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    Retention of pesticide Endosulfan by nanofiltration: Influence of organic matter-pesticide complexation and solute-membrane interactions

    Year: 2013

    Journal: Water Research, 47, pp 3484-3496, 20130926

    Authors: Annalisa De Munari, Andrea Joana Correia Semiao, Blanca Antizar-Ladislao

    Organizations: School of Engineering, The University of Edinburgh, Institute for Infrastructure and Environment, Edinburgh EH9 3JL, United Kingdom, School of Chemical and Bioprocess Engineering, University College Dublin, Dublin 4, Ireland

    Nanofiltration (NF) is a well-established process used in drinking water production toeffectively remove Natural Organic Matter (NOM) and organic micropollutants. The presenceof NOM has been shown to have contrasting results on micropollutant retention by NFmembranes and removal mechanisms are to date poorly understood. The permeate waterquality can therefore vary during operation and its decrease would be an undesiredoutcome for potable water treatment. It is hence important to establish the mechanismsinvolved in the removal of organic micropollutants by NF membranes in the presence ofNOM. In this study, the retention mechanisms of pesticide Endosulfan (ES) in the presenceof humic acids (HA) by two NF membranes, TFC-SR2 and TFC-SR3, a “loose” and a “tight”membrane, respectively, were elucidated. The results showed that two mechanisms wereinvolved: (1) the formation of ESeHA complexes (soluteesolute interactions), determinedfrom solid-phase micro-extraction (SPME), increased ES retention, and (2) the interactionsbetween HA and the membrane (solute-membrane interactions) increased membranemolecular weight cut-off (MWCO) and decreased ES retention. HA concentration, pH, andthe ratio between micropollutant molecular weight (MW) and membrane MWCO wereshown to influence ES retention mechanisms. In the absence of HA-membrane interactionsat pH 4, an increase of HA concentration increased ES retention from 60% to 80%for the TFC-SR2 and from 80% to 95% for the TFC-SR3 due to ESeHA complex formation. AtpH 8, interactions between HA and the loose TFC-SR2 increased the membrane MWCOfrom 460 to 496 g/mol and ES retention decreased from 55% to 30%, as HA-membrane interactionswere the dominant mechanism for ES retention. In contrast, for the “tight” TFCSR3membrane the increase in the MWCO (from 165 to 179 g/mol), was not sufficient todecrease ES retention which was dominated by ESeHA interactions. Quantification of thecontribution of both soluteesolute interactions and solute-membrane interactions is hencefundamental in understanding the removal mechanisms of micropollutant by NF membranesin the presence of NOM in order to optimize the treatment process.