Effect mechanism of individual and combined salinity on the nitrogen removal yield of heterotrophic nitrification-aerobic denitrification bacteria.

One of the biggest challenges of applying heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria to treat high salt organic wastewater lies in the inhibitory effect exerted by salinity. To study the inhibition effect and underlying mechanism induced by different ion types and ion composition, the individual and combined effects of NaCl, KCl and NaSO on HN-AD bacteria Acinetobacter sp. TAC-1 were systematically investigated by batch experiments. Results indicated that the ammonia nitrogen removal yield and TAC-1 activity decreased with increased salt concentration. NaCl, KCl and NaSO exerted different degrees of inhibition on TAC-1, with half concentration inhibition constant values of 0.205, 0.238 and 0.110 M, respectively. A synergistic effect on TAC-1 was found with the combinations of NaCl + KCl, NaCl + NaSO and NaCl + KCl + NaSO. The whole RNA resequencing suggested that transcripts of denitrification genes (nirB and nasA) were significantly downregulated with increased NaSO concentration. Simultaneously, NaSO stress disrupted cell respiration, DNA replication, transcription, translation, and induced oxidative stress. Finally, we proposed a conceptual model to summarize the inhibition mechanisms and possible response strategies of TAC-1 bacteria under NaSO stress.