as oxidation ponds. In addition, large urban areas utilize Individual Septic Tanks (IST). It

is estimated that there are over one million individual septic tanks in Malaysia.

These tanks only partially treat sewage, discharging an effluent still rich in

organic material. This has the potential to create public health and environmental

problems, particularly in urban areas.

IWK is responsible for planning and rationalizing the public sewerage facilities to

reduce the number of treatment plants using the "multipoint concept" or regionalization.

Finally, sewerage pipeline networks will be layed in urban areas currently serviced by

IST to convey the domestic sewage to modern secondary treatment facilities.

In Malaysia, 38% of public sewage treatment plants in the country are mechanical

plants. These plants operate using mechanical equipment that accelerates sewage break

down.

It is hoped that in the long-term, Malaysia's sewerage system will be made more

efficient through the standardization of the types of plants used.

These extensive programs are nothing short of a revolution in the management of

domestic sewage in Malaysia. The entire sewerage infrastructure can expect to undergo

changes. Estimates have been made of the number and type of public treatment plants

currently in Malaysia.

The trend will be moving towards "mechanical plants" such as Extended Aeration

(EA), Oxidation Ditch (OD), Rotating Biological Contactors (RBC), Sequenced Batch

Reactors (SBR) and Trickling Filters. Careful management of this change will ensure the

future of Malaysia's public sewerage systems.

SEWAGE TREATMENT OBJECTIVE As populations increase by leaps and bounds, it places more pressure on the

environment and threatening sources of fresh water supplies, it was recognized that the

problem of 'human waste' needed proper management.

From the early 1900s there has been a steady evolution of sewage treatment into

today's modern sewage treatment plants producing high quality effluent, which can be

safely discharged to the environment or reused.

More recent developments in sewage treatment have been to improve the

reliability and efficiency of treatment systems to treat sewage to meet standards and

reduce the land area occupied by treatment works through accelerating natural treatment

rates under controlled conditions.

However, despite these developments sewage treatment systems are still mainly

concerned with the removal of suspended and floatable materials, the treatment of

biodegradable organic and in some cases the elimination of pathogenic organisms.

Sewage treatment methods may be classified into physical unit operations,

chemical unit processes and biological unit processes. The treatment methods that use at

Taman Desa Tebrau, sewage treatment plant is physical unit operations.

SEWAGE TREATMENT PROCESS

Physical unit operations are treatment methods, which use the application of

physical forces to treat sewage. These include screening, mixing, flocculation,

sedimentation, filtration and flotation. Generally sewage treatment process have 4 main

components that is preliminary treatment, primary treatment, secondary treatment and

treatment and disposal of sludge.

1) Preliminary Wastewater Treatment

Preliminary wastewater treatment is defined as the removal of wastewater

constituents that cause maintenance or operational problems with the treatment

operations, processes, and ancillary systems. Examples of preliminary operations are

screening and comminution for the removal of debris and rags, grit removal for the

elimination of coarse suspended matter that may cause wear or clogging of equipment,

and flotation for the removal of large quantities of oil and grease. Preliminary

wastewater treatment includes primary screen, secondary screen, grit removal and oil and

grease removal.

A) Primary Screen

The screening element may consist of parallel bars, rods or wires, grating, wire

mesh, or perforated plate, and the openings are rectangular slots. A screen composed of

parallel bars or rods is called a bar rack sometimes called a bar screen. The term screen is

used for screening devices consisting of perforated plates, wedge wire elements and wire

cloth. Primary screen is course screen to remove all large objects that are deposited in the

sewer system, such as rags, sticks, sanitary towels (sanitary napkins), cans, fruits and etc.

Primary screen for protection against clogging and damage. Located upstream of pumps

or treatment facilities. Clear opening between bars are not greater than 25mm and the

slope of 0 to 45 degrees to the vertical.

B) Secondary Screen

The secondary screen is to remove all the objects that are smaller than 25mm

which the clear opening between bars are 9-16mm. The screen that use at the Taman

Desa Tebrau sewage treatment plant is mechanical screen which is “Auto Bar Screen”.

The slope is 30 to 45 degrees to the vertical. The pump only can pump the wastewater

which have below 25mm suspended solid. In this treatment plant they us 6 pump to pums

the wastewater and 1 pump have 25kw. Raw water after screening flows into the hopper-

bottomed wet well where the pipe intakes are positioned near the bottom of the chamber

to prevent deposition of solids. Automatic control governing pump operation maintain the

water surface between preset levels. Mr. farid told us that at the high mark all the pumps

are running, except standby pump, while the water surface at level 2 the one of the pumps

will running. Normally the pumps have to maintain because the oil will make the pumps

no operate some times can overflow because of the pump no running.

