Cloth media surface filtration: Characterization of the performance of the needle felt and pile fabrics

The overall objective of this study was to investigate the capability of a cloth media surface filter utilizing two different fabrics (i.e., a needle felt and a pile fabric) to perform as a tertiary filtration device for municipal wastewater treatment. The five specific objectives of this study were: (1) to characterize the physical differences between the needle felt and pile fabrics; (2) to determine the particle removal characteristics of both the pile and needle felt fabrics; (3) to determine performance characteristics of a full scale cloth media disk filter (CMDF) utilizing both the needle felt and pile fabrics; (4) to determine if a full scale CMDF utilizing the needle felt and pile fabrics could meet the Title 22 California Water Recycling Criteria (CWRC) turbidity limit of 2 NTU; and (5) to investigate the effect that the performance characteristics of the CMDF can have on the secondary clarification design. During this study both bench and full scale cloth media surface filters were operated. Based on the results of this study it was determined that the CMDF employing both the needle felt and pile fabric met the Title 22 CWRC turbidity limit of 2 NTU, and performed equivalent to, or better than other Title 22 approved filtration technologies. Because the structure of the needle felt and pile fabrics are very different, large differences between the two fabrics in clean cloth removal, headloss development as mass accumulates, filter ripening, and effectiveness of backwashing were observed. It was determined that the mass accumulation capacity between required backwash intervals is more than double that of the needle felt, resulting in the pile fabric producing less than half the reject water rates of the needle felt fabric. No significant virus removal will be achieved by either the needle felt and pile fabrics when operated without chemicals and with a clean cloth. Prefiltration chlorination damaged the integrity of the floc structure and was shown to lead to severe performance degradation. For the CMDF to perform effectively as a filtration device when utilizing either the needle felt or pile cloths, the floc structure of the wastewater particles must be strong.