Chemical stress induced by copper: examination of a biofilm system

Biofilm systems have been widely used in wastewater treatment plants. However, little information is available on the impact of toxic chemicals on the performance of fixed film systems. This study was aimed at evaluating the impact of copper on a biofilm system by examining a variety of parameters, including reactor pH, DO, substrate concentrations, secretion of extracellular polymeric substances (EPS), and copper removal and accumulation. The microbial communities in the biofilms were also examined using automated ribosomal intergenic spacer analysis (ARISA). Four rotating drum biofilm reactors were used to produce biofilms. One reactor was used to produce biofilms under copper free conditions; while the others were used to produce biofilms grown under three different copper contamination levels, namely 100 ppb, 200 ppb, and 500 ppb, for a prolonged period. The following results were obtained: (1) biofilm reactor performance was not significantly impacted as demonstrated by the pH, DO, substrate removal, and total solids in the effluent; (2) however, copper contamination inhibited EPS production in the biofilms; (3) copper removal efficiencies of 25–31% were obtained for the three copper contamination levels studied; (4) fixed films functionalized as a reservoir to accumulate more copper over time; and (5) copper contamination selected for specific species that were able to tolerate this stress and that may contribute to its remediation.