Aerobic denitrification by a heterotrophic nitrifying-aerobic denitrifying (HN-AD) culture enriched activated sludge

Heterotrophic nitrifying bacteria capable of denitrification under aerobic conditions, which are known as HN-AD species, were investigated. Instead of the isolation and subsequent cultivation of a pure HN-AD strain, the activated sludge obtained from the domestic wastewater treatment plant was enriched to enhance the fraction and activity of the indigenous HN-AD species by adding ammonium and organic carbon. The enriched culture showed both rapid ammonium removal at a rate of 13.3 mg-N/L/hr and nitrate removal at a rate of 12.3 mg-N/L/hr, which was higher than those for the pure HN-AD bacteria reported in the literature. On the contrary, the activated sludge that was not enriched showed insignificant nitrification and aerobic denitrification. These results implied that the selective enrichment procedure improved the fraction and/or activity of the HN-AD culture in the mixed biomass. Consequently, the enriched HN-AD culture from activated sludge could be a feasible alternative over the conventional BNR process.