Reverse Osmosis System Design: Concentrate Recycle Loop
The main purpose of a concentrate recycle loop in a reverse osmosis system is to reduce the amount of concentrate or waste water flowing to the drain. Recycle loops are also used to maintain an optimum flow velocity across the membrane surface and reduce individual membrane recovery.
A recycle loop takes a portion of the concentrate flow which would have otherwise gone to drain and returns it to the feed of the RO pump in a continuous loop. Reducing the concentrate flow to drain achieves a higher system “recovery” percentage. Pump sizing needs to take the additional flow coming from the concentrate recycle loop into consideration.
Careful attention must be paid to the feed water analysis. Concentrating the waste stream to a higher degree can only be done to a certain point before fouling will occur in the membranes. This fouling point will vary with each feed water.
The examples shown below are for the same system operating at 70% recovery, the first example with recycle and the second without:
1. System Design Overview with Recycle Loop
Design Warnings: -None-
2. System Design Overview Without Recycle
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