Our Project

The Problem

Governments and private enterprises alike are gearing up for travel across our Solar System. Plans to colonize nearby planets are underway, with Elon Musk spearheading the initiative to put a human colony on Mars by 2030. In a parallel vein, NASA is planning a manned exploratory mission to Mars as soon as the 2030s. Several other space agencies have similar plans and timelines for their own respective Mars explorations. This exciting time in our history nonetheless comes with the challenges of long-term space travel.

Two ecological and economical challenges arise:

1. the sustainable management of waste produced in space, and
2. the high cost of shipping materials to space.

Waste management on Mars will be paramount because manned missions will need to recover as much water and oxygen as possible to sustain life. Human waste must also be treated to minimize health risks for the crew of a Mars mission. All of this must be accomplished while preserving the natural Martian environment.

The current cost of shipping materials up to space is $10,000 USD per pound due to the high price of fuel (Hsu, 2011). This expense will limit early Mars mission crews in the supplies that they can bring or ship from Earth to Mars, and may not allow astronauts to account for every tool they may require during their mission. One way to mitigate this challenge is to develop a system to produce necessary items in space as needs arise.

Our Solution

Our team is working on a unique solution to both of the aforementioned challenges of future Mars missions: we intend to upcycle human waste by using it as a feedstock for E. coli engineered to produce bioplastic, which can then be 3-D printed into useful tools onsite.

Poly(3-hydroxybutyrate) (PHB), a bioplastic, is produced in nature by many bacterial species. Literature has shown that PHB can be produced using a variety of feedstocks, including glucose and volatile fatty acids (VFAs) (Albuquerque et al., 2011). Since human waste contains both glucose and VFAs, it is a potentially useful feedstock for PHB production.

Our team engineered E. coli to express PHB-producing genes, which we codon-optimized to increase the efficiency of PHB production. We then modified native E. coli secretion pathways so the cells would release the PHB they produced. This allows for a continuous PHB production and secretion process, as opposed to a traditional batch process, which is not user-friendly and requires more time and maintenance. Thus, when employed together these genetic modifications create a novel means of bioplastic production.

We also developed a start-to-finish process involving both waste management and PHB production. In the first step of this process, solid human waste is collected and fermented with naturally occurring enterogenic bacteria to increase the concentration of VFAs. As a part of this process, the solids from the waste settle and the liquid rises to the surface of the fermentation tank. Next, the VFA-concentrated liquid in the fermentation tank is separated from the solid particles by centrifugation, sterilized by filtration, and passed to a bioreactor containing with our engineered PHB-producing E. coli. Once the PHB is synthesized and secreted, it can be continuously collected and extracted from the liquid stream. The resulting liquid can be recycled into drinking water, while PHB particles can be used in a Selective Laser Sintering (SLS) 3-D printer to generate items useful to astronauts.

This overall process is summarized below. Find more information on our Process Development page!

E. coli utilizes products of glycolysis and beta-oxidation pathway. Thus, glucose and short-medium chain length volatile fatty acids (VFAs) present in the feedstock are utilized. The three genes involved in conversion of glycolysis products are phaA, phaB, and phaC. Genes used for conversion of VFAs to PHB are phaC1 and phaJ4. PHB is secreted from bacteria via the Type I hemolysin secretion pathway, which is endogenous to E. coli. The hemolysin secretion tag (HlyA) is fused to phasin, which binds to PHB granules. This complex is then recognized by membrane transport proteins (HlyB, HlyD, and TolC) and secreted. VFA fermentation is the first step of the process, where astronauts feces are fermented for 3 days at 22 C with bacteria naturally found in human feces to increase the concentration of volatile fatty acids (VFAs) that are later consumed by engineered bacteria to produce PHB. Feces are collected into into a storage tank using a vacuum toilet before being transferred into the VFA fermenter. In second stage, VFA-rich stream is obtained by separating solid particles using centrifugation followed by filtration. The VFA-rich stream is then passed on to a PHB fermenter. In the third stage, continuous fermentation occurs in a stirred-tank bioreactor at 37C and under aerobic conditions. A self-cleaning filter is used to capture, separate and recycle bacteria from the harvest containing secreted PHB, allowing for a continuous fermentation process. The resulting bacteria-free harvest stream that contains PHB is then passed to PHB extraction and water recovery. In the final stage of the process, PHB particles are separated from the media via dissolved air flotation. Water oversaturated with Martian air is bubbled through the media in a flotation column whereby the PHB particles float up to the top. The top layer from the flotation column is then passed into a drying unit where PHB is finally obtained in powder form, ready for 3D printing. Click on the boxes above to learn more!