An idea that may be useful is to place this upstream of a reverse ausmosis filter. That way the inlets and outlets can feed into the same area. You would still need to separate the inlet and fresh water outlet far enough from each other and you would need to setup the pressure differential but you might be able to do that by keeping the water moving in the high salinity tank.

The advantage being reverse osmosis is more efficient when the salinity difference is smaller. Still I don't think the added complexity is going to be worth slightly lower energy costs.