Electro-Fenton treatment of a complex pharmaceutical mixture: Mineralization efficiency and biodegradability enhancement

Electrochemical degradation of favipiravir (anti-viral) drug from aqueous solution: optimization of operating parameters using the response surface method

The aim of the current study is to investigate the efficacy of the electro-Fenton process in the degradation of favipiravir drugs from aqueous solutions, which has increased in use as a result of the COVID-19 pandemic. The Response Surface Methodology (RSM) was developed using a Central Composite Design (CCD) in which five independent variables, including Fe2+ concentration, current density, initial FVP concentration, pH, and reaction time, were coded with high and low levels, and the maximum removal percentage of FVP (97.8%) and COD (91.65%) were determined as responses. In the EF process, 530 mg/L H2O2 was produced in-situ by cathodic reduction of O2 in aqueous solution and thus FVP has been successfully oxidized through hydroxyl radicals. The H2O2/Fe2+ ratio was determined to be 0.51 under optimum conditions. At the end of the experiment, the maximum energy consumption was found to be 2.12 kWh per g COD. The FVP was completely mineralized in a very short time by the EF process, according to the LC-MS/MS examination. The EF process followed the pseudo first-order kinetic model with the rate constants of 0.023, 0.016 and 0.006 1/min for pH 2, 3 and 4, respectively. According to the findings of this study, the electro-Fenton process is an effective method for removing FVP from aqueous solutions. To the authors' knowledge, this is the first study to show the degradation and optimum conditions of FVP in aqueous solution using the electro-Fenton (EF) process.

Pretreatment and composting technology of agricultural organic waste for sustainable agricultural development

With the continuous development of agriculture, Agricultural organic waste (AOW) has become the most abundant renewable energy on earth, and it is a hot spot of research in recent years to realize the recycling of AOW to achieve sustainable development of agricultural production. However, lignocellulose, which is difficult to degrade in AOW, greenhouse gas emissions, and pile pathogenic fungi and insect eggs are the biggest obstacles to its return to land use. In response to the above problems researchers promote organic waste recycling by pretreating AOW, controlling composting conditions and adding other substances to achieve green return of AOW to the field and promote the development of agricultural production. This review summarizes the ways of organic waste treatment, factors affecting composting and problems in composting by researchers in recent years, with a view to providing research ideas for future related studies.

Treatment of petroleum hydrocarbon contaminated soil by combination of electro-Fenton and biosurfactant-assisted bioslurry process

Removing petroleum hydrocarbons (PHCs) from polluted soil is challenging due to their low bioavailability and degradability. In this study, an experiment was carried out to treat soil polluted with petroleum hydrocarbon using a hybrid electro-Fenton (with BDD anode electrode) and biological processes stimulated with long-chain rhamnolipids (biosurfactants). Electro-Fenton treatment was applied as a pretreatment before the biological process to enhance PHC biodegradability, which would benefit the subsequent biological process. The effects of initial pH, hydroxide concentration, soil organic matter composition, PHCs intermediates during the electro-Fenton process, and total numbers of bacteria in the biological process were analyzed to determine the optimum conditions. The results showed that the optimized electrolysis time for the electro-Fenton was 12 h. The change induced during pretreatment at a specified time was found suitable for the biological process stage and led to 93.6% PHC degradation in combination with the electro-Fenton-and-biological process after 72 h. The combined system's performance was almost 40% higher than individual electro-Fenton and biological treatments. GC-MS analysis confirms the formation of 9-octadecen-1-ol (Z), 2-heptadecene, 1-nonadecene, 1-heneicosene, and pentacosane as fragmentation during the PHCs degradation process. Thus, the electro-Fenton process as pretreatment combined with a biological process stimulated with rhamnolipids (biosurfactants) could be effectively applied to remediate soil polluted with PHCs. However, the system needs further research and investigation to optimize electrolysis time and biosurfactant dose to advance this approach in the soil remediation process.

From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH•) generated from an oxidizing agent (H2O2 or O2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e− route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e− catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e− and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e− processes are summarized.

Removal of Iodine-Containing X-ray Contrast Media from Environment: The Challenge of a Total Mineralization

Iodinated X-ray contrast media (ICM) as emerging micropollutants have attracted considerable attention in recent years due to their high detected concentration in water systems. It results in environmental issues partly due to the formation of toxic by-products during the disinfection process in water treatment. Consequently, various approaches have been investigated by researchers in order to achieve ICM total mineralization. This review discusses the different methods that have been used to degrade them, with special attention to the mineralization yield and to the nature of formed by-products. The problem of pollution by ICM is discussed in the first part dedicated to the presence of ICM in the environment and its consequences. In the second part, the processes for ICM treatment including biological treatment, advanced oxidation/reductive processes, and coupled processes are reviewed in detail. The main results and mechanisms involved in each approach are described, and by-products identified during the different treatments are listed. Moreover, based on their efficiency and their cost-effectiveness, the prospects and process developments of ICM treatment are discussed.

