LEE Kuan Yew Water Prize winner Mark van Loosdrecht does not give up on solving a mystery, even if it takes 10 years.

In 1988, his colleagues at the Delft University of Technology in the Netherlands noticed ammonia disappearing from an industrial waste-water treatment plant at an unexpected rate, he said in a lecture at Singapore International Water Week yesterday.

It took 10 years of work before the environmental engineer and his colleagues discovered the bacteria responsible for converting the ammonia from waste into harmless nitrogen gas in a process called anammox.

It took four more years before they developed a waste-water treatment method that uses the bacteria.

The method uses less energy and produces less carbon dioxide emissions than conventional waste-water treatment.

Today, it is used in 46 waste- water treatment plants, from the Netherlands to China.

For the last two years, national water agency PUB has been trying out a variant of the anammox process at its Changi water reclamation plant, to see if it can be used in future plants or installed in existing ones.

In recent years, researchers have also found other bacteria performing the same function in the Black Sea and the open ocean. These organisms play a key role in the nitrogen cycle, the conversion of atmospheric nitrogen into nutrients and back that underpins all life on Earth.

'When you don't understand something, you want to know how it works,' Professor van Loosdrecht, 52, said. 'Four out of five times, you find it's trivial. But sometimes, like with the anammox bacteria, you see something strange.'

In his talk, he tossed up a number of ideas for reclaiming resources from waste water, from recovering toilet-paper cellulose from sewage to making bioplastics from organic carbon in waste water.

Prof van Loosdrecht is the fifth recipient of the Lee Kuan Yew Water Prize, which recognises outstanding contributions to solving global water problems.

The award, which comprises $300,000 in cash, a certificate and a gold medallion, was presented at a ceremony at Marina Bay Sands last night.