Enhanced Flux and Electrochemical Cleaning of Silicate Scaling on Carbon Nanotube-Coated Membrane Distillation Membranes Treating Geothermal Brines

• Published in: ACS applied materials & interfaces Vol. 9; no. 44; pp. 38594 - 38605
• Main Authors: Tang, Li, Iddya, Arpita, Zhu, Xiaobo, Dudchenko, Alexander V, Duan, Wenyan, Turchi, Craig, Vanneste, Johann, Cath, Tzahi Y, Jassby, David
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08.11.2017; American Chemical Society (ACS)
• Subjects: carbon nanotubes; electrochemical cleaning; GEOTHERMAL ENERGY; membrane distillation; silicate scaling; silicate scaling; carbon nanotubes; electrochemical cleaning; membrane distillation
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.7b12615

The desalination of inland brackish groundwater offers the opportunity to provide potable drinking water to residents and industrial cooling water to industries located in arid regions. Geothermal brines are used to generate electricity, but often contain high concentrations of dissolved salt. Here, we demonstrate how the residual heat left in spent geothermal brines can be used to drive a membrane distillation (MD) process and recover desalinated water. Porous polypropylene membranes were coated with a carbon nanotube (CNT)/poly­(vinyl alcohol) layer, resulting in composite membranes having a binary structure that combines the hydrophobic properties critical for MD with the hydrophilic and conductive properties of the CNTs. We demonstrate that the addition of the CNT layer increases membrane flux due to enhanced heat transport from the bulk feed to the membrane surface, a result of CNT’s high thermal transport properties. Furthermore, we show how hydroxide ion generation, driven by water electrolysis on the electrically conducting membrane surface, can be used to efficiently dissolve silicate scaling that developed during the process of desalinating the geothermal brine, negating the need for chemical cleaning.