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A new generation of chemically modified, FILMTEC* thin-film composite, aromatic polyamide membrane elements has been introduced that exhibits reduced rates for bacterial adhesion, longer induction periods before biofilm start developing, and extended operating times between chemical cleanings. When these biofouling-resistant (FR) elements are coupled with the optimized use of selected biocides to prevent biofilm growth, a significant reduction in chemical cleaning frequency is achieved. This paper reviews biofouling in membrane systems and describes the development of the FR elements through full-scale field trials over about 3 years, focusing in the improvement achieved in mitigating the negative effects of biofouling on the performance of reverse osmosis plants. Some economic guidelines are given to estimate the potential value of FR technology.

1. Modifying the chemistry at the surface of FILMTEC BW30 membranes can reduce the rate of microbial attachment and delay the start of biofilm formation, thus extending the time between chemical cleanings. 2. Further improvements to delay the start of biofilm formation in spiral-wound elements can be realized by modifying the physical characteristics of the feed channel spacer and employing shorter leaf lengths with a multiple leaf design (e.g., >25) for more uniform flow distribution [13–15]. 3. The periodic application of an effective biocide can dramatically extend the interval Relative cost of chemical cleaning 3–8× 2× 1× Relative useful life before replacement, y 0.5 1.0 2.0 Table 4 Parameters for biofoulant resistant FILMTEC elements BW30 365 FR1 Part no. Nominal active surface area, ft2 (m2) Product water flow rate, gpd (m3/d) Stabilized salt rejection, Cl , % BW30 365 FR2 365 (34) 365 (34) 9500 (36) 9500 (36) 99.5 99.5 Notes: 1. Permeate flow and salt rejection based on the following standard conditions: 2000 ppm NaCl, 225 psi (1.6 Mpa), 77 F (25 C), pH 8 and 15% recovery. 2. Flow rates for individual elements may vary but will be no more than 7% below the value shown. 3. Minimum salt rejection for individual elements is 98.0%. 4. Sales specifications may change as design revisions take place. 5. A 34 million brine channel spacer is used to facilitate chemical cleaning.