High Tech with a Human Touch
Distillation Brine Purification for Resource Recovery
The work will ultimately focus on brine electrolysis and the use of brine from distilled wastewater as a resource to generate high-value chemicals, e.g., HCl and NaOH for use in space exploration. Producing these chemicals in situ would reduce launch mass by allowing regeneration of ion exchange beds needed to produce potable water, and provide strong mineral acid and base for other uses, e.g., wastewater pretreatment. The test stand constructed would use brine electrolysis to purify the stream to produce acids and bases. This involves removing hardness (calcium and magnesium) and valuable anions (sulfate, phosphate, and nitrate) which can be used for fertilizer in hydroponic systems.
Waste water brine generated on the International Space Station contains high levels of calcium, magnesium, sulfates, and phosphates. If biological pretreatment is used it could also lead to high nitrate levels. The first step is to deharden the brine (remove calcium and magnesium) using a chelating cation exchange resin. Once de-hardened, the brine is processed to selectively remove phosphate using macroporous polystyrene beads impregnated with hydrous iron oxide. Then sulfate is selectively removed using a zirconium-hydroxide treated exchange resin. Nitrate is removed using commercial off the shelf anion exchange resins. Each of the above resins can be regenerated with HCL and KOH to produce valuable fertilizer chemicals for hydroponic systems. The remaining brine is pure enough for brine electrolysis to increase water recovery and produce the needed HCL and KOH (and NaOH).
Currently brine recovery is focused on dewatering the brine. It is hoped that through brine electrolysis that the brine itself can be used as a feedstock for chemicals that are currently consumables for space life support systems. Demonstrating our objectives would help close the materials loop for life support. NASA would benefit from reduced resupply of water, chemicals, and other consumables to the ISS, NEO, and future surface missions, and save operation costs.
Commercial applications of the brine electrolysis system would include private companies needing closed loop water recovery. If the process is sufficiently energy efficient and scalable, it can even allow localized (household) brine recovery from domestic waste water to produce useful chemicals (bleach).