title: Role of calcium ions on the removal of haloacetic acids from swimming pool water by nanofiltration: mechanisms and implications.
abstract: We investigated the removal of haloacetic acids (HAAs) from swimming pool waters (SPWs) by two nanofiltration membranes NF270 and NF90. The strong matrix effect (particularly by Ca2+) on membrane rejection prompts us to systematically investigate the mechanistic role of Ca2+in HAA rejection. At typical SPW pH of 7.5, NF90 maintained consistently high rejection of HAAs (>95%) with little influence by Ca2+, thanks to the dominance of size exclusion effect for this tight membrane (pore radius ∼ 0.31 nm). In contrast, the rejections of both inorganic ions (e.g., Na+and Cl-) and HAA anions were decreased at higher Ca2+concentration for NF270 (pore radius ∼ 0.40 nm). Further tests show that the rejection of neutral hydrophilic molecular probes and the membrane pore size were not affected by Ca2+. Although Ca2+is unable to form strong complex with HAAs, we observed the binding of Ca2+to NF270 together with a reduction in its surface charge. Therefore, the formation of membrane-Ca2+complex, which weakens charge interaction effect, was responsible for the reduced HAA rejection. The current study reveals important mechanistic insights of the matrix effect on trace contaminant rejection, which is critical for a better understanding of their fate and removal in membrane-based treatment.
authors.affiliation: Interdisciplinary Graduate School, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Residues and Resource Reclamation Centre (R3C), Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore.
authors.forename: Linyan
authors.initials: L
authors.lastname: Yang
authors.affiliation: Division of Environmental and Water Resources, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Singapore-Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST) Program, Berkeley Education Alliance for Research in Singapore (BEARS) Center, Singapore.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Singapore Membrane Technology Centre (SMTC), Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore.
authors.forename: Qianhong
authors.initials: Q
authors.lastname: She
authors.affiliation: School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Man Pun
authors.initials: MP
authors.lastname: Wan
authors.affiliation: Division of Environmental and Water Resources, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Singapore Membrane Technology Centre (SMTC), Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore.
authors.forename: Rong
authors.initials: R
authors.lastname: Wang
authors.affiliation: Residues and Resource Reclamation Centre (R3C), Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore; Division of Environmental and Water Resources, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. Electronic address: wcchang@ntu.edu.sg.
authors.forename: Victor W-C
authors.initials: VW
authors.lastname: Chang
authors.affiliation: Department of Civil Engineering, University of Hong Kong, Pokfulam, Hong Kong. Electronic address: tangc@hku.hk.
authors.forename: Chuyang Y
authors.initials: CY
authors.lastname: Tang
mesh_terms: D002118:Calcium; D005374:Filtration; D007477:Ions; D008567:Membranes, Artificial; D013551:Swimming Pools; D014874:Water Pollutants, Chemical / Q000737:chemistry; D018508:Water Purification
chemical_list: D007477:Ions; D008567:Membranes, Artificial; D014874:Water Pollutants, Chemical; D002118:Calcium
keywords: Calcium; Haloacetic acids; Matrix effect; Membranes; Swimming pool water