The effect of various carbon sources on stimulating bioprecipitation of heavy metals in the saturated zone

Abstract

In situ bioprecipitation (ISBP) seems to be one of the most promising processes for immobilization of heavy metals in soil. It is mainly performed by Sulfate Reducing Bacteria (SRB) that are anaerobic heterotrophs utilizing a range of organic substrates and sulphates as a terminal electron acceptor. Sulphides produced from sulphates reduction form insoluble complexes with a metal, which results in its immobilisation. SRB can be stimulated by the addition of various carbon (C) sources. The aim of this study was to evaluate the effect of various C sources on stimulating bioprecipitation of heavy metals (Zn, Ni, Cu, Pb, Cd) in the saturated zone. As C – sources, molasses, whey and ethanol were used to induce the ISBP process. Column tests were performed with natural aquifer materials from Piekary Slaskie, Poland and synthetic groundwater containing Zn, Ni, Cd, Pb, Cu. Two controls included: an abiotic control containing formaldehyde, and a natural attenuation control (not amended with an extra C – source). In the molasses and ethanol amended columns, redox potential decreased to -163 and -189 mV, the initial pH of ca. 6 decreased to 4.6 and heavy metals (Zn, Cd, Cu, Pb) were immobilized . In the NA column and abiotic control, almost no metals were immobilized. In the whey amended column precipitation of Zn was observed and no significant immobilized of Cu, Cd, Ni, Pb took place. The tested C sources promoted sulfate reduction within seven weeks, with average efficiencies of 60%. keywords: heavy metals, in situ bioprecipitation, sulphate reducing bacteria, carbon sources