Removal of dissolved organic matter and control of membrane fouling by a hybrid ferrihydrite-ultrafiltration membrane system

Abstract

This study investigated the pretreatment effect of ferrihydrite (FH) on the removal of dissolved organic matter (DOM) and membrane fouling control in a hybrid adsorption-ultrafiltration (UF) membrane system. Powdered activated carbon (PAC) was chosen for comparative study, and three surrogates, namely, humic acid (HA), sodium alginate (SA) and bovine serum albumin, were applied in feed water to simulate humic substances, polysaccharides and proteins, respectively. In the hybrid adsorption-membrane system, the impacts of adsorbent cake layers on DOM removal and membrane fouling were systematically investigated. The results demonstrated that FH effectively removed both high-molecular-weight (MW) and low-MW HA and SA molecules via ligand exchange and mitigated membrane fouling substantially, regardless of whether FH particles were removed from the feed water before UF. In addition, the large flocs induced by FH and calcium contributed to loose FH layers. In contrast, PAC had almost no capacity to adsorb high-MW DOM molecules due to the microporous structure. And FH was more efficient in removal of DOM and control of membrane fouling than PAC. The different DOM adsorption capacities of FH and PAC lead to different effects on membrane fouling caused by deposition of DOM molecules and cake layers. These results offer guidance for application of hybrid adsorption-membrane filtration systems.