Ethanol-based in situ bioremediation of acidified, nitrate-contaminated groundwater

•Ethanol was successfully used to enhance intrinsic denitrification in groundwater.•Denitrification in the acidified groundwater became effective above pH 6.•Ethanol was efficiently introduced into the groundwater via the unsaturated zone.•Clogging problems typical for in situ bioremediation of groundwater were avoided.

A novel approach for the in situ bioremediation of acidified, nitrate-contaminated groundwater was developed. Ethanol was introduced into the groundwater to enhance the activity of intrinsic denitrifying micro-organisms. Infiltration of the carbon source was made via an infiltration gallery constructed in the unsaturated zone to avoid clogging problems and to allow wider distribution of ethanol in the groundwater. The changes in the groundwater geochemistry and soil gas composition were monitored at the site to evaluate the efficiencies of the infiltration system and nitrate removal. Moreover, the impact of pH and ethanol addition on the denitrification rate was studied in laboratory. A reduction of 95% was achieved in the groundwater nitrate concentrations during the study. Neither clogging problems nor inefficient introduction of ethanol into the saturated zone were observed. Most crucial to the denitrifying communities was pH, values above 6 were required for efficient denitrification.

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