High-Recovery Low-Pressure Reverse Osmosis

Membrane performance parameters have been obtained for high water recovery operation in the pressure range up to 1.4 MPascals (200 psig) for system modeling. Simple equations can be fitted to these measurements, from which RO system performance can be predicted or simulated as part of a model of system performance. A single-pump configuration with feedback has been found useful in reaching high brine osmotic pressures in continuous-flow operation. Enhanced brine concentration as well as an enhanced fraction of product/feed water recovery can be obtained by recycling a second-stage permeate of intermediate quality. For spaceflight recycling of hygiene water this permits lower pressure-vessel ratings, or higher water recovery, or both.