Static-bed biodenitrification coupled with in-situ polishing for remediating nitrate-contaminated water supplies

The concern over nitrate contamination of groundwater is directly related to expansive use of fertilizers. Once ingested, nitrates can cause methemoglobinemia. Additionally, nitrites have been linked to the potential formation of carcinogens in laboratory animals.;Biodenitrification is not used to treat potable water in the U.S. because of concerns about organics imparted to water. Reversible flow biodenitrification systems have successfully treated water while imparting lower concentrations of organics than traditional systems. The reversible flow system maintains lead and follow reactors out of growth phase with each other and thus improves follow reactor utilization of residual constituents.;This investigation studied the long-term performance of the reversible flow system, compared the performance with a conventional series reactor system, and evaluated the potential of coupling the reversible flow system with an in-situ polishing step. Performance was measured by effluent water nitrate, nitrite, SCOD and TSS concentrations. The reactor systems were fed water containing 50 mg NO3-N L-1 for approximately eight months at a hydraulic retention time of 1 hour. The feed water carbon-to-nitrogen ratio was 1:1 with ethanol as the carbon source.;Performance data collected demonstrate the long-term effectiveness of the reversible flow system which had an overall nitrate-nitrogen removal efficiency of 96% or greater. The nitrite-nitrogen concentrations of the reversible flow reactor were significantly lower than the series reactor system. The increased biomass inventories of the follow reactor improved the system's ability to adjust to nitrate- and nitrite-nitrogen concentration fluctuations of the lead reactor. The artificial aquifer coupled with the reversible flow system resulted in reducing the nitrate-, nitrite-nitrogen, soluble COD and TSS concentrations to near zero levels. The aquifer column was operated for 150 days and resulted in only 250 mm of water increase in back-pressure at the influent of the column. This back-pressure increase occurred in the first 300 mm of column length. Additionally, the hydraulic characteristics of the reversible flow system appears to maintain better plug flow conditions than the series reactor system.