Kanapathipillai Wignarajah

Can incineration technology convert CELSS wastes to resources for crop production? A working hypothesis and some preliminary findings.

Considerable evidence exists to support the hypothesis that human-generated wastes can be utilized as resources in crop production. In the waste mix from a Closed Ecological Life Support System (CELSS), the elemental resources are found mainly in the solid fraction. In order to make these resources available for crop growth, it is necessary to convert the solid wastes to either an aqueous or a gaseous phase. Incineration is one method for processing solid wastes to produce a gaseous fraction and a small solid fraction of ash. Evidence from literature provides a compelling case for a working hypothesis that plants can utilize the gases of incineration. Although uptake and utilization of inorganic elements in the aqueous phase is well established, the uptake and utilization of inorganic elements in the gaseous phase, with the exception of CO2 and O2, is not fully understood. This paper attempts to (a) summarize existing literature on uptake/metabolism of inorganic elements in the gaseous fraction, with the exception of CO2 and O2 and (b) develop a working hypothesis to predict the use of incineration flue gases by plants. Preliminary experimental findings on effects of carbon monoxide, a component of the flue gas, are also presented.

Development of the Heat Melt Compactor for Waste Management during Long Duration Human Space Missions

Solid Waste handling and management in space habitats poses serious challenges for long duration human space missions. These wastes typically contain a high quantity of plastic from packaging as well as personal hygiene wastes, wet and dry wipes, gloves, duct tape, and unused food items. The unused food and personal hygiene wastes present substrates for growth of microorganisms that can seriously affect astronaut health and consequently mission success. The heat melt compaction process uses heat to sterilize and dry the waste, and the plastic content to bond and encapsulate the various waste items into a hard tile. The tile that is produced in the heat melt compaction process is tough, extremely compact, and has a predictable shape that allows the efficient use of very limited spacecraft storage volume. The encapsulation of the waste in the melted plastic isolates the growth substrate from spacecraft cabin air to prevent reinoculation of the waste. Plastic wastes contain a high percentage of hydrogen which is considered a desirable material for radiation shielding because it does not produce secondary radiation. Collaborative work with MSFC personnel on evaluating the effectiveness of tiles produced in the Heat Melt Compactor as a shielding material against radiation is in progress. Progress on the development of the next generation Heat Melt Compactor hardware is also presented.

Reactive Carbon from Life Support Wastes for Incinerator Flue Gas Cleanup

This paper presents the results from a joint research initiative between NASA Ames Research Center and Lawrence Berkeley National lab. The objective of the research is to produce activated carbon from life support wastes and to use the activated carbon to adsorb and chemically reduce the NO(sub x) and SO(sub 2) contained in incinerator flue gas. Inedible biomass waste from food production is the primary waste considered for conversion to activated carbon. Results to date show adsorption of both NO(sub x) and SO(sub 2) in activated carbon made from biomass. Conversion of adsorbed NO(sub x) to nitrogen has also been observed.

Microwave-Assisted Pyrolysis of Solid Waste

In this paper, results of further work on pyrolysis processing of mixed solid wastes for spacecraft applications are reported. A domestic microwave oven was modified for scoping studies in which the effects of sample size and the use of distributed versus central microwave absorbers were studied. Experiments were done with wheat straw and included those in which the sample was rotated during pyrolysis in order to improve heating uniformity. The experiments using central microwave absorbers of various compositions included a ferrite rod, a quartz tube filled with activated carbon, and silicon carbide. The ability to monitor the sample temperature and sample heating uniformity during microwave heating was demonstrated. A comparison was made with conventional pyrolysis experiments in an electrically heated furnace to a similar final temperature. In general, it was found that microwave heating reduced the energy demand by about 50% and increased the yield of gas products by about 100%, while reducing the char yield about 20%.

Impregnation of Catalytic Metals in Single-Walled Carbon Nanotubes for Toxic Gas Conversion in Life Support System

Carbon nanotubes (CNTs) possess extraordinary properties such as high surface area, ordered chemical structure that allows functionalization, larger pore volume, and very narrow pore size distribution that have attracted considerable research attention from around the world since their discovery in 1991. The development and characterization of an original and innovative approach for the control and elimination of gaseous toxins using single walled carbon nanotubes (SWNTs) promise superior performance over conventional approaches due to the ability to direct the selective uptake of gaseous species based on their controlled pore size, increased adsorptive capacity due to their increased surface area and the effectiveness of carbon nanotubes as catalyst supports for gaseous conversion. We present our recent investigation of using SWNTs as catalytic supporting materials to impregnate metals, such as rhodium (Rh), palladium (Pd) and other catalysts. A protocol has been developed to oxidize the SWNTs first and then impregnate the Rh in aqueous rhodium chloride solution, according to unique surface properties of SWNTs. The Rh has been successfully impregnated in SWNTs. The Rh-SWNTs have been characterized by various techniques, such as TGA, XPS, TEM, and FTIR. The project is funded by a NASA Research Announcement Grant to find applications of single walled nanocarbons in eliminating toxic gas Contaminant in life support system. This knowledge will be utilized in the development of a prototype SWNT KO, gas purification system that would represent a significant step in the development of high efficiency systems capable of selectively removing specific gaseous for use in regenerative life support system for human exploration missions.

