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A microwave powered solid waste stabilization and water recovery prototype was delivered to Ames Research Center through an SBIR Phase II contract awarded to Umpqua Research Company. The system uses a container capable of holding 5.7 dm3 volume of waste. The microwave power can be varied to operate either at full power (130 W) or in a variable mode from 0% and 100%. Experiments were conducted with different types of wastes (wet cloth, simulated feces/diarrheal wastes, wet trash and brine) at different levels of moisture content and dried under varying microwave power supply. This paper presents the experimental data. The results provide valuable insight into the different operation modes under which the prototype can be used to recover water from the wastes in a space environment. Further investigations and testing of the prototype are recommended.

Water is of critical importance to space missions due to crew needs and the cost of supply. To control mission costs, it is essential to recycle water from all available wastes - both solids and liquids. Water recovery from liquid water wastes has already been accomplished on space missions. For instance, a Water Recycling System (WRS) is currently operational on the International Space Station (ISS). It recovers water from urine and humidity condensate and processes it to potable water specifications. However, there is more recoverable water in solid wastes such as uneaten food, wet trash, feces, paper and packaging material, and brine. Previous studies have established the feasibility of obtaining a considerable amount of water and oxygen from these wastes (Pisharody et al, 2002; Fisher et al, 2008; Wignarajah et al, 2008).

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid and/or gaseous products. The pyrolysis processing of pure and mixed solid waste streams has been under investigation for several decades for terrestrial use and a few commercial units have been built for niche applications. Pyrolysis has more recently been considered for the processing of mixed solid wastes in space. While pyrolysis units can easily handle mixed solid waste streams, the dependence of the pyrolysis product distribution on the component composition is not well known. It is often assumed that the waste components (e.g., food, paper, plastic) behave independently, but this is a generalization that can usually only be applied to the overall weight loss and not always to the yields of individual gas species.

A Microwave Enhanced Freeze Drying Solid Waste (MEFDSW) processor was delivered to NASA-Ames Research Center by Umpqua Company having been funded through a Small Business Innovative Research Phase II program. The prototype hardware was tested for its performance characteristics and for its functionality with the primary focus being the removal of water from solid wastes. Water removal from wastes enables safe storage of wastes, prevents microbes from growing and propagating using the waste as a substrate and has potential for recovery and reuse of the water. Other objectives included measurements of the power usage and a preliminary estimate of the Equivalent System Mass (ESM) value. These values will be used for comparison with other candidate water removal technologies currently in development.

Since the mid 1980s, NASA has developed advanced waste management technologies that collect and process waste. These technologies include incineration, hydrothermal oxidation, pyrolysis, electrochemical oxidation, activated carbon production, brine dewatering, slurry bioreactor oxidation, composting, NOx control, compaction, and waste collection. Some of these technologies recover resources such as water, oxygen, nitrogen, carbon dioxide, carbon, fuels, and nutrients. Other technologies such as the Waste Collection System (WCS - the commode) collect waste for storage or processing. The need for waste processing varies greatly depending upon the mission scenario. This paper reviews the waste management technology development activities conducted by NASA since the mid 1980s and explores the drivers that determine the application of these technologies to future missions.

Handling and processing human feces in space habitats is a major concern and needs to be addressed for the Crew Exploration Vehicle (CEV) as well as for future exploration activities. In order to ensure crew health and safety, feces should either be isolated in a dried form to prevent microbial activity, or be processed to yield a non-biohazardous product using a reliable technology. During laboratory testing of new feces processing technologies, use of “real” feces can impede progress due to practical issues such as safety and handling thereby limiting experimental investigations. The availability of a non-hazardous simulant or analogue of feces can overcome this limitation. Use of a simulant can speed up research and ensure a safe laboratory environment. At Ames Research Center, we have undertaken the task of developing human fecal simulants. In field investigations, human feces show wide variations in their chemical/physical composition.

Pyrolysis is a technology that can be used on future space missions to convert wastes to an inert char, water, and gases. The gases can be easily vented overboard on near term missions. For far term missions the gases could be directed to a combustor or recycled. The conversion to char and gases as well as the absence of a need for resupply materials are advantages of pyrolysis. A major disadvantage of pyrolysis is that it can produce tars that are difficult to handle and can cause plugging of the processing hardware. By controlling the heating rate of primary pyrolysis, the secondary (cracking) bed temperature, and residence time, it is possible that tar formation can be minimized for most biomass materials. This paper describes an experimental evaluation of two versions of pyrolysis reactors that were delivered to the NASA Ames Research Center (ARC) as the end products of a Phase II and a Phase III Small Business Innovation Research (SBIR) project.