Anaerobic ammonium oxidation during soil aquifer treatment

Soil aquifer treatment (SAT) maintains and restores the natural water resources of an area by percolating treated wastewater through recharge basins. Basins are operated in wet/dry cycles to restore soil infiltration properties and alter soil redox conditions, which consequently drive nitrogen transformations. Systems recharging effluent containing ammonia have shown nitrogen removal efficiencies of 50–90%. Conventional understanding of biogeochemical cycles cannot explain these high nitrogen removal efficiencies.; The lack of available organic carbon in these SAT systems indicates nitrogen removal mechanisms in addition to typical heterotrophic denitrification. One proposed mechanism is anaerobic ammonium oxidation (Anammox), the microbial oxidation of ammonium with nitrate in the absence of molecular oxygen and organic carbon. Understanding nitrogen removal mechanisms during SAT can determine the sustainability of the system, operational guidelines, and required pretreatment.; The three main goals of this research are to assess Anammox activity during SAT, to identify the microorganisms involved using microbial tools, and to recommend engineering parameters that would enhance the nitrogen removal of relevant SAT systems based on understanding of biogeochemical cycles.; Anammox activity is confirmed by batch tests and soil column results that showed the presence of ammonia and nitrate enhanced the nitrogen removal and adsorbed ammonia can provide a sustainable source of electron donors. Polymerase chain reaction (PCR) and DNA sequencing identified the DNA of microorganisms in the test soils. New Anammox-specific primers were designed and used in a nested PCR. A 450 bp length of four separate DNA sequences were found to be 89–98 % similar to Anammox type bacteria identified in literature and 88–96% similar to each other.; A model was developed that shows the soil cation exchange capacity (CEC) sets the limit on depth of ammonia adsorption and the wet/dry cycle ratio controls the depth of oxidation. It is recommended that the basins be operated such that half of the adsorbed ammonia is converted to nitrate. This would provide the proper conditions to sustain the Anammox process and high nitrogen removals, while avoiding high nitrate concentrations observed after long drying periods.