Evaluation of a novel low-carbon to nitrogen- and temperature-tolerant simultaneously nitrifying–denitrifying bacterium and its use in the treatment of river water

In this study, a simultaneously heterotrophic nitrifying–aerobic denitrifying bacterium, designated KSND, was newly isolated from a lake wetland. Its removal efficiencies for 160 mg L(−1) ammonium, 105 mg L(−1) nitrate, and 8.39 mg L(−1) nitrite were 86.56%, 74.52%, and 100% in 24 h, with removal rates of 5.77 mg L(−1) h(−1) for NH(4)(+)–N, 3.26 mg L(−1) h(−1) for NO(3)(−)–N, and 0.35 mg L(−1) h(−1) for NO(2)(−)–N. The bacterium retained ∼63% of its maximal removal rate at 10 °C and 56% of its maximal removal rate at a carbon to nitrogen (C/N) ratio of 4 : 1, with no nitrite accumulation. Gene-specific PCR indicated the absence of the key genes for nitrification and denitrification, encoding hydroxylamine oxidoreductase and nitrite reductase, respectively, suggesting that KSND achieves effective nitrogen removal by another pathway. KSND was used to treat river wastewater by culturing it in a floating bed bioreactor. Ammonia nitrogen decreased significantly from 8.76 mg L(−1) initially to 1.87 mg L(−1) in 90 days, with no NO(3)(−)–N or NO(2)(−)–N toxicants, indicating the great potential utility of KSND in future full-scale applications in the treatment of low-C/N wastewater.