[lazide]

To be clear - unless there is work done to reduce the pressure at -230m below mean sea level, there is zero pressure gradient there. Anything sitting at -230m will feel a pressure gradient of essentially zero.

So you couldn't run a filter or anything, unless it's literally magic.

If someone put a pump at -230m and pumped out the water on one side of the membrane so that on one side the pressure was 'ocean' at -230m, and the other side was mean sea level, then yeah the membrane would work.

Notably, this requires roughly the same amount of work and energy as pumping water from the ocean at sea level into a filter so it has roughly the same pressure you would find if you did the first thing.

There is no free lunch.