Study of the optimum effluent quality of step feed A/O biofilm process

TKN, nitrate and TN concentrations of treatment units´ effluent of the step feed A/O biofilm process with equal flow distribution mode were analyzed based on the law of conservation of mass when the COD/TKN ratio of the influent were 4.77 and 8.32 respectively. The 3-step feed biofilm process was utilized to verify theoretical results, and removal efficiencies of this process to TKN and TN were studied. When the COD/TKN ratio was 8.32, return ratio was 1 and HRT was 36h, the theoretical and the actual removal efficiencies of TN were 83.3% and 84.9% respectively, and the actual removal efficiency of TKN was 99.5%. When the COD/TKN ratio was 4.77, return ratio was 1 and HRT was 36h, the theoretical and the removal efficiencies of TN were 68.2% and 80.3% respectively, and the removal efficiency of TKN was 96.0%. For simultaneous nitrification and denitrification occurring in the oxic unit and N assimilation by biomass synthesis, the removal efficiency of TN was higher than the theoretical values.