Plant Nutrient Solution Production Subsystem and Mineral Recycling in CEEF 2000-01-2335

In the Closed Ecology Experiment Facilities (CEEF), waste materials such as plant inedible parts, feces and urine of animal and human, and garbage are to be decomposed to inorganic materials by a physical and chemical (P/C) process; Wet Oxidation (W/O). It is known that significant part of nitrogen (N) in the waste materials is reduced to gaseous nitrogen (N₂) through W/O process. There is also some deposition of minerals such as iron (Fe) and phosphorous (P) through W/O process. Nitrogen Fixation Subsystem (NFS) produces ammonia (NH₃) which is one of end products of NFS, from N₂ separated from module air and hydrogen (H₂) derived from electrolyses of water, and also produces nitrate (HNO₃) from a part of the NH₃ and oxygen (O₂) derived from electrolyses of water. As another end product of NFS, ammonium nitrate (NH₄NO₃) is produced from the HNO₃ and a part of the NH₃. Solution including minerals such as NO₃⁻-N, NH₄⁺-N, P, potassium (K), calcium (Ca), magnesium (Mg), Fe, silica (Si) and other micro elements (S, Cl, Na, Mn, Zn, B, Mo etc.) are supplied by Nutrient Solution Production Subsystem (NSPS) to crops in the closed plantation module (PM). NSPS makes appropriate hydroponic solutions for each crop from wet oxidized (W/O) solution, NH₃, NH₄NO₃, condensed water, and also reagent solutions for complementation of deposited elements during W/O process.

NSPS is composed of hardware and software for solution sampling, element/ion concentration analysis and nutrient solution adjusting in 1999. Installations for element/ion concentration analysis include a NH₄ analyzer, a PO₄ analyzer, a multiple ion meter for K⁺, NO₃⁻ and Ca²⁺, and a atomic absorption spectrophotometer (AAS) for Mg and Fe. Before adjusting each solution, element/ion concentrations in W/O solution and remaining solution in the mixing tank are measured. Based on these measurements and target concentration of each element, volumes of W/O solution, water, and reagent solutions to be mixed are calculated, and then adjustment is conducted automatically. After each adjustment, each element/ion concentration in the nutrient solution is measured. So, information of mineral elements sent to PM can be obtained using data from NSPS.