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This study aims the development of photoelectrodes to be incorporated in a photoelectrocatalytic ozonation (PECO) process for tertiary treatment of urban wastewaters, targeting the removal of contaminants of emerging concern (CEC). PECO tests were performed using urban wastewater after secondary treatment fortified with Cefadroxil (CFX, C16H17N3O5S), as target model CEC. Three Nitrogen and Carbon doped TiO2 (CN-TiO2) electrodes were synthesized by anodizing at 50, 70, and 90 V, and calcined. These materials were characterized by X-Ray diffraction and Rietveld refinement, Scanning Electron Microscopy, Diffuse Reflectance Spectroscopy, X-ray photoelectron spectroscopy, chronoamperometry, and electrochemical impedance spectroscopy, to correlate defects with photoactivity. All photoanodes considerably reduced their main bandgaps by the incorporation of C and N species, to enable absorption capacities in the UV region using a Xe lamp. The lowest oxygen vacancy content and largest crystallite size were found for CN-TiO2-70, favoring the reduction of bulk defects that could act as recombination of charge carriers. Therefore, oxygen vacancies affect more the TiO2 photoactivity compared to the crystallite size or the light absorption capacity, confirming that a lower content of vacancies in the material bulk and surface doping significantly influence the activity as detected by Rietveld refinement, DRS, and XPS. The electrochemical techniques confirm that the highest photocurrent was obtained for CN-TiO2-70, whence this photoanode was chosen to carry out the CFX degradation. A point defect model simulating Nyquist plot reveals that the photoactivity depends on the speed to diffuse oxygen vacancies through the TiO2 coating. All abatement processes were followed by high-performance liquid chromatography, and Total Organic Carbon (TOC). At neutral and alkaline conditions, CFX is eliminated to levels below the analytical detection limit after 90 min of treatment (TOC removals of 87 and 91%, respectively), indicating that the coupling between the CN-TiO2-70 photocatalyst and ozone is effective in eliminating the contaminant due to parallel routes forming •OH species. Lower CFX degradation observed at acidic pH (TOC removal of 70%) is assigned to the difficulty of oxidizing protonated CFX species.

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Nowadays, the presence of persistent dissolved pollutants in water has received increasing attention due to their toxic effects on living organisms. Considering the limitations of conventional wastewater treatment processes for the degradation of these compounds, advanced oxidation processes such as electro-Fenton and sono-chemical process, as well as their combination, appear as potentially effective options for the treatment of wastewater contaminated with bio-recalcitrant pollutants. In view of the importance of the development of processes using real effluents, this review aims to provide a comprehensive perspective of sono-electro-Fenton-related processes applied for real wastewater treatment. In the first section, the fundamentals and effectiveness of both homogeneous and heterogeneous electro-Fenton approaches for the treatment of real wastewater are presented. While the second part of this work describes the fundamentals of ultrasound-based processes, the last section focuses on the coupling of the two methods for real wastewater treatment and on the effect of the main operational parameters of the process. On the basis of the information presented, it is suggested that sono-electro-Fenton processes substantially increase the efficiency of the treatment as well as the biodegradability of the treated wastewater. The combined effect results from mass transfer improvement, electrode cleaning and activation, water electrolysis, and the electro-Fenton-induced production of hydroxyl radicals. The information presented in this work is expected to be useful for closing the gap between laboratory-scale assays and the development of novel wastewater technologies.

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In this work, the occurrences of bacteria families and relevant pharmaceuticals in municipal wastewater effluents from Bogotá (Colombia), and their treatment by the photo-electro-Fenton process were studied. Twenty-five representative pharmaceuticals (azithromycin, carbamazepine, ciprofloxacin, clarithromycin, diclofenac, enalapril, gabapentin, iopromide, metoprolol, sulfamethoxazole, trimethoprim, valsartan, clindamycin, erythromycin, levamisole, lincomycin, norfloxacin, oxolinic acid, phenazone, primidone, salbutamol, sulfadiazine, tetracycline, tramadol, and venlafaxine) were quantified in the effluent by LC-MS/MS analysis. Four of these target compounds (azithromycin, diclofenac, trimethoprim, norfloxacin) were found at concentrations that represent an environmental risk. In addition, several bacteria families related to water and foodborne diseases were identified in such effluents (e.g., Pseudomonadaceae, Campylobacteraceae, Aeromonadaceae, Enterobacteriaceae, and Bacteroidaceae), via shotgun-metagenomic technique. Then, a bench-scale photo-electro-Fenton (PEF) system equipped with a DSA anode (Ti/IrO2-SnO2) and a GDE cathode was applied to treat such effluents. After 60 min, this treatment led to a decrease in the ratio of the bacterial content in the original samples, ~150 thousand times, and a pondered removal of 66.12% for the pharmaceuticals. The study of the process pathways indicated that the bacteria and pharmaceuticals elimination mainly occurred through attacks of hydroxyl and chlorine radicals. Interestingly, in the case of pharmaceuticals, their environmental risk quotients were diminished after the PEF application. Furthermore, the prolonged action of this electrochemical process induced ~15% of mineralization and a significant reduction of the total DNA (removal >85%). Hence, the photo-electro-Fenton process showed to be a promising alternative to deal with municipal effluents for limiting the waterborne diseases, pollution by pharmaceuticals, and mobility/availability of genetic material coming from microorganisms.

