Full scale evaluation of nitrification performance in an integrated fixed film activated sludge process

The nitrification performance of an integrated fixed film activated sludge (IFAS) process was compared to a parallel control system at full scale. The IFAS process utilized the Ringlace and Biomatrix looped cord media products. Monitoring and evaluation of the retrofit was divided into two periods. The first monitoring period was from October 3, 1995 to June 20, 1996. The second monitoring period was started on December 2, 1996 and was completed on March 28, 1997. During the first operating period, the maximum media nitrification rate was estimated to be 0.42 kg/d/1000 m of media at an average temperature of 10°C. Settling was also improved. To correct flow short circuiting observed during the first operating period additional aerators were mounted below the media frames and baffles were mounted above existing diffusers. Nitrification performance of the media during the second operating period was found to be marginal. Although the nitrification performance in the control train was not stressed to the same degree as in the 1995/96 period, the likely main cause of the deteriorated performance of the media was a proliferation of bristle worm in the biofilm. The results of this study indicate that proper aeration design, and the prevention and treatment of worm blooms are two important issues in the application of the IFAS process.