Scaling behavior of concentrated urine membrane distillation systems for space applications

Abstract

One challenge facing deep space exploration is the need to provide water with minimal input from Earth. Consequently, it is important to develop robust technology that can extract >90% of the water from urine produced by crew members. Current technologies are challenged by mineral scaling and precipitation at high recovery rates. Membrane distillation (MD), which uses a thermally-induced vapor pressure difference to distill water vapor through a microporous hydrophobic membrane, has shown promise for treating concentrated wastewaters, but scaling can still be a problem. Therefore, in this work, I characterize the scaling behavior of synthetic and real urine in a MD system using experimental and modeling approaches. Water recoveries of >90% were achieved with rejections of >99% for most contaminants, and citrate was shown to be a promising inhibitor for calcium scale formation. This is one of the first studies showing calcium phosphate or calcium oxalate precipitation during MD.