Novel Variable Configuration Design for Ultrahigh Recovery Reverse Osmosis Desalination of Brackish Water

A novel transient and cyclic design is proposed for ultrahigh recovery reverse osmosis (RO) desalination of brackish water. The designed system consists of two subsystems, a conventional multistage RO and a flow reversal and retentate recycle RO. The operation periodically switches between two different configurations, a series connection of the two subsystems for full production, and a parallel connection for partial production and flushing of the most concentrated membranes using the under-saturated fresh feed. Such a transient and cyclic design concept incorporates beneficial features of ROTEC’s flow reversal RO (FRRO) and DuPont/Desalitech’s closed-circuit RO (CCRO) in a single system. It offers operational flexibility at ultrahigh recoveries and requires a slight hardware modification to retrofit existing brackish water RO plants. Dynamic simulations show that concentration hotspots and overshoots are less severe than those in FRRO. It also avoids cycle-to-cycle salt buildups that are inevitable in CCRO given that it is an open-circuit design.