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 frequently used as filter media. The purpose of this study was to evaluate the attrition experienced by various media during backwashing by performing accelerated backwash tests in a pilot column, using a combined water and air backwash at combinations that gave the condition known as collapse-pulsing. Since the dominant mode of attrition was assumed to be abrasion, the effluent was sampled at a number of intervals to determine the amount of fine material in the effluent. Coal based GAC exhibited the highest weight loss (∼ 7%) and sand the least (∼ 2%).