Estimation of Flows of Carbon and Oxygen in the CEEF System Based on Data Collected in a Stable Phase of Sequential Crop Cultivation Lasting More than 100 Days

Closed habitation experiments are to be carried out using Closed Ecology Experiment Facilities (CEEF) from 2005 to 2009. The last target of duration of closed habitation is four months. Preliminary study and testing have been conducted in order to start the closed habitation experiments. In 2004 as the last year of the preliminary test phase for the 2005–2009 experiments, periodical harvesting from staggered cultivation of 23 crops including rice, soybean, peanut, and sugar beet was continued during 103 days. In order to balance with metabolisms of humans (named as “eco-nauts”) and animals, it is necessary to stabilize production of edible and inedible biomass, CO₂ uptake and O₂ production of crops. Although biomass production decreased rapidly during first five weeks of the 103-day period, it was relatively stable during last ten weeks. Average major foodstuffs in the harvested edible biomass met the requirement of two Eco-nauts although several minor ingredients were insufficient. It is considered that the underestimation of O₂ production of crops compared with CO₂ uptake came from troubles that air leak was somewhat greater than previous experiments and that O₂ sensors in the Plant Chambers (PCs) were unstable. The leak was found at the O₂ separator and repaired, and all O₂ sensors were replaced to more stable sensors. CO₂ uptake and O₂ production of the crops (150 m²) were determined to be 99.9 mol day⁻¹ and 104.8 mol day⁻¹, respectively, based on biomass and ingredient analysis. Total CO₂ and O₂ exchange for two goats and two men were 63 and 66% of those of crops, respectively. Flows of carbon and oxygen in the material circulation system including crops, eco-nauts, goats and physical/chemical (P/C) part were calculated using these data. The analysis showed that the waste processing systems of the Closed Plant Experiment Facility (CPEF) and the Closed Animal and Habitation Experiment Facility (CAHEF) will proceed solid waste of 307 g day⁻¹ (10.8 mol C day⁻¹) and 651 g day⁻¹ (25.8 mol C day⁻¹), respectively, and that the CO₂ separator of the CAHEF will separate 89.1 mol CO₂ day⁻¹. The result obtained in this study confirmed that crops will serve sufficient biomass and O₂ to the two eco-nauts and two Shiba goats in the 2005 experiments.