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Fouling of carbon electrode by humic substance and its cleaning in capacitive deionization

Wannacha Limthanakul, Taeyoung Kim, Seoni Kim, Jeyong YoonSchool of Chemical and Biological Engineering, College of Engineering, Seoul National University, Seoul, Korea

Introduction

Objectives

Experimental Works

Results

Summary

Carbon Electrode

Carbon Electrode

+-

++

++-

--

-- - - - -

++ + + + + + +

- -Treated WaterConcentrated Water

Anode

Cathode

Fig. 1. Schematic diagram of CDI process

Capacitive deionization (CDI) is a technology for desalination and water treatment in which ions are removed from water by applying an electric field between two porous (carbon) electrodes.

Advantages: - Environmentally clean technology- Energy and cost saving- Simply operating

Further study needBecause electrode materials used in CDI has been

fabricated from high-surface area carbon, the accumulation of organic material could effect the electrode property contributed to diminish the CDI performance.

Fig. 2. Accumulation of organic matter on carbon surfaceSource: wateensolutions.com.au

⧄ To investigate the effects of organic matter to CDI performance.

⧄ To investigate the electrochemical property change of the electrodes after organic fouling.

⧄ For organic fouling remediation, chemical cleaning approach has been applied to observe the recovery of CDI performance.

⧄ Carbon Electrodes:Materials: Activated carbon YP50 + Super P + PTFEFabrication: Rolling Press method(RP)

⧄ Dissolved Organic Solution100 mg/L of Humic Acid(HA)

⧄ Soaking period24 hr

100 mg/L of Humic Acid

Roller

Roller

Carbonmixture

50 mm0.3 mm

(a) (b)

Fig. 3. Schematic of organic fouling on carbon electrode. (a) electrodes were fabricated by RP method. (b) Fabricated electrodes were soaked in humic acid solution for 24 hr.

Desalination ⧄ ReactorCDI cell : Flow type ⧄ Feed SolutionNaCl : 10 mM ⧄ Operating ConditionsApplied potential : 1.2 V Cycle time :

5 min charging, 5 min discharging 5 cyclesFlow rate

10 ml/min

Organic fouling

Potentiostat

Outlet

Conductivity meter

CDI cell

NaCl 10mM

Peristaltic pump

Graphite sheet

Graphite sheet

Electrode

ElectrodeSpacers

Fig. 4. Schematic of experimental system for desalination

⧄ Cleaning agent: 10 mM of NaOH ⧄ Cleaning time: 10,25 and 50 min

Fouling Remediation

(1) Effect of organic fouling to desalination performance and electrochemical property of electrodes

(a)

(b)

Fig. 5. Desalination performance of HA fouled electrode and virgin carbon electrode: (a) ion removal aspect; (b) amount of accumulated ion removal during charging step

Electrodes Specific Capacitance (F/g carbon)

Virgin YP50 81

HA fouled 73

Fig. 6. Cyclic voltammograms of HA fouled electrode and virgin electrode.

(2) Recovery of desalination performance and electrochemical property by alkaline cleaning agent(NaOH)

(a)

(b)

Fig. 7. Desalination performance of HA fouled electrode and different time cleaned electrodes. : (a) ion removal aspect; (b) amount of accumulated ion removal during charging step

Electrodes Capacitance(F/g carbon)

Virgin YP50 81

Fouled YP50 73

10 min cleaning 78

25 min cleaning 77

50 min cleaning 91

Fig. 8. Cyclic voltammograms of HA fouled electrode and different time cleaned electrodes.

⧄ The deionization performance after operating with HA fouled electrodes was significantly declined Decreasing in amount of ion removal (11 3 mg/g) and capacitance (8173 F/g)

⧄ The deionization performance and capacitance were recovered by 10 mM of NaOH as a cleaning agent for 50 min.

⧄ In particular, the capacitance became higher than the virgin electrode after cleaning.

Contact InformationBiofilm Engineering Laboratoryenv.snu.ac.kr

302 Bld. Room No.513(5th floor)

Tel: 82-2-880-8941Fax: 82-2-876-8911

Email: wannachalimthan@snu.ac.kr

Acknowledgments

This research was supported by WCU (World Class University) program through the Korea Science and Engineering Foundation by the Ministry of Education, Science and Technology (R31-10013), and also supported by Korea Ministry of Environment as “Converging technology project” (223-111-003).