C) Grit Removal

Primary treatment typically includes a sand or grit channel or chamber where the

velocity of the incoming wastewater is carefully controlled to allow sand grit and stones

to settle, while keeping the majority of the suspended organic material in the water

column. This equipment is called a detritor or sand catcher. Sand grit and stones need to

be removed early in the process to avoid damage to pumps and other equipment in the

remaining treatment stages. Sometimes there is a sand washer (grit classifier) followed by

a conveyor that transports the sand to a container for disposal. The contents from the sand

catcher may be fed into the incinerator in a sludge processing plant, but in many cases,

the sand and grit is sent to a landfill. Grit was removed in grit chambers. Grit chambers

are provided to protect moving mechanical equipment from abrasion and accompanying

abnormal wear and reduce formation of heavy deposits in pipelines, channels, and

conduits and also reduce the frequency of digester cleaning caused by excessive

accumulations of grit. The removal of grit is essential ahead of centrifuges, heat

exchangers and high pressure diaphragm pumps.

D) Oil and Grease Removal

The oil and grease hinders biological process efficiency and removed by settling

and floatation (skimming). Oil and grease removal to avoid damage to pumps and other

equipment in the remaining treatment stages.

2) Primary Wastewater Treatment

In primary wastewater treatment, a portion of the suspended solids and organic

matter is removed from the wastewater. This removal is usually accomplished with

physical operations such as screening and sedimentation. The effluent from primary

treatment will ordinarily contain considerable organic matter and will have a relatively

high BOD. Treatment plants using only primary treatment will be phased out in the future

as implementation of the EPA secondary treatment requirements is completed. Only in

rare instances (for those communities having a secondary treatment waiver) will primary

treatment be used as the method of treatment. The principal function of primary

treatment will continue to be as a precursor to secondary treatment.

3) Secondary Wastewater Treatment

Secondary treatment is directed principally toward the removal of biodegradable

organics and suspended solids. Disinfection is included frequently in the definition of

conventional secondary treatment. Conventional secondary treatment is defined as the

combination of processes customarily used for the removal of these constituents and

includes biological treatment by activated sludge, fixed-film reactors, or lagoon systems

and sedimentation.

A) Oxidation Ditch

The Oxidation Ditch (OD) is a modified form of the activated sludge system.

Oxidation ditches are mechanical secondary treatment systems which are tolerant of

variations in hydraulic and organic loads.

The OD consists of a "ring or oval shaped channel" equipped with mechanical

aeration devices. Screened wastewater, which enters the ditch is aerated and circulated.

ODs typically have long detention times and are capable of removing between 75% and

95% of the Biological Oxygen Demand (BOD).

The proprietary "Orbal System" uses three channels or ditches concentrically placed.

Each channel is independently aerated and can be configured to act in parallel or series

with the other channels, depending upon the degree of treatment required.

After screening and grit removal, sewage enters the outer channel where most of the

biological reaction takes place. The second channel is held at a slightly higher dissolved

oxygen content for further BOD and nutrient reduction. The innermost channel is used

for polishing the effluent before it passes to a clarifier. 2 to 4 hours the process of

retention times for the raw water at the oxidation ditch.

The ODs can be easily adjusted to meet most combinations of incoming sewage

and effluent standards. This system achieves both high BOD reduction and some

nutrient removal.

ODs require more land than other processes but can be cheaper to construct and

operate. There are currently approximately 30 ODs in Malaysia.

B) Primary Clarifiers (Sedimentation)

Primary clarifiers at Taman Desa Tebrau IWK is circular in shape. Primary clarifiers

is the separation from water, by gravitational settling, of suspended particles that are

heavier than water. It is one of the most widely used unit operations in wastewater

treatment. The terms clarifiers or sedimentation and settling are used interchangeably. A

clarifiers basin may also be referred to as a sedimentation tank, settling basin or settling

tank.

Clarifiers is used for grit removal, particulate-matter removal in the primary settling

basin, biological-floc removal in the activated-sludge settling basin. It is also used for

solids concentration in sludge thickeners. In most cases, the primary purpose is to

produce a clarified effluent, but it is also necessary to produce sludge with a solids

concentration that can be easily handled and treated.

Raw wastewater enters through a series of ports near the surface along one end of the

tank. A short baffle dissipates the influent velocity directing the flow downward. Water

moves through at a very slow rate and discharges from the opposite and by flowing over

multiple effluent weirs. Settled solids are scraped to a sludge hopper at the intel end by

redwood flights that are attached to endless chains riding on sprocket wheels. Sludge is

withdrawn periodically from the sludge hopper for disposal. The upper run of flights

protrudes through the water surface pushing floating matter to a skimmer placed in front

of the effluent weir. The scum trough is a cylindrical tube with a slit opening along the

top. When the skimmer is manually or mechanically rotated, scum collected on the

surface flows through the slot into the tube that slopes toward a scum pit. Mr. farid told

us that flush return is 50% and the FBI test must do every 2 hours and also must do DO

test. Hydraulic retention times at minimum 2 hours at peak flow. After this process the

water will let go into the tebrau river and the standard water must a least standard B

required from SAJ.

