Effect of Copper on Viable Populations and Community Structures of Nitrifiers and Heterotrophs in Activated Sludge

Abstract

The purpose of this study was to investigate the toxicological response of nitrifying and heterotrophic populations in activate sludge to different copper concentrations. The changes in the active fraction of nitrifying and heterotrophic communities were quantitatively estimated by the respirometric analysis. Furthermore, the shift in community structure of mixed culture receiving continuous dose of copper was qualitatively determined by the fatty acid methyl esters (FAMEs) analysis and principal component analysis (PCA).Four bench-scale activated sludge units were fed with synthetic wastewater and operated at a mean cell residence time (MCRT) of 20 days. Copper concentrations in the influent were 0, 1, 3 and 6 mg/L. Toxicological responses of the nitrifying and heterotrophic populations were evaluated by the normalized ammonia uptake rate (AUR) and total organic carbon (TOC) removal rate, respectively. Substantial decrease in the performance of both nitrifiers and heterotrophs were observed at the copper concentrations of 3 and 6mg/L.In order to examine the effect of continuous dose of copper on viable population of nitrifiers and heterotrophs, the active fraction of both populations were estimated by a respirometric technique. Active fractions of the nitrifiers and hetertrophs in the noninhibited control unit were 1.0 and 30.1% of total biomass, respectively. The active fractions both populations decreased sharply to 0.1 and 0.5% (for nitrifier and heterotrophs, respectively) under the continuous dose of 3 mg/L, suggesting that the continuous loading of copper as low as 3 mg/L is enough to have detrimental effects on the viable communities in nitrifying activated sludge.Effect of copper on microbial community structure was evaluated by FAME analysis. Nineteen fatty acids were extracted from the samples harvested from the bench-scale activated sludge units. Of those fatty acids, seven were previously identified as fatty acids typically present in pure cultures of Nitrosomonas spp. and Nitrobacter spp. When fatty acid compositions of both nitrifying FAMEs and all FAMEs were examined by PCA, the resulting plots showed clear distinctions between populations in control units and those that exhibited decreased levels of nitrification. The combination of FAME analysis with PCA illustrated the significant shift in the nitrifying and heterotrophic community structure as a result of continuous copper dosage.