Electrochemical Oxidation of Anastrozole over a BDD Electrode: Role of Operating Parameters and Water Matrix

The electrochemical oxidation (EO) of the breast-cancer drug anastrozole (ANZ) is studied in this work. The role of various operating parameters, such as current density (6.25 and 12.5 mA cm−2), pH (3–10), ANZ concentration (0.5–2 mg L−1), nature of supporting electrolytes, water composition, and water matrix, have been evaluated. ANZ removal of 82.4% was achieved at 1 mg L−1 initial concentration after 90 min of reaction at 6.25 mA cm−2 and 0.1 M Na2SO4. The degradation follows pseudo-first-order kinetics with the apparent rate constant, kapp, equal to 0.022 min−1. The kapp increases with increasing current density and decreasing solution pH. The addition of chloride in the range 0–250 mg L−1 positively affects the removal of ANZ. However, chloride concentrations above 250 mg L−1 have a detrimental effect. The presence of bicarbonate or organic matter has a slightly negative but not significant effect on the process. The EO of ANZ is compared to its degradation by solar photo-Fenton, and a preliminary economic analysis is also performed.

Magnetic TiO2/Fe3O4-Chitosan Beads: A Highly Efficient and Reusable Catalyst for Photo-Electro-Fenton Process

Heterogeneous photo-electro-Fenton process is an attractive technology for the removal of recalcitrant pollutants. To better exploit the presence of an irradiation source, a bifunctional catalyst with TiO2 nanoparticles embedded into an iron–chitosan matrix was developed. The catalytic activity of the catalyst was improved by the optimization of the loaded TiO2content. The prepared composite catalysts based on TiO2, Fe3O4 and chitosan were called TiO2/Fe3O4-CS beads. The best catalyst with an optimal ratio TiO2/Fe = 2 exhibited a high efficiency inthe degradation and mineralization of chlordimeform (CDM) insecticide. Under the optimum conditions (concentration of catalyst equal to 1 g L−1 and applied current intensity equal to 70 mA), a real effluent doped with 30 mg L−1 of CDM was efficiently treated, leading to 80.8 ± 1.9% TOC reduction after 6 h of treatment, with total removal of CDM after only 1 h.The generated carboxylic acids and minerals wereidentified and quantified. Furthermore, the stability and reusability of the developed catalyst was examined, and an insignificant reduction in catalytic activity was noticed forfour consecutive cycles of the photo-electro-Fenton process. Analyses using SEM, XRD and VSM showed a good stability of the physicochemical properties of the catalyst after use.

Electrochemical removal of synthetic methyl orange dyeing wastewater by reverse electrodialysis reactor: Experiment and mineralizing model

In this paper, the synthetic methyl orange (MO) dyeing wastewater treated by a reverse electrodialysis reactor (REDR) with 40 member pairs was investigated first. The boron-doped diamond (BDD) and carbon felt were adopted as an anode and a cathode in the REDR. The influences of operation parameters on the chemical oxygen demand (COD) removal efficiency were detected and explored. Then, a mathematical model of organic mineralizing was developed for the REDR to predict the variation of COD removal efficiency with treating time under the different operation conditions. Finally, the energy consumption of the wastewater treated by the REDR was analyzed. The results showed that raising the working fluid flowing velocity and electrode rinse solution flowrate improved the COD removal efficiency and instantaneous current efficiency (ICE), and reduced the total energy consumption (TEC) of the REDR. Raising the initial MO concentration could significantly reduce the TEC despite the COD removal efficiency being near. Since the main energy consumed by the REDR was salinity gradient energy (SGE) from waste heat conversion or the natural environment, the energy cost of REDR treating wastewater has been reduced significantly.

Comparison of homogeneous and heterogeneous electrochemical advanced oxidation processes for treatment of textile industry wastewater

This study aimed at understanding the influence of the generation of oxidants in a heterogeneous way at boron-doped diamond (BDD) anode (anodic oxidation (AO)) or homogeneously in the bulk (electro-Fenton (EF)) during treatment of a textile industry wastewater. Both processes achieved high TOC removal. A yield of 95 % was obtained by combining EF with BDD anode during 6 h of treatment. The EF process was found to be faster and more efficient for discoloration of the effluent, whereas AO was more effective to limit the formation of degradation by-products in the bulk. An advantage of AO was to treat this alkaline effluent without any pH adjustment. Operating these processes under current limitation allowed optimizing energy consumption in both cases. However, using BDD anode led to the formation of very high concentration of ClO₃^-/ClO₄^- from Cl^- oxidation (even at low current density), which appears as a key challenge for treatment of such effluent by AO. By comparison, EF with Pt anode strongly reduced the formation of ClO₃^-/ClO₄^-. Operating EF at low current density even maintained these concentrations below 0.5 % of the initial Cl^- concentration. A trade-off should be considered between TOC removal and formation of toxic chlorinated by-products.

