The Nitrogen Removal Characteristics of a Novel Salt-Tolerant Bacterium, Enterobacter quasihormaechei DGFC5, Isolated from Municipal Sludge

A novel bacterial strain, <i>Enterobacter quasihormaechei</i> DGFC5, was isolated from a municipal sewage disposal system. It efficiently removed ammonium, nitrate, and nitrite under conditions of 5% salinity, without intermediate accumulation. Provided with a mixed nitrogen source, DGFC5 showed a higher utilization priority for NH₄⁺-N. Whole-genome sequencing and nitrogen balance experiments revealed that DGFC5 can simultaneously consume NH₄⁺-N in the liquid phase through assimilation and heterotrophic nitrification, and effectively remove nitrate via aerobic denitrification and dissimilatory reduction reactions. Single-factor experiments were conducted to determine the optimal nitrogen removal conditions, which were as follows: a carbon-to-nitrogen ratio of 15, a shaking speed of 200 rpm, a pH of 7, C₄H₄Na₂O₄ as the carbon source, and a temperature of 30 °C. DGFC5 showed efficient nitrogen purification capabilities under a wide range of environmental conditions, indicating its potential for disposing of nitrogenous wastewater with high salinity.