Double-acting batch-ro system for desalination of brackish water with high efficiency and high recovery

The batch-RO concept has been presented and demonstrated as a means of desalination that can approach the ideal minimum specific energy consumption, even as the recovery ratio is increased. It overcomes the configuration loss of conventional single or multi-stage constant flow processes, and it avoids the mixing of feed with re-circulated saline water inherent in closed-circuit desalination. A drawback of the batch system presented earlier, however, was the need to interrupt the output while the system was refilled between batches. In the new design presented here, the pressure exchange vessel is configured to be double-acting, such that one side is refilling while the other is pressuring. Thus, the output is maintained during refill, resulting in an increase in water output of about 25% compared to the earlier system, with membrane area remaining the same. The inconvenience of stopping and starting the feed pump is also avoided. A prototype of the double-acting system is under development and results will be presented at the conference, including specific energy consumption, recovery ratio, rejection fraction, and cycle time. The system is targeted for use in inland arid areas and may be powered by solar photovoltaic electricity.