Singapore to use food waste to boost energy creation

Technology that combines such waste with used water sludge to be tested at a new facility
By Siau Ming En, TODAY, 18 Jun 2015

When it comes to transforming waste to electricity, the sum of the parts is indeed greater than their whole. By adding food waste to the process of turning used water sludge into electricity, twice as much power can be produced compared with the conventional method that digests only used water sludge.

Such technology will be tested at a new facility launched by national water agency PUB and clean-energy firm Anaergia today (June 17) at the Singapore International Water Week Technology and Innovation Summit. The co-digestion plant will be Singapore’s first, though the technology is already in use in America and Europe.

Currently, electricity generated by converting only used water sludge can meet about 20 to 25 per cent of a water-reclamation plant’s needs. With the technology offered by the co-digestion plant, the electricity produced may meet about 50 per cent of the plant’s needs.

Used water sludge is a by-product from treating used water. This is anaerobically digested in PUB water-reclamation plants — the process of breaking down organic materials without oxygen. The resulting biogas is used as fuel to produce electricity.

At the new co-digestion plant, wet organic fraction from food waste will be mixed into used water sludge. The thickened mixture will then be anaerobically digested. The mix can produce more biogas because of the higher calorific value in food waste, said a PUB spokesperson.

As the technology is in its testing phase, the plant will be able to treat only up to 40 tonnes per day of combined used water sludge from the Ulu Pandan Water Reclamation Plant and food waste collected from an upcoming food-waste recycling pilot in Clementi. It can produce about 6,000kW of electricity each day, said Anaergia’s chairman and chief executive officer Andrew Benedek at the launch.

In March, Second Minister for the Environment and Water Resources Grace Fu announced plans for a district-level pilot, where segregated food waste would be collected from premises such as shopping malls, schools, hospitals and office buildings for anaerobic co-digestion. Clementi was chosen for its close proximity to the water-reclamation plant.

Food waste accounts for about 10 per cent of total waste generated in Singapore, but less than 15 per cent of it is recycled. Last year, 788,600 tonnes of food waste were generated, of which only 13 per cent was recycled. The rest was incinerated — a process that also generates electricity — and then disposed of in landfills.

Speaking to reporters, PUB chief technology officer Harry Seah said instead of incinerating food waste, more energy could be produced when food waste is first processed in a co-digestor. “We think that if we are to segregate food waste properly, segregate it first and produce biogas, then send for incineration, (we will get) more energy,” he said, adding that the co-digesting process produces 30 per cent more energy than directly incinerating food waste.

Currently under construction at the Ulu Pandan Water Reclamation Plant, the co-digestion plant will be ready in September. Mr Seah added: “The result of this demonstration plant will validate the efficiency and cost-effectiveness of co-digestion implementation in Singapore, potentially reducing its carbon footprint and maximising energy production.”

If successful, the technology could be used at the coming Tuas Water Reclamation Plant and the National Environment Agency’s Integrated Waste Management Facility.

“The success of this project will provide opportunities for a water-reclamation plant like ours to generate enough energy for process use and bring us closer to achieving energy self-sufficiency for used-water treatment in Singapore,” Mr Seah added.