AWWA JAW17314

This article describes research conducted to evaluate the use of coal-aluminum filters for the treatment of low-alkalinity, low-turbidity source waters. The process studied consisted of a coal-aluminum granular media filter in combination with pH adjustment of the influent water. The pH of the water was adjusted to the 4-6 range and was filtered through the coal-aluminum bed. Disinfection and pH adjustment of the filter effluent for stability completed the treatment scheme. Coal-aluminum filters do not require coagulation, flocculation, and sedimentation prior to filtration. Except for pH adjustment, the process does not require the addition of chemicals, thus reducing solids-handling requirements. The coal-aluminum filter successfully reduced turbidity in both a synthetic and natural raw water to less than 1.0 ntu. It was necessary to operate the coal-aluminum filter in an acidic or alkaline environment so that active corrosion of the aluminum media would occur. Effluent quality was found to be dependent on filtration rate. Physical and operating characteristics were found to be comparable to those of a conventional granular media filter. The performance of a control coal-sand filter was always substantially inferior to the coal-aluminum filter. Principal mechanisms involved in the reduction of turbidity through coal-aluminum filters are identified and discussed. Costs of the coal-aluminum process compare favorably with those of conventional treatment. Includes 7 references, tables, figures.