Forward osmosis dialysate production using spiral-wound reverse-osmosis membrane elements: Practical limitations

• Spiral-wound R.O. membrane elements can be used in F.O. mode.
• Medical dialysate can be produced directly from impaired water sources.
• Production depends on efficient membrane backwashing.
• Potential for energy efficient remote dialysate production.

We present here an experimental method of dialysate production by forward osmosis (FO) using an inexpensive reverse osmosis (RO) membrane element. This method was developed in response to the increasing need for dialysis treatment in remote and desert regions of Australia where water is precious and electricity supplies are generally unreliable.A 4040 RO membrane element was oriented for FO, using dialysate concentrate as a draw-solution and pre-treated tap-water as a feed-solution. Diluted draw-side output was collected and mixed over a range of target flow-rates. After each test the element was osmotically backwashed. Measurements were made of production time, volume and equivalent flow rates.The benefits of FO were diminished by the process׳ need for osmotic backwashing. Our system had an equivalent water recovery ranging from 65 to 75%. Its energy efficiency was 66% of its RO equivalent. Its operation was almost silent. Two 4040-size RO membrane elements would be necessary to complete a dialysis treatment. Dialysate production may be possible by this method, but its economic and conservation benefits appear to be modest.