Methane Production from Pyrolysis of Mixed Solid Wastes

There has recently been an increased interest in using pyrolysis of mixed solid wastes in space or on planetary surfaces to produce methane for applications in propulsion and for power generation using fuel cells. This paper involves a review of previous pyrolysis results collected at Advanced Fuel Research, Inc. (AFR) and elsewhere to determine how the pyrolysis conditions and feedstock composition affect methane yields. In general, the production of methane from primary pyrolysis of most biomass materials is pretty modest, 0.1 to 2.5 wt. % for a wide range of materials, with an average slightly above 1.2 wt. % (dry, ash-free basis). The primary pyrolysis yield variations for methane (and other species) with biomass sample type are well described using a simple Neural Network model. In pyrolysis experiments that include significant secondary reactions (e.g., tar cracking), the methane yield can be increased by a factor of 2-3. The methane yield can also be increased significantly by increasing the plastic component of the mixed waste stream (e.g., by the addition of polyethylene), but would be unlikely to exceed 15 wt. % by conventional, low-pressure pyrolysis of a typical mixed waste stream. The use of high pressure (>500 psig) pyrolysis in pure hydrogen is one approach that could be used to increase the methane yield even further. However, this approach would require a much heavier reactor unit, high pressures, and the associated safety concerns. An alternative pathway to higher methane yields would be to oxidize the waste completely to carbon dioxide and water and use the Sabatier reaction to convert the carbon dioxide to methane.

Investigating the Partitioning of Inorganic Elements Consumed by Humans between the Various Fractions of Human Wastes - An Alternative Approach

The elemental composition of food consumed by astronauts is well defined. The major elements carbon, hydrogen, oxygen, nitrogen and sulfur are taken up in large amounts and these are often associated with the organic fraction (carbohydrates, proteins, fats etc) of human tissue. On the other hand, a number of the elements are located in the extracellular fluids and can be accounted for in the liquid and solid waste fraction of humans. These elements fall into three major categories - cationic macroelements (e.g. Ca, K, Na, Mg and Si), anionic macroelements (e.g. P, S and Cl and 17 essential microelements, (e.g. Fe, Mn, Cr, Co, Cu, Zn, Se and Sr). When provided in the recommended concentrations to an adult healthy human, these elements should not normally accumulate in humans and will eventually be excreted in the different human wastes. Knowledge of the partitioning of these elements between the different human waste fractions is important in understanding (a) developing waste separation technologies, (b) decision-making on how these elements can be recovered for reuse in space habitats, and (c) to developing the processors for waste management. Though considerable literature exists on these elements, there is a lack of understanding and often conflicting data. Two major reasons for these problems include the lack of controlled experimental protocols and the inherently large variations between human subjects (Parker and Gallagher, 1988). We have used the existing knowledge of human nutrition and waste from the available literature and NASA documentation to build towards a consensus to typify and chemically characterize the various human wastes. It is our belief, that this could be a building block towards integrating a human life support and waste processing in a closed system.

Inhibitory effect of hypergravity on photosynthetic carbon dioxide fixation in Euglena gracilis.

Photosynthesis, the conversion of light energy into chemical energy, is a critical biological process, whereby plants synthesize carbohydrates from light, carbon dioxide (CO2) and water. The influence of gravity on this biological process, however, is not well understood. Thus, centrifugation was used to alter the gravity environment of Euglena gracilis grown on nutritive agar plates illuminated with red and blue light emitting diodes. The results showed that hypergravity (up to 10xg) had an inhibitory effect on photosynthetic CO2 fixation. Chlorophyll accumulation per cell was essentially unaffected by treatment; however, Chl a/Chl b ratios decreased in hypergravity when compared to 1xg controls. Photosynthesis in Euglena appears to have limited tolerance for even moderate changes in gravitational acceleration.

A Prototype Microwave Pyrolyzer for Solid Wastes

This paper continues previous work on pyrolysis processing of solid wastes for spacecraft and planetary surface applications. A prototype microwave pyrolyzer apparatus was designed, constructed and tested. Experiments were done with cellulose, wheat straw and two formulations of a feces simulant. A central microwave absorber was used consisting of a quartz tube filled with activated carbon. The pyrolyzer included a primary pyrolysis zone and a secondary cracking zone consisting of a SiC bed. The cracking zone temperature ranged from ~ 850 to 1000 °C. The sample was inserted into the (primary) microwave heating zone after the cracking bed temperature was stabilized to ~ 950 °C. Analysis of the gas products was performed by both FTIR spectroscopy and mass spectrometry. The sample sizes were 15-20 g for wheat straw, 40 g for cellulose and 100 g for the feces simulants. The cellulose sample was not run to completion, but was interrupted to provide photographic evidence that microwave heating using a central microwave absorber results in pyrolysis beginning near the center of the sample and proceeding in an outward fashion. For the wheat straw and feces simulant samples, it was found that, on a per-gram basis, the yields of ethylene, methane, and hydrogen were significantly higher than a previous pyrolyzer that was based on a modified domestic microwave oven. This result was mainly attributed to the presence of a separate cracking zone in the current pyrolyzer.

A Hybrid Pyrolysis / Oxidation System for Solid Waste Resource Recovery

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid, and/or gaseous products. The main disadvantages of pyrolysis processing are: (1) the product stream is more complex than for many of the alternative treatments; (2) the product gases cannot be vented directly into the cabin without further treatment because of the high CO concentrations. One possible solution is to combine a pyrolysis step with catalytic oxidation (combustion) of the effluent gases. This integration takes advantage of the best features of each process. The advantages of pyrolysis are: insensitivity to feedstock composition, no oxygen consumption, and batch operation. The main advantage of oxidation is the simplicity and consistency of the product stream. In addition, this hybrid process has the potential to result in a significant reduction in Equivalent System Mass (estimated at 10-40%) and system complexity. This paper includes data from a laboratory study of a hybrid pyrolysis/oxidation process, including results for the following cases: 1) without post-oxidation; 2) with post-oxidation; 3) with catalyzed post-oxidation.