SUSTAINABLE NITROGEN REMOVAL BY ANAEROBIC AMMONIA OXIDATION DURING SOIL AQUIFER TREATMENT

During soil aquifer treatment, nitrogen removal has been observed in full-scale systems and during research studies. Since insufficient organic carbon is present to sustain heterotrophic denitrification during soil aquifer treatment, alternative mechanisms for nitrogen removal were investigated. Anaerobic ammonia oxidation activity has been measured at soil aquifer treatment sites and has the potential to sustain biological removal of nitrogen when secondary effluent is applied. A mechanistic model was developed to provide guidelines for the operation of soil aquifer treatment systems to sustain nitrogen removal. The model calculates the depth of ammonia adsorption, the depth to which ammonia is nitrified in the soil during reaeration, and appropriate wet/dry cycle times for anaerobic ammonia oxidation. The cation exchange capacity of a soil is an important factor for determining if sufficient vadose zone depth is present to prevent breakthrough of ammonia to the aquifer. The wet/dry cycle time ratio is independent of the cation exchange capacity and depends primarily on the soil hydraulic properties. Clogging layer development and mounding impact hydraulics, therefore, site specific conditions must be considered.