A critical review on paracetamol removal from different aqueous matrices by Fenton and Fenton-based processes, and their combined methods

Paracetamol (PCT), also known as acetaminophen, is a drug used to treat fever and mild to moderate pain. After consumption by animals and humans, it is excreted through the urine to the sewer systems, wastewater treatment plants, and other aquatic/natural environments. It has been detected in trace amounts in effluents of wastewater plant treatments, sewage sludge, hospital wastewaters, surface waters, and drinking water. PCT can cause genetic code damage, oxidative degradation of lipids, and denaturation of protein in cells, and its toxicity has been well-proven in bacteria, algae, macrophytes, protozoan, and fishes. To avoid its harmful health problems over living beings, powerful Fenton and Fenton-based treatments as pre-eminent advanced oxidation processes (AOPs) have been developed because of the inefficient treatment by conventional treatments. This paper presents a comprehensive and critical review over the application of such Fenton technologies to remove PCT from natural waters, synthetic wastewaters, and real wastewaters. The characteristics and main results obtained using Fenton, photo-Fenton, electro-Fenton, and photoelectro-Fenton are described, making special emphasis in the oxidative action of the generated reactive oxygen species. Hybrid processes based on the coupling with ultrasounds, gamma radiation, photocatalysis, photoelectrocatalysis, zero-valent iron-activated persulfate, adsorption, and microbial fuel cells, are analyzed. Sequential treatments involving the initiation with plasma gliding arc discharge and post-biological process are detailed. Comparative results with other available AOPs are also described and discussed. Finally, 13 aromatic by-products and 9 short-linear aliphatic carboxylic acid detected during the PCT removal by Fenton and Fenton-based processes are reported, with the proposal of three parallel pathways for its initial degradation.

Decolorization and Degradation of Methyl Orange Azo Dye in Aqueous Solution by the Electro Fenton Process: Application of Optimization

In a batch reactor, the EF advanced oxidation decolorization of aqueous solutions of methyl orange MO, a commercial azo reactive textile dye, was investigated in the presence of two different electrodes. The evaluation included various operational variables such as the IC current intensity (60 mA, 80 mA, and 100 mA), initial concentration of pollutant MO (20 mg/L, 40 mg/L, and 60 mg/L), initial pH of solution (3, 5, and 7), temperature of solution (20 °C, 30 °C, and 50 °C), and initial concentration of catalyst [Fe2+] (0.1 mM, 0.2 mM, and 0.3 mM) on the discoloration rate. A Box-Behnken Design of Experiment (BBD) was used to optimize the parameters that directly affect the Electro-Fenton (EF) process. Under the optimal experimental conditions such as [Fe2+] = 0.232 mM, pH = 3, IC = 80 mA, [MO] = 60 mg/L, and T = 30 ± 0.1 °C, the maximum discoloration rate achieved was 94.9%. The discoloration of the aqueous MO solution during the treatment time was confirmed by analysis of the UV-visible spectrum. After a review of the literature on organic pollutant degradation, the EF system provided here is shown to be one of the best in terms of discoloration rate when compared to other AOPs.

Contribution of Illicit Drug Use to Pharmaceutical Load in the Environment: A Focus on Sub-Saharan Africa

Illicit drug abuse and addiction are universal issues requiring international cooperation and interdisciplinary and multisectoral solutions. These addictive substances are utilized for recreational purposes worldwide, including in sub-Saharan Africa. On the other hand, conventional wastewater treatment facilities such as waste stabilization ponds lack the design to remove the most recent classes of pollutants such as illicit drug abuse. As a result, effluents from these treatment schemes contaminate the entire ecosystem. Public health officials are concerned about detecting these pollutants at alarming levels in some countries, with potential undesirable effects on aquatic species and increased health hazards through exposure to contaminated waters or recycling treated or untreated effluents in agriculture. Contaminants including illicit substances enter the environment by human excreta following illegal intake, spills, or through direct dumping, such as from clandestine laboratories, when their manufacturer does not follow accepted production processes. These substances, like other pharmaceuticals, have biological activity and range from pseudopersistent to highly persistent compounds; hence, they persist in the environment while causing harm to the ecosystem. The presence of powerful pharmacological agents such as cocaine, morphine, and amphetamine in water as complex combinations can impair aquatic organisms and human health. These compounds can harm human beings and ecosystem health apart from their low environmental levels. Therefore, this article examines the presence and levels of illicit substances in ecological compartments such as wastewater, surface and ground waters in sub-Saharan Africa, and their latent impact on the ecosystem. The information on the occurrences of illicit drugs and their metabolic products in the sub-Saharan Africa environment and their contribution to pharmaceutical load is missing. In this case, it is important to research further the presence, levels, distribution, and environmental risks of exposure to human beings and the entire ecosystem.

Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes

The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups, further increasing the applied current lowered the degradation efficiency due to the formation of by-products and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical conditions, specifically at 200 °C, using 150 mM H₂O₂ and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H₂O₂ concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is not the most influential parameter. A comparison of the three methodologies in terms of performance as well as energy consumption and simplicity of operation highlighted the advantages of subcritical water oxidation.

