Long-term effect of Cr(VI) on ammonia-oxidizing and nitrite-oxidizing bacteria in an activated sludge system

Abstract

AbstractChromium (Cr) is a toxic compound in wastewater and can cause inhibitory effects on nitrification in a biological treatment system. However, different long-term inhibitory effects of Cr(VI) on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were seldom investigated in activated sludge systems. In this study, the influences of 1−10 mg/L Cr(VI) on bioactivities and quantities of AOB and NOB in long-term inhibition and recovery periods were investigated. The transformation of inorganic nitrogen, fluorescence in situ hybridization assay for analyzing micro-organism population, and specific oxygen uptake rates of activated sludge were examined. Results show that the inhibitory effect of Cr(VI) on nitrification increased with the Cr(VI) loading concentration and running cycle. The inhibited nitrification can be gradually recovered in a recovery period despite of a high accumulation of Cr (including Cr(VI) and Cr(III)) in activated sludge. AOB were more sensitive than NOB to Cr(VI)....