Microbiological damage of cellulose acetate RO membranes

Based on the data presented in this study, microorganisms can degrade wet c ellulose acetate (CA) reverse osmosis (RO) membranes during shutdown period s or under storage conditions. Fungal (and perhaps bacterial) metabolism of the membranes was measured from CA membranes using the C-14 isotope. Using uniformly labeled C-14 cellulose as the starting compound, CA polymer was synthesized, casting solutions were made, and CA membranes were produced. A fter inoculating membrane samples with the microorganisms, the metabolism o f the membranes was confirmed by measuring isotopically enriched carbon dio xide gas produced either by the respiration under aerobic or anaerobic cond itions using the Krebs metabolic cycle or by fermentation. Results show tha t the dense zone of the asymmetric membrane, where desalting occurs, could be compromised in 3 months or less. Membrane samples that were treated by s anding and hydrolyzing the surface to simulate a "used" membrane, degraded at a faster rate than new membranes, Removing oxygen from the system failed to slow or stop the rate of growth. Data showed that no "special" fungus f rom the RO industry is unique in degrading CA membrane. Instead, all organi sms tested degraded these membranes, including microorganisms found in the biofilms from a field RO system and microorganisms present as laboratory co ntaminates. (C) 2001 Published by Elsevier Science B.V.