Coupling ion-exchangers with inexpensive activated carbon fiber electrodes to enhance the performance of capacitive deionization cells for domestic wastewater desalination

• Published in: Water research (Oxford) Vol. 47; no. 7; pp. 2523 - 2530
• Main Authors: Liang, Peng, Yuan, Lulu, Yang, Xufei, Zhou, Shaoji, Huang, Xia
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2013; Elsevier
• Subjects: activated carbon; Activated carbon fiber; Adsorption; Applied sciences; Carbon - chemistry; Carbon - economics; Charcoal - chemistry; Charcoal - economics; Desalination; Desorption; dielectric spectroscopy; Direct current; Electric potential; Electricity; Electrochemical impedance spectroscopy; Electrodes; Electrodes - economics; Exact sciences and technology; Family Characteristics; General purification processes; Granular materials; granules; Ion Exchange; Ion Exchange Resins - chemistry; Ion-exchange resin membrane capacitive deionization (R-MCDI); Ion-exchangers; ions; Membranes, Artificial; Pollution; Rheology; saline water; Salinity; salt concentration; Salt water desalination; sodium chloride; Sodium Chloride - analysis; surface area; Waste water; Waste Water - chemistry; Waste Water - economics; wastewater; Wastewaters; water flow; Water Purification - economics; Water Purification - methods; Water treatment and pollution; Salt water desalination; Ion-exchangers; Ion-exchange resin membrane capacitive deionization (R-MCDI); Activated carbon fiber; Water treatment; Porous electrode; capacitive deionization (R-MCDI); Ion exchange chromatography; Domestic waste water; Ion exchange membrane; Ion-exchange resin membrane; Activated carbon; Desalination; Physicochemical purification; Adsorbent; Waste water purification; Ion exchange resin; Deionization; Carbon fiber; Modified material; Stationary phase; Electrochemical impedance spectroscopy
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2013.02.037

A capacitive deionization (CDI) cell was built with electrodes made of an inexpensive commercial activated carbon fiber (ACF), and then modified by incorporating ion-exchangers into the cell compartment. Three modified CDI designs were tested: MCDI – a CDI with electrodes covered by ion-exchange membranes (IEMs) of the same polarity, FCDI – a CDI with electrodes covered by ion-exchange felts (IEFs), and R-MCDI – an MCDI with cell chamber packed with ion-exchange resin (IER) granules. The cell was operated in the batch reactor mode with an initial salt concentration of 1000 mg/L NaCl, a typical level of domestic wastewater. The desalination tests involved investigations of two consecutive operation stages of CDIs: electrical adsorption (at an applied voltage of 1.2 V) and desorption [including short circuit (SC) desorption and discharge (DC) desorption]. The R-MCDI showed the highest electric adsorption as measured in the present study by desalination rate [670 ± 20 mg/(L h)] and salt removal efficiency (90 ± 1%) at 60 min, followed by the MCDI [440 ± 15 mg/(L h) and 60 ± 2%, respectively]. The superior desalination performance of the R-MCDI over other designs was also affirmed by its highest charge efficiency (110 ± 7%) and fastest desorption rates at both the SC [1960 ± 15 mg/(L·h)] and DC [3000 ± 20 mg/(L·h)] modes. The desalination rate and salt removal efficiency of the R-MCDI increased from ∼270 mg/(L h) and 83% to ∼650 mg/(L h) and 98% respectively when the applied voltage increased from 0.6 V to 1.4 V, while decreased slightly when lowering the salt water flow rate that fed into the cell. The packing of IER granules in the R-MCDI provided additional surface area for ions transfer; meanwhile, according to the results of electrochemical impedance spectroscopy (EIS) analysis, it substantially lower down the R-MCDI's ohmic resistance, resulting in improved desalination performance.
► Ion-exchange resin was first used in the MCDI cell to further enhance the desalination performance. ► The performances of different CDI designs modified with three ion-exchangers were compared. ► The desalination rate of the R-MCDI was 670 ± 20 mg/(L h), 50% higher than that of the MCDI.