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• B iofouling is a serious threat to economical operation of RO systems on bio-active water supplies. • A dvances in RO system design and cleaning p rocedures have resulted in limited improvement. • M odifying the chemistry at the surface of aromatic, thin film composite, polyamide m embranes can reduce the rate of microbial a ttachment and delay the onset of biofilm formation, thus extending the time between required chemical cleanings. • F urther improvements to delay the onset of biofilm formation in spiral wound elements c an be realized by optimizing flow d istribution through use of shorter membrane l eaf lengths, • T here is a strong synergy between the use of F R elements and the ability to select and o ptimize intermittent sanitization with a nono xidizing biocide.