Still, he kept working on the technology, which mimics nature's way of breaking down waste anaerobically, that is, in the absence of oxygen.

For coming up with a widely used, energy-saving, wastewater treatment reactor, the 72-year-old yesterday became the second recipient of the prestigious Lee Kuan Yew Water Prize. His invention beat 38 other nominations from 19 countries, all of which are projects tackling global water problems.

The emeritus professor from Wageningen Agricultural University in the Netherlands will be presented the $300,000 prize in June during the Singapore International Water Week, at which industry leaders, policymakers and experts will meet here to discuss water issues.

Last year's inaugural prize was won by Dr Andrew Benedek, the Canadian whose pioneering research in membrane filtration is now applied here to treat and purify sewage to produce Newater.

Prof Lettinga's design, called upflow anaerobic sludge blanket (UASB) technology, uses a layer of caviar-like sludge granules which contain a cocktail of bacterial micro-organisms.

These bugs digest contaminants in wastewater, leaving the treated water to be filtered off for discharge or further purification. The process produces methane gas, which can be collected as fuel.

UASB systems cost half as much as conventional aerobic treatment systems, and use 30 to 40 per cent less energy.

Professor Lettinga chose not to patent the technology, as he believes any technology which can improve the environment 'should be available to everybody'.

Read the full story in Tuesday's edition of The Straits Times.