Development and Design of a Low Temperature Solid Waste Oxidation and Water Recovery System

In February 2004 NASA released “The Vision for Space Exploration.” The goals outlined in this document include extending the human presence in the solar system, culminating in the exploration of Mars. A key requirement for this effort is to identify a safe and effective method to process waste. Methods currently under consideration include incineration, microbial oxidation, pyrolysis, drying, 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 work is to develop a low temperature oxidation process to convert waste cleanly and rapidly to carbon dioxide and water.

Previously, TDA Research, Inc. demonstrated the potential of a low temperature dry oxidation process using ozone in a small laboratory reactor. Currently, TDA and NASA Ames Research Center are developing a pilot scale low temperature ozone oxidation system to convert organic waste to CO₂ and H₂O. The system also disinfects the waste and remaining water, and recovers not only the water content of the waste but also generates additional water that can be utilized by the crew. Tests are being conducted with model wastes in a reactor design that maximizes the contact between the reactants by mixing the waste with water, which also makes the oxidation process extremely selective to CO₂ and H₂O and mitigates the rapid combustion events that were seen in the dry oxidation reactor. An ozone recycle loop was recently added to the system, which significantly increased the waste oxidation rates. The reactor operating conditions were then optimized using the design of experiments technique to maximize the waste oxidation rate. Currently, a pilot scale, fully automated system is being designed that will be capable of handling many different types of waste. The waste oxidation rates achieved to date, along with current waste generation rate models, indicate that all of the waste from a single crew member in one day can be processed in a vessel ranging in size from 8.2 liters (2.2 gallons) for a short term mission to 9.9 liters (2.6 gallons) for a long term mission. In addition, if the system were used solely as a fecal matter oxidizer the reactor size would be only 0.7 liters. At the conclusion of the project the system will be delivered to NASA Ames for evaluation.