3. ACTIVATED BIO-FILTER (ABF)3.1. DescriptionActivated bio-filters (ABF) are a recent innovation in the biological treatment field. Thisprocess consists of the series combination of an aerobic tower (bio-cell) with wood or otherpacking material, followed by an activated sludge aeration tank and secondary clarifier. Settledsludge from the clarifier is recycled to the top of the tower. In addition, the mixture ofwastewater and recycle sludge passing through the tower is also recycled around the tower, ina similar manner to a high rate trickling filter. No intermediate clarifier is utilized. Forwardflow passes directly from the tower discharge to the aeration tank (Fig. 16.6). The use ofthe two forms of biological treatment combines the effects of both fixed and suspendedgrowth processes in one system.Reliability of the VLR treatment process (76)
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