Direct land application of cement kiln dust- and lime-sanitized biosolids: extractability of trace metals and organic matter quality

Abstract

Direct-land application of biosolids can affect soil organic matter (SOM) quality and be a source of trace metals (TMs) which may then be exported outside soil systems by plants, animals, and surface and subsurface waters. Organic matter (OM) quality and the chemical distribution of Cu, Zn, Cr, Ni, Pb, Co, and As were evaluated in soil amended with cement kiln dust-(CDB) and lime-treated (LSB) biosolids. Forms of these metals were classified by sequential extractions as easily extractable and exchangeable, potentially extractable, and non-extractable. SOM quality was assessed by extraction with diethyl ether (DEE) and chloroform (CHCl 3). Soils amended with CDB and LSB contained more TMs than did the control soil. Sequential extractions showed that, after one growing season, easily extractable and exchangeable metals accounted for 1.8% and 0.9% of total metals in CDB-and LSB-amended soils, respectively. On the other hand, potentially extractable and exchangeable metals constituted 53.4% and 59.5% of total TMs in the two soils, whereas non-extractable and non-exchangeable metals made up 44.8% and 39.6% of total TMs in the same soils, respectively. Direct-land application of CDB- and LSB-treated biosolids led to strong modifications of SOM quality as indicated by DEE/CHCl 3 ratios (indicative of the biodegradability of SOM), respectively, although the C and N contents did not change. The results also indicate that the dynamics of TMs are related to the degree of stabilization of the OM.