Maximizing Energy Recovery from Sludge - Singapore's Approach

Recovery of energy from sludge is an important component of PUB's drive towards zero-energy input for used water treatment in its Water Reclamation Plants (WRPs). Driven by this vision, PUB has taken steps to boost biogas production from the conventional mesophilic digestion process via 1) ultrasonic sludge disintegration and 2) co-digestion of greasy waste and used water sludge. From trials in Ulu Pandan WRP, ultrasonic sludge disintegration can boost biogas production by 35%. The paper will describe the pilot-scale trial in detail, including the operational problems that were encountered. In addition, this paper covers the operation of a centralised facility at Jurong WRP - the first of its kind in Asia that has been built to receive fats, oils and greases (FOG) from grease interceptors in Singapore. By blending FOG with thickened sludge (5% TS) before anaerobic digestion, the production of electricity from biogas at Jurong WRP has increased to almost 50% of the total energy consumption necessary for its treatment processes. These exciting initiatives form the cornerstone of PUB's current efforts to reduce the carbon footprint for used water treatment.