M.Sc Thesis


M.Sc StudentLin Mu
SubjectRemoval of Synthetic Dyes with a Two-Step Electro-Fenton
Process
DepartmentDepartment of Civil and Environmental Engineering
Supervisors PROF. Jiaping Paul Chen
ASSOCIATE PROF. Youri Gendel


Abstract

Organic pollution is one of the severe global environmental problems. Traditional wastewater treatment practice has limited performance for their complete removal. Electro Fenton (EF) processes are proven effective for the mineralization of organic pollutants yet suffering from the practical challenge in applications. In this study, a cyclic process combining adsorption and electro Fenton process was developed to improve the practicality of the decontamination of organic pollutants. The process comprised two major steps: (i) adsorption of organic pollutants onto activated carbon fleece, and (ii) regeneration of the spent activated carbon fleece by the oxidants from the EF process. In the second step, the cell was operated with an optimized electrolyte solution, leading to the generation of H2O2 and other chemically active free radicals on the cathode for the regeneration of the spent activated carbon (located at the cathode) from the first step. The adsorption study showed a great adsorption performance for the removal of AR-14 (qmax=320mg/g at pH=3) and a clear enhancement on adsorption under lower pH. During the adsorption-electrochemical regeneration cycles, a sharp adsorption loss at the beginning of the cycles was observed, and the adsorption capacity further yielded to a plateau (52.4% of the initial capacity of ACF) without continuous loss. The analysis via Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and point of zero charge (pHPZC) confirmed the stability of the activated carbon in the process. The further pore structure analysis showed a complete recovery of the pores with sizes above 12 Å, with a poor recovery (only 31.52%) of pores with a diameter below 12 Å. The investigation of the degradation products demonstrated that the loss in adsorption is likely due to the formation of iron complexes ferrioxalate, which makes micropores inaccessible for ferric catalyst. Furthermore, the release of organic substances in the NaOH treatment from the spent activated carbon fleece electrodes confirmed the incomplete removal of degradation intermediates accumulating in the activated carbon during the electro-Fenton step. Overall, our study demonstrated the high feasibility of the cyclic process towards organic pollutants removal and provided a comprehensive image of the EF-based activated carbon regeneration process.