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The use of composting technology is attractive to NASA’s Bioregenerative Life Support System (BLSS) research because it offers a potential reduction in system costs when compared to other waste recycling approaches. Water-soluble leachates from 28-day composted fresh or oven-dried inedible wheat biomass were amended with reagent-grade nutrients to be inorganically equivalent to ½-strength Hoagland’s (control) replenishment solution. A portion of the fresh and oven-dried compost leachate was filtered to remove large organic particles and a majority of the microflora, and wheat plants were grown hydroponically on these amended leachates. For both the fresh and oven-dried compost leachate treatments, filtering the leachate had no effect on plant response. No significant difference was observed between the fresh compost leachate treatments and the control.

A primary challenge for supporting plants in space is to provide as much photosynthetically active radiation (PAR) as possible, while conserving electrical power. Light-emitting diodes (LEDs) and microwave lamps are innovative artificial lighting technologies with several appealing features for supporting plant growth in controlled environments. Because of their rugged design, small mass and volume, and narrow spectral output, red and blue LEDs are particularly suited for outfitting plant growth hardware in spaceflight systems. The sulfur-microwave electrode-less high-intensity discharge (HID) produces a bright broad-spectrum visible light at a higher electrical conversion efficiency than conventional light sources. Experiments compared the performance and productivity of spinach (Spinacia oleracea L.) grown under conventional lighting sources (high-pressure sodium and cool-white fluorescent lamps) with microwave lamps and various wavelengths of red LEDs.

Plant growth conditions must be optimized for use in advanced life support systems during space flight. Wheat cv. Apogee was grown in a nutrient delivery system (NDS) using porous tubes held at three levels of applied water pressure (Pw), or suction: −0.5 kPa, −0.3 kPa, and −0.1 kPa for 24 days. Measurements of leaf area and dry mass were made at 5, 9, 14, 18 and 24 DAP and used to determine the leaf area index (LAI), net assimilation rate (NAR), and crop growth rate (CGR). Pw did not have a significant effect on plant development until after 9 DAP, at which time growth at different treatments began to diverge. Plants grown at −0.1 kPa exhibited the largest CGR and LAI and had the greatest biomass, suggesting that −0.1 kPa was the optimal Pw. Growth analysis indicated that changes in CGR were due to changes in leaf area, rather than changes in photosynthesis.

Ground studies at Kennedy Space Center were conducted to determine microbial requirements of the Immobilized Microbe Microgravity Water Processing System (IMMWPS), a denitrifying, fixed-bed reactor designed for Shuttle flight-testing. The reactor was operated with a simulated graywater “waste stream” containing the surfactant Igepon TC-42TM as the sole carbon source. Experiments were conducted to determine the effect of hydraulic retention time (HRT) and feed nutrient composition on surfactant degradation. The source of inoculum as well as procedure for inoculating the reactor was also examined. A complete nutrient mix in the feed formulation was required for sustained Igepon degradation throughout the reactor runs at the short (1.4 days) and intermediate (1.9 days) hydraulic retention time (HRT), regardless of inoculum source.

Future large-scale ALS systems may use hydroponic nutrient delivery systems (NDS) for growing staple and salad crops. Crop performance is strongly dependent on dissolved O2 concentration (DOC), pH, and nutrient content of the hydroponic solution. DOC is influenced by solution temperature and flow rate, growth rate of the crop, and the bacterial community present in the solution. Solution temperature determines the solubility of O2 in water, and may increase as solution volume is reduced to minimize overall system mass. Flow may be altered when the height of the solution bathing the root zone is reduced because of dense root mats. These factors may produce anaerobic pockets where N2 losses by denitrification occur, but without yield losses, as long as sufficient O2 to meet root respiration is supplied. Bacterial communities may compete for DOC with the plants when the NDS is used for recycling gray water streams.

A 24-day test of the science protocols for the PESTO (Photosynthesis Experiment System Testing and Operation) experiment was conducted in the Biomass Production System (BPS) flight hardware. One objective of these experiments was to identify the optimum times during the life cycle for characterizing canopy level evapotranspiration and photosynthesis under closed atmosphere conditions in the BPS. Carbon dioxide and light response curves were obtained at three stages of development on two dwarf wheat cultivars, Apogee and Super Dwarf. Net daily carbon assimilation rates were derived from CO2 additions to each chamber and the relative growth rate of each cultivar was determined. Evapotranspiration rates were derived from water additions to the rooting matrix through the nutrient delivery system and water vapor removal from the atmosphere though the humidity control system.

The overall objective of a NASA Research Announcement funded project at Kennedy Space Center (KSC) is to determine the optimal Advanced Life Support (ALS) solid waste bioprocessing system with the limited goal of nutrient recycling as part of a potential hybrid biological-physical chemical (PC) system. Bioprocess research towards this objective has focused on comparing two bioreactor technologies: (1) continuous stirred tank reactor (CSTR)-suspension culture and (2) continuous flow fixed-film bioreactor (FFB)-which utilizes biofilms to remove organic constituents from crop residue leachate solutions. For optimizing the CSTR we studied the effects of solids loading rate (160, 240, and 320 grams dry weight [gdw] day−1) and stirrer speed (45, 90, 180, and 360 rpm) on the vertical distribution (5 depths) of dissolved oxygen (> 90% oxygen in aeration gas) and total suspended solids in a CSTR operated at an hydraulic retention time (HRT) of 1.25 days.