Study On Nitrogen Removal With Two-Stage Biological Aerated Filter

This paper focuses on the experimental study on the two-stage biological aerated filter for municipal wastewater treatment. The filter media adopted in this experiment is haydite. The paper analyzes the removal efficiency and regularity of the organic matter and nitrogen, and get the best operating parameters. Also, it will generalize the theory for the advance of the BAF process in wastewater treatment of our country.The experiment shows that the effluent quality is acceptable and meets the municipal grey water standard when the hydraulic loading is less than 4m/h, the influent COD concentrate is between 100～500mg/L, the gas water ratio of first stage is between 3:1～5:1 and that of the secondary stage is between 1:1～2:1.Two-stage BAF can stand the high turbidity load in short time. COD removal is obtained almost in the first stage. The secondary stage can stabilize the effluent quality and remove nitrogen. When the influent COD concentrate is more than 600mg/L, the NH3-N removal efficiency is obviously reduced. This shows that high concentrate of organic matter will restrain the NH3-N removal. When the ratio of gas vs water of the secondary stage is low, the microorganism in the reactor will distribute logically and it will get high nitrogen removal efficiency.In the inlet part of the reactor, the denitrification is stronger than the nitrification. Along with increasing of the media height, the nitrification velocity exceeds denitrification velocity. In the secondary reactor, the denitrification is obvious. The simultanous nitrification and denitrification is observed in the reactor.When the air flow velocity is low, the effluent NH3-N concentrate is lower than the influent, the effluent NO₂-N concentrate is higher than NO₃-N, NO₂-N is accumulated and TN is removed partly. This case indicates that the short-cut nitrification and denitrification reacts.DO should be controled between 2.5～3.5mg/L in carbone removal part, 3～4mg/L in nitrification part. When water temparature increases from 10℃to 25℃, the backwash interval of first stage reactor will reduce from 3 to 1 day and will reduce from 5 to 3 days in the secondary srage.