Origin and Fate of Industrial Ammonium in Anoxic Ground Water—15N Evidence for Anaerobic Oxidation (Anammox)

Abstract

AbstractElevated ammonium concentrations in pump‐and‐treat effluent from a volatile organic compounds–contaminated municipal aquifer originate from two industrial sources: infiltration of drainage from the blending operations of a fertilizer company (FC) located in the recharge area ( of 500 to 700 parts per million [ppm] N and of 150 to 300 ppm N) and leakage from waste water treatment ponds maintained by an adjacent chemical company (CC) ( of 50 to 70 ppm N, with no ). Geochemical and isotope data are used to trace the mechanisms for the strong attenuation observed between the source areas and the municipal ground water treatment wells ( < 10 ppm N). Conservative mixing calculations demonstrate a loss of and along the flowpath relative to K+ and Cl−. Reactive loss of in these anoxic ground water is attributed to anaerobic oxidation by anammox bacteria. Lines of evidence leading to this conclusion include (1) loss of both and under anoxic conditions along the flowpath; (2) a progressive enrichment of and , indicating reactive loss of ammonium and nitrate; (3) values greater than coexisting , which precludes loss by nitrification to ; and (4) significant N2 overpressuring with increasing values. Anaerobic ammonium oxidation by anammox bacteria uses nitrate as the electron donor: . The recently discovered anammox reaction is more energetically favorable than denitrification and is now considered to play a major role in the global nitrogen cycle. It has been observed in waste water bioreactors and sea water but not previously in ground water.