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This study examined the removal of phenol from aqueous solutions through electro-Fenton and electro-persulfate processes using iron electrodes. The effect of operational parameters such as initial pH, current density, initial concentration of phenol, hydrogen peroxide dose, and persulfate (PS) concentration on the removal of phenol were investigated. The results showed that the efficiency of phenol removal was directly related to the initial concentrations of hydrogen peroxide and PS, and was inversely correlated with a highly alkaline pH and elevated concentration of phenol. The efficiency of phenol removal was significantly increased by increasing PS and H 2 O 2 concentrations from 0.1 to 0.4 mM, but there was little influence on removal efficiency with greater quantities of PS and H 2 O 2 . Ultimately, phenol was almost completely removed after 45 min in both processes.

Background This work studied the performance of UV/PS/TiO2NPs and UV/PI/TiO2NPs as hybrid advanced oxidation processes for degradation of paraquat in aqueous solution, because this very toxic herbicide is used third most widely. Results The effects of several factors such as UV irradiation, initial oxidant concentration, TiO2 nanoparticles dosage, and pH on the degradation efficiency were investigated. The process optimization was performed by the central composite design as a tool of response surface methodology for 30 mgL−1 of the herbicide initial concentration at 25 ℃ and 40 min of degradation process. Based on the results, a degradation efficiency of 77% and 90% were obtained for the UV/PS/TiO2NPs and UV/PI/TiO2NPs processes, respectively, in the optimum conditions. The mineralization efficiency of the paraquat solution using UV/PS/TiO2NPs and UV/PI/TiO2NPs processes are about 32% and 55%, respectively, after 40 min. The kinetic studies show that both processes follow a pseudo-first-order kinetic model, and the kinetic constants are 0.0299 min−1 for the PS process and 0.0604 min−1 for the PI process. The electrical energy consumption was estimated to be about 481.60 kWhm−3 for the PS process and 238.41 kWhm−3 for the PI process. Conclusions The degradation and mineralization efficiency of the paraquat solution using the UV/PI/TiO2NPs process was more than that of the UV/PS/TiO2NPs process at the optimum conditions after 40 min.