(278h) Design of Ultrafiltration (UF), Nanofiltration (NF) and Low-Pressure Reverse Osmosis (LP-RO) Hollow Fiber Membranes for Pressure Retarded Osmosis (PRO) Pretreatment

Pressure retarded osmosis (PRO) has been widely investigated to harness the osmotic energy from salinity gradient. Seawater desalination brine (SWBr) and wastewater retentate (WWRe) are employed as the draw and feed solutions respectively due to a large salinity difference between them and reuse of wastewater, but the fouling caused by WWRe on PRO membranes is too severe. In order to mitigate fouling on PRO membranes, one-step spun ultrafiltration (UF), thin-film composite (TFC) nanofiltration (NF) and TFC low-pressure reverse osmosis (LP-RO) hollow fiber membranes were designed and fabricated into 1-inch modules to pretreat the WWRe. The filtrate from each pre-treatment method was used as the feed solution in the subsequent PRO tests. Results showed that the newly developed NF and LP-RO were effective to remove foulants and scalants. Using NF-filtrates, the PRO process could produce a stable power density of 7.3 W/m². It was a 10.7% drop from the initial power density. Using LP-RO-filtrates, the PRO process could produce a stable power density of 8.4 W/m², which was only a 7% drop from the initial power density. With the help of Separation Technologies Applied Research and Translation (START), the LP-RO hollow fiber membrane module was successfully scaled up to 4 inch in diameter. The LP-RO membrane fabrication was also optimized and the RO fluxes of both 1 inch and 2 inch LP-RO modules were more than 3 LMH/bar with NaCl rejection more than 99%.