Energy-efficient reverse osmosis desalination process

Energy-efficient reverse osmosis desalination: Effect of retentate recycle and pump and energy recovery device efficiencies

“…The osmotic potential energy in the brine from the EERO process can be twice as concentrated as that from conventional SSRO at the same operating pressure i.e. at 55.5 bar, the 4-stage EERO can achieve recovery of 75% as compared to recovery of 50% in SSRO [8]. As such, it can be used to significantly increase the energy density in the pressure-retarded osmosis (PRO) process for harvesting this energy.…”

“…The benefit of improved recovery is the more effective use of the process pretreatment stage, although attention has to be paid to control of scale formers. Desalination xxx (2015) xxx-xxx In a recent paper Chong et al [8] introduced the novel energyefficient reverse osmosis (EERO) process that combines single-stage reverse osmosis (SSRO) with either a 2-stage or 3-stage countercurrent membrane cascade with recycle (CMCR) to increase the water recovery while reducing osmotic pressure differential (OPD), which is the osmotic pressure difference across the membrane between the brine and permeate, at an acceptable specific energy consumption (SEC). Chong et al [8] discussed in detail the limitations with respect to increasing the water recovery of conventional SSRO, a commonly used process configuration for desalination, two SSRO stages in series, which is typically used for water reclamation to achieve high recovery, and just a CMCR.…”

“…SEC EERO /SEC SSRO b 1 at the same recovery level) where the SSRO process is used as a baseline for comparison. Chong et al [8] showed that for a 75% overall water recovery, for a 3-stage EERO, the net SEC and OPD are 2.74 kWh/m 3 and 74 bar, respectively, that represent reductions of 11% in the SEC and 33% in the OPD relative to conventional SSRO; whereas the 4-stage EERO has a net SEC of 3.08 kWh/m 3 (same as SSRO) and OPD of 55.5 bar that represents a 50% reduction relative to conventional SSRO.…”

“…Chong et al [8] mentioned that increasing the recovery in the terminal stage of the EERO process could potentially improve its efficiency; however, they did not explore this option. The maximum water recovery in each stage was limited to 50% in order to ensure a safety factor of one to minimize membrane fouling.…”

“…The maximum water recovery in each stage was limited to 50% in order to ensure a safety factor of one to minimize membrane fouling. In addition, Chong et al [8] commented that incorporating non-ideal pump and energy recovery device (ERD) efficiencies would favor the EERO process since it achieves the same recovery at a lower operating pressure relative to SSRO; however, they did not explore this in detail. In this paper the effect on the performance of the EERO process of having a higher recovery in the terminal stage of the EERO process and employing non-ideal pump and ERD efficiencies will be explored.…”