Progress of homogeneous and heterogeneous electro-Fenton treatments of antibiotics in synthetic and real wastewaters. A critical review on the period 2017-2021

Antibiotics are widely supplied over all the world to animals and humans to fight and heal bacteriological diseases. The uptake of antibiotics has largely increased the average-life expectancy of living beings. However, these recalcitrant products have been detected at low concentrations in natural waters, with potential health risks due to alterations in food chains and an increase in the resistance to bacterial infection, control of infectious diseases, and damage of the beneficial bacteria. The high stability of antibiotics at mild conditions prevents their effective removal in conventional wastewater treatment plants. A powerful advanced oxidation processes such as the electro-Fenton (EF) process is being developed as a guarantee for their destruction by ^•OH generated as strong oxidant. This review presents a critical, exhaustive, and detailed analysis on the application of EF to remediate synthetic and real wastewaters contaminated with common antibiotics, covering the period 2017-2021. Homogeneous EF and heterogeneous EF involving iron solid catalysts or iron functionalized cathodes, as well as their hybrid and sequential treatments, are exhaustively examined. Their fundamentals and characteristics are detailed, and the main results obtained for the removal of the most used antibiotic families are carefully described and discussed. The role of generated oxidizing agents is explained, and the by-products generated, and reaction sequences proposed are detailed.

Comparative degradation of 5-fluorouracil in aqueous solution by using H2O2-modified subcritical water, photocatalytic oxidation and electro-Fenton processes

This study investigated the degradation of the antineoplastic agent 5-fluorouracil (5-FU) widely applied to treat different cancers using different advanced oxidation processes such as electro-Fenton (EF), photocatalysis with TiO_2, and H₂O₂-modified subcritical water oxidation. The treatment with the EF process was the most efficient compared to others. Interestingly, in the EF process, the oxidative degradation of 5-FU behaved differently depending on the anode used. At low currents (20 and 40 mA), Pt and DSA anodes performed better than BDD and Ti₄O₇ anodes. In contrast, at the higher current of 120 mA, the production of heterogeneous hydroxyl radicals (M(^•OH)) became important and contributed significantly to the oxidation of 5-FU in addition to homogeneous ^•OH generated in the bulk solution. These latter have high O₂-evolution overpotential leading to the high amount of physisorbed M(^•OH) compared to Pt and DSA. The oxidative degradation of 5-FU was then performed by titanium dioxide-based photocatalytic oxidation and subcritical water oxidation processes, both of which showed a lower degradation efficiency and failed to achieve complete mineralization. Finally, a comparison was performed in laboratory-scale, taking into account the following performance indicators: the degradation efficiency, the mineralization power, the cost of equipment and reagents, and the energy required for the treatment of 5-FU.

Removal of azimsulfuron and zoxamide using a tapered variable diameter biological fluidized bed combined with electrochemistry: Mass fraction division, energy metabolism activity and carbon emissions

The performance of the combination system of tapered variable diameter biological fluidized bed (TVDBFB) with electrochemistry (EC) was evaluated for removing azimsulfuron and zoxamide under different temperatures and influent concentrations. Maximum removal efficiency of azimsulfuron and zoxamide could reach 94% and 98% under higher influent concentration (about 780 mg/L). As temperature decreased from 32 ℃ to 8 ℃, the mS_e increased from 48% to 56%, and the mS_o and mS_xv decreased from 30% to 22% and 27% to 24%, respectively. As the influent COD equivalent concentration of azimsulfuron and zoxamide enhanced from 260 mg/L to 780 mg/L, the K_d increased from 0.06 d^-1 to 0.23 d^-1. Temperature and influent concentration were main influencing factors of DHA, ATP and ETS. Increasing aeration in TVDBFB and HRT in EC under shock conditions could improve azimsulfuron and zoxamide removal efficiency, however, it was also accompanied by higher carbon emissions.

Degradation of isoniazid by anodic oxidation and subcritical water oxidation methods: Application of Box-Behnken design

Pharmaceutical compounds released into the aquatic environment are known to cause toxic effects on the environment. Isoniazid is widely used in the treatment of tuberculosis and is, therefore, frequently encountered in environmental waters. In this study, the degradation of isoniazid was investigated by anodic oxidation and subcritical water oxidation method which are members of Advanced Oxidation Processes. The Box-Behnken Design was used to determine the effects of current, initial concentration, and electrolysis time on mineralization in the anodic oxidation process, which carried out a cell with a Pt cathode and boron-doped diamond anode. The highest mineralization value of 78.14% was achieved at optimal conditions of 300 mA, 3 h, and 100 mg/L initial concentration. The degradation of Isoniazid was also investigated under subcritical water conditions using an ecological oxidizing agent, H₂O₂. The maximum mineralization rate of 72.23% was obtained when 100 mM H₂O₂ was used for a 90 min treatment at 125 °C for 100 mg/L Isoniazid solution in the subcritical water oxidation process. The LC-MS results showed that the degradation products obtained by AO and SWO methods were different from each other. Finally, possible degradation mechanisms are proposed according to the degradation products obtained for both processes.

