Electrocoagulation pretreatment of seawater prior to ultrafiltration: Bench-scale applications for military water purification systems

The objectives of this research were to investigate the use of in-line electrocoagulation (EC) as a pretreatment for seawater prior to ultrafiltration (UF) at the bench-scale and to compare EC with equivalent doses of ferric chloride. UF membrane performance was evaluated by transmembrane pressure (TMP) and hydraulic resistances at sub- and super-critical fluxes, and by flux recovery after hydraulic and chemical cleanings. Modified Atlantic Ocean seawater was used. Constant flux UF operation (50 to about 350 lmh) was used to evaluate short-term performance at sub- and super-critical fluxes, and constant feed-pressure (15 psi) experiments were used to investigate filter cake stability under high TMP conditions. In-line EC improved UF membrane performance for all coagulation and flux conditions. Compared to no coagulant pretreatment, ferric chloride improved UF membrane performance under short-term, constant flux conditions that resulted in TMP < 8 psi, but produced increased TMP and resistance to filtration at 15 psi. EC always resulted in lower resistance and improved flux recovery after cleaning compared to an equivalent dose of ferric chloride. Overall, EC is a feasible and competitive pretreatment strategy at the bench-scale, but scale-up issues, electrode cleaning requirements, and sustainability during long-term operation need further study.