Description: Wastewater reclamation is a vital aspect of prolonged space travel. One area that is particularly challenging is urine reclamation. Current International Space Station (ISS) systems allow for 70% recovery. NASA aims to increase wastewater recovery to 85% or greater. A further challenge with water recovery from wastewater brines is minimization of mineral scaling on processing equipment. The overall goal is to introduce pervaporation, a membrane process new to NASA, for high recovery (≥85%) of water from ISS wastewater and brines while simultaneously developing new membranes for pervaporation. This will include evaluating routes to replace current wastewater processing, vapor compression distillation (VCD), with pervaporation. Pervaporation is a membrane process, where the driving force for transport is vapor pressure differences (often created via either a vacuum pump or a sweeping gas) of the permeating species across the membrane. Pervaporation is advantageous, compared to processes like distillation, in that it can easily be operated at ambient temperatures. It can break azeotropes and limit transfer of volatile organic compounds (VOCs), thus limiting the transmission of undesired species into the purified water. Pervaporation is capable of handling highly concentrated brines when compared to conventional processes, since it is not limited by the concentration of solutes in the feed. Pervaporation is a unique process that it can produce clean water in the presence of salt compounds and organic compounds, both of which are present in urine brine. To achieve this goal, there are three objectives: 1) improve anti-scaling properties of promising pervaporation membranes, 2) design a pervaporation module to integrate urine brine waste processing with the humidity condensate system on the ISS, and 3) evaluate feasibility of replacing VCD with pervaporation in existing wastewater processing. In Objective 1, to improve anti-scaling properties of pervaporation membranes, we will add a zwitterionic thin film layer on the membrane surface. Our team has recently developed high flux pervaporation membranes for desalination. Zwitterions are species with localized positive and negative charges, but overall neutral charges. Current research on zwitterions show promise for both increase in water flux through a pervaporation membrane, as well as a decrease in scaling (buildup of salts and inorganic species) on membranes. We hypothesize that the addition of a zwitterionic layer will increase the hydrophilicity of the membrane surface, which will aid in increased water recovery. These modified membranes will then be tested using simulated urine brine to investigate the selectivity and degradation of these membranes. In Objective 2 we will design a pervaporation module to integrate urine brine waste processing with the humidity control system on the ISS. We hypothesize that addition of a pervaporation step in space exploration water reclamation systems will allow for higher water recovery rates. We will design and build a pervaporation unit for direct integration with the current ISS humidity control system. The new pervaporation unit will utilize the current air processing system as a sweeping gas, and then the stream will proceed to the condenser and be processed until it achieves potable water standards. In Objective 3, we will analyze the potential for replacing the current VCD system for initial urine processing with a pervaporation unit. VCD is an energy intensive process, and pervaporation shows promise to lower the energy requirement while limiting transfer of VOCs and increasing purity of reclaimed water. The initial pervaporation unit from phase two will be scaled up to process 9 kg/day of urine, consistent with the needs of a full ISS crew. Through development of novel pervaporation membrane technologies, and integration with current ISS systems, increased water recovery is achievable for long term space flight.

Benefits: Through development of novel pervaporation membrane technologies, and integration with current ISS systems, increased water recovery is achievable for long term space flight.