Removal of Tricyclazole and Total Organic Carbon in Real Pesticide Wastewater by Electro-Fenton

In this study, electro-Fenton (EF) was employed for the removal of tricyclazole (TC) and total organic carbon (TOC) in real pesticide wastewater (RPW). The central composite design (CCD) with three parameters, that is, current density, Fe2+ concentration, and electrolysis time, has been conducted to predict the TOC and TC removal efficiency. The high correlation of the quadratic models of 0.9842 and 0.9781 for TC and TOC removal, respectively, indicates the significance of the models. The obtained results revealed that the high-efficiency removal of both TC and TOC in RPW. Approximately 99.6% of TC was decomposed under the optimum conditions of a current density of 2.2 mA/cm2 and an Fe2+ concentration of 0.2 mM during 188 min with an operating cost of 121.392 $/kg TC or ∼2.692 $/m3, while 84.2% TOC was eliminated at a current density of 2.2 mA/cm2 and an Fe2+ concentration of 0.2 mM during 217 min with an operating cost of 3.019 $/kg TOC or 3.916 $/m3. Acute toxicity tests at optimal condition revealed moderate exhibition toxicity of treated wastewater against Daphnia magna with LC50 values of 3.12%, 2.05%, 1.84%, and 1.36% at 24 h, 48 h, 72 h, and 96 h, respectively. The removal of TC and TOC followed pseudo-first-order kinetic with an R2 of ∼0.993 and 0.923, respectively.

In-house-prepared carbon-based Fe-doped catalysts for electro-Fenton degradation of azo dyes

Compounds used in the fashion industry effect the water bodies in the vicinity of textile factories, resulting in the visible coloration of surface water. Fe-doped graphite-based in house prepared electrodes were used in the Fenton- -like degradation of Reactive Blue 52 (RB52). The electrodes consisting of high-density graphite in three granulation sizes and three levels of Fe content were characterized using scanning electron microscopy (SEM). The amount of Fe in the electrodes and H2O2 concentration in synthetic textile wastewater were optimized. Additionally, the size of graphite grains was varied to investigate whether it effects the degradation rate. Under only 10 min of electro-Fenton degradation, a system with 10 mmol dm-3 of H2O2 and an electrode made of 7 % of Fe and 70 ?m of granulation size of graphite, degraded over 75 % of RB52, and over 99 % after 40 min of treatment. The obtained results indicate that the proposed approach could be beneficial in the field of novel materials for environmental application and that in house prepared carbon could be an excellent replacement for commercially available supports.

Photo-Fenton Oxidation of Methyl Orange Dye Using South African Ilmenite Sands as a Catalyst

In this study, the viability of South African ilmenite sands as a catalyst in the photo-Fenton-like degradation of methyl orange (MO) dye was investigated. The mineralogy and other properties of the material were characterized. Complete decolorization occurred under acidic conditions (pH < 4) in the presence of ilmenite and H2O2. Light irradiation accelerated the rate of reaction. Parameter optimization revealed that a pH of 2.5, UVB irradiation, 2 g/L catalyst loading, and a hydrogen peroxide concentration of 1.0 mM were required. Under these conditions, complete decolorization was observed after 45 min. Degradation kinetics were best described by the pseudo-first order (PFO) model. Rate constants of 0.095 and 0.034 min−1 were obtained for 5 and 20 mg/L MO concentrations, respectively. A 37% total organic carbon removal was observed after 60 min. This suggests a stepwise MO degradation pathway with intermediate formation rather than complete mineralization. Although iron leaching was detected, the mineralogy of the catalyst recovered after the reaction was similar to the fresh catalyst.

Pesticide production wastewater treatment by Electro-Fenton using Taguchi experimental design

In this study, the electro-Fenton (EF) method was applied to remove total organic carbon (TOC) from the pesticide production wastewater containing tricyclazole (TC). Statistical Taguchi method was used to optimize the treatment performance. Analysis of variance (ANOVA) indicated that the polynomial regression model fitted experimental data with R² of 0.969. The optimal conditions for eliminating 75.4% TOC and 93.7% TC were 0.2 mM of Fe²⁺, 990 mg/L of Na₂SO₄, 180 min of reaction time at pH 3 with 2.22 mA/cm² of current density. The removal of TC present in the wastewater followed the first-order reaction kinetic model (R² = 0.993); while that was the second-order kinetic model in the case of the TOC removal (R² = 0.903). In addition, the experimental results and theory approaches (density functional theory and natural bond orbital calculations) also showed the C-N bond breaking and nitrate ions cleavage to ammonia. Acute toxicity of the pesticide wastewater after treatment (PWAT) on microcrustaceans showed that the treated wastewater still exhibited high toxicity against D. magna, with LC₅₀ values of 3.84%, 2.68%, 2.05%, and 1.78% at 24 h, 48 h, 72 h, and 96 h, respectively.

A novel system coupling an electro-Fenton process and an advanced biological process to remove a pharmaceutical compound, metronidazole

The objective of this study was to improve the mineralization of metronidazole, a recalcitrant antibiotic by the development of a new combined process coupling electro-Fenton and a biological process. For biotreatment, various strategies were considered bioaugmentation, bioacclimatation and biostimulation alone or combined. So, the novelty of this strategy is to combine advanced oxidation process with advanced biological process. The conventional biotreatment with activated sludge after 120 h of culture, led to 58.1% mineralization, whereas the pure isolated strains, from activated sludge culture in the presence of metronidazole by-products, identified as Pseudomonas putida (strain A) and Achromobacter sp. (strain B), led to 37.2% and 40.1% respectively. After original acclimation of the isolated strains to electrolysis by-products, the mineralization levels reached 75.6% and 72.9% for strains A and B respectively after 120 h of culture. The results showed that the mineralization of metronidazole by-products was the most important in the case of the combination of autochthonous bioaugmentation and biostimulation, with 96.1% after 120 h of treatment. By coupling the two processes, the global treatment reached therefore a mineralization yield of 97% with a reduction in processing time of 16 days compared to previous conventional biological treatment.

