Several variations of SBR processes are reported in the literature; one of these uses the acronym CAST, Cyclic Activated Sludge Technology, and has been developed specifically for large-scale domestic wastewater treatment application (20,000 to 400,000 P.E.). This process was used to relieve existing overload conditions at the Groβarl WWTP which treats sewage from a ski resort using a conventional nitrifying/denitrifying (N/DN) process. The efficacy of the conventional and cyclic processes were compared through parallel operation over a one year period. Through examination and comparison of the nitrification rates, the stability of co-current nitrification/denitrification and the biological phosphorus removal it was found that the cyclic system was demonstrably superior in treatment efficiency when operated at the same loading conditions as the conventional process. Nitrification rates were about 35 percent higher in the cyclic system. Phosphorus elimination was about 83 per cent in the cyclic system and 55 per cent in the conventional system at the same loading conditions. Applying the results of the design criteria used for the cyclic system, a volumetric saving of about 30 per cent compared to the use of conventional treatment technology is obtainable for the proposed full-scale amplification. The optimization strategy of selecting set-point dissolved oxygen concentration in the basins according to the on-line measured oxidation reduction potential (ORP) and its rate of change throughout a cycle proved to be a valuable tool for optimizing nitrogen and phosphorus removal.
Significant load variation is imposed on wastewater treatment infrastructure at resort centres. The type of resort centre plays a large part in both hydraulic and organic loading dynamics. Climatic conditions may also be a determining factor on the loading pattern. Holiday patterns also have a large impact upon loading dynamics. Performance of the Portage/Catawba Cyclic Activated Sludge System, located on the shores of Lake Erie, is described relative to the loading dynamics of the Summer/Winter populations.
Cyclic activated sludge technology was selected for the Potsdam Wastewater Treatment Plant (90,000 p.e.). The cyclic activated sludge facility comprises four modules integrated into two circular basins. Construction was commenced in February 1998 with seeding of the plant for start up taking place in October 1998. Process performance has been met since Spring 1999 at 80-90% of design load. In order to optimize start-up procedures, respiration rates were used as a guidance for process stabilization and online process optimization during normal operation. Operation for co-current nitrification denitrification provided an ammonia removal of 1.1 mg NH4-N/g MLSS.h (15 degrees C) and a corresponding nitrate respiration rate of 0.85 mg NO3-N/g MLSS.h under aerated conditions. Enhanced biological phosphorus removal generated an effluent mean total phosphorus concentration of 0.38 mg/L without precipitant addition.
The performance of three full-scale cyclic activated sludge facilities, operated for biological phosphorus removal is demonstrated. The facilities are operated without formal mixed anoxic or anaerobic sequences in a variable volume mode. The system is independent of fill-ratio operation for filamentous sludge bulking control.
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