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Solid Waste Management (SWM) systems of current and previous space flight missions have employed relatively uncomplicated methods of waste collection, storage and return to Earth. NASA's long-term objectives, however, will likely include human-rated missions that are longer in both duration and distance, with little to no opportunity for re-supply. Such missions will likely exert increased demands upon all sub-systems, particularly the SWM system. In order to provide guidance to SWM Research and Technology Development (R&TD) efforts and overall system development, the establishment of appropriate SWM system requirements is necessary. Because future long duration missions are not yet fully defined, thorough mission-specific requirements have not yet been drafted.

Long duration missions pose substantial new challenges for solid waste management in Advanced Life Support (ALS) systems. These possibly include storing large volumes of waste material in a safe manner, rendering wastes stable or sterilized for extended periods of time, and/or processing wastes for recovery of vital resources. This is further complicated because future missions remain ill-defined with respect to waste stream quantity, composition and generation schedule. Without definitive knowledge of this information, development of mission requirements is hampered. Additionally, even if waste streams were well characterized, other operational and processing needs require clarification (e.g. resource recovery requirements and planetary protection constraints). Therefore, the development of solid waste management (SWM) subsystem requirements for long duration space missions is an inherently uncertain, complex and iterative process.

Solid Waste Management (SWM) requirements need to be defined prior to determining what technologies should be developed by the Advanced Life Support (ALS) Project. Since future waste streams will be highly mission-dependent, missions need to be defined prior to developing SWM requirements. The SWM Working Group has used the mission architectures outlined in the System Integration, Modeling and Analysis (SIMA) Element Reference Missions Document (RMD) as a starting point in the requirement development process. The missions examined include the International Space Station (ISS), a Mars Dual Lander mission, and a Mars Base. The SWM Element has also identified common SWM functionalities needed for future missions. These functionalities include: acceptance, transport, processing, storage, monitoring and control, and disposal. Requirements in each of these six areas are currently being developed for the selected missions.

Bioprocessing of human fecal wastes may be an important means for recycling of crop nutrients within a closed Advanced Life Support System. The objectives of this study were to determine the levels of key crop nutrients that can be extracted from human feces that had been autoclave sterilized vs. those that had not. When compared with inedible ALS grown wheat residues, the contribution of feces, which has an ash content 13% to the total potential, recoverable minerals may be small. This paper discusses results from bioreactor runs obtained using continuous stirred tank reactors with an 8 day batch culture of autoclaved or not autoclaved feces. The results suggest that feces should not be autoclaved if mineral recovery is desired. Biodegradation of feces ranged from 27 to 39% in 8 days, with 67 to 79% reduction in soluble total organic carbon (TOC) and concomitant production of carbon dioxide (CO2).

As part of NASA’s continued interest in the feasibility of Bioregenerative Life Support Systems (BLSS), research has focused on increasing the efficiency of bioregenerative technology. To reduce the costs associated with recovery of plant nutrients from inedible crop biomass, composting combined with leaching appears to be an attractive alternative to continuously stirred tank reactors. Tests at Kennedy Space Center investigating the effects of pre-processing of inedible wheat biomass composted for 21 days prior to leaching on nutrient recovery and growth of a subsequent wheat crop have been performed. In long-term hydroponic tests, pre-processed compost leachate was amended with reagent grade nutrients to approximate half-strength Hoagland’s solution. Although reductions in growth and yield were observed for plants grown on pre-processed compost leachate compared to the control, the differences were not statistically significant.

Bioreactor technology for bioprocessing graywater solutions in microgravity is under development by NASA at Johnson Space Center and at major aerospace companies. Inoculum sources have been inconsistent. Startup and subsequent operation of ground-based bioreactors may have been adversely affected by this inconsistency and/or by inoculation procedures. The goal of the research reported in this paper is to develop an inoculum that will completely biodegrade Igepon T42 soap to carbon dioxide and water under anaerobic, denitrifying conditions and with process conditions set by bioreactor design requirements for microgravity operation. Potential inoculum sources from two habitats within the KSC-ALS breadboard project were developed for potential use. The effects of pH (7.2 vs. 9.0, buffered) on soap degradation by the two inocula was determined in a flask study. Nearly all of the soap was degraded at pH 7.2 while nearly none was degraded at pH 9.0. Both inocula behaved similarly.

