Inducing Sulfate-Reducing Bacteria in the Saturated Zone Near a Nonferrous Industry

摘要

To remediate three sites in the vicinity of a nonferrous industrial site, where groundwater was historically contaminated with metals, the best available technique should be selected. Because the groundwater contained not only high concentrations of metals (site 3 about 300 ppm Co, site 2 about 2000 ppm Zn and site 1 about 300ppm Zn) but also high sulfate concentrations (up to 2000 ppm), the feasibility of sulfate reduction and subsequent metal immobilization due to metalsulfide precipitation was examined in the lab before selecting an appropriate remediation technology. However, because of the very high metal concentrations in the groundwater and their potential toxic effects on microbial life, chemical reagents were selected in addition to biological substrates to immobilize the metals in situ. The first site (site 1) was characterized by a contamination of Zn (140ppm-3ppm) up to a depth of 130m-bg. A screening for inducibility of biological activity was performed at two depths I.e. 30m-bg and 65m-bg using microcosm experiments containing both aquifer and groundwater. Different electron-donors were selected including pure chemical agents like lactate and waste products like molasses and glycerol. Glycerol resulted in the most efficient metal and sulfate removal after about 106 days. Extremely high Zn concentrations were found in the groundwater of the second site (site 2), I.e., up to about 2000 ppm. Similar lab tests applied for site 1 were performed, but additionally chemical agents (NaS_2 and CaS_x) were used. Whereas the sulfide containing chemical agents immediately resulted in low Zn concentrations in the groundwater, it took > 140 days before biological activity in terms of sulfate removal started. Glycerol, lactate, and molasses resulted in efficient Zn removal. Site 3 was characterized by a relative shallow contamination ( < 10 m-bg) of mainly Co (30-300 ppm) and contained typical sulfate concentrations in the range of 300-1200 ppm. Rapid microbial sulfate reduction (within 50 days) was induced in the conditions containing nutrient amended lactate, cheese whey and soy oil. All data obtained will be used to decide which in situ application to implement for the pilot-scale demonstration and remediation. A more detailed presentation for site 3 is given in Van den Broeck et al. (2007).