Potential of pyrolysis of spacecraft solid waste for water recovery and plant-growth media production

Abstract Manned spaceflight outside of low-Earth orbit requires significant advances in closed-loop life support systems, especially the recycling of solid and liquid wastes to produce oxygen, food, and fresh water. Here, moderate temperature (400–600 °C) slow pyrolysis was tested to transform a high-fidelity spacecraft solid waste simulant into nutrient-rich crop growth medium for food production in space, while recovering water and carbon dioxide. Qualitative results indicated that water recovered from a simple drying process was of poor quality. Produced biochars approximated the characteristics of saline-sodic soils with P, K and micronutrients, low nitrogen, and no meaningful heavy metals, which suggests applicability as growth media. Before being used as growth media, biochar would likely need to be rinsed to remove sodium and supplemented with a source of nitrogen. If uncatalyzed slow pyrolysis is to be used, observations suggest that the produced volatiles should be directly combusted and water recovered from the flue gas, rather than trying to condense and separate the watery bio-oil product. This proof of concept study determined that low-temperature pyrolysis can be used to generate biochar-based soil, which may support agriculture during spaceflight while recycling nutrients and water from waste materials.