Impact of pretreatment on UF operation and removal of dissolved organics

Pilot testing of low-pressure membrane filtration (microfiltration and ultrafiltration) was performed on surface waters at two different pilot locations: the Alameda County Water District (ACWD) in Fremont, CA and the Medina River outside San Antonio, TX. Clarification pretreatment and adsorption pretreatment were evaluated at each site for impacts on operational membrane performance and on removal of dissolved organic compounds including total organic carbon (TOC), UV254, color and precursors to disinfection by-products. At the ACWD test site, studies were also conducted with spiking of taste and odor-causing compounds. In both pilot studies, clarification pretreatment was demonstrated to achieve some apparent improvement in operating efficiency. For example, an apparent increase in sustainable flux between 25% and 50% was demonstrated for clarified feedwater operation as compared to raw feedwater operation at the ACWD pilot site. Removal of dissolved organic compounds was achieved primarily through the pretreatment with clarification and/or addition of powdered activated carbon (PAC); however, some reduction of TOC and color was achieved via membrane filtration presumably due to removal of particulate/colloidal constituents.