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

In agricultural areas, nitrate (NO3−) is a common groundwater pollutant as a result of extensive fertilizer application. At elevated concentrations, NO3− consumption causes methemoglobinemia in infants and has been linked to several cancers; therefore, its removal from groundwater is important. The addition of hydrogen gas (H2) 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 H2 in situ. In this study, we show that this novel technology was capable of treating highly contaminated (25 mg/L NO3−-N) and oxygenated (5.5 mg/L dissolved oxygen) water, but that nutrient addition and gas pressure adjustment was required. Complete NO3− reduction was possible without the accumulation of either NO2− or N2O when the H2 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 H2 addition, did not increase. The results from these experiments demonstrate that this technology can be optimized to provide effective NO3− removal in even challenging field applications.