Electrically conductive spacers for self-cleaning membrane surfaces via periodic electrolysis

Abstract

The use of an electrically conductive membrane has attracted significant interest in water treatment technology due to remarkable performance in fouling mitigation domain. In electrochemical systems, when external potential is applied, water electrolysis occurs and the generated gases efficiently clean the membrane surface. However, fabricating and integrating conductive membranes in current water treatment modules is challenging. The present work applies, for the first time, the electrolysis concept at the spacer component of the module rather than the membrane. Two types of materials were tested, a titanium metal spacer and a polymeric spacer. The polymeric spacer was made conductive via coating with a carbon-based ink comprised of graphene nanoplates (GNPs). A membrane system composed of the carbon coated/titanium metal spacer attached to the surface of a polyvinylidene fluoride (PVDF) microfiltration membrane and was assembled to the case of membrane module. The conductive spacers worked as an electrode (cathode) in electrochemical set-up. The membrane system was subjected to fouling and then exposed to periodic electrolysis, wherein in-situ cleaning of membrane surface by hydrogen bubbles generation at the spacer is applied.

A review of efforts to reduce membrane fouling by control of feed spacer characteristics

“…An emerging methodology is to modify feed spacer configuration to reduce fouling. Generally, several strategies have been adopted to develop mesh-type spacers such as by surface coating [54], altered geometry design [55] or three-dimensionally printed feed spacers [41], and use of electrically conductive spacers [43].…”

“…As a result, application of the electrical potential to the electro-conductive feed spacer, rather than the membrane surface, is a promising alternative modification, wherein foulant mitigation either through oxidation (spacer acts as an anode in electrochemical system) [84] or bubble generation (spacers acts as a cathode) [85,86] to cause disruption and release of fouling layers. However, self -cleaning membrane fouling mitigation very challenging [43]. Baek et al [44] used a lab-scale crossflow setup with an electro-conductive feed spacer to simulate a SWM employed in industrial applications.…”

“…When electrochemical treatment was applied, the flux was recovered to a significant extent. Abid et al [43] investigated the ability of the application of electrical potential to a coated plastic feed spacer to function as a tool for controlling organic fouling in a lab-scale crossflow membrane system. The plastic feed spacer was made conductive through dip coating with a carbon-based ink containing graphene nanoplates (GNPs).…”

“…The majority of feed spacer modification investigations are either experimental or numerical modelling studies aimed at estimation of the underlying phenomena and with optimizing the feed spacer configuration [42]. The effect of hydraulics on spiral-wound membrane systems performance as well as electrically conductive spacer meshes, for application of effective cleaning strategies using electrolysis have been of much recent interest [43,44]. Approaches for controlling biofouling focussing attention on the feed spacer have comprised changing the feed spacer thickness or orientation [45], periodic air/water cleaning [46],and coating of biocides on the net-spacer [47,48].…”

Periodic electrolysis technique for in situ fouling control and removal with low-pressure membrane filtration

“…This is the principal mechanism on which electrochemical membrane fouling mitigation is based [52]. However, it has recently been suggested that whilst bubble formation via electro-reduction is an efficient mechanism for in situ cleaning of membranes, the oxidation method may damage the membrane itself [55][56][57][58][59]. Bubbles offer a promising option for a clean, inexpensive and environmentally friendly technique appropriate for in situ cleaning of conducting substrates.…”