Abstract
Pervaporative irrigation is a membrane technology that can be used for desalination and subsurface irrigation simultaneously. To irrigate, the tube-shaped polymer membrane is buried in soil and filled with water. Because of the membrane transport process, water enters the soil in the vapor phase, drawn across the membrane when the relative humidity in the air-filled pores is low. Soils are typically humid environments; however, the presence of hygroscopic compounds such as fertilizers decreases the humidity. For example, at 20°C the humidity in air in equilibrium above a saturated ammonium nitrate solution is 63%. Here, experiments showed that the presence of fertilizers in sand increased the water flux across the membrane by an order of magnitude. An expression for vapor sorption into sand containing different hygroscopic compounds was developed and combined with a model of vapor and liquid flow in soil. The success of the model in simulating experimental results suggests that the proposed mechanism, adsorption of moisture from the vapor phase by hygroscopic compounds, explains the observed increase in the flux from the irrigation system.
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Acknowledgments
We gratefully acknowledge the EPSRC Imperial College doctoral prize fellowship that supported LCT and the in-kind support of DTI-r Ltd. and DuPont, without which this work would not have been possible. We also thank two anonymous reviewers for their comments and suggestions that helped improve this work.
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Published In
Journal of Environmental Engineering
Volume 144 • Issue 7 • July 2018
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This work is made available under the terms of the Creative Commons Attribution 4.0 International license, http://creativecommons.org/licenses/by/4.0/.
History
Received: May 2, 2017
Accepted: Dec 8, 2017
Published online: Apr 30, 2018
Published in print: Jul 1, 2018
Discussion open until: Sep 30, 2018
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