Effective removal of the antibiotic Nafcillin from water by combining the Photoelectro-Fenton process and Anaerobic Biological Digestion

Efficient mitigation of emerging antibiotics residues from water matrix: Integrated approaches and sustainable technologies

The prevalence of antibiotic traces in the aquatic matrices is a concern due to the emanation of antibiotic resistance which requires a multifaceted approach. One of the potential sources is the wastewater treatment plants with a lack of advance infrastructure leading to the dissemination of contaminants. Continuous advancements in economic globalization have facilitated the application of several conventional, advanced, and hybrid techniques for the mitigation of rising antibiotic traces in the aquatic matrices that have been thoroughly scrutinized in the current paper. Although the implementation of existing mitigation techniques is associated with several limiting factors and barriers which require further research to enhance their removal efficiency. The review further summarizes the application of the microbial processes to combat antibiotic persistence in wastewater establishing a sustainable approach. However, hybrid technologies are considered as most efficient and environmental-benign due to their higher removal efficacy, energy-efficiency, and cost-effectiveness. A brief elucidation has been provided for the mechanism responsible for lowering antibiotic concentration in wastewater through biodegradation and biotransformation. Overall, the current review presents a comprehensive approach for antibiotic mitigation using existing methods however, policies and measures should be implemented for continuous monitoring and surveillance of antibiotic persistence in aquatic matrices to reduce their potential risk to humans and the environment.

Comprehensive understanding of electrochemical treatment systems combined with biological processes for wastewater remediation

The presence of toxic pollutants in wastewater discharge can affect the environment negatively due to presence of the organic and inorganic contaminants. The application of the electrochemical process in wastewater treatment is promising, specifically in treating these harmful pollutants from the aquatic environment. This review focused on recent applications of the electrochemical process for the remediation of such harmful pollutants from aquatic environments. Furthermore, the process conditions that affect the electrochemical process performance are evaluated, and the appropriate treatment processes are suggested according to the presence of organic and inorganic contaminants. Electrocoagulation, electrooxidation, and electro-Fenton applications in wastewater have shown effective performance with high removal rates. The disadvantages of these processes are the formation of toxic intermediate metabolites, high energy consumption, and sludge generation. To overcome such disadvantages combined ecotechnologies can be applied in large-scale wastewater pollutants removal. The combination of electrochemical and biological treatment has gained importance, increased removal performance remarkably, and decreased operational costs. The critical discussion with depth information in this review could be beneficial for wastewater treatment plant operators throughout the world.

Degradation of antibiotics by electrochemical advanced oxidation processes (EAOPs): Performance, mechanisms, and perspectives

Global consumption and discharge of antibiotics have led to the rapid development and spread of bacterial antibiotic resistance. Among treatment strategies, electrochemical advanced oxidation processes (EAOPs) are gaining popularity for treating water/wastewater containing antibiotics due to their high efficiency and easiness of operation. In this review, we summarize various forms of EAOPs that contribute to antibiotic degradation, including common electrochemical oxidation (EO), electrolyte enhanced EO, electro-Fenton (EF) processes, EF-like process, and EAOPs coupling with other processes. Then we assess the performance of various EAOPs in antibiotic degradation and discuss the influence of key factors, including electrode, initial concentration and type of antibiotic, operation conditions, electrolyte, and water quality. We also review mechanisms and degradation pathways of various antibiotics degradation by EAOPs, and address the species and toxicity of intermediates produced during antibiotics treatment. Finally, we highlight challenges and critical research needs to facilitate the application of EAOPs in antibiotic treatment.

Nanostructured electrochemical sensor applied to the electrocoagulation of arsenite in WWTP effluent

A sensitive electroanalytical method for the determination of arsenite, based on a heterostructure of aminated multiwalled carbon nanotubes and gold nanoparticles, was applied in an electrocoagulation (EC) treatment for the elimination of arsenite. A sensitive quantitative response was obtained in the determination of As³⁺ in a secondary effluent from a wastewater treatment plant from Santiago (Chile). The preconcentration stage was optimized through a Central Composite Face design, and the most sensitive peak current was obtained at 200 s and -600 mV of time and accumulation potential, respectively, after a differential pulse voltammetry sweep. Electroanalytical determination was possible in an interval between 42.89 and 170.00 μg L^-1 with a detection limit of 0.39 μg L^-1, obtaining recoveries over 99.1%. The developed method was successfully applied in an electrocoagulation treatment to remove 250 μg L^-1 of arsenite from a polluted effluent in a batch system. Complete arsenite removal was achieved using a steel EC system with a current density of 6.0 mA cm^-2 in less than 3 min of treatment.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

