Sustainable Approach for the Immobilization of Metals in the Saturated Zone: In Situ Bioprecipitation
In order to remediate three sites in the vicinity of a non-ferrous industrial site, where groundwater was historically contaminated with metals, the best available technique should be selected. Because the groundwater contained high concentrations of metals and high sulphate concentrations (up to 2000 ppm), the feasibility of sulphate reduction and subsequent metal immobilization due to metal sulphide precipitation was examined in the lab before selecting an appropriate remediation technology. Because of the very high metal concentrations in the groundwater and their potential toxic effects on microbial life chemical reagents were also evaluated for immobilization of the metals in situ. The first site (site 1) was characterized by a contamination of Zn (500ppm-3ppm) up to a depth of 130 m-bg. A screening for inducibility of biological activity was performed at two depths – 30 m-bg (below ground) and 65 m-bg -- using microcosm experiments containing both aquifer solids and groundwater. Different electron-donors were selected including pure chemical agents such as lactate and waste products such as molasses and glycerol. Glycerol resulted in the most efficient metal and sulphate 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 in addition chemical agents (NaS2 and CaSx) were used. Whereas the sulphide containing chemical agents immediately resulted in low Zn concentrations in the groundwater, it took >140 days before biological sulphate removal started. Glycerol, lactate and molasses resulted in efficient Zn removal. Site 3 was characterized by relative shallow contamination (<10 m-bg) of mainly Co (30-300 ppm), and containing typical sulphate concentrations in the range of 300-1200 ppm. Rapid microbial sulphate reduction (within 50 days) was induced in the tests containing nutrient-amended lactate, cheese whey and soy oil.
Axel Schippers, Wolfgang Sand, Franz Glombitza and Sabine Willscher
K. Vanbroekhoven et al., "Sustainable Approach for the Immobilization of Metals in the Saturated Zone: In Situ Bioprecipitation", Advanced Materials Research, Vols. 20-21, pp. 261-266, 2007