Effects of acidity on bacterial sulphate reduction and the bioprecipitation of metals in groundwater.

Large-scale column experiments were carried out to determine the effect of a step decrease in groundwater pH on metal remediation by bioprecipitation. Metal-contaminated groundwater at pH 5.5 was amended with 1 g/l of ethanol in one column using a polymer mat ethanol delivery system to promote bioprecipitation, while another column was left unamended and used as a control. Sulphate reduction and Zn removal were observed after eight weeks. Zn removal was observed in the zone of sulphate reduction, indicating precipitation as ZnS, while Cu was removed in the denitrification zone. Once steady-state bioprecipitation of Zn had been established, the pH of the metal-contaminated influent groundwater was reduced stepwise from 5.5 to 4.25. The change in pH resulted in a significant increase in Cu concentration in both columns. In the ethanol column, the zones of denitrification and Cu removal migrated up the column, while both sulphate reduction and Zn removal ceased. Bioprecipitation of metal-contaminated groundwater through sulphate reduction was shown to be an effective remediation strategy for Zn removal. However, this in situ process was sensitive to changes in groundwater pH.
Large-scale column experiments were carried out to determine the effect of a step decrease in groundwater pH on metal remediation by bioprecipitation. Metal-contaminated groundwater at pH 5.5 was amended with 1 g/l of ethanol in one column using a polymer mat ethanol delivery system to promote bioprecipitation, while another column was left unamended and used as a control. Sulphate reduction and Zn removal were observed after eight weeks. Zn removal was observed in the zone of sulphate reduction, indicating precipitation as ZnS, while Cu was removed in the denitrification zone. Once steady-state bioprecipitation of Zn had been established, the pH of the metal-contaminated influent groundwater was reduced stepwise from 5.5 to 4.25. The change in pH resulted in a significant increase in Cu concentration in both columns. In the ethanol column, the zones of denitrification and Cu removal migrated up the column, while both sulphate reduction and Zn removal ceased. Bioprecipitation of metal-contaminated groundwater through sulphate reduction was shown to be an effective remediation strategy for Zn removal. However, this in situ process was sensitive to changes in groundwater pH.