Adsorption-enhanced photocatalytic property of Ag-doped biochar/g-C3N4/TiO2 composite by incorporating cotton-based biochar

In this study, the biochar obtained from waste cotton fibers was introduced into the Ag-doped g-C3N4/TiO2 hybrid composite through a facile one-step hydrothermal process. The morphology, elemental composition, crystal structure, microstructure, specific surface area, chemical bonding state, energy band structure, and separation efficiency of photoinduced charge carriers of the resultant composite were examined using scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, transmission electron microscope, surface area analyzer, X-ray photoelectron spectroscope, Ultraviolet-visible spectrophotometer, ultraviolet photoelectron spectroscope, and photoluminescence spectroscope. The adsorption isotherms, kinetics and thermodynamics of the biochar, Ag-doped g-C3N4/TiO2 and Ag-doped biochar/g-C3N4/TiO2 were evaluated using the model methyl orange dye. The photoacatalytic degradation of the model pollutants including methyl orange, methylene blue, congo red, and tetracycline hydrochloride and the photocatalytic reduction of Cr(VI) ions were also assessed under visible light. Experimental results indicated that the photocatalytic property of the Ag-doped biochar/g-C3N4/TiO2 was significantly enhanced through the adsorption enhancement compared with the Ag-doped g-C3N4/TiO2. This was due to the uniform doping of multi-scale porous biochar with g-C3N4 nanosheet, Ag and TiO2 nanoparticles. The adsorptive enhancement induced by the biochar resulted in the narrowed band gap, suitable electronic energy band structure, and fast separation of photoinduced charge carriers of the Ag-doped biochar/g-C3N4/TiO2, which was probably due to the coexistence of multi-valence Ti+4/+3 and Ag0/+1 species and oxygen-containing groups of biochar. The major reactive species of the Ag-doped biochar/g-C3N4/TiO2 were 1O2 and h+. The MO dye adsorption onto the Ag-doped biochar/g-C3N4/TiO2 followed the Langmuir isotherm model, pseudo-first-order and pseudo-second-order kinetic models, and the adsorption process was an endothermic reaction with entropy reduction effects. As such, the Ag-doped biochar/g-C3N4/TiO2 exhibited a promising application for the treatment of wastewater containing multi-pollutants especially organic dyes and heavy metal ions.

Anodic Oxidation of Industrial Winery Wastewater Using Different Anodes

Winery wastewater represents the largest waste stream in the wine industry. This deals with the mineralization of the organic matter present in winery wastewater using anodic oxidation and two types of anodes—namely, a boron-doped diamond electrode (BDD) and two mixed metal oxides (MMO), one with the nominal composition Ti/Ru0.3Ti0.7O2 and the other with Ti/Ir0.45Ta0.55O2. To conduct the study, the variability of different quality parameters for winery wastewater from the Chilean industry was measured during eight months. A composite sample was treated using anodic oxidation without the addition of supporting electrolyte, and the experiments were conducted at the natural pH of the industrial wastewater. The results show that this effluent has a high content of organic matter (up to 3025 ± 19 mg/L of total organic carbon (TOC)), which depends on the time of the year and the level of wine production. With MMO electrodes, TOC decreased by 2.52% on average after 540 min, which may be attributed to the presence of intermediate species that could not be mineralized. However, when using a BDD electrode, 85% mineralization was achieved due to the higher generation of hydroxyl radicals. The electrolyzed sample contained oxamic, acetic, and propionic acid as well as different ions such as sulfate, chloride, nitrate, and phosphate. These ions can contribute to the formation of different species such as active species of chlorine, persulfate, and perphosphate, which can improve the oxidative power of the system.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Simultaneous degradation of 30 pharmaceuticals by anodic oxidation: Main intermediaries and by-products

