Improvement of MCDI operation and design through experiment and modelling: Regeneration with brine and optimum residence time

Abstract

Membrane Capacitive Deionization (MCDI) is an energy efficient, electrochemical desalination technology, in which ions are removed from a salty stream upon applying a constant voltage or current. The ions are stored in carbon electrodes and then released back into the stream by reversing the polarity. In this work, we aimed to assess the feasibility of using a brine stream to regenerate the MCDI unit in order to improve water recovery. We further aimed to determine the optimum residence time in the MCDI unit. To achieve these objectives, we first enhanced the ion transport model previously developed for MCDI by independently measuring the counter-ion and co-ion diffusion coefficients in the ion-exchange membranes. These experiments allowed for an asymmetric model of the MCDI unit where the voltage drop across the cation exchange membrane was greater than that across the anion exchange membrane. Using this revised model, we found that in batch operation, a brine to feed water concentration ratio of around two was optimum. In continuous operation, over 40% enhancement in water recovery could be achieved when the regeneration brine was partially recycled, but water productivity dropped. We further showed that the maximum desalination capacity did not increase beyond a critical residence time in the MCDI cell, while the water recovery decreased.

A comparison of multicomponent electrosorption in capacitive deionization and membrane capacitive deionization

“…The activated carbon used by Hou and Huang showed a wider pore size distribution to that 267 used in this work (Hassanvand et al 2017), which might facilitate the diffusion of larger 268 hydrated ions such as calcium. Our own results show K + with the strongest normalized sorption capacity, but this is closely followed by Ca 2+ (Table 2).Ion analysis shows a different trend for the MCDI experiments.…”

“…Preparation of carbon electrodes using AC Norit SA4 as the carbon source, PVDF as the binder and DMF as the solvent is explained in detail in our previous work (Hassanvand et al 2017).…”

“…The BET surface area was calculated as 540 ± 4 m 2 132 g -1 , and pore size distribution was indicative of a microporous structure with pore diameters ranging from 0.7 to 1.5 nm. For more details see our previous work (Hassanvand et al 2017).…”

Separation Technologies for Salty Wastewater Reduction in the Dairy Industry

“…This approach may be a viable alternative to ion exchange processes as it does not use chemicals for regeneration and thus does not add to the salty waste load of the factory. The use of a brine feed for the regeneration step was recently investigated by Hassanvand et al (155). It was found that the optimum ratio of brine to feed water concentration is around two in batch operation, allowing for a maximum water recovery of ~90%.…”

Energy Recovery in Capacitive Deionization Technology

“…In this variant of capacitive deionization, ion-selective membranes are interposed between the electrodes and the solution. In this way, it is possible to use the polarity reversal in the electrodes periodically, drastically improving the efficiency in the cleaning phase [8,9].…”