Thermal conversion of crew waste to gases that can be vented from spacecraft for mass reduction has been investigated by NASA and others within the Trash-to-Gas program. One concern with operating thermal waste processors onboard spacecraft is the potential for contamination of cabin atmosphere with volatile organic compounds (VOCs) from gaseous reactor effluent. Recent efforts at Kennedy Space Center's Applied Chemistry Laboratory have developed and reported on a recirculating plasma gas system for the rapid reduction of VOCs. In this case, a direct-current thermal plasma was used to break down VOCs into simpler, and preferably more benign chemical species. Previous work reported the application of this system on gases with carbon dioxide as the background. Here the authors report the results of plasma VOC abatement with an improved recirculation system. The VOCs studied included a set in a nitrogen background (benzene, pentane, ethanol, and Freon 113) and a set in a carbon dioxide background (benzene, pentane, ethanol, and acetone). Each of these analyte species is included in NASA's Spacecraft Maximum Allowable Concentrations list. The plasma abatement system showed a greater than 99.999% reduction in VOC concentrations within 2 minutes of plasma treatment for the nitrogen background, and greater than 95% VOC reduction within 2 minutes for the carbon dioxide background. This is a significant improvement over what was reported previously. All analytes obeyed first-order rate kinetics in agreement with the previous work.
Olson et al. (Sun,) studied this question.