FeS2/carbon felt as an efficient electro-Fenton cathode for carbamazepine degradation and detoxification: In-depth discussion of reaction contribution and empirical kinetic model

Carbamazepine (CBZ) decay by electro-Fenton (EF) oxidation using a novel FeS₂/carbon felt (CF) cathode, instead of a soluble iron salt, was studied with the aim to accelerate the reaction between H₂O₂ and ferrous ions, which helps to produce more hydroxyl radicals (^•OH) and eliminate iron sludge. First, fabricated FeS₂ and its derived cathode were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Anodes were then screened, with DSA (Ti/IrO₂-RuO₂) showing the best performance under EF oxidation regarding CBZ degradation and electrochemical characterization. Several operating parameters of this EF process, such as FeS₂ loading, current density, gap between electrodes (GBE), initial [CBZ], and electrolyte type, were also investigated. Accordingly, a nonconsecutive empirical kinetic model was established to predict changes in CBZ concentration under the given operational parameters. The contribution of different oxidation types to the EF process was calculated using kinetic analysis and quenching experiments to verify the role of the FeS₂-modified cathode. The reaction contributions of anodic oxidation (AO), H₂O₂ electrolysis (EP), and EF oxidation to CBZ removal were 12.81%, 7.41%, and 79.77%, respectively. The ^•OH exposure of EP and EF oxidation was calculated, confirming that ^•OH exposure was approximately 22.45-fold higher using FeS₂-modified CF. Finally, the 19 intermediates formed by CBZ degradation were identified by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Accordingly, four CBZ degradation pathways were proposed. ECOSAR software was used to assess the ecotoxicity of intermediates toward fish, daphnia, and green algae, showing that this novel EF oxidation process showed good toxicity reduction performance. A prolonged EF retention time was proposed to be necessary to obtain clean and safe water, even if the targeted compound was removed at an earlier time.

High efficiency photocatalytic degradation of Ambroxol over Mn doped TiO2: Experimental designs, identification of transformation products, mineralization and mechanism

Ambroxol (AMB) is a drug commonly used for chronic bronchitis prevention. Once released in surface water, this recalcitrant chemical becomes a hazardous pollutant. Here, we investigated the ability of 1% Mn-doped TiO₂ (Mn-TiO₂) to mineralize AMB by photocatalysis. We studied the morphology, and the physical and electrochemical properties of Mn-TiO₂ using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, X-ray fluorescence, BET method, UV-visible, and electrochemical study and optimized the AMB degrading experimental conditions through response surface methodology (RSM). Mn-TiO₂ at the dose of 0.625 g·L^-1 allowed the complete photodegradation of AMB (30 ppm) at pH 7 under UVA light irradiation for 30 min while total mineralization in CO₂ (>96%) was achieved after 24 h of irradiation. Mn-TiO₂ was 1.6-time more efficient than TiO₂ Degussa P25. Product studies were also carried out by liquid chromatography coupled to electrospray high resolution mass spectrometry. Twenty-one photodegradation products were detected and identified. In addition, ionic chromatography analyses revealed the release of Br^-, NH₄⁺, and NO₃^- at respectively 97, 63 and 35% of the total Br, and N initially present in AMB. Finally, the reusability of the photocatalyst was also tested. After four cycles, the almost complete photodegradation of AMB was achieved showing that Mn-TiO₂ was highly stable. This work brings new physical characteristics on Mn-TiO₂ photocatalyst. Moreover, it is the first study investigating the photocatalytic degradation of recalcitrant AMB drug.

Effectiveness of Advanced Oxidation Processes in Wastewater Treatment: State of the Art

In recent years, many scientific studies have focused their efforts on quantifying the different types of pollutants that are not removed in wastewater treatment plants. Compounds of emerging concern (CECs) have been detected in different natural environments. The presence of these compounds in wastewater is not new, but they may have consequences in the future. These compounds reach the natural environment through various routes, such as wastewater. This review focuses on the study of tertiary treatment with advanced oxidation processes (AOPs) for the degradation of CECs. The main objective of the different existing AOPs applied to the treatment of wastewater is the degradation of pollutants that are not eliminated by means of traditional wastewater treatment.

