| The effects of 7 groups of different influent C/N ratio（2.75，4.28，5.7，6.5，6.97，8.08，11.19）on the removal efficiencies of total nitrogen, phosphorus and COD as well as the sludge settling performance were investigated in a UniFed SBR lab-scale apparatus treating actual domestic wastewater. The results showed that when the C/N ratio was lower than 5.7, TN removal efficiency increased sharply as C/N ratio increased, from 43.6% of 2.75 to 80.84% of 5.7. Afterwards, TN removal efficiency increased very slowly as C/N ratio increased, because only TN removal efficiency caused by SND during aeration period could be enhanced. P removal efficiency increased as C/N ratio increased, because PAOs could get more organic carbon source from the influent to produce PHB and release PO3-4, avoiding the adverse influence of NO-X on PO3-4 release. The higher the C/N ratio, the more the quantities of P release and uptake, the quicker P uptake rate, the better P removal performance was. Regardless of the C/N ratio, excellent COD (average 93.15%) removal efficiencies were maintained throughout the experiment. When Influent C/N ratio was bigger than 6.97 and organic load exceeded 0.38 kg/(kg·d), SVI rose quickly as C/N ratio increased. Non-silk bacteria sludge bulge appeared because of low DO and high organic load. |
