Water & Wastewater Asia • July / August 2019 16 | FROM THE GROUND Co-Digestion: The Way Forward With Singapore’s water consumption expected to double by 2060, how do we as a nation look toward more sustainable efforts? Water & Wastewater Asia speaks to Dr Kelvin Koh, General Manager of the Ulu Pandan Water Reclamation Plant, to find out more. Dr Kelvin Koh, General Manager of Ulu Pandan Water Reclamation Plant, Water Reclamation Plants Department, PUB WATER & WASTEWATER ASIA (WWA): How far is co-digestion projected to get Singapore in economic terms, including electricity offsets and the sludge not needing to be incinerated? In terms of PUB’s roadmap for Singapore’s water sustainability, where does co-digestion put us? DR KOH (DK): Water demand is projected to double by 2060 from our current 430 million gallons per day (MGD). Our energy needs and waste generation would increase significantly if we continue to function as usual. A key pillar of Singapore’s water sustainability is to meet future water demand at today’s energy footprint. This means creating energy self-sufficient water reclamation plants which uses only as much energy as its treatment process generates. Co-digestion of used water sludge and food waste is one of the key initiatives towards achieving this target. The current biogas production from the anaerobic digestion stage of used water treatment in Ulu Pandan Water Reclamation Plant (without food waste addition) can supplement approximately 25 per cent of the plant’s total electricity consumption. Results have shown that the synergistic effects in co-digesting used water sludge and food waste can increase biogas production by up to 40 per cent, compared to if the two waste sources are digested separately. This could potentially increase our biogas production, and when implemented on a full scale, could helpWater Reclamation Plants (WRPs) achieve the long-term target of energy self-sufficiency for used water treatment processes, and 50 per cent reduction in sludge generation. Co-digestion also promotes a circular economy approach towards waste management. It maximises resource recovery from food waste and supports Singapore’s vision towards a Zero Waste Nation. By co- locating a used water treatment plant and wastemanagement facility in the Tuas Nexus, it allows us to harness potential synergies and benefits of aWater-Energy-Waste Nexus. This maximises both resource and energy recovery while minimising environmental footprint. In the long run, co-digestion will allow both PUB and NEA to lower cost of operating the facilities, making waste management more sustainable. WWA : Is co-digestion projected to help alleviate Singapore’s water-energy nexus, where the price of water is paid with energy? DK: Higher biogas yield from co-digestion means more energy can be produced using the biogas. This energy can then be used to offset the energy required to treat used water and enable us to meet future water demand in a sustainable way. Our goal is to make used water treatment fully energy self-sufficient while reducing sludge generation in the long run.