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Pasir Ris PUB plant can treat sea and canal water

Sungei Tampines has been home to the $7.4mil variable salinity plant. -TNP
Koh Hui Theng

Thu, Jun 14, 2012
The New Paper

At the edge of Pasir Ris, where monitor lizards and turtles play, there's a water plant tucked away from prying eyes.

Stationed beyond the MRT tracks, it is eclipsed by the next-door belle called Downtown East. Access is limited to plant workers, PUB staff and the odd journalist.

Since 2007, the site at Sungei Tampines has been home to the $7.4 million variable salinity plant (VSP).

A world first, the VSP does double duty - it can generate clean water from both canal water and sea water.

That means it could turn almost all of Singapore into water catchment areas, up from the current two-thirds.

Depending on whether a wet or dry spell reigns, water is channelled either from the canal or the sea to the plant, where it is filtered and treated.

A PUB spokesman said the VSP was more cost-effective compared to a full scale plant that is productive only during the wet or dry spell, as it could process canal water during heavy rain and switch to sea water desalination during dry weather.

The plant produces about 9 million litres of water daily from treating rain and canal water, or half that amount daily if sea water is treated.

The amount meets 0.5 per cent of Singapore's daily water consumption (1.7 billion litres), but it's still early days.

"The plant is at the demonstration stage now," said PUB engineer Sarah Hiong.

"We already have the four taps (water from local catchment, Newater, desalination and imported water), so this is a potential option for Singapore to increase its water supply, if the need arises."

What the plant produces is used by industries, which make up 55 per cent of demand. The processed water surpasses drinking water quality guidelines set by the World Health Organisation and the United States Environmental Protection Agency.

So far, eight potential VSP sites have been identified and conditions like potential water yield and land availability will be studied, MsHiong added.

Although there's no definite date for expanding the technology, one thing's for sure: When it comes to water know-how, Singapore remains thirsty for more.

When rain falls, the weir acts like a dam, trapping water instead of letting it flow to the sea. The canal water is channelled to the variable salinity plant (VSP) for treatment. If the pressure sensors on the canal walls sense an extremely heavy downpour, the weir will deflate and storm water is released to the sea to prevent flooding upstream.

Reverse osmosis

High pressure forces the water through semi-permeable membranes, leaving unwanted salt and bacteria behind. Due to the high salt content, sea water will pass through the membranes twice. The treated water is stored in tanks before it is sent to customers.


Then the water passes through columns which are packed with tiny, straw-like membrane fibres. The membranes have 0.1 micrometre-sized pores - smaller than a strand of hair - to trap suspended fine particles.

Clean filtered water is then channelled to the reverse osmosis membranes.

Mechanical filters

Water is screened and strained to remove large solids like debris and leaves.

During dry spells, the canal's water level is low. Sea water is pumped to the plant from an intake point 190m offshore.


This article was first published in The New Paper.

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