The anodic oxidation (AO) of 30 pharmaceuticals including antibiotics, hormones, antihistaminics, anti-inflammatories, antidepressants, antihypertensives, and antiulcer agents, in solutions containing different supporting electrolytes media (0.05 M Na₂SO₄, 0.05 M NaCl, and 0.05 M Na₂SO₄ + 0.05 M NaCl) at natural pH was studied. A boron-doped diamond (BDD) electrode and a stainless-steel electrode were used as anode and cathode, respectively, and three current densities of 6, 20, and 40 mA cm^-2 were applied. The results showed high mineralization rates, above 85%, in all the tested electrolytic media. 25 intermediaries produced during the electrooxidation were identified, depending on the supporting electrolyte together with the formation of carboxylic acids, NO₃^-, SO₄^2- and NH₄⁺ ions. The formation of intermediates in chloride medium produced an increase in absorbance. Finally, a real secondary effluent spiked with the 30 pharmaceuticals was treated by AO applying 6 mA cm^-2 at natural pH and without addition of supporting electrolyte, reaching c.a. 90% mineralization after 300 min, with an energy consumption of 18.95 kW h m^-3 equivalent to 2.90 USD m^-3. A degradation scheme for the mixture of emerging contaminants in both electrolytic media is proposed. Thus, the application of anodic oxidation generates a high concentration of hydroxyl radicals that favors the mineralization of the pharmaceuticals present in the spiked secondary effluent sample.

Electro-kinetic washing of a soil contaminated with quinclorac and subsequent electro-oxidation of wash water

This work deals with the remediation of a soil that has been enriched with Quinclorac (QNC), one of the herbicides most used in Chile for weed control in rice fields. Quinclorac damages the microflora and macrofauna of soils and is toxic to some susceptible crops, which results in economic loses during crop rotation. Furthermore, Quinclorac a potential contaminant of water resources and soils, given its high mobility and persistence. This has created the need to lower its concentrations in soils intensively cultivated. In this study, an electro-kinetic soil washing system (EKSW) for mobilizing this pesticide in the soil was explored. The performance of this technology was compared by assessing the effect of direct (DP) and reverse (RP) polarity during 15 days under potentiostatic conditions and applying an electric field of 1 V cm^-1 between electrodes. Among the main results, the highest removal of QNC was obtained through the EKSW-RP process, which also contributed to the prevention of acidity and alkaline fronts in the soil, compared to the EKSW-DP system. In both cases, the highest accumulation of QNC occurred in the cathodic well by mobilizing the non-ionized contaminant through the electroosmotic flow (EOF) from anode to cathode. After the treatment with EKSW, the wash water accumulated in the anodic and cathodic wells, which contained an important concentration of pesticide, was subjected to electro-oxidation (EO) by applying different current densities (j). The high generation of •OH on the surface of a boron-doped diamond electrode (BDD) allowed for the complete degradation and mineralization of QNC and its major intermediate compounds to CO₂. The results of this study show that the application of both coupled stages in this type of remediation technologies would enable the removal of QNC from the soil without altering its chemical and physical properties, constituting an environmentally friendly process.

Defect-boosted molybdenite-based co-catalytic Fenton reaction

High-defect molybdenite acts an efficient co-catalyst to substantially enhance the Fenton reaction.

Occurrence, statutory guideline values and removal of contaminants of emerging concern by Electrochemical Advanced Oxidation Processes: A review

A wide variety of chemical compounds are used in human activities; however, part of these compounds reach surface water, groundwater and even water considered for potable uses. Due to the limited efficiency of water treatment by the Water and Wastewater Treatment Plants, the presence of these compounds in natural and human consumption waters can be very harmful due to their high persistence and adverse effects; these characteristics define the contaminants of emerging concern (CECs). Water treatment by Electrochemical Advanced Oxidation Processes (EAOPs) has been evaluated as a promising process for the removal of persistent and recalcitrant organic contaminants. With this background, the present review aims to gather studies and information published between 2015 and 2020 regarding the occurrence of CECs in surface, potable and groundwater, its treatment by EAOPs, the main operating conditions and by-product generation of EAOPs, contaminant toxicity assessments and international statutory guideline values concerning CEC standards and allowable concentrations in the environment and treated drinking water. Therefore, in this review it was found that the compounds bisphenol A (BPA), diethyltoluamide (DEET), 17α-ethinyl estradiol (EE2), perfluorobutanoic acid (PFBA), carbamazepine, caffeine and atrazine were the most frequently detected in water sources, with concentrations ranging from 35.54-4800, 1.21-98, 0.005-38.5, 5-742.904, 0.0071-586, 0.89-1040, and 100-323 (ng L-1), respectively. Among the operational conditions of EAOPs, current density, pH and oxidant concentration are the main operational parameters that have an influence on these treatment technologies, besides the by-products generated, which might be removed by the integration of EAOPs with biological digestion treatments. Regarding the values of water quality standards, many CECs do not have established standard allowable concentration values, which represents a concern toward the possible toxic effects of these compounds on non-target organisms.

