Metabolic uncouplers reduce excess sludge production in an activated sludge process

Abstract

This study compared the effectiveness of four metabolic uncouplers ( p-chlorophenol, m-chlorophenol, m-nitrophenol and o-nitrophenol) in reducing sludge production from an activated sludge process. A series of batch experiments fed with different concentrations of individual metabolic uncouplers were conducted at constant initial biomass and glucose concentrations. Results showed that sludge production was reduced with the increase of metabolic uncoupler concentration from 0 to 20 mg l −1. Among four metabolic uncouplers studied, m-chlorophenol was the most effective in reducing sludge production, and had less effect on the process performance, e.g. 86.9% of sludge reduction was achieved at a m-chlorophenol concentration of 20 mg l −1, while the COD removal efficiency was lowered only by 13.2% as compared to the control test. The acidity constant (p K a) of a metabolic uncoupler highly influenced its effectiveness in sludge reduction, i.e. metabolic uncoupler with a lower p K a value has a higher potential to reduce sludge production. It appears that selection of metabolic uncoupler and optimization of its dosage should be based on a compromise of the desired sludge reduction and system performance.