Composting inedible crop residue for advanced life support systems: Nutrient extraction and recycling for hydroponic plant growth

In-vessel composting is being testing as a solid waste processing approach as part of the development of Advanced Life Support (ALS) systems to mainta in humans during long-term space missions such as a lunar or Mars base. Pre liminary studies conducted at Kennedy Space Center have focused on composti ng of inedible residue from hydroponically grown plants, a large and unique waste stream generated as part of biomass production within ALS systems. T his report focuses on the 1) nutrient mass balance during the composting pr ocess, 2) the efficiency of nutrient leaching from the compost, and 3) the effects of recycling leachate to hydroponic systems. Over 90% of most eleme nts (K, Ca, Mg, and P), but only 64% of N, present in the feed material was present in the compost after 21 days. Nitrogen losses were most likely due to denitrification, although untrapped volatilized ammonia was another pot ential sink. Recovery of nutrients from the compost by leaching ranged from 13% for Ca to 100% for K, and values were generally higher than previously reported data for other composts, particularly for N and P. Use of compost leachate in hydroponic systems supporting wheat plants resulted in increas ed microbial cell density in the rhizosphere, one potential mechanism for o bserved reductions in plant growth.