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Pharmaceuticals, such as dipyrone (DIP), paracetamol (PCT), and propranolol (PPN), are widely used analgesics and beta-blockers with the greatest presence in wastewaters and, consequently, in natural waters. The present work evaluated solar light-driven photocatalyst from petrochemical industrial waste (PW) as a strategy for the degradation of three pharmaceuticals in different water matrices (distilled water-DW, simulated wastewater-SWW, and real hospital wastewater-RHWW). All experiments were carried out in a solar photo-reactor with a capacity of 1 L and the experimental condition employed was a catalyst concentration of 350 mg L-1 at pH 5.0; these conditions were selected considering the Doehlert design validation spreadsheet and the desirability function. All materials prepared were conveniently characterized by zeta potential, small-angle X-ray scattering (SAXS), diffuse reflectance ultraviolet-visible (DRUV), and infrared spectroscopy. According to the results of the characterization, significant differences have been observed between the PW and the photocatalyst such as vibrational modes, optical absorption gap, and acid-basic characteristics on the surface, which suggests the potential use of the photocatalyst in the degradation of contaminants of emerging concern. Based on pharmaceutical degradation, DIP showed the highest photosensitivity (87.5%), and therefore the highest photocatalytic degradation followed by PPN; both compounds achieved final concentrations below the limit of quantification of the chromatographic method in DW. However, PCT was the most recalcitrant pharmaceutical in all matrices. Radicals from chromophoric natural organic matter (NOM) could improve PCT degradation in the SWW matrix (56%). Nevertheless, the results in RHWW showed a matrix effect with decreased the oxidation percentages (DIP-99%; PPN-71%; PCT-17%); hence, the addition of an oxidant such as H2O2 was studied as a pharmaceutical oxidation boost in RHWW. PPN was the molecule most sensitive to this strategy of oxidation (98%). Furthermore, 20 transformation products (TPs) generated throughout the treatment were identified by LC-QTOF MS using a customized TPs database. According to quantitative structure activity relationship (Q)SAR analysis, more than 75% of the TPs identified were not biodegradable. About 35% of them have oral toxicity characteristics indicated by Cramer's rules, and the DIP TPs represent high toxicity for different trophic levels.

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Glucocorticoids are widely used to treat a variety of diseases. Consequently, these compounds have been found in water and wastewater matrix. Despite studies have proven its toxicity, just a few works investigate techniques to degrade and mineralize them. To solve this issue, this work presents the degradation and mineralization of prednisone (PRED) by electrochemical advanced oxidation (EAO) using a boron-doped diamond supported on niobium (Nb/BDD) anode in synthetic and real wastewater. Cyclic voltammetry (CV) was performed to investigate the PRED oxidation mechanisms. CV suggest that PRED will be oxidized via HO• and other oxidants generated from the ions present in the liquid matrix (S2O82-, SO4•-, HClO, ClO- etc.). Different EAO conditions as initial pH (3, 7 and 11) and applied current densities (5, 10 and 20 mA cm-2) were evaluated. The best result was obtained at alkaline pH (11) and a current density of 20 mA cm-2, achieving 78% of degradation and 42% of mineralization. Using the best conditions, the EAO was applied as a polishing treatment stage to remove PRED from a biological pre-treated municipal wastewater spiked with PRED. The results indicate that EAO applied in the real matrix provides better results than the synthetic solution, probably associated with the presence of ions that can be electrochemically converted into oxidant species, resulting in higher kinetic constant, mineralization current efficiency and lower energetic consumption. Therefore, the EAO process without the addition of chemicals has proven to be an effective alternative as a tertiary treatment of municipal wastewater contaminated with PRED.

