School of Engineering, The University of Edinburgh, Institute for Infrastructure and Environment, Edinburgh EH9 3JL, United Kingdom.
Water Res. 2013 Jun 15;47(10):3484-96. doi: 10.1016/j.watres.2013.03.055. Epub 2013 Apr 6.
Nanofiltration (NF) is a well-established process used in drinking water production to effectively remove Natural Organic Matter (NOM) and organic micropollutants. The presence of NOM has been shown to have contrasting results on micropollutant retention by NF membranes and removal mechanisms are to date poorly understood. The permeate water quality can therefore vary during operation and its decrease would be an undesired outcome for potable water treatment. It is hence important to establish the mechanisms involved in the removal of organic micropollutants by NF membranes in the presence of NOM. In this study, the retention mechanisms of pesticide Endosulfan (ES) in the presence of 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 were involved: (1) the formation of ES-HA complexes (solute-solute interactions), determined from solid-phase micro-extraction (SPME), increased ES retention, and (2) the interactions between HA and the membrane (solute-membrane interactions) increased membrane molecular weight cut-off (MWCO) and decreased ES retention. HA concentration, pH, and the ratio between micropollutant molecular weight (MW) and membrane MWCO were shown to influence ES retention mechanisms. In the absence of HA-membrane interactions at 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 ES-HA complex formation. At pH 8, interactions between HA and the loose TFC-SR2 increased the membrane MWCO from 460 to 496 g/mol and ES retention decreased from 55% to 30%, as HA-membrane interactions were the dominant mechanism for ES retention. In contrast, for the "tight" TFC-SR3 membrane the increase in the MWCO (from 165 to 179 g/mol), was not sufficient to decrease ES retention which was dominated by ES-HA interactions. Quantification of the contribution of both solute-solute interactions and solute-membrane interactions is hence fundamental in understanding the removal mechanisms of micropollutant by NF membranes in the presence of NOM in order to optimize the treatment process.
纳滤 (NF) 是一种成熟的饮用水生产工艺，可有效去除天然有机物 (NOM) 和有机微污染物。已证明 NOM 的存在对 NF 膜中微污染物的保留有相反的结果，并且去除机制至今仍知之甚少。因此，在运行过程中渗透水质会发生变化，而降低渗透水质则是饮用水处理所不希望的结果。因此，确定 NF 膜在 NOM 存在下去除有机微污染物的机制非常重要。在这项研究中，阐明了两种 NF 膜（TFC-SR2 和 TFC-SR3，分别为“疏松”和“紧密”膜）在腐殖酸 (HA) 存在下对杀虫剂硫丹 (ES) 的保留机制。结果表明，涉及两种机制：(1) 通过固相微萃取 (SPME) 确定 ES-HA 复合物的形成（溶质-溶质相互作用）增加了 ES 的保留，以及 (2) HA 和膜之间的相互作用（溶质-膜相互作用）增加了膜的分子量截止值 (MWCO) 并降低了 ES 的保留。HA 浓度、pH 值以及微污染物分子量 (MW) 与膜 MWCO 之比被证明会影响 ES 保留机制。在 pH 值为 4 时不存在 HA-膜相互作用的情况下，由于 ES-HA 复合物的形成，HA 浓度的增加使 TFC-SR2 的 ES 保留从 60%增加到 80%，使 TFC-SR3 的 ES 保留从 80%增加到 95%。在 pH 值为 8 时，HA 与疏松的 TFC-SR2 之间的相互作用将膜 MWCO 从 460 增加到 496g/mol，ES 保留从 55%降低到 30%，因为 HA-膜相互作用是 ES 保留的主要机制。相比之下，对于“紧密”的 TFC-SR3 膜，MWCO 的增加（从 165 增加到 179g/mol）不足以降低 ES 保留，因为 ES-HA 相互作用占主导地位。因此，为了优化处理过程，在 NOM 存在下理解 NF 膜去除微污染物的机制的基础是定量分析溶质-溶质相互作用和溶质-膜相互作用的贡献。
