In February 2004 NASA released “The Vision for Space Exploration.” The important goals outlined in this document include extending human presence in the solar system culminating in the exploration of Mars. Unprocessed waste poses a biological hazard to crew health and morale. The waste processing methods currently under consideration include incineration, microbial oxidation, pyrolysis and compaction. Although each has advantages, no single method has yet been developed that is safe, recovers valuable resources including oxygen and water, and has low energy and space requirements. Thus, the objective of this project is to develop a low temperature oxidation process to convert waste cleanly and rapidly to carbon dioxide and water.
In the Phase I project, TDA Research, Inc. demonstrated the potential of a low temperature oxidation process using ozone. In the current Phase II project, TDA and NASA Ames Research Center are developing a pilot scale low temperature ozone oxidation system. We are conducting tests in a reactor design that maximizes the contact between the ozone and the waste bed. In initial tests with a large volume reactor we were able to achieve higher oxidation rates than we obtained in the Phase I portion of this project. However, on occasion, the waste began to burn rapidly, producing high temperature and pressure spikes in the reactor. Therefore, we redesigned the reactor to mitigate the rapid ignition of the waste. In initial tests, we found that adding water to the waste bed and flowing ozone through the water-waste mixture provides much better control of the low temperature oxidation process. The addition of water likely produces a more uniform temperature throughout the waste, reducing localized hot spots that initiated the rapid combustion process. In addition, we have obtained better agreement between the gravimetric data and the results calculated with integrated CO2 data, indicating that a higher percentage of waste has been oxidized to CO2 and H2O before exiting the reactor.
Once we have optimized the reactor design and waste oxidation process we will incorporate the design into a closed loop, fully automated system that will convert the waste into H2O and CO2, remove both compounds, and replenish the circulating gas stream with oxygen and ozone as needed. In addition, the system will contain the analytical equipment necessary to carry out a complete material balance and monitor the formation of pollutants such as NOX and SOX. At the conclusion of the project the system will be delivered to NASA Ames for their use and evaluation.