Process

Overview

Our proposed process is shown in Figure 1.

In the first step of the process, astronaut’s feces are collected into a storage tank using a vacuum toilet. Feces are then transferred into another tank and left to ferment for 3 days with natural gut flora to increase the concentration of volatile fatty acids (VFAs) that are later consumed by engineered E. coli to produce PHB. Next, the liquid containing VFA is separated from solid particles using centrifugation followed by filtration. The resulting liquid containing VFA is then passed to another storage tank. From there, VFA are added to a fermenter inoculated with PHB-producing E. coli. Lastly, produced PHB is extracted from the liquid harvest stream. Produced PHB can be used in Selective Laser Sintering (SLS) 3D printer without additional processing.

Applied Design

We continuously improved our process design based on feedback received from space industry professionals including astronauts Dr. Robert Thirsk and Chris Hadfield, Dr. Matthew Bamsey, who is a Chief Systems Engineer at the German Aerospace Center, and Dr. Pascal Lee, who is a principal investigator of the Haughton-Mars Project at NASA Ames Research Center and a co-founder of the Mars Institute. We used Equivalent System Mass guidelines, a method advised by NASA, to evaluate the feasibility of various process designs and followed NASA’s Life Support Baseline Values and Assumptions. Furthermore, we considered applications for solid human waste that NASA is studying and whether the by-products of our process have any useful applications. Lastly, we considered the safety of our design as it was identified as an important design criteria by many of the experts we interviewed. More detailed description of the applied design can be found here.