Urine volume reduction during long-duration cave exploration by a light-weight and portable forward osmosis system

Abstract

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.