PUB project will make water cheaper to treat in the reservoirs
Tania Tan, Straits Times 7 Oct 08;
TUCKED away in the heart of industrial MacPherson is a small garden that does more than look pretty.
When it rains, this patch of green becomes a natural filter, catching soil contaminants from surface runoff, thus producing cleaner water which will be cheaper to treat when the water reaches the reservoirs later.
Called a 'rain garden' by its creator, the national water agency PUB, the 0.6ha plot has 14 plant species growing in a blend of coarse sand and fine gravel.
You could say hope grows in this pilot garden: It is PUB's hope that one day, green filters like this will dot the island's carparks, housing estates and private homes, soaking up pollutants and filtering out particles. They would be the first natural step in transforming dirty runoff into drinking water.
PUB senior manager Ong Geok Suat, who is on the project's team, said rainwater at the outset of a rain shower is extremely dirty from having washed the dirt off carparks, rooftops and small drains. Also called 'first flush', it often contains contaminants like petrol, particles and minerals.
'It's like when you scrub the floors. The first rinse is always the dirtiest,' she said.
The dirt in the runoff clogs up and destroys the costly membranes used in treating drinking water, making it necessary for them to be replaced every few years.
The idea of using rain gardens did not come up earlier because most of Singapore's soil is lumpy, non-porous clay, which does not make a good filter, she added.
Water that filters through the man-made rain garden is several times cleaner than normal surface runoff, she said.
The garden also acts like a sponge, holding water and releasing it slowly into the canals, reducing the chance of flooding during heavy rain.
Next June, when the pilot rain garden is a year old, it will be handed over to the Marine Parade Town Council which will take over its maintenance.
Ms Ong described the garden as a marriage of 'form and function', in that it looks good and is useful.
Researchers from the Singapore-Delft Water Alliance (SDWA) - a body funded by the National University of Singapore and the Dutch water institute Delft Hydraulics - are now studying various combinations of local species of plants and soil types to determine which pairings work best to absorb minerals and chemical pollutants.
Local plants such as cattails and umbrella sedge are some plants which work with the soil to play a filtering role.
SDWA research fellow Umid Man Joshi said: 'Ultimately, contaminants go into our water supplies, which can be costly to remove. If we can use plants to remove them, then it's a cheap, green way of doing things.'
Larger scale tests will be conducted at the group's Aquatic Science Centre in Ulu Pandan when it opens next year.
