ATTRITION OF GRANULAR FILTER MEDIA DURING BACKWASHING WITH COMBINED AIR AND WATER

Attrition resistance of granular filter media is becoming increasingly important as materials such as GAC and anthracite are being more freq uently used as filter media. The purpose of this study was to evaluate the attrition experienced by various media during backwashing by perf orming accelerated backwash tests in a pilot column, using a combined water and air backwash at combinations that gave the condition known a s collapse-pulsing. Since the dominant mode of attrition was assumed t o be abrasion, the effluent was sampled at a number of intervals to de termine the amount of fine material in the effluent. Coal based GAC ex hibited the highest weight loss (similar to 7%) and sand the least (si milar to 2%).