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.

Membrane technologies in toilet urine treatment for toilet urine resource utilization: a review

“…Following that, the performance of an Aquaporin Inside hollow ber FO module (Sterlitech) used for urine volume reduction without DS for long-duration cave expeditions was tested, and a portable FO prototype was introduced, which was able to reduce the urine volume by approximately 75% and reject approximately 86% of the TN. 79 In addition to the nutrient and water recovery, the urine-FO combination can be used in other elds, such as microalgae culture. 80 The concentration of algae increased by four times with a water ux of 14.2 L m À2 h À1 using hydrolyzed urine as the DS.…”

“…Following that, the performance of an Aquaporin Inside hollow fiber FO module (Sterlitech) used for urine volume reduction without DS for long-duration cave expeditions was tested, and a portable FO prototype was introduced, which was able to reduce the urine volume by approximately 75% and reject approximately 86% of the TN. 79 …”

Water and nutrient recovery from stored urine by forward osmosis with an ammonium bicarbonate draw solution

“…Previous studies have investigated the use of FO for urine volume reduction, to decrease transport costs and protect nutrient sensitive environments such as caves during exploration (Nikiema et al, 2017;Engelhardt et al, 2020), or to recover nutrients such as ammonium (Engelhardt et al, 2019;Ray et al, 2020), urea (Engelhardt et al, 2019), nitrogen (Zhang et al, 2014;Nikiema et al, 2017;Volpin et al, 2018;Volpin et al, 2019a), phosphorus (Zhang et al, 2014;Volpin et al, 2018;Volpin et al, 2019b), and potassium (Zhang et al, 2014). Despite promising nutrient concentration and water flux results, previous studies have employed a DS where permeated water separation from the DS is challenging for clean water recovery (i.e.…”