Trash to treasure: Turning waste to energy

A collection truck pouring food waste into a bunker for treatment. Workers at food distributor Tian Sheng Fresh Produce packing apples and picking out rotting ones, which will be set aside as food waste that is combined with water sludge to be treate
Workers at food distributor Tian Sheng Fresh Produce packing apples and picking out rotting ones, which will be set aside as food waste that is combined with water sludge to be treated at PUB's facility in Old Toh Tuck Road.ST PHOTO: CHONG JUN LIANG
A collection truck pouring food waste into a bunker for treatment. Workers at food distributor Tian Sheng Fresh Produce packing apples and picking out rotting ones, which will be set aside as food waste that is combined with water sludge to be treate
A collection truck pouring food waste into a bunker for treatment. ST PHOTO: CHONG JUN LIANG

PUB, NEA find a way to mix used water sludge with scraps to produce biogas that can power water reclamation plants

What gets flushed down the toilet daily may be worth its weight in gold.

A two-year trial by Singapore's national water agency PUB and the National Environment Agency (NEA) has found a way to ensure that used water sludge is not wasted.

Mix what is flushed down the loo with table scraps, and the stomach-churning recipe becomes a potent recipe for energy.

If it is scaled up, the biogas produced in the process can power a large portion of Singapore's water reclamation plants.

This is a prime example of how Singapore is turning trash to treasure, particularly in view of 2019 being designated as the Republic's Year Towards Zero Waste.

The trial, which started in December 2016, involved 40 tonnes of used water sludge (from toilets) and food waste treated at the PUB's facility in Old Toh Tuck Road.

Two truckloads arrive daily from 23 premises across Singapore, including Maju Camp, University Town at the National University of Singapore and food distributor Tian Sheng Fresh Produce.

  • 40%
  • How much more biogas yield from the combined digestion of food waste and water sludge, compared with when they are digested separately, at the PUB's facility in Old Toh Tuck Road.

The sludge and food waste are combined, and will go through what the agencies call "anaerobic digestion", also known as a biological process that breaks down organic materials to produce biogas - a natural fuel that is produced when organic matter reacts with bacteria.

The sludge and food waste were previously digested separately to produce biogas. But when combined, the PUB and NEA found the biogas yield tripled, compared with when used water sludge was digested alone.

 
 
 

Also, the biogas yield from combined digestion was about 40 per cent more than when food waste and water sludge were digested separately at the facility.

The agencies are aiming for this co-digestion process to provide the large amounts of energy required daily to treat used water.

They hope it will maximise the recovery of resources from food waste, while letting Singapore take a step towards energy self-sufficiency in the used water treatment process.

But only 16 per cent of food waste, a major waste stream here, is recycled, said Mr Tan Meng Dui, NEA's chief executive. He added that the rate is low, compared with Singapore's overall recycling rate of about 60 per cent.

"As the second-largest waste stream disposed of, there is great potential to not only reduce food wastage at the point of consumption, but also to recycle better by developing technologies to turn food waste into higher-value products, like biogas for energy recovery," Mr Tan said.

"We look forward to the continued support of the community and industry to co-create zero waste solutions in this Year Towards Zero Waste," he added.

Mr Harry Seah, PUB assistant chief executive for future systems and technology, said: "Positive results from the trial show it is possible to make the used water treatment process in water reclamation plants more energy self-sufficient."

Mr Seah added that as a result of the technology's success, the process is likely to be scaled up, in the form of co-locating the facilities of water sludge and food waste treatment at the new Tuas Nexus.

The Tuas Nexus, comprising the Integrated Waste Management Facility and Tuas Water Reclamation Plant, is scheduled to be completed in 2025.

A version of this article appeared in the print edition of The Straits Times on January 30, 2019, with the headline 'Trash to treasure: Turning waste to energy'. Print Edition | Subscribe