Hypersaline brines treatment using osmosis-based processes: fundamentals and feasibility

Abstract

High salinity brines have been studied as potential fresh water sources due to the scarcity of other supplies and elevated saline effluent generation in activities such as oil and gas extraction and CO2 capture. Although their availability is remarkably abundant in some regions, there are concerns regarding its cost-effective treatment. Novel reverse osmosis (RO) based process are being developed with promising energy consumption and cost advantages. The main objective of this work is to investigate the effects of high salinity on RO-based processes, as well as in the process treatment feasibility. Cost optimization showed the osmotically assisted reverse osmosis process have the lowest cost when compared to conventional processes, such as mechanical vapor compression. Membrane transport properties as permeabilities and structural parameter are important to the cost technology feasibility. Aiming to investigate whether the membrane transport properties would remain constant in higher salt concentration, cellulose triacetate membranes were tested under variable pressure and salinity. Water and salt permeability were found to decrease with increasing average salinity while the structural parameter increased with increasing pressure. Pervaporation tests supported the hypothesis of variable membrane performance, reaching a plateau for average salinities higher than 50 g/L. A possible explanation is membrane deswelling, previously reported for different materials. Further studies are needed to understand the transport under high salinity and to stablish directions for membrane tailoring and applications under extreme environments.