Reverse Osmosis Filtration for Ersatz Space Mission Wastewaters

Adequate rejection of a variety of inorganic and organic compounds is necessary if reverse osmosis (RO) and nanofiltration (NF) membranes are to be used for space mission wastewater reuse. Three ersatz space mission wastewaters having different pH, conductivities, and amounts of organic compounds were tested to determine the membrane flux and the solute rejection for five RO and two NF membranes that are commercially available. The results show that the rejection of ions depend upon the solution pH which influences electrostatic repulsion, while for organic solutes the removal depends mainly upon the solute radius and molecular structure. In addition, the rejection of dissolved organic carbon depends upon the composition of the wastewater. The ratio of solute radius (r_i,s) to effective membrane pore radius (r_p) can be employed to predict the rejection of ions and organic compounds.