Recovery of Nutrients from Inedible Biomass of Tomato and Pepper to Recycle Fertilizer
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Plants can be used as a source food, oxygen, and help remove carbon dioxide for human life support in space. But to grow these plants will require sufficient nutrients (fertilizer). This fertilizer can be stowed and resupplied, but this imposes a mass cost to the mission. Depending on the crop, a large portion of the biomass will be inedible. This inedible biomass contains various nutrients that can be recycled for subsequent crops, hence reducing the need for imported fertilizer. Previous studies demonstrated that continuously stirred tank bioreactors and composters can be used to retrieve many of these nutrients. This can provide a liquid effluent that is easily used in hydroponic systems. We explored various approaches to achieve more complete recovery of nutrients from inedible biomass, and focused our testing on pepper and tomato leaves and stems. Approaches included water leaching, acid treatment, microbial degradation, photocatalytic oxidation, thermal methods, and various combinations of these. Acid (0.1 M or 1.0 M HCl) pretreatment with contact times as low as 10 minutes proved effective in combination with many approaches. To date, these treatments have not been able to recover more than 70% of some macronutrients regardless of combination of treatments. This recalcitrant inorganic fraction needs additional study to explore cost effective approaches for closing the mass loop for crop growth systems.