Activated sludge treatment by electro-Fenton process: Parameter optimization and degradation mechanism

This study was conducted to evaluate the mineralization of activated sludge (MAS) by a facile and environmentally friendly electro-Fenton process (EFP). The effects of initial H2O2 concentration, pH value, applied current density and operating time on MAS through determining the removal rate of chemical oxygen demand (COD) and total coliform (TC) were studied. 72 of COD was removed by indirect oxidation double-mediated based on the electro-generation of hydroxyl radical and active chlorine, under the following optimum conditions: 127mmol L-1 of hydrogen peroxide, pH=3.0, 10 mA cm(-2) of DC current, 120min of operating time, and 0.22mol L-1 of NaCl as the supporting electrolyte. Only in 10 min and pH 3.0 approximately 100 of TC was removed. The findings indicated that EFP can be applied efficiently for MAS by selecting appropriate operating conditions. The bottom line is that the process is entirely effective owing to the application of green oxidants (hydroxyl radical and active chlorine) and lack of being influenced by environmental situations, which can be introduced as an alternative to current conventional methods

Multi-walled carbon nanotubes-CoFe2O4 nanoparticles as a reusable novel peroxymonosulfate activator for degradation of Reactive Black 5

In this study, CoFe2O4 nanoparticles supported on multi-walled carbon nanotubes (MWCNTs), as novel peroxymonosulfate (PMS) activator, were synthesized for degradation of Reactive Black 5 (RB5). The results showed that the maximum removal efficiencies of RB5 (100), chemical oxygen demand (83.12), and total organic carbon (65.5) could happen at pH of 7, catalyst dosage of 100 mg/L, PMS dosage of 2 mM, RB5 concentration of 50 mg/L, and time of 30 min. The results of the temperature effect showed that the activation energy (Ea = 20.92 kJ/mol) for the synthesized catalyst is much lower compared to other studies. The PMS/MWCNTs-CoFe2O4 system had higher decolorization efficiency and kinetic rates compared to other adsorption and oxidation systems. Quenching experiments proved that RB5 was degraded by sulfate and hydroxyl radicals. The MWCNTs-CoFe2O4 catalyst showed suitable stability and reusability even after five consecutive catalytic reactions. The continuous treatment of RB5 in real water resources was performed using catalyst packed in a column reactor, and its results showed the high efficiency of the column in the catalytic treatment of the dye at long reaction time. Based on the proposed degradation pathway, the azo bands and the naphthalene structure of RB5 are oxidized to compounds with low molecular weight. Practitioner points: MWCNTs-CoFe2O4 was used as a novel recyclable catalyst for the activation of peroxymonosulfate and dye degradation. The rate of dye degradation and peroxymonosulfate activation by MWCNTs-CoFe2O4 was much higher than that of the catalysts alone. Radical (Formula presented.), with contribution percentage of 73.20, was the main agent for degradation of Reactive Black 5 dye. MWCNTs-CoFe2O4 in the dye degradation process showed excellent stability and reusability, lower activation energy, and easier separation. The dye degradation products were identified by gas chromatography and UV-vis spectrophotometric analyses, and their degradation pathway was suggested. © 2020 Water Environment Federatio