Co-digestion of food waste and used water sludge enhances biogas production for greater energy generation

30-01-2019

Success of demonstration project brings us closer to achieving energy self-sufficiency in used water treatment, and marks a milestone in maximising resource recovery from food waste.

Results from a trial project to co-digest food waste and used water sludge have shown that the process can triple biogas yield, compared to the treatment of used water sludge alone. The maximisation of resource recovery from food waste through co-digestion also supports Singapore’s vision towards a Zero Waste Nation and the adoption of a circular economy approach to manage waste.

Through the two-year trial, which started in December 2016, PUB, Singapore’s National Water Agency, and the National Environment Agency (NEA), explored the viability of collecting and transporting source-segregated food waste from various premises, to the demonstration facility at the Ulu Pandan Water Reclamation Plant for co-digestion with used water sludge.

As part of the trial, up to 40 tonnes of used water sludge and food waste from 23 premises were treated daily at the facility. The mixture of used water sludge and food waste then undergoes anaerobic digestion, a biological process that breaks down organic materials in the absence of oxygen, to produce biogas for energy generation. Results showed that synergistic effects in the co-digestion of used water sludge and food waste can increase biogas production by up to 40% compared to the separate digestion of the two inputs1.

“Positive results from the trial show that it is possible to make the used water treatment process in water reclamation plants more energy self-sufficient. We can therefore achieve greater synergy by co-locating the facilities of used water sludge and food waste treatment, which will be implemented at the new Tuas Nexus. This is also in line with our continued efforts to innovate and leverage technologies that will allow us to meet future water demand at today’s energy footprint,” said Mr Harry Seah, PUB Assistant Chief Executive, Future Systems and Technology.

The biogas yield from co-digestion of used water sludge and food waste is tripled when compared to the digestion of used water sludge alone. When compared to the separate digestion of used water sludge and food waste, the biogas yield from co-digestion is 40 per cent more.
energy footprint,” said Mr Harry Seah, PUB Assistant Chief Executive, Future Systems and Technology.

“Food waste is a waste stream which all of us are familiar with. What may be less well known is its low recycling rate, at only 16 per cent, which is well below 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, such as biogas for energy recovery. We are grateful for the active participation of various premises owners and stakeholders in this pilot project, who have been conscientiously segregating their food waste for collection and subsequent treatment. We look forward to the continued support of the community and industry to co-create zero waste solutions in this Year Towards Zero Waste,” said Mr Tan Meng Dui, CEO of NEA.

Co-digestion of food waste and used water sludge will be implemented at the new Integrated Waste Management Facility (IWMF) and Tuas Water Reclamation Plant (WRP) - collectively known as the Tuas Nexus – which are scheduled to be completed in 2025. Tuas WRP is a key component of Singapore’s Deep Tunnel Sewerage System (DTSS) Phase 2, the backbone of Singapore’s used water management system that also ensures long-term water sustainability. The IWMF is an integral part of Singapore long term plans to meet its solid waste management needs, with treatment processes for multiple waste streams. The Tuas Nexus will harness potential synergies and reap the benefits of a Water-Energy-Waste Nexus to maximise both resource and energy recovery while minimising environmental footprint.