Impact of molecular size and electrical polarity on fouling of capacitive electrodes during water desalination

Abstract

The fouling of capacitive deionization (CDI) electrodes can adversely affect the CDI performance. One major foulant during water treatment relies on natural organic matter (NOM). A better understanding of the electroadsorption and electrochemical behavior of different groups NOM could clarify their relative contributions in electrode fouling. In this study, commercial sodium alginate (SA), humic acid (HA), and bovine serum albumin (BSA) were selected as representative model substances of NOM. During CDI process Salt ions were removed from brackish water during CDI and porous electrodes surfaces were covered by NOM to block the surface sites and micropores. After 50 CDI cycles, the salt adsorption capacity decreased by 78.2%, 47.6% and 66.0%, while the energy consumption increased by 213.6%, 63.3% and 129.1% for SA, HA and BSA, respectively. The charge efficiency diminished to 20.0%, 44.9% and 27.8% for SA, HA and BSA. The presence of NOM degraded the practical performances of porous activated carbons in terms of salt storage capacity, ion diffusion, and electron transport. Both SA and HA showed the worst impacts on the cathode, and BSA aggravated the oxidation process of the anode. The valuable information might be useful for future studies and applications.