Double-acting batch reverse osmosis configuration for best-in-class efficiency and low downtime

Energy consumption in reverse osmosis has decreased substantially over the last few decades thanks to the implementation of energy recovery devices, high efficiency pumps, and improved membranes. However, to further increase the adoption of the technology, its energy needs must still be reduced. Batch and semi-batch reverse osmosis configurations have shown potential to be the most energy efficient reverse osmosis variants, but have remaining inefficiencies from brine mixing and high downtime. In this study, we modeled in new detail a further improved double-acting batch reverse osmosis system that uses a high-pressure tank with a reciprocating piston. A high-pressure pump is used to fill the inactive side of the high pressure tank with feed that pressurizes the reverse osmosis system during the permeate production stage; the feed is then used as the working fluid for the next cycle of the system. Additionally, to account for the dynamic behavior of the system under different operational conditions, a hydraulic simulation model was developed to accurately predict the evolution of the pressure and other important parameters over time. A specific energy consumption of 1.88 kWh/m³ was calculated for seawater with a salinity of 35 g/kg, recovery of 50%, and a permeate flux of 15 LHM, and lower values SEC were obtained for lower permeate fluxes. Moreover, the downtime was found to be below 10% of the cycle time, without significantly increase the energy consumption of the system. This design also showed the potential to reduce the start-up time compared to previously proposed batch RO configurations.