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Groundwater remediation was evaluated for combined autotrophic and heterotrophic denitrification under high (154 mg/L as CaCO3) and low (95 mg/L as CaCO3) alkaline conditions. Two levels of acetate (47 and 94 mg/L) and ethanol (24 and 48 mg/L) were added to the reactors. Obtained denitrification rates were 2.89, 2.58, 3.55, 1.96, and 2.0 mg-N/L · h for high alkaline conditions, whereas under low alkaline conditions has given 2.36, 1.94, 2.47, 2.74, and 2.29 mg-N/L · h for control, 47 and 94 mg/L acetate, and 24 and 48 mg/L ethanol, respectively. Nitrite was accumulated for controls but reactors with acetate and ethanol did not accumulate nitrite. Acetate and ethanol addition decreased sulfate to nitrate ratios in the range of 4.5-7.58 for high alkaline conditions (12.77 for control) and 4.43-6.78 for low alkaline conditions (7.90 for control). Acetate was more efficient compared with ethanol in controlling sulfate production and pH maintenance.

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