Advanced removal efficiency of organic carbon, phosphorus and nitrogen from municipal wastewater was achieved by using an anaerobic-anoxic-oxide (A2/O) process with the addition of fully and partially submerged RBC biofilms. The experiments were carried out in a range of F/M ratio 0.21 to 0.32 kg BOD/kg MLSS/d and at a various total hydraulic detention times (HRT), return activated sludge ratio (r) and mixed liquid recycle ratio (R). Another pilot plant A2/O process without adding RBC was conducted for control experiments. Compared with A2/O process, this new process could achieve a higher degree of nitrification rate without decreasing the removal efficiencies of organic carbon and phosphorus. The new process provides an environment for combining the long solid retention time (SRT) biofilm and the short SRT suspended activated sludge. This concept can resolve the conflict in SRT between nitrogen and phosphorus removal simultaneously. Correspondingly, the benefits of the new process are shorten the hydraulic detention time, progress the efficiency of nutrient removal, more stable for operation and more economic for required land cost. (C) 1997 IAWQ. Published by Elsevier Science Ltd.
