Combined adsorption-UF process increases TOC removal

Addition of heated iron oxide particles (HIOPs) as adsorbents to the feedwater of an ultrafiltration (UF) membrane system significantly increased removal of dissolved organic carbon (DOC) and reduced trihalomethane formation potential (THMFP). Treatment by the HIOP-UF process met the TOC removal criteria set by the enhanced coagulation provision of the proposed Disinfectants/Disinfection By-products Rule in all 16 water sources tested, even though those criteria were not met by enhanced coagulation with alum or ferric sulfate in many of the water sources. At pH 6.5 and for the operational conditions studied, 40-75 percent of the DOC was removed; this percentage might be increased at lower pH or a higher HIOP dosage. THMFP was reduced even more (approximately 5-10 percent more) than DOC. Although HIOPs tended to reduce membrane fouling, both soft water with extremely high DOC concentrations and hard, alkaline water with moderate DOC concentrations fouled the HIOP-UF system. Fouling was less severe at lower pH values.