Alexander Szabo and Oscar Engle - Svenskt Vatten

arrangements which can process sludge. A careful selection of the sludge-treatment method has to
be made, as costs for stabilization, dewatering and disposal of sludge may be higher than the
operating cost for the activated-sludge treatment (Hammer, 1986).
In Malaysia facilities for treating sludge are limited and today most of the sludge is treated in
sludge lagoons or dried on large sludge-drying beds. Only in semirural areas are these methods
seen as long term solutions. A more long-term solution for urban areas would be to install
digesters and mechanical dewatering facilities. Then the gas produced from the digestion
chamber could be captured and utilized as fuel.
According to Malaysian standards presented in Sewerage Services Department (1998) a sludge
strategy consists of three main stages:
Stage 1 – Preliminary treatment and digestion
Stage 2 – Conditioning and dewatering
Stage 3 – Utilization and disposal
In stage 1, the sludge can be thickened in a centrifuge in order to increase the dry-solids content.
After the sludge has been thickened, it is sent to an aerobic or anaerobic digestion chamber.
In stage 2, the stabilized sludge is dewatered in a filter press and the dry-solids content in the
sludge is raised to more than 25% (Sewerage Services Department, 1998). Sludge lagoons or
drying beds can also be used in rural areas.
In stage 3, a sludge tank which can handle sludge for more than 30 days must be provided
(Sewerage Services Department, 1998). The final step is composting or disposal of the sludge.
The treated sludge can for example be utilized as fertilizers on fields.
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