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In this work, magnetic cobalt nanoparticles (CoNPs) were synthesized and applied to the removal of Remazol golden yellow RNL (RGY) from aqueous solutions and textile wastewater. The CoNPs were characterized and the Co content found in the CoNPs was 60.38% (m/m). The analysis of X-ray Diffraction (XRD) and Raman Spectroscopy indicated the presence of Co0 and CoO in the composition of the material, as confirmed by Thermogravimetric Analysis coupled to Mass Spectrometry (TG-MS). Images obtained by the Transmission Electron Microscope (TEM) showed that the CoNPs have sizes smaller than 10 nm, sphere morphology and high agglomeration capacity. The results obtained by nitrogen adsorption-desorption suggested that the nanomaterial presented a mesoporous characteristic, low specific surface area (15.70 m2 g-1) and a pore volume and pore diameter of 0.072 cm3 g-1 and 3.64 nm, respectively. CoNPs removed the RGY with high efficiency, reaching almost 100% removal in 30 min. The kinetic results showed that the reaction followed pseudo-second-order kinetics. Additionally, the removal process can be altered depending on the experimental condition. For instance, under acidic conditions, the reductive degradation prevailed, while in neutral or basic conditions, two simultaneous processes occur: reductive degradation and adsorption. Finally, CoNPs were applied to textile wastewater. The results showed high discoloration, reaching almost 88%. However, there was only a 32% decrease in chemical oxygen demand, showing that CoNPs are efficient at removing organic dyes from aqueous solutions.

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This work explores the role of electrode material and the oxidation ability of electrochemical advanced oxidation processes (EAOPs), such as electro-oxidation (EO) with or without H2O2 production, electro-Fenton (EF), and UVA photoelectron-Fenton (PEF), in the degradation of metolachlor. The performance of the EAOPs using Boron-doped diamond (BDD) or Pt as anode has been compared from the analysis of decay kinetics, mineralization profile, and energy consumption using small undivided batch cell. Metolachlor concentration always decays following a pseudo-first-order kinetics. Using the Pt anode, none of the processes reaches 30% mineralization, including PEF. In contrast, the BDD anode showed a higher mineralization rate allowing almost total mineralization in PEF due to the synergetic action of UVA light and oxidant hydroxyl radicals formed in the bulk from Fenton's reaction, as well as in the BDD, which has large reactivity to oxidize the pollutants. The increase in current density and decrease in metolachlor concentration accelerated the mineralization in PEF, although lower current efficiency and higher energy consumption was obtained. The GC-MS and HPLC analysis allowed the identification of up to 17 aromatics intermediates and 7 short-chain carboxylic acids. Finally, a reaction pathway for metolachlor mineralization by EAOPs is proposed. PEF with BDD allowed total removal of the herbicide in real water matrix and a high mineralization (83.82%).

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Solutions with 0.65 mM of the antituberculosis drug isoniazid (INH) in 0.050 M Na2SO4 at pH 3.0 were treated by electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) processes using a cell with a BDD anode and a carbon-PTFE air-diffusion cathode. The influence of current density on degradation, mineralization rate, and current efficiency has been thoroughly evaluated in EF. The effect of the metallic catalyst (Fe2+ or Fe3+) and the formation of products like short-chain linear aliphatic carboxylic acids were assessed in PEF. Two consecutive pseudo-first-order kinetic regions were found using Fe2+ as catalyst. In the first region, at short time, the drug was rapidly oxidized by ●OH, whereas in the second region, at longer time, a resulting Fe(III)-INH complex was much more slowly removed by oxidants. INH disappeared completely at 300 min by EF, attaining 88 and 94% mineralization at 66.6 and 100 mA cm-2, respectively. Isonicotinamide and its hydroxylated derivative were identified as aromatic products of INH by GC-MS and oxalic, oxamic, and formic acids were quantified by ion-exclusion HPLC. The PEF treatment of a real wastewater polluted with the drug led to slower INH and TOC abatements because of the parallel destruction of its natural organic matter content.

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The roles of the anode material, boron-doped diamond (BDD), with different boron (B) and substrate Silicon (Si) or Niobium (Nb) content, and one dimensionally stable anode (DSA®), were evaluated in the oxidation of norfloxacin (NOR) by electrochemical advanced oxidation process (EAOP). The effect of other components in real wastewater on the performance of EAOP was also studied. The anode materials were characterized by cyclic voltammetry, regarding diamond quality, electro-generation of oxidants and NOR oxidation mechanism (direct and/or indirect). The results showed that the anode material influences on the NOR oxidation pathway, due to distinct characteristics of the substrate and the coating. Apparently, low difference in diamond-sp³/sp2-carbon ratio (Si/BDD100 × Si/BDD2500) does not leads to significant differences in the EAOP. On the other hand, the variation in the sp³/sp2 ratio seems to be higher when Si/BDD2500 and Nb/BDD2500 are compared, which would explain the best current efficiency result for Si substrate. However, the Nb substrate presented a similar current efficiency and a 60% lower energy consumption. Dissolved organic matter (DOM) present in the real wastewater affect the EAOP-Nb/BDD due to HO and persulfate ions scavenged. However, when supporting electrolyte was added to a real wastewater spiked with NOR, the NOR decay reaches similar values found to the synthetic one. Due to the energy saving and mechanical properties, Nb substrate presents some technological advantages in relation to Si, which can facilitate the application to industrial levels.

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