Inquiry: draw and feed circulation paths in FO modules

Schematic diagram of a forward osmosis membrane in action

How do draw and feed streams circulate in an FO module?

Most of us who are interested in forward osmosis technologies and their applications are familiar with the general concept of how forward osmosis works. There’s a draw solution, a feed solution, a forward osmosis membrane, and some circulation of feed and draw solutions of either sides of the membrane. However, picturing the exact circulation paths inside FO modules with varying geometries and form factors can sometimes be challenging.
Recently we receive a series of questions from Jose on exactly this topic:
Please help!
I can not understand the disposition on each design of plate and frame, spiral and tubular geometries. How does the raw water and draw solution flow inside these modules?
Could you describe the circulation path of each design for the FO membrane? I understand the circulation in the flow chart but I can´t understand it on the real module.
I think each module is like a RO module, but where is the path for the draw solution?
Is the membrane the same in RO than in FO?
Thanks in advance for your helping
Best regards

Here are ForwardOsmosisTech’s answers to Jose’s questions

Is the membrane the same in RO than in FO?

No. Since the driving force in reverse osmosis processes is hydraulic pressure compared to osmotic pressure in forward osmosis processes, reverse osmosis membranes and forward osmosis membranes are inherently different. A good RO membrane is a poor FO membrane and vice versa. We have previously published a guide on forward osmosis membranes and membrane processes, which gives an introduction to the difference between RO and FO membranes.

What are the circulation paths for feed (raw water) and draw solutions inside spiral wound FO modules, plate and frame FO modules, and tubular FO modules?

In general, forward osmosis processes require flow (typically cross flow) of draw and feed solutions on either side on the forward osmosis membrane. This requirement is the same in modules with varying geometric form factors.

Sterlitech have made a useful animation showing the counter current flow of feed and draw solutions in a forward osmosis test cell.

As for the flow path in different types of modules, I’m afraid we do not have any specific FO animations to help. Having said that, Hydranautics have made a useful animation on the flow paths in an RO spiral wound module. When viewing the animation try to imagine the permeate side being replaced by a flowing stream of draw solution; that’s pretty much how the flow path will be in a spiral wound forward osmosis module.

 We hope this is helpful Jose!
The ForwardOsmosisTech Team

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