A study was undertaken to demonstrate on pilot plant scale the performance of a turbine foam breaking system and to develop the design parameters for large scale application. Among various configurations a 3‐blade vaned‐disc turbine was found to be optimal for foam breaking. Major process variables controlling foam breaking were system design, tip velocity, rotation speed, and foam load. A foam breaking system with only restricted liquid draw‐off performed 3 ‐ 16 times better than a conventional flow through system. A 38 cm diameter turbine operating at 1800 τ/min (3600 cm/s tip velocity) collapsed up to 1.2 m3/min (42 ft3/min) of foam. Design equations developed for sizing of foam breakers suggest that a 61 cm (2‐ft) diameter 21 kW turbine will collapse 4.7 m3/min of foam. For a 95 × 103m3/d foam separation plant, approximately 12 foam breakers are required. Capital costs are estimated at $108,000.

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.

The spent sulphite liquor derived from Abitibi Paper Company, Iroquois Falls Mills Arbiso process contained about 11.3% dissolved solid, 0.52% (W/V) residual SO2 and had a low pH of 4.3. The COD of the liquor was about 109,000 ppm and BOD5 26,000 ppm. The objective of the study was to investigate the technical feasibility of utilizing biodegradation to reduce the BOD5 of the spent liquor to acceptable levels. Upon first analysis, it appeared that the liquor would be amenable to biological degradation because of the presence of wood sugars. However, biological oxidation was retarded due to the presence of SO2. The maximum SO2 concentration tolerated by the microbes was about 0.32% (W/V). Boiling and lime treatment were found to be effective in reducing the SO2. Other major factors affecting biological activity were initial pH adjustment and nutrient addition. Nutrients required and optimal operating conditions are discussed. Under optimal conditions, a batch biological system was capable of removing 60% BOD5, in 11 days and 80% BOD5 in 16 days.