Zwitterionic Copolymers for Anti-Scaling Applications in Simulated Spaceflight Wastewater Scenarios

Water reclamation in spaceflight applications, such asthose encounteredon the International Space Station (ISS), requires complex engineeringsolutions to ensure maximum water recovery. Current vapor compressiondistillation (VCD) technologies are effective but produce highly concentratedbrines and often cause scaling within a separation system. This workevaluates initial steps toward integrating pervaporation, a membraneseparation process, as a brine management strategy for ISS wastewaters.Pervaporation performs separations driven by a chemical potentialdifference across the membrane created by either a sweep gas or avacuum pull. Pervaporation membranes, as with most membrane processes,can be subject to scaling. Therefore, this work studies the anti-scalingproperties of zwitterions (polymeric molecules with covalently tetheredpositive and negative ions) coated onto sulfonated pentablock terpolymerblock polymer (Nexar) pervaporation membrane surfaces. We report amethod for applying zwitterions to the surface of pervaporation membranesand the effect on performance parameters such as flux and scalingresistance. Membranes with zwitterions had up to 53% reduction inpermeance but reduced scaling. The highest amount of scaling occurredin the samples exposed to calcium chloride, and uncoated membraneshad weight percent increases as high as 1617 +/- 241%, whereaszwitterion-coated membranes experienced only about 317 +/- 87%weight increase in the presence of the same scalant.