RISK ASSESSMENT AND SPECIATION OF Zn, Cu, Ni AND Cr IN SEWAGE SLUDGE AMENDED WITH ATTAPULGITE

摘要

Land application of sewage sludge may be limited by its metal contaminations. A sequential extraction method was employed to evaluate the effect of attapulgite as an additive for remediation of sewage sludge. The raw sludge had high direct toxicity and a large percentage of a potentially toxic fraction. Amendment with attapulgite markedly decreased the availability of Zn, Cu, Ni and Cr, and the exchangeable, carbonate and iron manganese oxide combined metals were converted into relatively immobile residues because of adsorption and complexation to attapulgite. Attapulgite was able to immobilize the soluble fraction of Cr and Cu. The content of Cr, Ni and Zn in the diethylenetriaminepentaacetic acid extractable fraction showed a downward trend with increasing attapulgite application while the content of Cu rose. With increasing attapulgite amendment, the germination index climbed from 28 to 73%. Attapulgite appeared promising as an amendment to reduce the hazard potential of metals in sludge by converting them into less soluble, mobile, or available forms.