PUB moves to protect desalination plants from algae in seawater

SIAU MING EN Today Online 23 Mar 15;

SINGAPORE — With the drier weather conditions of late, national water agency PUB has for the first time installed silt curtains at the waters off Tuaspring and Singspring desalination plants, to protect the plants’ reverse osmosis membranes from higher levels of algae in the water. The Maritime and Port Authority of Singapore put up a notice last Thursday alerting the shipping community that there would be installation works for the silt curtains from March 13 to April 20 at the Johor Strait off Tuas View.

In response to queries, PUB said it was installing the silt curtains at the intake points of Singapore’s two desalination plants, as it had noticed a slight increase in levels of algae in the seawater around that area. “They act as an additional barrier to protect the reverse osmosis membranes from fouling,” said the PUB spokesperson.

The spokesperson added that the agency would continue to monitor the situation and, if necessary, the silt curtains will stay on beyond April 20.

Silt curtains, which drop to the seabed, can help keep out silt particles or other materials. Desalinated water is one of Singapore’s four national taps and the two plants currently can meet up to 25 per cent of Singapore’s current water demand.

Director of Nanyang Technological University’s Maritime Research Centre Tan Soon Keat said in this instance, the silt curtains would be able to block out primarily suspended solids and, to a certain degree, oil slicks.

“In the case of a desalination plant, the objective is to ensure (that the) quality of water entering the intake structure (is not) being affected by suspended solids in the water column, and flotsam and oil slicks (to some degree), and to buy time to respond in the case of potential influx of suspended solid plume or other flotsam,” said Assoc Prof Tan.

For the optimal operation of a desalination plant, the raw water supply must meet certain water quality standards, he said. In the case of lower-quality raw water, the plant may then need to include additional pre-treatment processes that would incur additional cost, added Assoc Prof Tan.

During dry weather, he noted, the surrounding lands around desalination plants would be drier, leading to more land-based washoff with sudden rain. He added that there may be elevated levels of phosphorus and nitrate in the runoff. Installing silt curtains is good practice, as it can buy time for the desalination plant to respond.

Singapore has experienced dry weather in the first two months of the year and to maintain healthy water levels in the reservoirs despite the dry weather, PUB has had to adjust the production of NEWater and desalinated water in order to meet demand. Rainfall for the whole of this month is expected to be below average, according to the National Environment Agency’s fortnightly outlook.

An algal bloom in the East Johor Strait in recent weeks has killed up to 600 tonnes of fish at fish farms here. Such blooms can be triggered by unpredictable weather, a higher concentration of nutrients in the seawater and poor water exchange between the high and low tides.

Over the past few months, concerns have also been raised over the possible environmental impact from the reclamation works carried out for the Forest City project in Johor, which will see four man-made islands built in the waters in Tanjung Kupang between south-west Johor and north-west Singapore.