The Effect of Organic Fouling Formed by Humic Acid to the Desalination Performance in Capacitive Deionization

Abstract

Capacitive deionization (CDI) technology has served as an energy efficient technique of salt removal to produced fresh water for supporting water scarcity. The presence of humic acid in water sources contributed to the concern of its effect to the CDI system. This study has experienced in effect of organic fouling to CDI by investigating in deposition of humic acid on carbon electrode surface and long-term stability operation with the presence of humic acid in the feed solution. With the deposition of humic acid on the carbon electrode surface, the severe decrease in salt removal performance and electrode electrochemical property was observed due to the active surface area of the carbon electrode was covered by humic acid particle (increasing in hydrophilicity). To observe the long-term operating effect of humic acid to the CDI, feed contaminated with 3.6 mg/L of humic acid was used as the influent feed. After 20 hr of desalination, the salt removal efficiency of the system fed with solution contained humic acid was approximately 26% decreased. In water containing humic acid, the characteristic peak in concentration profile of CDI treated effluent indicating the degradation of electrode surface was observed much earlier (3 hr) in comparison with control system (12 hr). Moreover, the anode was significantly affected by humic acid than the cathode as could be observed by the anode wettability seriously changed to hydroplilic and the specific capacitance decreased. These declines in salt removal performance and electrode electrochemical property could be recovered by applying cleaning method after operation. DI water and NaOH solution was used as cleaning agent. High cleaning efficiency was reached within short period of time with high concentration of NaOH and also increasing in flow rate. Therefore, pre-treatment steps to remove humic acid from water streams must be required to reduce its effects to the CDI performance and carbon electrodes. Chemical cleaning with alkaline solution were able to effectively restore the recovery of the CDI performance after suffering with humic acid accumulation.