Degradation of oxytetracycline (OTC) and nitrogen conversion characteristics using a novel strain

A high residue of oxytetracycline (OTC) and high concentrations of ammonia and nitrate remain in aquaculture wastewater, and it is therefore important to identify a heterotrophic nitrification-aerobic denitrifying bacterium that also provides highly efficient OTC degradation for use in practical applications. In this study, a novel OTC degrading strain with aerobic denitrification, Ochrobactrum sp KSS10, was isolated and identified, and the heterotrophic nitrification and denitrification processes were investigated under aerobic conditions. Results suggest that 97.41% of ammonia and 82.86% of nitrate were removed by strain KSS10 within 112 h. Interestingly, a large amount of nitrite accumulation was observed in the middle stage, but this finally disappeared, and a nitrogen balance analysis showed that approximately 75% of nitrogen was lost in the form of gas products. The relationship between OTC degradation and the nitrogen conversion effect was then explored, and a maximum OTC reduction rate of 0.012 mg.L-1.h(-1) and removal rates of 0.848 mg.L-1.h(-1) of NH4+-N and 1.189 mg.L-1.h(-1) of TN were observed from 24 h to 104 h, respectively. The nitrate concentration decreased sharply from 40 h to 80 h with a maximum removal rate of 1.967 mg.L-1.h(-1) of NO3 (-)-N. Furthermore, dissolved organic matter (DOM) and chemical functional groups were detected to analyze the main mechanisms involved in the degradation of OTC and nitrogen (N) removal. In conclusion, the results show that the use of strain KSS10 in aquaculture wastewater can potentially be used in the biodegradation of antibiotics and nitrogen removal.