Pyrolysis Processing for Solid Waste Resource Recovery in Space

The NASA objective of expanding the human experience into the far reaches of space will require the development of regenerable life support systems. A key element of these systems is a means for solid waste resource recovery. The objective of this work was to demonstrate the feasibility of pyrolysis processing as a method for the conversion of solid waste materials in a Controlled Ecological Life Support System (CELSS). A pyrolysis process will be useful to NASA in at least four respects: 1) it can be used as a pretreatment for a combustion process; 2) it can be used as a more efficient means of utilizing oxygen and recycling carbon and nitrogen; 3) it can be used to supply fuel gases to fuel cells for power generation; 4) it can be used as the basis for the production of chemicals and materials in space. A composite mixture was made consisting of 10% polyethylene, 15% urea, 25% cellulose, 25% wheat straw, 20% Gerepon TC-42 (space soap) and 5% methionine. Pyrolysis of the composite mixture produced light gases as the main products (CH₄, H₂, CO₂, CO, H₂O, NH₃) and a reactive carbon-rich char as the main byproduct. Significant amounts of liquid products were formed under less severe pyrolysis conditions, but these were cracked almost completely to gases as the temperature was raised. A primary pyrolysis model was developed for the composite mixture based on an existing model for whole biomass materials. An artificial neural network model was also used successfully to model the changes in gas composition with the severity of pyrolysis conditions.