A review on the photoelectro-Fenton process as efficient electrochemical advanced oxidation for wastewater remediation. Treatment with UV light, sunlight, and coupling with conventional and other photo-assisted advanced technologies

Wastewaters containing recalcitrant and toxic organic pollutants are scarcely decontaminated in conventional wastewater facilities. Then, there is an urgent challenge the development of powerful oxidation processes to ensure their organic removal in order to preserve the water quality in the environment. This review presents the recent development of an electrochemical advanced oxidation process (EAOP) like the photoelectro-Fenton (PEF) process, covering the period 2010-2019, as an effective treatment for wastewater remediation. The high oxidation ability of this photo-assisted Fenton-based EAOP is due to the combination of in situ generated hydroxyl radicals and the photolytic action of UV or sunlight irradiation over the treated wastewater. Firstly, the fundamentals and characteristics of the PEF process are described to understand the role of oxidizing agents. Further, the properties of the homogeneous PEF process with iron catalyst and UV irradiation and the benefit of sunlight in the homogeneous solar PEF one (SPEF) are discussed, supported with examples over their application to the degradation and mineralization of synthetic solutions of industrial chemicals, herbicides, dyes and pharmaceuticals, as well as real wastewaters. Novel heterogeneous PEF processes involving solid iron catalysts or iron-modified cathodes are subsequently detailed. Finally, the oxidation power of hybrid processes including photocatalysis/PEF, solar photocatalysis/SPEF, photoelectrocatalysis/PEF and solar photoelectrocatalysis/SPEF, followed by that of sequential processes like electrocoagulation/PEF and biological oxidation coupled to SPEF, are analyzed.

Nafcillin degradation by heterogeneous electro-Fenton process using Fe, Cu and Fe/Cu nanoparticles

Heterogeneous electro-Fenton (HEF) is as an alternative to the conventional electro-Fenton (EF) process. HEF uses a solid phase catalyst, whereas EF employs a solubilized one. This implies that in HEF, material can be recovered through a simple separation process such as filtration or magnetic separation in HEF. HEF also has the advantage of not requires a previous pH adjustment, which facilitates working in a higher pH range. In this work, Fe, Cu and Fe/Cu bimetallic nanoparticles (Fe/Cu NPs) were synthesized, characterized and used for the degradation of Nafcillin (NAF). The effect of the adsorption and the anodic oxidation (AO-H₂O₂) process was tested to assess their influence on HEF. NAF adsorption did not exceed 24% of antibiotic removal and the AO-H₂O₂ process eliminated the total NAF after 240 min of electrolysis. Through the HEF process, the antibiotic was completely removed using Fe/Cu NPs after 7.0 min of electrolysis, while these NPs, mineralization reached 41% after 240 min. In this case, NAF degradation occurs mainly due to the generation of hydroxyl radicals in the BDD electrode, and the Fenton reaction with Fe and Cu NPs. The main organic intermediates produced during the degradation of NAF by HEF were identified allowing the proposal of degradation pathway. Finally, the antibiotic was also completely eliminated from a wastewater from slaughterhouse after 15 min of treatment by HEF and using Fe/Cu bimetallic NPs.

Degradation of the emerging concern pollutant ampicillin in aqueous media by sonochemical advanced oxidation processes - Parameters effect, removal of antimicrobial activity and pollutant treatment in hydrolyzed urine

This work presents the degradation of ampicillin (a highly consumed β-lactam antibiotic) in aqueous media by sonochemical advanced oxidation processes. Initially, effects of frequency, power and operation mode (continuous vs. pulsed) on the antibiotic degradation by sonochemistry were analyzed. Then, under the suitable operational conditions, pollutant degradation and antimicrobial activity (AA) evolution were monitored. Afterwards, computational calculations were done to establish the possible attacks by the hydroxyl radical to the ampicillin structure. Additionally, the antibiotic degradation in synthetic hydrolyzed urine by ultrasound was performed. Finally, the combination of sonochemistry with Fenton (sono-Fenton) and photo-Fenton (sono-photo-Fenton) was evaluated. Our research showed that ampicillin removal was favored at low frequency, high power (i.e., 375 kHz, 24.4 W) and continuous mode (exhibiting an initial degradation rate of 0.78 μM min^-1). Interestingly, ampicillin degradation in the hydrolyzed urine by sonochemistry alone was favored by matrix components (i.e., the pollutant showed a degradation rate in urine higher than in distilled water). The sonochemical process decreased the antimicrobial activity from the treated water (100% removal after 75 min of treatment), which was related to attacks of hydroxyl radical on active nucleus (the computational analysis showed high electron density on sulfur, oxygen and carbon atoms belonging to the penicillin core). Sono-photo-Fenton system achieved the fastest degradation and highest mineralization of the pollutant (40% of organic carbon removal at 180 min of treatment). All these aspects reveal the good possibility of sonochemical advanced oxidation technologies application for the treatment of antibiotics even in complex aqueous matrices such as hydrolyzed urine.

