Flux decline during nanofiltration of naturally-occurring dissolved organic matter: effects of osmotic pressure,membrane permeability,and cake formation |
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| Institution: | 1. Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, 110 8th Street/317 MRC Building, Troy, NY 12180, USA;2. Isermann Department of Chemical Engineering, Rensselaer Polytechnic Institute, 110 8th Street/Rickets Building, Troy, NY 12180, USA;1. Membrane Science, Engineering and Technology Center and Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, USA;2. Materials Science and Engineering Program, University of Colorado, Boulder, CO 80309-0596, USA;1. Nanyang Environment & Water Research Institute, Interdisciplinary Graduate School, Nanyang Technological University, Singapore 637141, Singapore;2. Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore 637141, Singapore;3. School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore;4. School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore;1. Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, The Netherlands;2. Wetsus, Centre of Excellence for Sustainable Water Technology, Agora 1, P.O. Box 1113, 8900 CC Leeuwarden, The Netherlands;3. Vitens N.V., P.O. Box 1205, 8001 BE Zwolle, The Netherlands;4. Department of Environmental Technology, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands;5. Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands;6. King Abdullah University of Science and Technology, Water Desalination and Reuse Center, Thuwal, Saudi Arabia;1. National Engineering Laboratory for Industrial Wastewater Treatment, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, PR China;2. Shaanxi Research Design Institute of Petroleum and Chemical Industry, 60 Xiyan Road, Xi''an, 710054, PR China;3. The 210th Institute of the Sixth Academy of CASIC,8 Dianzi First Road Xi''an 710065, PR China;4. Shaanxi Yanchang Tsingshan Technology &Engineering Co., Ltd. 60 Xiyan Road, Xi''an, 710054, PR China;1. State Key Laboratory of Urban Water Resource and Environment (SKLUWRE), School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China;2. Soniya Education Trust’s College of Pharmacy, Dharwad, 580002, Karnataka, India |
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| Abstract: | Nanofiltration of naturally-occurring dissolved organic matter (NOM) by an aromatic polyamide membrane was measured in a crossflow bench-scale test cell and modeled using a semi-empirical osmotic pressure/cake formation model. Our objective was to examine flux decline due to NOM fouling while explicitly accounting for flux decline due to osmotic effects and changes in membrane permeability. This approach allowed quantification of the effect of ionic composition on specific NOM cake resistance, and yielded insight into flux decline due to enhanced NaCl rejection by the NOM deposit. In the absence of NOM, increasing NaCl concentration reduced salt rejection and decreased membrane permeability. Flux decline was modeled by accounting for changes in osmotic pressure with time, and by employing an effective permeability. The addition of calcium significantly reduced rejection of sodium and feed conductivity, and thus mitigated flux decline. Increasing pH from 4 (near membrane pI) to 10 increased the effective permeability but also increased NaCl rejection, which resulted in greater flux decline. The presence of NOM caused greater flux decline resulting from a combination of NOM cake resistance and increased rejection of NaCl by negatively charged NOM functional groups. Increasing NaCl concentration had little effect on the mass of NOM deposited, but significantly increased the specific resistance of the NOM cake. The effect of ionic strength on specific resistance correlated with a reduction in NOM size, estimated by separate UF permeation experiments and size exclusion chromatography analysis of UF permeate. Therefore, increased specific cake resistance is consistent with a more compact, less porous cake. Flux decline by NOM solutions showed a maximum at pH 7, where salt rejection was also a maximum. Binding of calcium reduced the ability of NOM to enhance NaCl rejection, and likely increased NOM cake resistance. Flux decline caused by NOM fouling in the presence of calcium was only significantly different than that caused by NOM in a solution of NaCl at the same ionic strength when the calcium concentration corresponded to saturation of NOM binding sites. |
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