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

Abstract

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.

Porous Hydrophobic–Hydrophilic Composite Hollow Fiber and Flat Membranes Prepared by Plasma Polymerization for Direct Contact Membrane Distillation

“…However, commercial hydrophobic PTFE membranes with a hydrophilic polyurethane (PU) surface layer were used successfully in DCMD on real poultry, fish, and bovine stick waters [17]; a metal microfiltration membrane was used to capture fats prior to DCMD. Tang et al [18] showed how hydroxide ion generation, driven by water electrolysis on the electrically conducting membrane surface consisting of carbon nanotubes and a polyvinyl alcohol layer over a hydrophobic layer, can be used to efficiently dissolve silicate scaling that developed during the process of desalinating the geothermal brine by MD, negating the need for chemical cleaning. Note: a previous study employing coated HFMs with porous polyfluorosiloxane coatings operated with crossflow mode of hot produced water containing silica did not show any fouling [11].…”

Virus Inactivation in Water Using Laser-Induced Graphene Filters

“…On the other hand, in the presence of electrical potential conductive filters can instantly remove, kill or inactivate microorganisms by various mechanisms such as direct and indirect oxidation, Coulombic repulsion, bubble generation, Joule heating, and local pH change. [46][47][48][49][50][51][52][53] The electrical conductivity of the conductive filters might also contribute to lipid membrane disruption through the electroporation process. 14,[54][55][56] Thus the physicochemical and electrochemical manifold effects of graphene, including LIG filters, can potentially also be useful for inactivation of viruses.…”

Coupling hydrothermal liquefaction and membrane distillation to treat anaerobic digestate from food and dairy farm waste

“…(Supplementary Material). As the feed becomes more concentrated, due to continuing water recovery, membrane fouling becomes more pronounced; this is caused by accelerated deposition of foulants, such as organic molecules and particulate matter onto the membrane surface, which blocks the flow of water (Tang et al, 2017). Membrane autopsies of the fouled membranes were performed using SEM (a qualitative measure) and XPS (a quantitative measure).…”