Immobilization of heavy metals in the saturated zone by sorption and in situ bioprecipitation processes

Abstract

An ex-mining site located in Katowice, Poland, where silver, zinc and lead mining along with other activities took place for decades is now heavily contaminated with heavy metals. Especially the Quaternary and Triassic aquifers and surface water in the surrounding area are polluted. One serious risk is the threat of the contamination to drinking water, since the Triassic aquifer provides drinking water for more than 300 000 inhabitants. The main pollutants of concern are B, Ba, Zn, Cd, Cu, As and Sr. Remediation measures proposed for the Quaternary aquifer include a combination of natural attenuation, sorption barriers and in situ bioprecipitation. Dolomites, Fly Ash, and Peat are considered as suitable adsorbent materials for removing barium and strontium from the contaminated groundwater. However, no adsorbent has been found to efficiently remove B. In situ bioprecipitation (ISBP), a process during which sulfate reducing bacteria are stimulated by the addition of various C-sources resulting in the reduction of sulfate to sulfide and the concomitant precipitation of heavy metals, has been tested on both clay and sand aquifer taken from the site. Zn, Cu and sulfate were removed in the sandy and in the clayey aquifer material. In situ bioprecipitation combined with sorption was evaluated over a 120 days time period for the Triassic aquifer. Zeolites in combination with HRC® or molasses gave the best results, removing 100% of Ba and Sr in less than 2 days and 35% of B after 120 days. However, no sulfate was removed under these conditions. In addition, when Zeolite was solely or combined with HRC® or molasses, > 98% Zn was removed in 88 days. Zn was also removed using MRC®, lactate, molasses, HRC® and Diatomic Earth in combination with HRC® or molasses. A combination of ISBP and sorption offers the potential to contain the metal contamination in this Triassic aquifer.