Insufficient desorption of ions in constant-current membrane capacitive deionization (MCDI): Problems and solutions

Zhizhao He; Yingnan Li; Yuan Wang; Christopher J Miller; John Fletcher; Boyue Lian; T David Waite

doi:10.1016/j.watres.2023.120273

Insufficient desorption of ions in constant-current membrane capacitive deionization (MCDI): Problems and solutions

Water Res. 2023 Aug 15:242:120273. doi: 10.1016/j.watres.2023.120273. Epub 2023 Jun 26.

Authors

Zhizhao He¹, Yingnan Li¹, Yuan Wang¹, Christopher J Miller², John Fletcher³, Boyue Lian², T David Waite⁴

Affiliations

¹ UNSW Centre for Transformational Environmental Technologies, Yixing, Jiangsu Province 214206, P. R. China; School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia.
² School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia.
³ School of Electrical Engineering and Telecommunications, UNSW Sydney, Sydney 2052, Australia.
⁴ UNSW Centre for Transformational Environmental Technologies, Yixing, Jiangsu Province 214206, P. R. China; School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: d.waite@unsw.edu.au.

PMID: 37393810
DOI: 10.1016/j.watres.2023.120273

Abstract

Membrane capacitive deionization (MCDI) is a water desalination technology that involves the removal of charged ions from water under an electric field. While constant-current MCDI coupled with stopped-flow during ion discharge is expected to exhibit high water recovery and good performance stability, previous studies have typically been undertaken using NaCl solutions only with limited investigation of MCDI performance using multi-electrolyte solutions. In the present work, the desalination performance of MCDI was evaluated using feed solutions with different levels of hardness. The increase of hardness resulted in the degradation of desalination performance with the desalination time (Δt_d), total removed charge, water recovery (WR) and productivity decreasing by 20.5%, 21.8%, 3.8% and 3.2%, respectively. A more serious degradation of WR and productivity would be caused if Δt_d decreases further. Analysis of the voltage profiles and effluent ion concentrations reveal that the insufficient desorption of divalent ions at constant-current discharge to 0 V was the principal reason for the degradation of performance. The Δt_d and WR can be improved by discharging the cell using a lower current but the productivity decreased by 15.7% on decreasing the discharging current from 161 to 107 mA. Discharging the cell to a negative potential was shown to be a better option with the Δt_d, total removed charge, WR and productivity increasing by 27.4%, 23.9%, 3.6% and 5.3%, respectively, when the cell was discharged to a minimum voltage of - 0.3 V. Use of such a method should be feasible for operation of full scale MCDI plants and would be expected to lead to better regeneration of the electrode, improved desalination performance and, potentially, a significant reduction in the need for use of clean-in-place procedures.

Keywords: Electrode regeneration; Insufficient desorption; Ion accumulation; Membrane capacitive deionization; Performance degradation.

MeSH terms

Adsorption
Electrodes
Ions
Sodium Chloride
Water
Water Purification* / methods

Substances

Ions
Sodium Chloride
Water