Development of Low-Toxicity Wastewater Stabilization for Spacecraft Water Recovery Systems
Mitchell, Julie L.
Pickering, Karen D.
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Wastewater stabilization was an essential component of the spacecraft water cycle. The purpose of stabilizing wastewater was twofold. First, stabilization prevents the breakdown of urea into ammonia, a toxic gas at high concentrations. Second, it prevents the growth of microorganisms, thereby mitigating hardware and water quality issues due to biofilm and planktonic growth. Current stabilization techniques involve oxidizers and strong acids (pH=2) such as chromic and sulfuric acid, which are highly toxic and pose a risk to crew health. The purpose of this effort was to explore less-toxic stabilization techniques, such as food-grade and commercial care preservatives. Additionally, certain preservatives were tested in the presence of a low-toxicity organic acid. Triplicate 300- mL volumes of urine were dosed with a predetermined quantity of stabilizer and stored for 2 weeks. During that time, pH, total organic carbon, ammonia, and turbidity were monitored. Preservatives that showed the lowest visible microbial growth and stable pH were further tested in a 6-month stability study. The results of the 6-month study are also included in this paper.