Nitrification performance of a pilot-scale UBAF treating secondary effluent of municipal sewage

A pilot-scale of up-flow biological aerated filter (UBAF)treating secondary effluent of municipal sewage was constructed and operated for 189 days from April 12th to October 18th. The nitrification performance of UBAF under two different air flow rates (0.6 and 1.0 m(3)/h) was studied. The Run I (air flow rate =0.6 m(3)/h) and Run II (air flow rate =1.0 m(3)/h) worked for 90 and 99 days respectively. During the whole operating process, the influent ammonium concentration varied within the range of 9.27-223 mg/L and the inflow hydraulic load was kept at 15.92 m(3)/m(substratum)(3).d. The water temperature was 16.9-26.2 degrees C. Air and water backwashing was conducted once per 48h and lasted 15 min. The corresponding backwash superficial velocities were set as 50 and 15 m/h. The experiment results showed that the average ammonium removal efficiency were 64.5% in Run I and 90% in Run II. About 95% removal ammonium was converted to nitrate in the two Runs. As the air flow rate was 0.6 m3/h, the nitrite accumulation phenomenon occurred in the bottom but it was undetectable in the final effluent. In Run II, the nitrite accumulation phenomenon could not be detected thoroughly in the reactor.