Data on treatment of nafcillin and ampicillin antibiotics in water by sonochemistry

Ampicillin and nafcillin antibiotics were treated by high frequency ultrasound (at 375 kHz and 24.4 W). Degradations followed pseudo-first order kinetics, which constants were k: 0.0323 min⁻¹ for AMP and k: 0.0550 min⁻¹ for NAF. Accumulation of sonogenerated hydrogen peroxide and inhibition degree of sonochemical removal (IDS) in presence of a radical scavenger were also stablished. Afterwards, ultrasound was combined with UVC light (sono-photolysis), with ferrous ion (sono-Fenton), and with ferrous ion plus UVC light (sono-photo-Fenton) to degrade the antibiotics. Furthermore, treatment of the pollutants in a complex matrix and removal of antimicrobial activity (AA) were considered. The antibiotics evolution was followed by HPLC-DAD technique and the accumulation of sonogenerated H₂O₂ was measured by an iodometry-spectrophotometry methodology (77.6 and 57.3 μmol L⁻¹ of H₂O₂ after 30 min of sonication were accumulated in presence of AMP and NAF, respectively). IDS was analyzed through treatment of the antibiotics in presence of 2-propanol (87.1% for AMP and 56 % for NAF) and considering the hydrophobic character of pollutants (i.e., Log P values). Antimicrobial activity evolution was assessed by the Kirby-Bauer method using Staphylococcus aureus as indicator microorganism (sono-photo-Fenton process removed 100% of AA after 60 and 20 min for AMP and NAF, respectively). Finally, for degradations in the complex matrix, a simulated effluent of municipal wastewater treatment plant was utilized (sono-photo-Fenton led to degradations higher than 90 % at 60 min of treatment for both antibiotics). The data from the present work can be valuable for people researching on treatment of wastewaters containing antibiotics, application of advanced oxidation technologies and combination of sonochemical process with photochemical systems.

Oxide-Clay Mineral as Photoactive Material for Dye Discoloration

Titanium and zirconium oxides (TiO2 and ZrO2, respectively) were obtained from alkoxides hydrolyses, and then deposited into palygorskite clay mineral (Pal) to obtain new materials for photocatalytic applications. The obtained materials were characterized by structural, morphological, and textural techniques. X-ray diffraction (XRD) results confirmed the characteristic peaks of oxides and clay transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the modified palygorskite with both oxides showed that the clay was successfully modified by the proposed method. The increase in the specific surface area of the clay occurred when TiO2 and ZrO2 were deposited on the surface. The photocatalytic activity of these materials was investigated using the Remazol Blue anion dye under UV light. The evaluated systems presented high photocatalytic activity, reaching approximately 98% of dye discoloration under light. Thus, TiO2–Pal and ZrO2–TiO2–Pal are promising clay mineral-based photocatalysts.

Expanding the application of photoelectro-Fenton treatment to urban wastewater using the Fe(III)-EDDS complex