Comparative overview of advanced oxidation processes and biological approaches for the removal pharmaceuticals

Nowadays, pharmaceuticals are the center of significant environmental research due to their complex and highly stable bioactivity, increasing concentration in the water streams and high persistence in aquatic environments. Conventional wastewater treatment techniques are generally inadequate to remove these pollutants. Aiming to tackle this issue effectively, various methods have been developed and investigated on the light of chemical, physical and biological procedures. Increasing attention has recently been paid to the advanced oxidation processes (AOPs) as efficient methods for the complete mineralization of pharmaceuticals. Their high operating costs compared to other processes, however, remain a challenge. Hence, this review summarizes the current and state of art related to AOPs, biological treatment and their effective exploitation for the degradation of various pharmaceuticals and other emerging molecules present in wastewater. The review covers the last decade with a particular focus on the previous five years. It is further envisioned that this review of advanced oxidation methods and biological treatments, discussed herein, will help readers to better understand the mechanisms and limitations of these methods for the removal of pharmaceuticals from the environment. In addition, we compared AOPs and biological treatments for the disposal of pharmaceuticals from the point of view of cost, effectiveness, and popularity of their use. The exploitation of coupling AOPs and biological procedures for the degradation of pharmaceuticals in wastewater was also presented. It is worthy of note that an integrated AOPs/biological system is essential to reach the complete degradation of pharmaceuticals; other advantages of this hybrid technique involve low energy cost, an efficient degradation process and generation of non-toxic by-products.

Preparation of Fe@Fe2O3/3D graphene composite cathode for electrochemical removal of sulfasalazine

In the present study, heterogeneous electro-Fenton (EF) process was applied to remove the sulfasalazine (SU) pharmaceutical from aqueous solutions. In the first part, 3D graphene loaded with Fe@Fe₂O₃ core-shell nanowires (Fe@Fe₂O₃/3D-GO) was used as a cathode electrode in the EF process. Graphene oxide (GO) was synthesized for the synthesis of 3D graphene nanocomposites using the improved Hummers' method and subsequently 3D graphene synthesized by the hydrothermal method using glycine. Finally, Fe@Fe₂O₃/3D-GO composite was synthesized and its properties were assessed by Scanning electron microscopy, Atomic force microscopy, Brunauer-Emmett-Teller, Fourier-transform infrared spectroscopy and X-ray diffraction methods. Then, the cathode electrode was prepared using the resulting composite and its performance was evaluated using Cyclic Voltammetry analysis. In the final part of this work, the Fe@Fe₂O₃/3D-GO electrode was used as the cathode electrode in the heterogeneous EF process to remove SU from aqueous solutions. The effect of operating parameters such as applied current (mA), initial pH of solution, initial pharmaceutical concentration (mg L^-1) and process time (min) on pharmaceutical removal efficiency under heterogeneous EF process was investigated by response surface methodology. The results showed that the optimum values for applied current, pH, initial pharmaceutical concentration and electrolysis time were respectively 300 mA, 7, 30 mg L^-1 and 100 min, resulting 99.60% of SU removal. Finally, the intermediates of SU degradation were determined by Gas chromatography-mass spectrometry analysis and the amount of mineralization was determined by total organic carbon analysis. About 5.2% drop in the SU removal efficiency was observed within 8 operational runs.

Environmental aspects of UV-C-based processes for the treatment of oxytetracycline in water

This study is focused on oxytetracycline (OTC) degradation by direct photolysis (UV-C) and photobased advanced oxidation processes (AOPs) (UV-C/H₂O₂ and UV-C/S₂O₈^2-). OTC degradation pathways were revealed by LC-MS/MS and GC-MS/MS analyses. The evolution/degradation profiles of 12 detected byproducts were correlated with changes in biodegradability and toxicity toward Vibrio fischeri recorded during the treatment. Both photobased AOPs yielded higher OTC degradation and mineralization rates than direct photolysis. The OTC degradation pathway was found to be rather specific regarding the main reactive species (HO• or SO₄•^-)/mechanism, yielding different patterns in toxicity changes, while biodegradability profiles were less affected. Biodegradability was correlated with the observed degradation and mineralization kinetics. The recorded toxicity changes indicate that byproducts formed by initial OTC degradation are more toxic than the parent pollutant. The prolonged treatment resulted in the formation of byproducts that contributed to a decrease in toxicity and an increase in biodegradability, as particularly emphasized in the case of UV-C/S₂O₈^2-.

Efficient reactive blue 19 decolorization by the comparison of ozonation membrane contacting process and Fenton oxidation

The decolorization of Reactive Blue 19 (RB 19) wastewater by an ozonation membrane contactor and Fenton oxidation was studied. The aims of the study were to investigate the affecting parameters and to compare the performance of RB 19 decolorization by two different processes. The results showed that Fe²⁺ and H₂O₂ concentrations for Fenton oxidation and ozone concentration with different membranes for the membrane contacting process played the most important roles in RB 19 decolorization. The optimum conditions for RB 19 decolorization by Fenton oxidation were initial pH 3.0, 1.5 mM H₂O₂ and 0.25 mM Fe²⁺; in contrast, the optimum conditions for the membrane contactor were initial pH 11 and 40 mg L⁻¹ ozone concentration. Under these conditions, the decolorization of RB 19 by the membrane contactor was almost completed and was higher than by Fenton and photo-Fenton oxidations for 90 min. The decolorizations of RB 19 by Fenton and photo-Fenton oxidations were constant after 30 min, but the decolorization of RB 19 by ozonation with a membrane contactor gradually increased via ozone consumption until 90 min operation, which was higher than that of Fenton oxidations. The use of a PVDF-PAM membrane in the membrane contactor resulted in higher decolorization efficiency than a PVDF membrane. The results demonstrated a COD removal efficiency of 63% by an ozonation membrane contacting process using PVDF-PAM, which was lower than that of Fenton oxidation (73%), but resulted in higher BOD₅/COD and NO₃⁻ and SO₄²⁻ releases. Under these conditions, the ozonation membrane contacting process showed the lowest electric energy consumption.

