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Changi Water Reclamation Plant


Changi Water Reclamation Plant (Changi WRP) treats used water by effectively removing the solids and nutrients that are present in the used water. After treatment, the treated used water is safe to be returned to the environment or channelled to NEWater factory to be further treated into highly purified NEWater.​

The treatment processes are divided into liquid and solid treatment.

DTSS Pumping Station

​The DTSS pumping station consists of one coarse screen shaft, two pump shafts with 5 large pumps in each shaft. Used water from the deep tunnel enters the plant site at 40m below ground level into the coarse screens where large debris is removed to avoid damaging the pumps. ​​

The pumps then lift the used water to the top before allowing it to flow by gravity to the Headworks. This marks the start of the Liquid Treatment Process.​

(A) Liquid Treatment


The Headworks comprises the preliminary treatment consisting of fine screens to remove smaller particles, grit, oil and grease to avoid hindering treatment process.​​​​

Fine Screen​​​

Primary Sedimentation Tanks

As used water passes through the double-deck sedimentation tanks, heavy particles, mostly organics, settle out at the bottom as sludge. Scrapers move slowly along the floors of each deck to remove these solids.​​


After the heavier organic particles have settled out during primary sedimentation, the used water then flows into the bioreactors. Naturally occurring micro-organisms in the used water helps to consume and break down impurities and colloidal organic matter that are suspended in the used water. Air is released from the diffusers at the bottom of the bioreactor to provide an aerated condition that is conducive for micro-organisms to grow and agglomerate. Resulting biomass clumps can be settled out and remove. By keeping the right balance of organisms and food, most of the dissolved solids are removed.​


Secondary Sedimentation Tanks and Outfalls

The heavy micro-organisms, known as the activated sludge, settle in the secondary sedimentation tanks and are recycled back to the bioreactors. Some are sent for solid processing.

Once the liquid treatment process is completed, the clear used water from the sedimentation tanks is then pumped and discharged from the effluent junction chamber, through the 5km long outfall pipes, into the Straits of Singapore. There, the treated used water, which has been treated to meet international standards, is dispersed in the swift currents more than 40m below the sea surface.​

(B) Solid Treatment

Blending and Thickening of Solids


The solid particles that settles in the pr​imary and secondary sedimentation tanks are removed as sludge from the used water. It is then rendered harmless into a safe, biologically stable product.

The sludge is blended and thickened before being pumped to the anaerobic digesters for digestion.​​​


Anaerobic Digesters

In the digesters, special micro-organisms decompose and stabilise the sludge. After about 20 or 30 days, the volume of the sludge is reduced, making it ready for dewatering and drying.

A useful by-product of the decomposition is biogas, which is rich in methane. The biogas produced are used as fuel for dryers to dry the sludge.


Sludge Dewatering

The digested sludge is then dewatered in centrifuges to remove more water before it is further processed.

Sludge Dryers

The dewatered sludge from the dewatering centrifuges is send to a series of rotary dryers. Biogas created in the digestion process runs the dryers, making them self-sufficient in energy.

​The use of dryers further remove moisture from the sludge to about 95% dry solid and the result is a product that is greatly reduced in bulk and easy to handle.