Effects of Cd(II) and Cu(II) on a Biofilm System

Abstract

There is little information available in the literature to describe the effect of heavy metals on a fixed‐film biological waste treatment system. The primary objective of this study is to evaluate the toxic effect of Cd(II) and Cu(II) on a fixed‐film biological reactor (rotating biological contractor) in treating a sugar waste. Different levels of cadmium (5 and 20 mg/L) and copper (1, 5, 10, 25, and 50 mg/L) were dosed to a three‐stage RBC unit treating an influent of 300 mg/L sugar solution. Experimental results indicated that the treatment efficiency was not adversely affected by the presence of copper at a concentration of 10 mg/L or less. However, when the copper concentrations were increased to 25 and 50 mg/L, removal of dissolved organic carbon was reduced by 7 and 10%, respectively. Toxicity was also observed when cadmium was present. Biological treatment efficiency was reduced by about eight percent when the cadmium concentration was either 5 or 20 mg/L. The major portion of the dosed metal was effectively retained by the biofilm. The efficiency of metal removal in the treatment system varied from 85 to 95% for cadmium, and 30 to 90% for copper, depending on their initial concentrations in the feed solution.