[Effect of carbon source and dissolved oxygen on denitrification by aerobic denitrifier Pseudomonas mendocina AD6]

Aerobic denitrifying performances of P. mendocina AD6 at various C/N ratios, dissolved oxygen (DO) concentrations and carbon sources including citrate, acetate, and glucose were evaluated through flask experiment. At an insufficient carbon concentration, namely C/N ratio of 3, total nitrogen (TN) removal efficiency was 42% by aerobic denitrification. When the C/N ratio was increased to 8, 15, and 23, the TN removal efficiency by AD6 quickly increased to 55%, 70%, and 69%, in which 7%, 20%, and 25% of TN losses could be contributed to the aerobic denitrification by AD6, respectively. Batch cultures were carried out in a series of 250 mL conical flasks containing 100, 50, and 25 mL of the nitrate-supplemented basal medium with C/N ratio of 15, DO of 7.15-8.08 mg/L and strain AD6. Flasks were shaken in a rotary shaker at 28 degrees C and 180 r/min to allow better gas exchange. DO concentration of culture medium declined rapidly to anoxia condition at the beginning of reaction followed by an aerobic level with above 2 mg/L of DO after 24 h reaction. Different carbon sources had strong influence on the aerobic denitrifying performance of strain AD6. The maximum consumption rates of citrate, acetate, and glucose by strain AD6 were 90%, 92%, and 41%, respectively. In the medium spiked with acetate as carbon source, TN removal efficiency and N losses due to aerobic denitrification increased to 14% and 5%, respectively, with comparison to that spiked with citrate. Evaluation on nitrogen removal performances of aerobic denitrifier should be cautious with flask experiment because aerobic, partial aerobic and total anoxic growing conditions could be changed by C/N ration and carbon source of medium.