AWWA ACE70793

This paper discusses a 13-month pilot test of four different filtration systems to determine the optimum pretreatment approach to minimize fouling on seawater desalination reverse osmosis (RO) membranes. Of the nine major project investigations that were done, this paper focuses on a comparison of pretreatment alternatives that include: slow sand filters; conventional treatment - coagulation and clarification + granular media filters; immersed ultrafiltration (UF) membranes; pressure UF membranes; UF operated with and without coagulation and clarification; and, each pretreatment system is followed by a separate RO train. Background on a red tide simulation event is presented, along with results of pretreatment testing, and RO fouling trends. Study conclusions indicate that: both biological filtration and ultrafiltration can provide successful pretreatment for seawater RO desalination; granular media filters require more careful optimization than UF or slow sand filters; effective removal of algal cells upstream of granular media filters or UF will reduce biofouling; and, slow sand filters are simple and effective, but require a 50% larger footprint. Includes tables, figures.