Effects of heavy metal on activated sludge treatment process

This paper describes the investigation of the effect of selected heavy metals on the treatment performance of activated sludge process. Oxygen uptake rates were measured and heavy metal speciation was determined by the dialysis method. The extracellular polymer of biomass floc was determined by biochemical analysis. The affinity series of the metals in the sludge flocs was: Cu > Cd > Co > Ni > Sb > Zn. In the case of extracted polymer: Cu > Ni > Cd > Co > Sb > Zn. Copper was the metal bound most strongly by activated sludge flocs, followed by Cd, Co and Ni. The oxygen uptake measurements were conducted at two concentrations of 1 and 10 mg/l of heavy metal concentration and at 3 levels of MLVSS (mixed liquor volatile suspended solids) of 600, 900 and 1500 mg/L. Duplicate measurements were made. Results indicated that 1 mg/l Co and Sb and 10 mg/l Zn were the most inhibitory to the activated sludge process. Zn was not inhibitory at the MLVSS concentrations investigated. The inhibitory effect of Ca, Co and Zn and Sb decreased as the MLVSS concentration increased.