Pre-ozonation for the mitigation of reverse osmosis (RO) membrane fouling by biopolymer: The roles of Ca2+ and Mg2+. (15th March 2020)

• Record Type: Journal Article
• Authors: Yin, Zhonglong; Wen, Tiancheng; Li, Yan; Li, Aimin; Long, Chao
• Is Part Of: Water research. Volume 171(2020)
• Publication Date: 2020-03-15
• Subjects: Biopolymer -- Reverse osmosis -- Calcium -- Magnesium -- Pre-ozonation -- Membrane fouling; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2019.115437
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Despite plenty of literatures focused on the application of pre-ozonation prior to membrane, it was still unclear about the role of divalent cations (Ca 2+ and Mg 2+ ) in reverse osmosis (RO) membrane fouling mitigation. In this study, ozone pre-treatment (0.10, 0.25 and 0.50 mg O3 /mg DOC (dissolved organic carbon)) was employed to oxidize model biopolymer, which was represented by bovine serum albumin (BSA) and sodium alginate (SA) in the presence of Ca 2+ and Mg 2+ (0.5, 1.0 and 2.0 mM). Cross-flow filtration was conducted to investigate RO membrane fouling by concentration mode. The results showed that at appropriate ozone dose there were measurable changes in physicochemical properties of BSA and SA, including increases in particle size, hydrophilicity, density of negative charge and carboxylic groups. Pre-ozonation markedly alleviated RO fouling by BSA at ozone dose of 0.25 mg O3 /mg DOC when Ca 2+ and Mg 2+ concentrations raised from 0.5 to 2.0 mM since the increase in electrostatic (EL) repulsion and decrease in hydrophobic (HP) interaction compensated the increase in divalent cation bridging. Similar results were obtained for SA fouling in the presence of Mg 2+ . In contrast, the effect of pre-ozonation on SA fouling strongly depended on the concentration of Ca 2+ . In brief, it mitigated SA fouling at 0.5 mM Ca 2+, whereas accelerated irreversible fouling at higher Ca 2+ concentration (1.0 and 2.0 mM) due to the overwhelming effect of divalent cation bridging compared to EL and HP interactions, as revealed by adsorption experiments (in-situ streaming potential measurement). Pre-ozonation shifted the fouling layer from compact to porous and weakened the adhesion forces between foulants and membrane (foulants) except for SA containing 1.0 and 2.0 mM Ca 2+ . This study may provide the guidance for the application of pre-ozonation prior to RO filtration. Graphical abstract: Image 1 Highlights: Pre-ozonation (PO) markedly mitigated RO fouling by BSA + Ca 2+ /Mg 2+ and SA + Mg 2+ . PO accelerated irreversible fouling by SA+1.0/2.0 mM Ca 2+, but not for 0.5 mM Ca 2+ . PO weakened foulants-membrane (foulants) interaction except for SA+1.0/2.0 mM Ca 2+ . Streaming potential measurement well predicted RO membrane fouling behavior.