Reduction of Nitrate in Aquifer Microcosms by Carbon Additions

Abstract

Aquifer microcosms were used to examine the effects of NO − 3 and C amendments on groundwater from the Claiborne aquifer. Nitrate concentrations of 12.17 mg L −1 in aquifer microcosms were reduced 0.92%/d to 5.84 mg L −1 by the addition of 10 mg C L −1 for 35 d. Nitrate disappearance correlated with increases in number of denitrifiers and dissolved N 2 O concentration and decreases in dissolved oxygen, suggesting biological denitrification. Nitrate/chloride ratios decreased in microcosms with 10 mg C L −1 added and then increased when the C addition was removed. Carbon additions of 0.4 mg C L −1 had no effect on the microbial or chemical properties of the microcosms. Nitrous oxide levels in wells sampling the Claiborne aquifer showed an increase with depth, indicating N 2 O production within the aquifer. Microcosms are useful tools to examine biological transformations of chemical contaminants in unconsolidated aquifer material. The remediation of NO − 3 contaminated aquifers by organic infusion is possible and appears to be a function of microbial denitrification.