Drying and Pyrolysis of Solid Waste on Spacecraft for Water Recovery and Biochar

Manned spaceflight outside of low-Earth orbit will require significant advances in closing loops within life support systems, especially the recycling of solid and liquid wastes to produce oxygen, food, and fresh water. Pyrolysis is one waste conversion method that has received considerable attention due to its potential to enable improvements in waste reduction, material recovery, and energy production.

Here, we describe the development of a slow pyrolysis reaction system that can transform solid waste and brine from the water treatment system into a nutrient-rich crop growth medium, while recovering water and carbon dioxide. The feedstock for the process followed a standard s recipe used by NASA to represent the average daily solid waste produced by astronauts on manned missions. This recipe included packaging materials (polyethylene, nylon, aluminum foil), clothing and towels (mostly cotton), personal care products (i.e. shampoo, toothpaste, facial tissue, hand wipes, diapers, etc.), food waste, metabolic waste simulant, and miscellaneous materials such as nitrile gloves, duct tape, and cleaning wipes. Solid waste processing consisted of two steps: drying to recover water and pyrolysis at moderate temperatures (400-550°C). Process steps were optimized to recover the most water and produce the most suitable biochar for plant growth applications within the assumed 8 hour total operational time window. Recovered water and biochars were characterized using a variety of physical, chemical and soil nutrient analysis methods. We discuss the challenges of working with this waste feedstock compared to lignocellulosic materials, how this system fits into an overarching life support architecture, and future work needed to adapt this system to a microgravity environment.