Comparison of media and membrane filtrations for seawater desalination pretreatment

We compared microfiltration (pressurized and submerged) and media filtration as pretreatment to increase the removal of organics and to reduce reverse osmosis (RO) membrane fouling. The studied plant (feed rate = 2,500 m3/d, production rate = 1,000 m3/d) was taking seawater from East Sea of Korea and originally consisted of strainers, coagulation, dissolved air flotation, dual media filters (DMF), and RO membrane processes. A pressurized microfiltration (MF) and a submerged microfiltration (SMF) were installed and compared with DMF as pretreatment to the RO process. Upon pilot test results over one year, MF exhibited higher removal of dissolved organic materials. Average removals of UVA254 were 23, 19, and 13% at MF, SMF, and DMF, respectively. These results were confirmed with molecular weight distribution, and compositions of humic and fulvic acids. Silt density index (SDI) values were lower in membrane processed waters, and the SDI results correlated with transparent exopolymer particles (r = 0.73). The results indicated that MF can be an effective pretreatment to reduce RO membrane fouling with higher removal of organic materials.