The KSC Breadboard Scale Aerobic Bioreactor (B-SAB) was used to bioprocess inedible wheat crop residues to provide recycled nutrients to support crop growth in the JSC Variable Pressure Growth Chamber (VPGC) as part of the 91 day JSC-Lunar/Mars Life Support Test Project Phase III. To meet the wheat nutrient demand at JSC, the KSCB-SAB was operated at both a higher loading rate (35 gdw L-1 compared with 20 gdw L-1) and at a slower retention time (21 days compared with 8 days) than we had used in previous bioreactor (continuous stirred tank reactor - CSTR) studies. The bioreactor operated for 19 weeks-8 weeks startup and steady state stabilization then 11 weeks of operation with the broth harvested weekly. Filtered broth was amended with nutrients and transported to JSC for integration into the VPGC wheat growth component of L/MLSTP Phase III. Biodegradation of JSC wheat residues was a constant 45% during steady state bioreactor operation, and similar to previous B-SAB runs.

NASA's Advanced Life Support Breadboard Project at Kennedy Space Center focuses on biological regeneration of essential commodities for long-term space missions. If plants are grown on these missions, roughly 50% of the biomass will be inedible. Composting can reduce the volume of inedible biomass, reduce levels of leachable soluble organics, and produce a mineral-rich leachate that can be used to provide nutrients to subsequent generations of plants. Other wastes will also be generated on space missions; co-composting of these wastes should increase the rate and extent of degradation and should assist in control of moisture content during composting. To investigate these assumptions, we added simulated human solid waste to freshly harvested inedible wheat biomass and composted the mixture for 21 days.

Bioregenerative resource recovery components for Advanced Life Support systems will need to be reliable and stable for long duration space travel. Since 1989, bioregenerative life support research at the ALS Breadboard Project has examined processing of inedible crop residues in bioreactors for recovery of nutrients for replenishment of crop hydroponic solutions. Bioreactor operation has been reliable as demonstrated by continuous operation for up to 418 days with long periods of steady state conditions. Bioreactors have demonstrated stability following unplanned, non-lethal perturbations in pH, temperature, dissolved oxygen, and inedible residue supply. In each instance, a rapid return to steady state conditions was observed.

Regenerative life support systems are under development to reduce the need for resupply of essential commodities during long duration space missions. If higher plants are used to supply food, oxygen, and potable water, composters could be used to stabilize solid wastes, provide CO2 and nutrients to the plants, and achieve pathogen reduction. Small-scale aerobic composting was used successfully to degrade organic compounds in inedible potato biomass. Soluble nutrients were extracted from the compost at concentrations that supported seed germination. Further work is indicated to understand the inhibitory effects of some leachates. Future composter designs should allow improved performance through better instrumentation and process control.

A Breadboard-Scale Aerobic Bioreactor (B-SAB) has been designed and integrated with the Kennedy Space Center's Biomass Production Chamber (BPC). The bioreactor utilizes a mixed microbial community to biodegrade inedible plant residues, a component of a Controlled Ecological Life Support System (CELSS) waste-stream. The continuously stirred tank reactor (120 L working volume) supports nutrient recycling and secondary food production experiments, and can process an influent with a solids loading as high as 50 g L-1. The volumetric oxygen mass transfer coefficient, kLa, is 0.013 s-1. Nutrient solution for BPC lettuce and wheat crops has been produced. Currently, B-SAB is supplying 80% of the nutrients for 10 m2 of potato plants in a continuous production experiment.