Characterization of a novel marine aerobic denitrifier Vibrio spp. AD2 for efficient nitrate reduction without nitrite accumulation

Abstract

Aerobic denitrifiers have the potential to reduce nitrate in polluted water under aerobic conditions. A salt-tolerant aerobic denitrifier was newly isolated and identified as Vibrio spp. AD2 from a marine recirculating aquaculture system, in which denitrification performance was investigated via single-factor experiment, Box–Behnken experiment, and nitrogen balance analysis. Nitrate reductase genes were identified by polymerase chain reaction. Results showed that strain AD2 removed 98.9% of nitrate-nitrogen (NO₃⁻-N) with an initial concentration about 100 mg·L⁻¹ in 48 h without nitrite-nitrogen (NO₂⁻-N) accumulation. Nitrogen balance indicated that approximately 17.5% of the initial NO₃⁻-N was utilized for bacteria synthesis themselves, 4.02% was converted to organic nitrogen, 39.8% was converted to nitrous oxide (N₂O), and 31.1% was converted to nitrogen (N₂). Response surface methodology experiment showed that the maximum removal of total nitrogen (TN) occurred under the condition of C/N ratio 11.5, shaking speed 127.9 rpm, and temperature 30.8 °C. Sequence amplification indicated that the denitrification genes, napA and nirS, were present in strain AD2. These results indicated that the strain AD2 has potential applications for removing NO₃⁻-N from high-salinity (3%) wastewater.