Hyunook Kim (Prof.)Joon Wun Kang (Prof)Shimelis Kebede (PhD)Redae Nuguse2024-03-122024-03-122023-12https://etd.aau.edu.et/handle/123456789/2463Discharging colored industrial wastewater effluents into natural water bodies is one of the main sources of environmental contamination globally and locally. The textile industry is one of the main water consuming and wastewater producing industries that needs serious attention. Conventional industrial textile wastewater treatments are not designed to treat emerging organic dyes (EODs). These compounds mainly remain unaffected even after the secondary biological treatment processes. Advanced oxidation processes (AOPs) are thought to be a successful and promising method of removing EODs. These processes rely on in situ liberation of reactive oxygen species (ROS), which have an active role in the degrading of EODs. The integration of wastewater treatment systems, which calls for knowledge in interdisciplinary domains, is a current focus. Although integrating wastewater treatment systems are challenging endeavors in the field of wastewater technology, various coupled systems have been developed. For example, systems such as bio-electrochemical system (BES) and electro-Fenton systems (EFS) for oxidation combine biological and electrochemical processes. The objective of the study was to combine the high oxidation power of EFS and cost-effectiveness of BES to oxidize textile wastewater effluents. Hence, a coupled system of BES-EFS oxidation system was developed in four phases to optimize the treatment process and offer a potential solution to oxidize EODs. To begin, different sized Fe3O4 nanoparticles (INPs) were synthesized using modified co-precipitation method. The synthesized INPs (C, S, and M) possessed an average hydrodynamic diameter of 23, 17 and 48 nm with a saturation magnetization of 76 ± 2.4, 79 ± 2.6 and 66 ± 2.8 emu g 1 respectively and fluidized microelectrodes were prepared from each INPs (C, S, and M). The fluidized electrodes were tested for catalytic degradation of Acid orange 7 and 89.4 ± 1.7%, 93.2 ± 1.5% and 83.7 ± 2.3% degradation efficiency was determined respectively. On a second phase, a carbon felt (CF) was activated to synthesize activated functional cathode (ACF). The cathode was checked to have carboxyl functional groups (-C =O-OH) to drive H2O2 generation during EF oxidation. The selectivity of ACF toward H2O2 generation, i.e., two electron oxygen reduction reaction (2e-ORR) was estimated to be more than 89 ± 3.1%. Over 40-min of EF reaction test and 94.3 ± 1.7% removal efficiency for Congo red (CR) was achieved. Similarly, total organic carbon (TOC) and mineralization current efficiency were achieved as 82.7 ± 2.8% and 58 ± 2% over 40-min, respectively. The chemical quenching, LC-MS and IC analysis confirmed the role of ∙OH and O2-. radicals in CR degradation into NO3- and SO42- ions. On third phase, functional composite electrode (Fe3O4/CNT/ACF) was synthesized and characterized. Fe3O4 and carbon nanotubes (CNTs) were used as surface modifiers, i.e., to ease charge-transfer by forming multilayered channels and to enhance the thermal and structural strength of the electrode respectively. Using Fe3O4/CNT/ACF cathode, 93.7 ± 3.7% methylene blue (MB) removal was obtained within 1 h, following 2.7  10−2 M−1 min−1 pseudo-second-order rate kinetics. Based on TOC analysis, 57.8 ± 2.9% of MB could be mineralized. On fourth phase, a four-electrode-based coupled BEF system with ACF and iron strips as cathode and anode of BES and polarizable Fe3O4@ACF and iron strip as cathode and anode of EFS was developed. Methyl orange (MO) was used as a model pollutant for oxidation. After stabilization of the BES about 275.23 ± 9.4 mW cm-2 power density was generated, which could drive the EFS. At 20 mg L-1 of MO concentration, an external resistance of 100 Ω, a catholyte pH of 3.5, and an aeration rate of 300 mL min-1, 82.5 ± 4.3% removal efficiency was achieved over 40 hours. Simultaneously, sewage wastewater was oxidized and accompanied with TOC, COD and NH4+-N removal efficiencies of 67.4 ± 3.6%, 71.2 ± 3.8% and 69.3 ± 3.7%, respectively. The results showed that the coupled BES-EFS system achieved satisfactory MO oxidation efficiency, indicating the synergistic effect of combining these two systems. Finally, the BES-EFS system was assessed for actual textile wastewater degradation which showed to be an effective system for industrial applications. Thus, the overall study provides an insight for an innovative mechanism of well-performing and easily recyclable composite electrodes and stable BEF system for degradation of recalcitrant EODs.en-USAdvanced oxidation processBio-electro-FentonCathode synthesisDye degradationElectro-Fenton oxidationMagnetic nanoparticlesWastewater TreatmentThesis