Torrefaction Processing for Human Solid Waste Management

The NASA SBIR Phase I project addressed the technical feasibility of an innovative torrefaction (mild pyrolysis) processing system that can be used to sterilize feces and produce a stable, odor-free solid product than can be easily stored or recycled, while simultaneously recovering moisture and producing small amounts of other useful products. The Phase I project demonstrated that mild heating (200-250 C) was adequate for torrefaction of a fecal simulant and other analogs of human solid waste (canine feces). The net result was a nearly undetectable odor, complete recovery of moisture, some additional water production, a modest reduction of the dry solid mass and the production of small amounts of gas (mainly CO2) and liquid (mainly water). The amount of solid vs gas plus liquid products can be controlled by adjusting the torrefaction conditions (final temperature, holding time). The solid product was a dry material that did not support microbial growth and was hydrophobic relative to the starting material. In the case of canine feces, the solid product was a mechanically friable material that could be easily compacted to a significantly smaller volume (~50%). In addition, the torrefaction method can be applied using the same or similar conditions to other types of wet solid wastes and is compatible with the Universal Waste Management System (UWMS), now under development by NASA. The torrefaction process could also be accomplished with minimal crew interactions and modest energy requirements, which could be improved even further in an optimized and innovative Phase II Torrefaction Processing Unit (TPU), which is the objective of the current proposal.