Light-weight oxygen supply for portable biological nitrogen removal from urine and sweat

Abstract

The weight or availability of potable water often limits foot travel into remote arid regions for recreational, or government-sponsored activities. To address this limitation, a portable bioprocessing unit, intended to be one treatment stage in the continuous regeneration of drinking water from urine and sweat was prototyped. Biological treatment of urine requires oxygen, and the goal of this work was to determine the oxygen supply option that is the least weight to carry for safe and sustained treatment. Four oxygen supply options were modeled; battery powered aeration, battery powered electrolysis, diffused oxygen gas generated from hydrogen peroxide (H2O2), and platinum catalyzed liquid phase oxygen supply (PtLPOS) from H2O2. Modeling focused on a small reactor (<0.3 L) operating at 3 mg O2 L − 1, using hydrogel immobilized bacteria. The results indicated PtLPOS adds the least amount of weight per additional day of travel at 123 g d − 1 compared to 290, 572, 654 g d − 1, for aeration, electrolysis, and oxygen gas via H2O2, respectively. PtLPOS was prototyped for urine treatment using a hydrogel immobilized culture seeded with urease positive Nitrospira inopinata (comammox) and an enrichment of Ca. Brocadia sinica (anammox), which were chosen because prior work showed the co-culture is capable of producing nitrate free effluent. The prototype provided oxygen efficiently, achieving 86% of the maximum nitrogen removal per H2O2 consumed via a theoretical comammox-anammox partnership. This work demonstrated for the first time that Pt catalyzed LPOS has the potential to enhance the portability of bioprocessing technologies and specifically works with autotrophic nitrogen removal in the treatment of natural urine.

Keywords

• Hydrogen peroxide
• Comammox-anammox partnership
• Liquid phase oxygen supply (LPOS)
• Platinum and urease as catalyst
• Hydrogel immobilization