The decolorization of Reactive Blue 19 (RB 19) wastewater by an ozonation membrane contactor and Fenton oxidation was studied.

Degradation and mineralization of the emerging pharmaceutical pollutant sildenafil by ozone and UV radiation using response surface methodology

Pharmaceuticals and their degradation products which are present in wastewater and superficial waters are becoming an ecological issue. This research investigated the degradation and mineralization of synthetic solutions of the pharmaceutical compound sildenafil citrate (SC) by single ozonation and ozonation jointed with UV radiation (O₃/UV). The effects of initial drug concentration (50-125 mg L^-1), inlet ozone concentration (35-125 g Nm^-3), and UV radiation on SC degradation and decrease of total organic carbon (TOC) were investigated using response surface methodology based on a central composite experimental design. Through the RSM analysis, it was possible to confirm the removal of SC for the entire experimental range. Major intermediates of SC degradation were identified and a degradation pathway was proposed. The kinetics of SC degradation was modeled as a pseudo-first-order reaction with a rate constant ranging between 0.072 and 1.250 min^-1. The SC degradation and TOC removal were strongly enhanced by increasing the concentration of gaseous ozone at the inlet and incorporating UV radiation. The highest TOC removal reached at 60 min was 75%, in the O₃/UV system, with initial SC content of 50 mg L^-1 and inlet ozone concentration of 125 g Nm^-3. The degradation rate of SC was increased 3 to 9 times in the presence of UV radiation. Ozone-based advanced oxidation processes appear as a suitable alternative for treatment of the emerging pollutant SC.

Electro-Fenton oxidation of a β-lactam antibiotic cefoperazone: Mineralization, biodegradability and degradation mechanism

Oxidation of a commonly-used β-lactam pharmaceutical, cefoperazone (CFPZ), was systematically investigated by anodic oxidation (AO), AO in presence of H₂O₂ electro-generation (AO-H₂O₂) and electro-Fenton (EF) processes with an activated carbon fiber cathode from the biodegradability viewpoint. The degradation and mineralization rates increased in a sequence of AO < AO-H₂O₂ < EF. Even CPFZ could be efficiently degraded in EF process, achieving complete CFPZ mineralization was rather difficult. Thereby, the biodegradability of the effluent after electrochemical pretreatment was examined to test the feasibility of the combination of electrochemical and biological processes. The results suggested that compared with AO and AO-H₂O₂, EF process could effectively transform the non-biodegradable CFPZ into biocompatible materials with a high BOD₅/COD value (0.33 after 720 min), allowing the possible biotreatment for further remediation. This behavior was relatively accorded with the average oxidation state (AOS) results, evidencing the potential of EF process in enhancing the biodegradability of CFPZ. The determination of inorganic ions revealed that N in CFPZ molecular was oxidized into NH₄⁺ and NO₃^- ions in EF process. Oxalic, succinic, oxamic, fumaric and formic acids were also formed. Besides, six aromatic by-products were qualified and a possible pathway involving hydrolysis, hydroxylation and decarboxylation during CFPZ mineralization was proposed.

Degradation of Acid Violet 19 textile dye by electro-peroxone in a laboratory flow plant

This paper deals with the degradation of Acid Violet 19 (AV19) textile dye by the electro-peroxone (E-peroxone) process in a laboratory flow plant using a filter press cell fitted with a 3D gas diffusion electrode (3D GDE) containing a graphite felt positioned on carbon-cloth PTFE as cathode, and a Ti|IrSnSb-oxides plate as anode. H₂O₂ was formed by the oxygen reduction reaction (ORR) in the cathode; the air was supplied by an external compressor. The O₃ produced externally by an ozonator was added in the pipeline at the outlet of the electrolyzer to promote the reaction between the H₂O₂ and O₃ to produce OH, which is the responsible for the mineralization of the dye. The effect of electrolyte flow rate (Q), current density (j), and initial concentration of AV19 dye on its degradation was addressed. The best electrolysis in a solution containing 40 mg TOC L^-1, 0.05 M Na₂SO₄, at pH 3, was obtained at j = 20 mA cm^-2, Q = 2.0 L min^-1, using a pressure of the air fed to the 3D GDE of P_GDE = 3 psi, and an ozone inlet mass flow rate of [Formula: see text]  = 14.5 mg L^-1, achieving 100% discoloration, 60% mineralization, with mineralization current efficiency and energy consumption of 36% and 0.085 kWh(gTOC)^-1. The degradation of AV19 dye was also performed by anodic oxidation plus H₂O₂ electrogenerated (AO-H₂O₂) and ozonation. The oxidation power was AO-H₂O₂ < ozonation < E-peroxone. Three carboxylic acids were quantified by chromatography as oxidation end products.