Performance Comparison And Energy Consumption Analysis Of Capacitive Deionization And Membrane Capacitive Deionization Cells

Capacitive deionization (CDI) is a state-of-the-art water treatment technology,which removes the salt by the adsorption of the flow-through capacitor electrodes,with low energy consumption, environment friendly method and high waterproduction yield. Membrane capacitive deionization (MCDI) integrates thecharacteristics of CDI technology and membrane separation technology, which canimprove the desalting performance by ion permeability of ion exchange membrane.The comparison on desalination performance and energy consumption of CDI andMCDI cells was studied, which had a practical significance to reinforce desaltingprocess and to reduce energy consumption.In this paper, the dedicated graphite cloths for supercapacitor were used aselectrode material. The CDI and MCDI cells were assembled and an automaticprocess control system was designed. At the working voltage of3.0V, the isothermaladsorption laws (25°C) of CDI and MCDI cells were studied and the results showdthat the isothermal adsorption laws of both cells were consistent with the Langmuiradsorption isotherm at different concentrations of NaCl solution. At the workingvoltage of3.0V, the desalination performance, regeneration ability and the currentvariation of CDI and MCDI cells were studied with the feed concentration of400mg/L and flow rate of2.25L/h. The experimental results showed that the adsorptioncapacity of MCDI was5.617mg/g about twice of that of CDI (2.863mg/g) andMCDI had a more stable operation process. The current efficiency of CDI and MCDIcells were16.33%and70.15%, respectively. However, the energy consumption ofMCDI was merely18.8%of CDI, which further proved that the MCDI couldeffectively improve the availability of energy and then reduce energy consumption.The desalination performance and energy consumption of the CDI cells wasstudied at different working voltages (1.5~3.5V) with different feed concentrations(200~1000mg/L) and different feed flow rates. It was found that for the CDI cell, themaximum specific adsorption capacity of the electrodes achieved to4.12mg/g at theworking voltage of3.0V, with specific energy consumption of3.99Wh/g removalsalt. With the increase of the feed concentration, the specific adsorption capacity andthe specific energy consumption growed accordingly. With the increase of the flow rate, the specific adsorption capacity declined, yet with the specific energyconsumption growing.Under the same conditions, the desalination performance and energy consumptionof the MCDI cells was also studied. The experimental results showed that both thespecific adsorption capacity and specific energy consumption increased with theincreasing working voltage. When the feed concentration increased, the specificadsorption capacity significantly improved, with a reducing the specific energyconsumption in terms of removal salt. With the increase of the flow rate, the specificadsorption capacity decreased slightly, but the specific energy consumptionsignificantly reduced. The adsorption performence for different charge properties andhydration radius of ions were investigated in the MCDI cell. The results showed thatwith the increasing of the hydration radius and the charges of the ions, the removalefficiency of the MCDI cell presented a slightly decreasing tendency.