Molecular weight (MW) of organics was one of the important factors influencing membrane fouling propensity. This study identified critical foulants of reverse osmosis (RO) membranes in reclaimed water by MW fractionation. MW > 10 kDa component was identified as the critical fouling contributor (CFC) in secondary effluent (SE), which accounted for only 13 ± 5% of dissolved organic carbon (DOC) but contributed to 86 ± 11% of flux decline. Throughout 12-month monitoring, SE and MW > 10 kDa component showed a similar fouling variation tendency: apparently higher fouling potential in winter and lower in summer, while MW < 10 kDa component presented minor fouling changes. Morphology of membrane fouled by CFC characterized a smooth and thick foulant layer on membrane surface. CFC was mainly composed of proteins and polysaccharides, and a protein-polysaccharide-protein “sandwich” fouling layer structure was preferentially formed on membrane surface. extended Derjaguin–Landau-Verwey–Overbeek (xDLVO) analysis demonstrated that strong attractive interactions between CFC and membrane surface dominated the fouling process. Furthermore, computational fluid dynamics (CFD) simulation revealed strong filtration resistance of CFC, confirming its significant fouling potential. Dual effects including attractive interactions and advantageous ridge-and-valley surface appearance accounted for the significant fouling propensity of MW > 10 kDa component and glean valuable insights into RO fouling mechanisms of reclaimed water in practical application.

有机物的分子量（MW）是影响膜污染倾向的重要因素之一。本研究通过兆瓦分馏确定了再生水中反渗透 (RO) 膜的关键污染物。 MW 10kDa组分被确定为二级出水（SE）中的关键结垢贡献者（CFC），其仅占溶解有机碳（DOC）的13±5％，但造成通量下降的86±11％。在12个月的监测中，SE和MW > 10 kDa成分表现出相似的污染变化趋势：冬季污染潜力明显较高，夏季较低，而MW < 10 kDa成分污染变化较小。被CFC污染的膜的形态特征是膜表面光滑且厚的污垢层。 CFC主要由蛋白质和多糖组成，膜表面优先形成蛋白质-多糖-蛋白质“三明治”污垢层结构。扩展的 Derjaguin-Landau-Verwey-Overbeek (xDLVO) 分析表明，CFC 和膜表面之间的强吸引力相互作用主导了结垢过程。此外，计算流体动力学 (CFD) 模拟显示 CFC 具有很强的过滤阻力，证实了其显着的结垢潜力。包括吸引相互作用和有利的脊谷表面外观在内的双重效应解释了MW > 10kDa组分的显着结垢倾向，并为实际应用中的再生水RO结垢机制提供了宝贵的见解。