Assessment of Forward Osmosis as a Possible Mitigation Strategy for Urine Management During Extended Cave Exploration

Abstract

Extended expeditions into caves for the purpose of survey, exploration, and scientific studies pose unique challenges to cavers, but also create the potential for environmental degradation as a result of human activities. Human waste disposal can present particular challenges during extended trips underground. Urine may cause rapid microbe proliferation and substantial odor when deposited in areas that do not receive frequent flooding, but weight and bulk make it impractical to carry many days worth of urine to the surface. In this study, we evaluated the feasibility of a forward osmosis system to concentrate nitrogen-containing and carbon-containing compounds, which would allow for cleaner treated liquid to be deposited in the cave. The concentrated waste solution, with lower weight and volume than the raw urine, could then be removed from the cave. In our analysis of volume and chemical changes of a urine solution treated over the course of a week-long trial, we determined that the system, as tested, does reduce the weight and concentrate the chemical constituents in urine, allowing some chemical separation from the treated liquid. Unfortunately, the drawbacks of this system (chemical breakthrough, added weight of the system, and unknown ecological effects associated with substantial sodium chloride additions to the cave) outweigh the benefits. We do not recommend this forward osmosis system, as tested, as an effective mitigation strategy, although other treatment strategies may hold promise.