Comparative study on the removal of humic acids from drinking water by anodic oxidation and electro-Fenton processes: Mineralization efficiency and modelling

The management of natural organic matter in drinking water treatment plants is an important matter of concern. It can generate toxic disinfection by-products as well as decrease the efficiency of membrane filtration and oxidation processes. This is the first study that investigates the use of anodic oxidation (AO) and electro-Fenton (EF) for the removal of humic acids (HAs) from aqueous solutions. Both sorption and catalytic oxidation of HAs are assessed and discussed. These electrochemical advanced oxidation processes are based on the in situ production of hydroxyl radicals, a highly oxidizing agent. The EF process involves the use of carbon-based porous materials (carbon sponge) as cathode, leading to the fast adsorption of hydrophobic HAs. It has been observed that adsorbed HAs can react with hydroxyl radical produced in the bulk from Fenton's reaction. Then, the release in the solution of more hydrophilic by-products from the oxidation of HAs leads to a rebound effect of the organic matter concentration. Therefore, the AO process using non-carbonaceous cathode materials appears to be more suitable for HAs removal. Using boron-doped diamond anode and stainless steel cathode, the mineralization efficiency of a HAs solution (TOC0 = 16.2 mg L-1) reached more than 99% after 7 h of AO treatment with a current intensity of 1000 mA. By considering both sorption and oxidation processes, this study proposed a new modelling approach to monitor TOC evolution during AO and EF processes