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Major product: PHB

The major process product is PHB (Plyhydroxybuterate) plastic. PHB can be used in SLS 3D printing on Mars and on the ISS. The advantages of producing PHB plastic on Mars are:

availability of resource for production of urgently needed tools
the plastic is biodegradable and hence the Carbon-Hydrogen cycle can eventually be closed (once the 3D printed tool is on no use any more)
Solve the problem of high cost of material shipping to space
Solve the problem of waste management on Mars

PHB characteristics and properties:

physical properties (Manufacturing and properties of PHB)

Molecular weight = 2-3×10^3 kDa
Melting point = 173°C
Crystallinity = 55 %

General properties

Eco-friendly
Biodegradable
Can be decomposed into water and CO2 by microorganisms
Chain of 14 monomeric units
Can be a good substitute for synthetic plastic

By-Product: Char

The sludge by-product comes out of the Solid-liquid separation and filtration stages. Sludge can either be fed into the general wastewater processing unit, where it would be combined with the other sludge for treatment, or it can be treated using Torrefaction (mild pyrolysis) technology.

The two streams that would leave the torrefaction processing unit (TPU) are water with some VFAs and char - black solid matter. Our team believes that torrefaction is the most efficient approach to treatment of the sludge-like matter as it holds a couple of benefits:

it is biologically stable - doesn’t support biological activity
torrefaction allows for production of pyrlytic water – meaning extra water recovery
char can be used as a building material
char can be used for radiation shielding
char can be used as a food substrate
char can be used as a carbon/hydrogen storage

The torrefaction technology is just emerging and was not yet tested large scale, however a couple of papers (M. Serio, J. Cosgrove, M. Wojtowicz, 2016), (M. Serio, M. Wojtowicz, K. Wignarajah, 2014)) by NASA outline the potential of the system and see it as a promising solution for the sludge management in space and on Mars.

By-Product: Water and VFA stream

Our team suggests the water and VFAs by-product stream to be fed into one of the final stages of the water processing unit (WPU), where it can be cleaned to the required water quality standard. Such treatment allows to close the water loop in the feces treatment (recycle all the water).

Works cited

A. Serio, M., E. Cosgrove, J., & A. Wojtowicz, M. (2016). Torrefaction Processing for Human Solid Waste Managment. In 46th International Conference on Environmental Systems (pp. 1-18). East Hartford: Advanced Fuel Research, Inc.