Evaluating the performance of two denitrifying bacteria and their synergistic relationship in remediating nitrate-polluted wastewater

This study compared the performance of two denitrifying bacteria and investigated their cooperative relationship to enhance heterotrophic denitrification to remediate nitrate-polluted wastewater.The selected denitrifying bacteria were Pseudomonas nitritireducens (H6) and Klebsiella sp.(D5).The results showed that sodium acetate was the best carbon source for strain H6, resulting in removal efficiency of 98.7% with negligible nitrite accumulation in 36 h.Sodium citrate was more suitable for strain D5, resulting in removal efficiency of 94.4% in 36 h; however, nitrite accumulation was significant, with a maximum concentration of 22.24 mg NO 2 --N/L.These findings indicate that strain H6 exhibited excellent performance because of its high nitrate removal efficiency and low nitrite accumulation during denitrification.The strain D5 could achieve effective denitrification, but also caused nitrite accumulation.Additionally, at 15°C, the nitrate removal efficiency was only 32.3% (H6) and 8.5% (D5), respectively, but increased significantly when the temperature was raised to 25°C and 30°C, which increased the removal efficiency above 95%.Moreover, when strains H6 and D5 were inoculated together, the nitrate removal efficiencies were above 98%, and nitrite accumulated was negligible.These findings indicate that synergy exists between strains H6 and D5 during denitrification, which can improve the nitrate removal efficiency, thus avoiding nitrite accumulation in wastewater treatment for nitrogen removal.