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Although chemical methods have been proposed to remove soluble organic matter (SOM) from hydroponic solutions, it may be a benefit to retain this material to improve nutrient solution mineral bioavailability. Like chelates, SOM can enhance bioavailability by complexing nutrient ions, and thus, preventing precipitate formation. Iron phosphate is a common precipitate that forms in hydroponic and soil solutions. Initial studies have shown that wheat (Triticum aestivum L. cv. Apogee) plants grown in solution culture containing 35 μM Fe supplied as either FeCl3 + HEDTA, or FeCl3 + HA (commercial humic acid) resulted in comparable growth and seed yields. Leaf tissue Fe content was similar between treatments but Zn concentrations were greater in leaves grown with HA until 42 days, after which there were no treatment differences. Ongoing studies will isolate and chemically characterize the SOM obtained from bioreactor effluents and examine their role in nutrient bioavailability.

A CELSS has been defined based on current or near-term technology. The CELSS was sized to support the metabolic load of four people on the Moon for ten years. A metabolic load of 14 MJ/person/day is assumed, including an average of 2.6 hr of EVA/person/day. Close to 100% closure of water, and oxygen, and 85% closure of the food loop is assumed. With 15% of the calories supplied from Earth, this should provide adequate dietary variety for the crew along with vitamin and mineral requirements. Other supply and waste removal requirements are addressed. The basic shell used is a Space Station Freedom 7.3 m (24 ft) module. This is assumed to be buried in regolith to provide protection from radiation, meteoroids, and thermal extremes. A solar dynamic power system is assumed, with a design life of 10 years delivering power at 368 kWh/kg. Initial estimates of size are that 73 m2 of plant growth area are required, giving a plant growth volume of about 73 m3.