Nitrate removal from low C/N wastewater at low temperature by immobilized Pseudomonas sp. Y39-6 with versatile nitrate metabolism pathways

For solving the challenge in nitrate removal from low C/N wastewater at low temperature, Pseudomonas sp. Y39-6 was isolated and used in nitrate removal. It showed aerobic-heterotrophic denitrification with rate of 1.77 ± 0.31 mg/L·h and unusual aerobic-autotrophic nitrate removal (rate of 0.324 mg/L·h). The aerobic-autotrophic nitrate removal mechanisms were deep investigated by analyzing the nitrate removal process and genomic information. At aerobic-autotrophic condition, the strain Y39-6 could assimilate nitrate to amino acid (NO3− + PHA + CO2 → C5H7O2N) with the carbon source from Polyhydroxyalkanoic acid (PHA) degradation and CO2 fixation. Flagella motivation, swarming activity and extracellular polymeric substances (EPS) production regulated Pseudomonas sp. Y39-6 forming biofilm. Carriers immobilized with Pseudomonas sp. Y39-6 were used in moving bed biofilm reactor (MBBR) and achieved 24.83% nitrate removal at C/N < 1 and 4 °C. Results of this study provided a practical way for nitrogen removal from low C/N wastewater in cold region.