The competition among heterotrophs under anoxic conditions for carbon source

Bacterial utilization of molecules is recognized as an important step in the cycling of organic matters. In this study, a bench-scale continued-flow intermittent-aeration biological reactor (CIBR) was applied and the competition for acetate among heterotrophs with different influent C/N ratios under anoxic conditions was investigated. The results revealed that phosphorus release occurred after the depletion of nitrate when influent C/N ratio was lower than 400:30. With the influent C/N ratios of 800:30 and 1200:30, the denitrification and phosphorus release occurred simultaneously, and the activity of polyphosphate accumulating organisms (PAOs) was inhibited by the intermediates (NO3 -N, NO2-N, NO, NH2OH, etc) produced in denitrification. Based on the COD mass balance calculation, the theoretical C/P ratio for phosphorus release was 1.99, and the theoretical C/N ratios for the denitrification, denitratation and denitritation were 3.89, 2.33 and 3.56, respectively. The competitiveness for carbon source among heterotrophs follows the order: denitrifiers > PAOs > other heterotrophic organisms. The mechanisms include the competition for carbon source and the inhibition of intermediates (NO3-N, NO2-N, NO, NH2OH, etc) in denitrification. The low influent C/N ratio and nitrite accumulation during denitrification were both beneficial to improve the efficiency of carbon utilization.