COCURRENT NITRIFICATION DENITRIFICATION AND BIOLOGICAL P-REMOVAL IN CYCLIC ACTIVATED-SLUDGE PLANTS BY REDOX-CONTROLLED CYCLE OPERATION/

Several variations of SBR processes are reported in the literature;one of these uses the acronym CAST, Cyclic Activated Sludge Technology, a nd has been developed. specifically for large-scale domestic wastewate r treatment application (20,000 to 400,000 P.E.). This process was;sed to relieve existing overload conditions at the Gro ss arl WWTP which treats sewage from a ski resort using a conventional nitrifying/denitr ifying (NIDN) process. The efficacy of the conventional and cyclic pro cesses were compared through parallel operation over a one year period . Through examination and comparison of the nitrification rates, the s tability of cc-current nitrification/denitrification and the biologica l phosphorus removal it was found that the cyclic system was demonstra bly superior in treatment efficiency when operated at the same loading conditions as the conventional process. Nitrification rates were abou t 35 percent higher in the cyclic system. Phosphorus elimination was a bout 83 per cent in the cyclic system and 55 per cent in the conventio nal system at the same loading conditions. Applying the results of the design criteria used for the cyclic system, a volumetric saving of ab out 30 per cent compared to the use of conventional treatment technolo gy is obtainable for the proposed full-scale amplification. The optimi zation strategy of selecting set-point dissolved oxygen concentration in the basins according to the on-line measured oxidation reduction po tential (ORP) and its rate of change throughout a cycle proved to be a valuable tool for optimizing nitrogen and phosphorus removal. Copyrig ht (C) 1996 IAWQ.