This work reports the first investigation on the use of EDDS as chelating agent in photoelectro-Fenton (PEF) treatment of water at near-neutral pH. As a case study, the removal of the antidepressant fluoxetine was optimized, using an electrochemical cell composed of an IrO₂-based anode an air-diffusion cathode for in-situ H₂O₂ production. Electrolytic trials at constant current were made in ultrapure water with different electrolytes, as well as in urban wastewater (secondary effluent) at pH 7.2. PEF with Fe(III)-EDDS (1:1) complex as catalyst outperformed electro-Fenton and PEF processes with uncomplexed Fe(II) or Fe(III). This can be explained by: (i) the larger solubilization of iron ions during the trials, favoring the production of ^•OH from Fenton-like reactions between H₂O₂ and Fe(II)-EDDS or Fe(III)-EDDS, and (ii) the occurrence of Fe(II) regeneration from Fe(III)-EDDS photoreduction, which was more efficient than conventional photo-Fenton reaction with uncomplexed Fe(III). The greatest drug concentration decays were achieved at low pH, using only 0.10 mM Fe(III)-EDDS, although complete removal in wastewater was feasible only with 0.20 mM Fe(III)-EDDS due to the greater formation of ^•OH. The effect of the applied current and anode nature was rather insignificant. A progressive destruction of the catalytic complex was unveiled, whereupon the mineralization mainly progressed thanks to the action of ^•OH adsorbed on the anode surface. Despite the incomplete mineralization using BDD as the anode, a remarkable toxicity decrease was determined. Fluoxetine degradation yielded F^- and NO₃^- ions, along with several aromatic intermediates. These included two chloro-organics, as a result of the anodic oxidation of Cl^- to active chlorine. A detailed mechanism for the Fe(III)-EDDS-catalyzed PEF treatment of fluoxetine in urban wastewater is finally proposed.

Waste-wood-derived biochar cathode and its application in electro-Fenton for sulfathiazole treatment at alkaline pH with pyrophosphate electrolyte

For the first time, a biomass-derived porous carbon cathode (WDC) was fabricated via a facile one-step pyrolysis of recovered wood-waste without any post-treatment. The WDC along with pyrophosphate (PP) as electrolyte were used in electro-Fenton (EF) at pH 8 for sulfathiazole (STZ) treatment. The H₂O₂ accumulation capacity of WDC was optimized via the following parameters: pyrolysis temperature, applied current and electrolyte. Results showed that the WDC cathode prepared at 900 °C achieved the highest H₂O₂ accumulation (13.80 mg L^-1 in 3 h) due to its larger electroactive surface area (28.81 cm²). Interestingly, it was found that PP decreased the decomposition rate of H₂O₂ in solution as compared to conventional electrolyte, which resulted in higher H₂O₂ accumulation. PP allowed operating EF at pH of 8 due to the formation of Fe²⁺-PP complexes in solution. Moreover, Fe²⁺-PP was able to activate oxygen to produce OH. In this way, the degradation of STZ took place through four main pathways: 1) via OH from the Fe²⁺-PP complex, 2) via OH from EF reactions, 3) via surface OH at the boron doped diamond electrode (BDD) and 4) via SO₄- from BDD activation. Finally, microtox tests revealed that some toxic intermediates were generated during WDC/BDD/PP EF treatment, but they were removed at the end of the process.

A review on Fenton process for organic wastewater treatment based on optimization perspective

Water pollution caused by organic wastewater has become a serious concern worldwide. Fenton oxidation process is one of the most effective and suitable methods for the abatement of organic pollutants. However, the process has three obvious shortcomings: the narrow working pH range, the high costs and risks associated with handling, transportation and storage of reagents (H₂O₂ and catalyst), the significant iron sludge related second pollution. In order to overcome these shortcomings, various optimized Fenton processes have been widely studied. Therefore, a summary of the study status of Fenton optimization processes is necessary to develop a novel and high efficiency organic wastewater treatment method. Based on the optimization perspective, taking shortcomings of Fenton process as a breakthrough, the fundamentals, advantages and disadvantages of single Fenton optimization processes (heterogeneous Fenton, photo-Fenton and electro-Fenton) for organic wastewater treatment were reviewed and the corresponding reaction mechanism diagrams were drawn in this paper. Then, the feasibility and application of the coupled Fenton optimization processes (photoelectro-Fenton, heterogeneous electro-Fenton, heterogeneous photoelectro-Fenton, three-dimensional electro-Fenton) for organic wastewater treatment were discussed in depth. Additionally, the effect of some important operation parameters (pH and catalyst, H₂O₂, organic pollutants concentration) on the degradation efficiency of organic pollutants was studied to provide guidance for the optimization of operation parameters. Finally, the possible future research directions for optimized Fenton processes were given. The review aims to assist researchers and engineers to gain fundamental understandings and critical view of Fenton process and its optimization processes, and hopefully with the knowledge it could bring new opportunities for the optimization and future development of Fenton process.

