In situ conductive spacers for early pore wetting detection in membrane distillation

Abstract
Membrane distillation (MD) suffers from pore wetting which deteriorates membrane separation properties and causes water protrusion to permeate side. The early detection of pore wetting is a challenge which needs to be addressed to achieve stable MD performance. In this study, electrically-conductive Pt-coated spacers placed inside the feed and coolant channels with a dual purpose of maximizing permeate flux and instantaneous wetting detection once first membrane pores are compromised are proposed. Upon wetting, permeate salt concentration increases thereby initiating redox reactions at two spacer electrodes under the applied electrical potential. As a result, electrical current is produced and measured. The competence of the proposed wetting detection method was explored in MD process in the presence of organic substances with high wetting propensity. An increase in generated electrical current upon wetting development and substantial signal amplification with the voltage increase was demonstrated. The new wetting detection method achieved a faster response comparing to conventional conductivity measurements. Moreover, this method allows to define the wetting onset which can serve as an indication of early membrane impairment. Different spacer geometries and observed no adverse effect of spacer coating on MD performance were further compared. Experimental and numerical simulations accentuated an importance of spacer design by providing specific permeate flux gain for a 1-helical spacer comparing to a spacer with a smooth cylindrical filament. This effect became more evident at higher feed water temperature, condition that favors greater temperature polarization.

Citation
Alpatova, A., Qamar, A., Alhaddad, M., Kerdi, S., Soo Son, H., Amin, N., & Ghaffour, N. (2022). In situ conductive spacers for early pore wetting detection in membrane distillation. Separation and Purification Technology, 294, 121162. https://doi.org/10.1016/j.seppur.2022.121162

Acknowledgements
Supported by King Abdullah University of Science and Technology (KAUST), Saudi Arabia. The authors would like to acknowledge Dr. Li from KAUST Nanofabrication Core Lab for his assistance in Pt coating and Mrs. Popalzai and Abdulkareem from KAUST Electrical Workshop for their assistance in assembling electrical part of the method. The authors acknowledge help, assistance and support from the Water Desalination and Reuse Center (WDRC) staff and KAUST Supercomputing Laboratory (KSL). Mr. Heno Hwang, a graphical illustrator at KAUST, is acknowledged for preparing Figs. 1 and 2.

Publisher
Elsevier BV

Journal
Separation and Purification Technology

DOI
10.1016/j.seppur.2022.121162

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S1383586622007195

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