Granular iron oxide adsorbents to control natural organic matter and membrane fouling in ultrafiltration water treatment

Abstract

Fine iron oxide particles (IOPs) are effective in removing natural organic matter (NOM) that causes membrane fouling in water treatment, but the separation of used IOPs is problematic. This study focused on the fabrication and use of granular iron oxide adsorbents, in combination with ultrafiltration (UF) membranes while investigating the NOM removal efficiency and fouling control. Sulfonated styrene-divinylbenzene copolymer beads were coated with two types of iron oxides (ferrihydrite and magnetite) and their performances were compared to that of fine IOPs. A significant amount of iron oxide coating (52–63 mg of Fe per g bead) was achieved by means of electrostatic binding and hydrolysis of iron ions. Iron oxide coated polymer (IOCP) beads were able to remove some amounts (∼20%) of dissolved organic carbon (DOC) comparable to that achieved by IOPs within a short period of time (<15 min). Regenerated IOCPs exhibited the same sorption capacity as the fresh ones. The integrated IOCP/UF system operation with a 15-min empty bed contact time and 10-h cyclic regeneration maintained the 20% DOC removal with no sign of significant membrane fouling. In contrast, a sharp transmembrane pressure buildup occurred in the UF system when no iron oxide pretreatment was applied, regardless of the types of membranes tested. Iron oxide adsorbed the NOM fraction with molecular weights of >1000 kDa which is believed to be responsible for severe UF fouling.