• Forward osmosis (FO) was tested as a strategy for urine mitigation during cave exploration
  • Urea rejection was determined for a novel aquaporin-based membrane (ABM) module
  • A light-weight and portable FO prototype was introduced and tested
  • Urine volume could be reduced by over 80% using the proposed system
  • Draw solution recovery without nitrogen loss could be achieved by evaporation


The preservation of caves is a challenge during long-duration cave expeditions where human waste can add significant nitrogen to the cave ecosystem. Since the removal of urine that accumulates during a multi-day caving trip is not always feasible due to weight and volume constraints, a light-weight and portable filtration system that is capable of reducing urine volume would be desirable. In this study we tested the Aquaporin Inside hollow fiber membrane in a forward osmosis (FO) setup to evaluate its capability to reduce urine volume while rejecting nitrogenous compounds using different draw solution chemistries and water recovery rates. As a result, we introduce a light-weight and portable FO prototype that was able to reduce urine volume by over 80%. Although total nitrogen (TN) rejection in this process did not exceed 70%, allowing some nitrogen to move across the membrane into the draw solution, evaporation allowed draw solution recycling without loss of nitrogenous compounds into the atmosphere. These data suggest that FO may be a suitable strategy to reduce urine volume and improve methods for nitrogenous waste handling during long-term cave exploration.



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