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    -   To understand the concept of wastewater treatment (sewage treatment)


        Indah Water Konsortium Sdn Bhd, a national sewerage company, wholly-owned by the
Minister of Finance Incorporated, is responsible for providing sewerage services, operating and
maintaining over 5,750 public sewage treatment plants and 13,000km networks of sewerage
pipelines since April 1994.

       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

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.

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Sewage Treatment Methods

Historically unit operations have been grouped together to provide various levels
of treatment. Preliminary and/or Primary Treatment refers to physical unit
operations and is the first stage of treatment applied to any sewage. Secondary
Treatment refers to biological and chemical unit processes, while Tertiary refers to
combinations of all three.

1) Preliminary Sewage Treatment
Preliminary sewage treatment is defined as the removal of sewage constituents
that may cause maintenance or operational problems with the treatment
operations. This includes screening and comminution (grinding) for the removal of
debris and rags, grit removal by sedimentation and flotation for the removal of
excess oil and grease.

2) Primary Sewage Treatment
In primary treatment screening and sedimentation remove some of the suspended
solids and organic matter. The effluent from primary treatment will contain high
amounts or organic matter.

3) Secondary Sewage Treatment
Secondary sewage treatment is directed at the removal of biodegradable organic
and suspended solids, mainly using biological unit processes. Disinfection may be
included in secondary sewage treatment.

4) Tertiary Sewage Treatment
Tertiary sewage treatment includes the removal of nutrients, toxic substances
including heavy metals and further removal of suspended solids and organic.
Effluent from tertiary treatment is of a high standard and suitable for reuse.

There is no plan to build tertiary treatment systems in Malaysia. The focus has
been providing a basic standard of preliminary, primary and secondary treatment.

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Sewage Treatment Systems

Various methods of sewage treatment systems have been developed over the last
fifty years to meet the need to protect public health and the environment. For
urban centres where the population is concentrated and the receiving
environment is not able to cope with the waste discharge, sophisticated treatment
systems have evolved, which produces a high quality effluent. Simpler systems
have been used to service small communities although ever increasing
environment standards means that even these areas must eventually install better
treatment systems.

Sewage Treatment Systems For Urban Areas

Treatment processes are divided into treatment, which utilises oxygen to
breakdown organic matter (aerobic) and treatment, which doesn't utilises oxygen
(anaerobic). The breakdown of organic matter can occur while in suspension
(suspended growth) or on the surface of some type of media (attached growth). In
addition, processes using ponds are also sometimes used where large areas of land
are available. Treatment processes are categorised in this manner as shown in
Table 1.

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Sewage Systems For Small Communities

Because of their size, small communities have traditionally faced the problems of high per
capital costs, limited finances and limited operation and maintenance budgets for sewage

Where populations are less dense, the receiving environment is able to cope with lesser
level of treatment, often only primary treatment will be provided. However as population
increases, these primary treatment systems must be replaced with secondary treatment

Sewage treatment plants for small communities are now prefabricated before delivery to
site and these are commonly known as "package plants". They are only suitable for small
communities. Treatment processes are categorized in this manner as shown in Table 2.

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Extended Aeration Systems (EA)

Fine Bubble Diffused Air Extended Aeration Systems (FBDAEA) or (EA) are mechanical
secondary treatment systems. FBDAEA systems are robust and can withstand surges in
hydraulic or organic load.

To breakdown the organic material in sewage, bacteria require oxygen. This may be
introduced by agitation (using surface aerators) or by submerged "diffusers".

As the name implies FBDAEA systems introduce air in the form of fine bubbles through
submerged diffusers. Fine bubbles promote higher oxygen transfer efficiency and are
therefore used in preference to coarse bubbles.

Sewage entering a plant in passed through primary treatment where coarse material and
grit is removed. The sewage then passes to secondary treatment in the form of any aeration
tank where it is injected with fine bubbles of air from submerged diffusers.

Solids in the sewage are held in suspension by the bubbles and bacteria in the sewage break
down organic materials. Sewage is held in the aeration tank between 18-24 hours.

The effluent with suspended material is then passed into a "clarifier" (sedimentation tank)
where the material settles as sludge. The sludge is drawn off with some being returned to
the aeration tank to ensure enough bacteria are present in the tank to continue the process
of breaking down newly introduced sewage.

The effluent is then polished and/or discharged to the receiving environment.

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Parameter for Wastewater Treatment

2 parameters had been used for wastewater treatment. These parameters are BOD
(Biochemical Oxygen Demand) and SS (Suspended Solid)

         Parameter                                      Standard (mg/L)
                                              A                              B
            BOD                               20                             50
             SS                               50                            100

For domestic, the parameter is slightly different.

         Parameter                                      Standard (mg/L)
            BOD                                            250
             SS                                            280

As for commercial domestic, the standard for BOD and SS is 4 times from the domestic

Bacteria used in Wastewater Treatment

There are two types of bacteria that had been used in wastewater treatment

1) Aerobic – The bacteria that needs oxygen to process the wastewater

2) Anaerobic- The bacteria that do not need oxygen to process the wastewater

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Description: Site Visit to Indah Water