Identification and denitrification performance of a high ammonia nitrogen-resistant aerobic denitrifying bacteria

Ammonia (NH₄ ⁺-N), nitrate (NO₃ ⁻-N) and nitrite (NO₂ ⁻-N) are the main contaminants in industrial aquaculture systems. High nitrogen concentration in water is likely to cause aquaculture water pollution and endanger the safety of aquatic animals. Aerobic denitrifying bacteria are widely used to remove nitrogen-containing aquaculture wastewater. In order to obtain a strain that can safely and efficiently treat wastewater with high ammonia nitrogen concentration, we studied the aerobic denitrifying bacteria WM28 with high ammonia nitrogen resistance screened from aquaculture ponds. The strain was identified through morphological observation, physiological and biochemical tests and 16S rRNA gene sequencing. The environmental and biological safety of the strains were evaluated through antibiotic tests and zebrafish (Danio rerio) toxicity tests. The growth and denitrification performance were measured in three single nitrogen source simulated wastewater, and the denitrification capacity was tested in high concentration ammonia nitrogen simulated wastewater. WM28 was identified as Rhodococcus ruber with high antibiotic sensitivity and good biosafety. The removal rates were 100%, 76.3% and 66.99% after 48 h incubation in single NH₄ ⁺-N, NO₃ ⁻-N and NO₂ ⁻-N media, respectively. Their removal rates of NH₄ ⁺-N reached 100% at high concentrations of 100–500 mg·L⁻¹ NH₄ ⁺-N in simulated wastewater experiment after 48 h. 700 mg·L⁻¹ NH₄ ⁺-N was removed by more than 88% after 116 h. At 120^th hour, the initial NH₄ ⁺-N concentration of 1 000 mg·L⁻¹ was still capable of denitrification with a removal rate of 74.38%, which indicates that strain WM28 has great tolerance to high ammonia nitrogen. In summary, strain WM28 is a safe and efficient aerobic denitrifying bacteria with high ammonia tolerance, and has promising application prospects in the treatment of aquaculture and industrial wastewater.