[Characteristics of aerobic biofilter backwash]

Periodic backwash is the vital stage to keep up the aerobic biofilter's performance. Under the same backwash conditions, a thorough study was done to review the influences on the performances of backwash in such aspects as backwash regimes, biofilter shapes. The experimental results show that the impulse backwash regime was superior to continuous backwash in the backwash performance and that the expansive flow aerobic biofilter was superior to the uniform flow aerobic biofilter in the performances of both backwash process and filter bed recovery. Then the optimal combination of the two factors i.e. the combination of impulse backwash mode and expansive flow filter was determined. Under the fixed filtration conditions, the appropriate impulse backwash parameters of expansive aerobic biofilter were determined as follows: the backwash air-flow intensity was 8-10 L/(s.m2), the backwash water-flow intensity was 2-4 L/(s.m2), and the backwash duration was 5 min.