Extractability and fractionation of heavy metals in chemically treated sewage sludges

Abstract

Four chemically treated sludges, lime-treated (LS), lime/sodium silicate-treated (LSS), cement-treated (CS), and cement/sodium silicate-treated (CSS) were produced form the chemical treatment of aerobic digested sewage sludge cake, using lime, cement, and sodium silicate as additives. Ex tractability and fractionation of the heavy metals (Cu, Pb, Cr, and Zn) in these products and untreated sludge (S) were investigated using sequential extraction, single extraction, and 13C cross-polarization magic angle spinning nuclear magnetic resonance analysis (13C-NMR). These approaches revealed that chemical treatment of sewage sludge makes sludge Cu, Pb, and Cr more extractable. It was attributed to the irreversible dissolution of a portion of organics at very high pH during chemical treatment of sludge. The enhanced extraction of some metals having higher affinity to organics, e.g. Cu and Pb, from the chemically treated sludges was due to their complexion with the above soluble organics.