The role of extracellular polymeric substances in reducing copper inhibition to nitrification in activated sludge

Abstract

This study presents the role of extracellular polymeric substances (EPS) in reducing the inhibitory effects of copper towards nitrifying activated sludge. EPS could ameliorate copper toxicity in activated sludge by binding metal ions. A series of copper inhibition experiments were conducted with activated sludge taken from laboratoryscale sequencing batch reactor (SBR) systems operated under different feast-famine cycles, which provided the different conditions to the EPS-producing heterotrophic populations. The toxicity of copper to both nitrifiers and heterotrophs decreased with increasing the feast-famine period. Average EPS contents were substantially higher in SBR sludge with longer feast-famine periods indicating that the decrease in the toxicity of copper at a longer feastfamine period was attributed to the presence of higher amounts of EPS. Comparison of the responses of nitrifiers and heterotrophs to free copper suggests that nitrifiers were no more sensitive to copper than heterotrophs.