Point-of-Generation Nitrogen Recovery from Wastewater

An anaerobic/ion exchange process was developed for point-of-generation recovery of nitrogen from household wastewater. The modular multi-chamber unit couples solids blanket anaerobic biotreatment with ammonium ion exchange onto natural zeolite, and operates passively without energy input. Nitrogen recovery effectiveness was evaluated in a 57 L empty bed prototype that received domestic wastewater entering the Mayo Wastewater Treatment Plant in Anne Arundel County, Maryland. The system was operated for 320 days at 5.6 day empty bed contact time (EBCT). Total nitrogen reduction exceeded 95% and retention of nitrogen as ammonium ion was virtually complete. Low oxidation reduction potentials prevailed through the chambers and oxidized nitrogen species (NO3-, NO2-) were not detected. EBCT was substantially reduced in the last operational phase to accelerate NH4+ breakthrough: EBCT was 1.9 days for 24 days followed by an 11 day period at 0.81 day. NH4+ rapidly increased in effluent but the treatment process was not adversely affected otherwise. Results can be used to design a single family home nitrogen recovery system and estimate life cycle costs. The advantages of the anaerobic/ion exchange process include passive operation, limited maintenance, no energy input, low headloss, and the capability of discontinuous operation. These features make anaerobic/ion exchange an appropriate technology for local-scale recovery of nitrogen. Methods for beneficial recycling of nitrogen are being evaluated.