In Malaysia, extensive use has been made of primary treatment systems such as communal septic tank's and Imhoff tanks and unreliable low cost secondary systems such as oxidation ponds. In addition, large urban areas utilise 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.
It is hoped that in the long-term, Malaysia's sewerage system will be made more efficient through the standardisation of the types of plants used.
These extensive programmes 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.
Imhoff tanks is a simple form of sewage treatment plant that requires minimal operating 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 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 tank is discharged to the air. Scum is accumulated in the upper tank.
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 supplanted ITs as the popular method of servicing small communities.
Oxidation Ponds (or Stabilisation Ponds) are a popular sewage treatment method for small communities because of their low construction and operating costs. Oxidation ponds represent 12 per cent (500 numbers) of all sewage treatment plants. New oxidation ponds can treat sewage to Standard B effluent level but require maintenance and periodic desludging in order to maintain this standard.
OPs may comprise one or more shallow ponds in a series. The natural processes of algal and bacteria growth exist in a mutually dependent relationship.
OPs require large amounts of land and the degree of treatment is weather dependent. They are incapable of achieving a good standard of effluent consistently. It is this variation in performance, which require the gradual phasing out of this type of treatment plant.
Depending upon the design, OPs must be desludged approximately every 10 years.
Commercially available prefabricated treatment plants known as "package plants" are often used to serve small communities up to population equivalent (PE) of 5,000.
Package plants require little design work and can be installed quickly although they require the same operational and maintenance care as conventional treatment plants. Claims that package plants produce no sludge is incorrect.
Care must be taken in using package plants where large variations in flow (hydraulic shock is experienced), in addition adequate provision must be made for sludge removal, scum and grease removal and the proper control of air supply.