4) Treatment and Disposal of Sludge

The sludges accumulated in a wastewater treatment process must be treated and

disposed of in a safe and effective manner. The purpose of digestion is to reduce the

amount of organic matter and the number of disease-causing microorganisms present in

the solids. The most common treatment options include anaerobic digestion, aerobic

digestion, and composting. The choice of a wastewater solid treatment method depends

on the amount of solids generated and other site-specific conditions. However, in general,

composting is most often applied to smaller-scale applications followed by aerobic

digestion and then lastly anaerobic digestion for the larger-scale municipal applications.

A) Sludge Thickener Tank

Gravity thickening is performed in circular settling tanks that are equipped with

scraper arms having vertical pickets. Mr. Farid told us that 50% sludge withdrawn from

primary clarifiers is applied to the gravity thickener through a central intel well. Overflow

containing the nonsettleable fraction is returned to the wet well for reprocessing, while

the concentrate is drawn from the tank bottom for processing and disposal.

Treated wastewater is mixed with the sludge entering the thickener to enhance

settling by washing out fine suspended solids and to reduce odors by maintaining a

moving water layer over the top of the blanket of consolidating solids in the tank.

Dissolved air flotation is achieved by releasing fine air bubbles that attach to sludge

particles and cause them to float. On pressure release, air dissolved in the recirculated

pressurized flow forms fine bubbles that agglomerate with the suspended solids. Process

underflow is returned to wastewater treatment, and the overflow, discharged by a

mechanical skimming device, is the thickened sludge.

B) Sludge Dewatering

Sludge dewatering is the process drying the sludge until 95% for disposal and just left

10% of sludge. After that is the process of filtration which is for removes much of the

residual suspended matter. Filtration over activated carbon removes residual toxins.

Drying time ranges from several days to weeks depending on gravity drainage of water

from the wet sludge and suitable weather conditions for evaporation. Dewatering may be

improved and exposure time shortened by chemical conditioning by addition of a

polymer.

C) Sludge Reception Facility( Sludge Imhoff Tank)

Imhoff tanks are simple form of sewage treatment plants requiring very little operator

skill. There is no mechanical equipment to maintain and operation consists of removing

scum, reversing the flow to keep an even distribution of sludge and removing sludge.

Imhoff tanks constitute 24 per cent (800 numbers) of all sewage treatment plants in

Malaysia and are the second most common form of treatment plant. They provide limited

treatment of sewage and are not a suitable long-term solution. The effluent from Imhoff

tanks can rapidly deteriorate if the tanks are not properly maintained.

An IT comprises two chambers positioned one above the other. In the upper

compartment sedimentation occurs with solids passing through an opening into the lower

chamber. Settled solids form sludge in the lower chamber and undergo anaerobic

digestion. Gases from the lower tanks are discharged to the air. Scum is accumulated in

the upper tank.

Sewage from the connected premises enters the sedimentation tank where settlement

of solids occurs. Heavier solids settle at the bottom of the tank as sludge. Liquid effluent

from the sedimentation tank then trickles through a rock filter bed. The sedimentation

tank needs to be desludged regularly. Organisms living in the rock filter feed on the

sewage, treating it in the process. Treated effluent is collected and discharged into a

nearby drain. Usually, the sedimentation process in the upper chamber is followed by

percolating effluent over a coarse stone media before discharge to a receiving water.

ITs are normally used to service small communities up to a population equivalent (PE)

of 1,000. They are relatively cheap to install, operate and maintain. However, ITs, like

ISTs, only partially treat sewage. The effluent from these tanks will not meet the

environmental requirements of the Department of Environment (DOE). Small package

treatment plants have more recently sur-planted ITs as the popular method of servicing

small communities.

D) Sludge Drying Bed

Open-air drying of anaerobically digested sludge has been used since the practice of

sludge digestion was started. Large beds are partitioned by concrete walls, and pipe

header from the digesters with gated openings allows application of sludge independently

to each cell. Seepage collected in the underdrains is returned to the plant wet well for

treatment with the raw wastewater. Cleaning dried sludge cake from the beds is a

laborious job. The cake has to be shoveled and taken off in wheelbarrows for loading in a

truck. Attempts to use mechanical equipment result in excessive loss of sand and

disturbance of the gravel underdrain.

CONCLUSION

As a conclusion benefits of wastewater treatment compared to benefits of sewage collection in developing countries. Waterborne diseases that are prevalent in developing countries, such as diarrhea, typhus and cholera, are caused primarily by poor hygiene practices and the absence of improved household sanitation facilities. The public health impact of the discharge of untreated wastewater is comparatively much lower. Hygiene promotion, on-site sanitation and low-cost sanitation thus are likely to have a much greater impact on public health than wastewater treat

SEWAGE TREATMENT PLANT