Study on performance of ultrafiltration membrane-based pretreatment for application to seawater reverse osmosis desalination

The objective of the work was to study at lab-scale the efficiency of hybrid process- coupling powdered activated carbon (PAC) adsorption or FeCl₃ coagulation and UF- for marine organic matter removal. Regenerated cellulose membrane with 30 kDa and actual seawater from Mediterranean Sea were used. The coagulant was FeCl₃ and adsorbents were two PAC types, with different surface area and pore size distribution. The results showed that PAC adsorption/UF performed higher efficiency in terms of organic removal than FeCl₃ coagulation/UF. Organic matter removal up to 50% was obtained for a PAC dose of 200 mg/L. According to high performance size exclusion chromatography (HP-SEC) analysis, the organics removed by PAC/UF are approximately 10 kDa. Therefore, the effect of PAC adsorption was deeply evaluated in terms of UF membrane fouling rate. The fouling rate was reduced when increasing PAC dose for both PAC types, in particular when PAC with a higher BET surface area and larger fraction of micropores was used. On the other hand, the results showed that UF unit could highly reduce SDI₃ from 26 to 9. The addition of PAC and FeCl₃ to UF allowed a further reduction of SDI₃ from 9 to 4–6.