Enhanced Nitrogen Removal of Wastewater at Low Temperature by Iterative Screening of Cold-Tolerant Denitrifying Bacteria

Abstract

The biological denitrification for wastewater treatment in winter is often seriously compromised due to the effects of low-temperature (<13 °C) on metabolic activity of microorganism. In this study, an excellent cold-tolerant denitrifying bacterium, Moraxella osloensis LT-01 was isolated by iterative domestication. The strain LT-01 retained about 60% maximal growth activity at 10 °C. Under initial concentrations of 100 mg/L, average ammonium, nitrate and nitrite removal efficiencies for domestic wastewater (C/N 4:1) at 10 °C were 70.35%, 65.39% and 61.74% in 24 h, respectively. Nitrogen balance analysis showed that about 46% of TN was directed toward in the dissimilation form of gas, and 16% of TN was assimilated for cell growth. Key genes hydroxylamine reductase gene (HAO) and nitrite reductase (NirS) involved in nitrification and denitrification processes were identified by gene-specific PCR, indicating that strain LT-01 perform nitrogen removal efficiently via unique simultaneous nitrification and denitrification. These results suggest the bacterium LT-01 has great potential as an effective performer for treating domestic wastewater in winter.