Water is the lifeblood of human survival and civilization on Earth. It is also critical for our sustained exploration beyond Earth. Mars has plenty of water to sustain our exploration and colonization in the form of subsurface ice. However, it is not clean water. It is contaminated by toxic perchlorates which are a serious environmental hazard on Earth. Perchlorate and chlorate are potent oxidizers that cause equipment corrosion. They are also hazardous to human health even at low concentrations.
It is critical that Martian water be detoxified to remove these contaminating solutes before it can be used in propellant production, food production, or human consumption in a Martian colony. The scale of anticipated water demand on Mars highlights the shortcomings of traditional water purification approaches. These require large amounts of consumable materials, high electrical draw, or water pretreatment.
Is there any efficient and cheap way to remove the perchlorates? This innovative solution has been proposed for a NASA NAIC 2024 Phase 1 project. It takes advantage of the reduction of chlorate and perchlorate to chloride and oxygen being thermodynamically favorable, if kinetically slow. This is the promise of the proposed regenerative perchlorate reduction system. It applies synthetic biology to take advantage of and improve upon natural perchlorate reducing bacteria. These terrestrial microbes are not directly suitable for use is space and other celestial bodies. Their key genes pcrAB and cld, which catalyze the reduction of perchlorates to chloride and oxygen, have been previously identified and well-studied.
This proposed work is based on the prior work studying perchlorate-reducing bacteria by engineering this perchlorate reduction pathway into the spaceflight proven Bacillus subtilis strain 168, under the control of a robust, active promoter. This solution is both highly sustainable and scalable. Unlike traditional water purification approaches, it outright eliminates perchlorates rather than filtering them to dump somewhere.
Phase I will explore whether this approach is feasible through these objectives:
1. The genes PcrAB and cld will be engineered into B. subtilis 168 under the control of the strong promoter pVeg then tested to quantify the efficacy of perchlorate reduction under the modeled conditions.
2. Bacillus subtilis strains will be developed that secrete the enzymes to test intracellular vs extracellular efficacy.
3. A trade study will be performed to compare the performance of biological water detoxification from Objectives 1 & 2 to traditional engineering approaches in terms of mass, power, and crew time.
4. A plan will be developed to include this technology in human Mars missions. Development of detoxification biotechnology will also lead to more efficient solutions to natural and particularly industrial terrestrial perchlorate contamination on Earth. It will also reveal the potential of using life rather than only industrial solutions to address our environmental problems. This may stimulate further innovations for other terrestrial environmental challenges such as climate change.
5. The biological decontamination system will be launched as inert, dried spores stable at room temperature for years. Upon arrival at Mars, the spores will be rehydrated and grown in a bioreactor that satisfies planetary protection standards. Martian water will be processed by the bioreactor to carry out perchlorate reduction. The processed water will then be used or further purified as required.