Membrane bioreactors and electrochemical processes for treatment of wastewaters containing heavy metal ions, organics, micropollutants and dyes: Recent developments

Research and development activities on standalone systems of membrane bioreactors and electrochemical reactors for wastewater treatment have been intensified recently. However, several challenges are still being faced during the operation of these reactors. The current challenges associated with the operation of standalone MBR and electrochemical reactors include: membrane fouling in MBR, set-backs from operational errors and conditions, energy consumption in electrochemical systems, high cost requirement, and the need for simplified models. The advantage of this review is to present the most critical challenges and opportunities. These challenges have necessitated the design of MBR derivatives such as anaerobic MBR (AnMBR), osmotic MBR (OMBR), biofilm MBR (BF-MBR), membrane aerated biofilm reactor (MABR), and magnetically-enhanced systems. Likewise, electrochemical reactors with different configurations such as parallel, cylindrical, rotating impeller-electrode, packed bed, and moving particle configurations have emerged. One of the most effective approaches towards reducing energy consumption and membrane fouling rate is the integration of MBR with low-voltage electrochemical processes in an electrically-enhanced membrane bioreactor (eMBR). Meanwhile, research on eMBR modeling and sludge reuse is limited. Future trends should focus on novel/fresh concepts such as electrically-enhanced AnMBRs, electrically-enhanced OMBRs, and coupled systems with microbial fuel cells to further improve energy efficiency and effluent quality.

Effect of surface properties of activated carbon fiber cathode on mineralization of antibiotic cefalexin by electro-Fenton and photoelectro-Fenton treatments: Mineralization, kinetics and oxidation products

Solutions of 200 mg L^-1 cefalexin (CLX), an antibiotic with high usage frequency and biodegradation resistance, have been comparatively degraded by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes using two kinds of activated carbon fiber (ACF) cathodes with different physical properties. These two ACFs shared similar pore volumes and pore diameters but varied BET surface areas, which were confirmed to be 0.5210 cm³ g^-1, 2.26 nm and 921 m² g^-1 for ACF1, while 0.6508 cm³ g^-1, 2.16 nm and 1206 m² g^-1 for ACF2, respectively. Their oxidation abilities were comparatively assessed in terms of degradation kinetics and mineralization rates, which increased in the order: ACF1-EF < ACF2-EF < ACF1-PEF < ACF2-PEF. These results confirmed the superiority of ACF with higher surface area, which was correlated to faster H₂O₂ and OH accumulation in more reaction sites provided. After 120 min electrolysis, ACF1 exhibited 1510 μM H₂O₂ and 37 μM OH accumulation, while ACF2 generated 1934 μM H₂O₂ and 85 μM OH. Moreover, ACF cathode with more developed pore structure also revealed faster formation of degradation by-products like inorganic ions (NH₄⁺ and NO₃^- ions) and short-chain carboxylic acids (acetic, formic, oxamic and oxalic acids), as well as enhanced removal for partial acids. In order to gain a deeper understanding of degradation mechanisms for ACF2-PEF system, evolutions of six aromatic by-products generated from sulfoxidation, hydroxylation and decarboxylation were confirmed by UPLC-QTOF-MS/MS determination. Based on the above identifications of the degradation intermediates, a plausible reaction pathway for CLX removal was proposed.

A recyclable nanosheet of Mo/N-doped TiO2 nanorods decorated on carbon nanofibers for organic pollutants degradation under simulated sunlight irradiation

A novel nanosheet of Mo/N-codoped TiO₂ nanorods immobilized on carbon nanofibers (MNTC nanosheet) was self-synthesized through two facile steps. The Mo/N-doped TiO₂ nanorods dispersed through in situ growth on the network constructed by long and vertical carbon nanofibers (CNFs). The fabricated MNTC nanosheet displayed superb photocatalytic activity of methylene blue (MB), and the degradation ratio by the MNTC nanosheet was nearly twice than that of pure nanoparticles. The photocatalytic activities during the degradation process in the presence of environmental media such as inorganic salts and natural organic matter (NOM) were also determined. Intermediates were analyzed by ion chromatography and electrospray ionization-mass spectrometry to unravel the potential degradation pathways, and the excellent mineralization ratio for MB over MNTC nanosheet was 79.8%. The trapping active species experiments verified that h⁺ was the main active species in the degradation process. Notably, the recycling experiment proved that the MNTC nanosheet was more stable, and it was successfully applied in purifying practical wastewater. Lastly, the fabricated MNTC nanosheet also displayed remarkable degradation performance towards sulfamethoxazole and bisphenol A.