| Scope and Method of Study. The fate of lead, zinc, and cadmium and their effect on the activated sludge process were studied. To achieve the objectives of this study, several bench-scale activated sludge units were employed and operated at three different solids retention times (SRT) for each metal. Each metal was applied at various concentrations. The effect of heavy metals on the biokinetic constants computed by three current design models (Kincannon and Stover, Eckenfelder, and Lawrence and McCarty) were also studied.;It was found that the addition of cadmium at different dosages generated lower values of U(,max) and k(,B) when compared with control values. The results indicated that k(,B) and U(,max) (in terms of COD) increased as zinc concentrations increased. Lead concentrations of 0.56 and 3.32 mg/l produced loer vaues of U(,max) and k(,B), in terms of COD, than control values.;Addition of lead caused a reduction in the ability of the system to remove influent substrate when operated at a 12 day SRT, but had no effect on the 3 and 6 day SRT systems. Zinc had no effect on treatment removal efficiencies in terms of COD and TOC. The COD removal efficiency was reduced by an average of 5 percent when cadmium was added to the 3 day SRT reactor at 4.06, 6.02, 9.67, and 21.60 mg/l. Invluent cadmium did not have an adverse effect on the COD removal efficiency in the 6 day SRT unit. No effect was observed upon addition of 4.14, 6.60, and 9.20 mg/l cadmium for the 20 day SRT system; however, 17.28 mg/l of cadmium did show an adverse effect.;The results showed that the metals studied were accumulated in the sludge.;Findings and Conclusions. From the results of the study, it was found that lead up to concentrations of 18.08 mg/l could be more effectively removed by a 12 day SRT unit than a 3 day or 6 day SRT system. Zinc was removed approximately 97.1 percent by the activated sludge system. The 3, 6, and 20 day SRT units were able to remove cadmium very efficiently (greater than 92.1%). |
