Reclaiming wastewater with increasing salinity for potable water reuse: Water recovery and energy consumption during reverse osmosis desalination

Abstract With reverse osmosis membranes being industry-standard in many potable reuse facilities, an opportunity exists to desalinate higher-salinity streams (e.g., brine and regional brine interceptor streams) to augment traditional wastewater supplies and reduce brine disposal requirements. This study evaluates the energy consumed in recovering water from these streams at advanced water purification facilities. Scenarios without and with seawater inflow and infiltration at coastal wastewater reclamation facilities are considered. It was found that as wastewater salinity increases with increasing seawater inflow and infiltration, base case energy consumption increases, but the percent increase of energy consumption caused by mixing higher-salinity streams decreases. Multiple energy-saving strategies were evaluated, including energy recovery devices, closed-circuit reverse osmosis, and desalination of the higher-salinity streams separately from the treated wastewater. The energy savings was greater for closed-circuit reverse osmosis than for energy recovery devices and increased for both as influent salinity increases. The energy savings from desalinating higher-salinity streams separately increased as the salinity difference between the two streams increased. Addition of higher-salinity streams was also considered within the context of inorganic scaling potential, product water requirements, and discharge permits that may limit recoveries.