Stimulating hydrogenotrophic denitrification in simulated groundwater containing high dissolved oxygen and nitrate concentrations

In agricultural areas, nitrate (NO 3 −) is a common groundwater pollutant as a result of extensive fertilizer application. At elevated concentrations, NO 3 − consumption causes methemoglobinemia in infants and has been linked to several cancers; therefore, its removal from groundwater is important. The addition of hydrogen gas (H 2) via gas-permeable membranes has been shown to stimulate denitrification in a laboratory-scale reactor. This research, using large columns packed with aquifer material to which a simulated groundwater was fed, was conducted to further identify the conditions required for the use of membrane-delivered H 2 in situ. In this study, we show that this novel technology was capable of treating highly contaminated (25 mg/L NO 3 −-N) and oxygenated (5.5 mg/L dissolved oxygen) water, but that nutrient addition and gas pressure adjustment was required. Complete NO 3 − reduction was possible without the accumulation of either NO 2 − or N 2O when the H 2 lumen pressure was increased to 17 psi and phosphate was added to the groundwater. The total organic carbon content of the effluent, 110 cm downgradient of H 2 addition, did not increase. The results from these experiments demonstrate that this technology can be optimized to provide effective NO 3 − removal in even challenging field applications.