Analyses of calcium carbonate scale deposition on four RO membranes under a seawater desalination condition

Inorganic fouling is one of the critical operational issues in reverse osmosis membrane. Few researches investigated effects of membrane surface characteristics on inorganic fouling and on anti-scaling techniques although the fouling occurs on the membrane surface. The objective of this paper was to examine whether different characteristics of deposition of calcium carbonate solids would occur on four membranes having distinctive surface properties. A lab-scale cell reactor with a crossflow velocity was installed and two coupons were used for one type of membranes. Two feed waters were examined: concentrated synthetic seawater simulating a 30% recovery and a concentrate from a seawater RO plant in operation at Changwon, Korea. The amounts of solid deposition on the attached membranes were increased in all four membranes but the degree of deposition on each membrane was different. Various types of calcium carbonate solids were clearly detected by both XRD and SEM analyses. In general, a membrane with greater roughness and negative surface charge appeared to form more scales. This implied that membrane surface characteristics such as roughness and surface charge affected inorganic fouling, presumably by providing favourable sites for precipitation and enhancing attraction of species to the membrane surface.