Comparative seawater RO pretreatment evaluation using bench- and pilot-scale testing

Desalination using seawater reverse osmosis (SWRO) technology is an important option available to water-scarce coastal regions. Recent full-scale experiences have shown that pretreatment is the key for this application of RO technology. In this article, a unique series of bench- and pilot-scale tests are presented. These tests were conducted to determine the effect of pretreatment on SWRO performance. Seawater in the San Diego, Calif., region was first characterized to elucidate the difference between open-ocean and enclosed-bay water quality with respect to selection of an appropriate site for an SWRO plant. Two pretreatment schemes for SWRO-conventional pretreatment (coagulation/media filtration) and membrane filtration-were then evaluated using water obtained from two locations within the San Diego Bay, and the effluent water quality from these pretreatments was characterized. RO systems were then operated on these pretreated waters to evaluate the effect of pretreatment type on RO fouling and to correlate the pretreated water quality with the extent of RO fouling. The results show that for both source water types the seawater treated by microfiltration caused lower RO flux decline when compared with conventionally treated seawater. It was also found that the pretreated water silt density index was generally a good indicator of RO fouling for the experiments conducted.