Removal of chelated heavy metals from soil washing effluent by a sulfate-reducing bacterium and its re-washing potential
摘要
Soil washing can effectively remediate heavy metal-contaminated soils; however, the treatment of its effluent, which contains high concentrations of chelated heavy metals, remains challenging. This study employed a sulfate-reducing bacterium Shewanella sp. JN01 to remove chelated heavy metals from soil washing effluent and explored its re-washing potential. The results showed that Shewanella sp. JN01 achieved significantly higher removal efficiencies for chelated Cd, Pb, and Cu from the actual effluent (72.62%, 22.63%, and 80.12%, respectively) than in the optimized simulated system (46.42%, 17.14%, and 66.73%, respectively). This observation was attributed to that the total organic carbon, nitrogen content, and pH of the actual effluent promoted the bacterial strain activity to remove these chelated heavy metals. Additionally, the removal efficiencies of chelated Zn in both the simulated and actual systems were low (less than 5% and 1.2–8.5%, respectively). Nevertheless, the removal amounts of chelated Zn (1.2–6.3 mg) from the actual effluent are comparable to those of chelated Cd (3.7–4.1 mg) and Cu (4.8–5.3 mg) because its much higher concentration. Shewanella sp. JN01 was likely to remove chelated heavy metals by reducing sulfate to produce S2− ions, promoting metal sulfide precipitation. X-ray photoelectron spectroscopy analysis revealed that CuS dominantly enriched in the inner layer while ZnS segregated to the surface, indicating a heterogeneous distribution of precipitates. The removal efficiencies of heavy metals in soil by the treated effluents with acidification reached 45–85% of those by the fresh washing agent, demonstrating partial restoration of its washing capacity. These results will be beneficial for establishing effective strategies to remove chelated heavy metals from soil washing effluents and reuse the regenerated agents.