The principle has been around for a while but it is not cost effective
except in very large scale plants. In RO the TDS rejection rate is
fairly stable and the volume of product flow varies with pressure. In
nanofiltration salinity of the product water is directly related to
pressure so very precise regulation is required. Also, RO is self
cleaning because the flow of the brine is parallel to the membrane
surface while nanofilters force brine directly against the fliter so
they have to be brought off line for maintenance on a regular basis.

Nanofiltration would be cost effective for a municipal water system or
maybe an aircraft carrier where personel are available for operation and
maintenance but RO is more practical on a yacht.

Panama wrote:
See the Long Beach diagram page
http://www.lbwater.org/pdf/lb_graphic.pdf

This uses 2 pressure stages and nanofiltration not reverse osmosis
membranes - 525 psi and 250 psi - much less energy per gallon.

Any marine watermaker development in this direction?


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com