Potential use of uncouplers to reduce activated sludge production

Activated sludge is one of the main processes used for wastewater treatment. Activated sludge is associated with the production of excess sludge, commonly referred to as wasted activated sludge (WAS). The handling and disposal of this sludge accounts for more than 40% of operational costs in a typical waste water treatment plant (WWTP). There were 26,000 tonnes of dry sludge produced in Melbourne during the years 2009-2010 according to the annual report by Melbourne Water and $43 million has been invested in Western Treatment Plant to improve the sludge treatment. 5840 tonnes of the sludge was collected and sent to a landfill for disposal, at a total cost of $494,210. Therefore, attention has been given to modifications to the activated sludge process with potential for minimization of excess sludge. One possible modification is the use of metabolic uncouplers, chemicals that can uncouple the energy transfer in cells and ultimately reduce activated sludge yield. The aim of this research was to evaluate two uncouplers, 3, 3’, 4’, 5-tetrachlorosalicylanilide (TCS) and para-nitrophenol (PNP also known as 4-nitrophnol or 4-NP) for their potential for reducing sludge production. A series of laboratory scale batch tests were carried out. The results obtained showed that TCS, at a concentration of 0.8 mg/L, can reduce activated sludge production by 45%, with little effect on COD removal. In comparison, a high concentration of 30 mg/L PNP was required to reduce sludge production by 30% but little effect on COD removal was observed.