Heterotrophic nitrification-aerobic denitrification characteristics and zinc-containing wastewater treatment potential of pseudomonas hunanensis SK-4: screening, application, and mechanistic insights.

To alleviate the detrimental impacts of zinc-containing wastewater on biological nitrogen removal systems, Pseudomonas hunanensis SK-4 was isolated and screened from a heavy industrial wastewater treatment facility. The efficient heterotrophic nitrification aerobic denitrification ability of Pseudomonas hunanensis was confirmed for the first time. The maximum removal efficiencies achieved by strain SK-4 for ammonium (100 mg/L), nitrate (100 mg/L), and nitrite (50 mg/L) were 99.81%, 82.31%, and 96.10%, respectively. Under the conditions of C/N 10, 35 °C, pH 7, 140 rpm, inoculum size 3%, with sodium citrate utilized as the carbon source, NH₄⁺-N was effectively removed. The nitrogen removal mechanisms employed by strain SK-4 were revealed through detailed whole-genome sequencing analysis. The nitrification and denitrification efficiencies of strain SK-4 were not affected under 100 mg/L Zn(II) stress. The inhibitory effects of varying Zn(II) concentrations on the nitrogen removal efficiency of strain SK-4 were predicted through model fitting. Such results showed that strain SK-4 had strong tolerance to Zn(II). The complete metabolic mechanisms of tolerance, transport, regulation and detoxification of Zn(II) in strain SK-4 were elucidated. Such findings indicated that strain SK-4 has a strong potential for the treatment of Zn(II) and nitrogen composite pollutants.