Effect of Cr(VI) on the microbial activity of aerobic granular sludge

Abstract

Cao (2015): Effect of Cr(VI) on the microbial activity of aerobic granular sludge, Desalination and Water Treatment, A B S T R A C TThe effects of different chromium (Cr(VI)) concentrations (0, 5, 10, 25, and 50 mg/L) on pollutant removal, nitrification ability, and microbial activity of aerobic granular sludge in sequencing batch reactors were analyzed. When compared with the control system, Cr(VI) decreased the average chemical oxygen demand (COD) and ammonia nitrogen removal rates. Significant correlations between the inhibitory rate of specific ammonia utilization rate (sAUR) and Cr(VI) concentration suggested that sAUR inhibition rate could be an effective indicator to predict the biological nitrification process in the aerobic granular sludge system. Although appropriate Cr(VI) concentration stimulated electron transport system activity of the granules, more than 25 mg/L Cr(VI) obviously inhibited the activity. The total polysaccharide and protein contents of the extracellular polymeric substances (EPS) linearly increased with increasing Cr(VI) concentrations of up to 25 mg/L. Furthermore, Cr(VI) exhibited greater inhibitory effects on the nitrification process than on the organic substrate removal process. This may be owing to the lower tolerance of nitrifying bacteria to Cr(VI), when compared with that of organics-degrading heterotrophic bacteria; distribution of nitrifying and heterotrophic bacteria, which occurred at the outer and inner layers of the granular sludge, respectively; and improvement in the COD removal rate of the micro-organisms as a result of EPS secretion.