The removal of ammonia nitrogen via heterotrophic assimilation by a novel Paracoccus sp. FDN-02 under anoxic condition.

A novel strain FDN-02 was isolated from a sequencing batch biofilm reactor. FDN-02 was identified as Paracoccus sp., and the Genbank Sequence_ID was MW652628. Comparing with the removal efficiency of ammonia nitrogen (NH-N) by bacterium FDN-02 under different growth conditions, the optimal initial pH, carbon source, and C/N ratio were 7.0, sucrose, and 16, respectively. The maximum removal efficiency and rate of NH-N were respectively 96.2% and 10.06 mg-N/L/h within 8 h under anoxic condition when the concentration of NH-N was 44.87 mg/L. Specifically, 71.9% of NH-N was utilized by strain FDN-02 through heterotrophic assimilation to synthetize organic nitrogen, and approximately 24.1% of NH-N was lost in the form of gaseous nitrogen without the emission of nitrous oxide. Bacterium FDN-02 was also found to be a denitrifying organism, and nitrate nitrogen and nitrite nitrogen of lower concentrations were removed by denitrification after the enlargement of biomass. Further investigation showed that the biomass after the removal of NH-N by strain FDN-02 had resource utilization potential, and the contents of proteins and amino acids were 635 and 192.97 mg/g, respectively, especially for the usage as an alternative nutrient source for livestock and organic fertilizers. This study provided a promising environmentally friendly biological treatment method for the removal of NH-N in the wastewater.