Performance of High-Recovery Recycling Reverse Osmosis with Wash Water

Inclusion of a recycling loop for partially-desalted water from second-stage reverse-osmosis permeate has been shown useful for achieving high-recovery at moderate applied pressures. This approach has now been applied to simulated wash waters, to obtain data on retention by the membranes of solutes in a mixture comparable to anticipated spacecraft hygiene wastewaters, and to generate an estimate of the maximum concentration that can be expected without causing membrane fouling.

A first experiment set provides selectivity information from a single membrane and an Igepon detergent, as a function of final concentration. A reject concentration of 3.1% Total Organic Carbon has been reached, at a pressure of 1.4 MegaPascals, without membrane fouling. Further experiments have generated selectivity values for the recycle configuration from two washwater simulations, as a function of applied pump pressure. Reverse osmosis removal has also been tested

for washwater containing detergent formulated for plant-growth compatibility (containing nitrogen, phosphorous and potassium functional groups).