Plasma Assisted Acid Leaching of Inedible Biomass for Nutrient Recovery

Sustaining a human presence on the moon, Mars or deep space will require closing loops on many life support systems. Some form of agriculture will be required because plants produce the vitamins, antioxidants, and essential oils in our diets that degrade over time in stored foods. In addition, they provide dietary fiber, restore air, and purify water. It is estimated that 93 Kg of plant nutrients are required to support one crew member per year. Growing plants will require recycling nutrients trapped in inedible vegetation. Researchers at Kennedy Space Center have investigated the use of a thermal plasma with various carrier gases to thermally degrade inedible plant biomass for nutrient recovery. Previous work demonstrated a thermally degrading environment such as a muffle furnace improved nutrient recovery from inedible biomass prior to an acid leaching process. However, a muffle furnace is an inefficient process. We have explored the use of a small scale, thermal plasma for degradation of pellets to enhance the breakdown of plant stems, leaves and debris to further close the nutrient loop. Plasma carrier gases such as carbon dioxide, nitrogen, and air were used to explore variations in recovery and potential chemical by-products. Plasma processed inedible biomass was added to varying concentrations of acid solution for leaching of nutrients (e.g. potassium, magnesium, calcium, and phosphorus) for reuse in the crop production cycle. We also examine total nitrogen recovery. Results are presented showing the impact of plasma processing prior to acid leaching on recovery of plant nutrients.