Metronidazole removal by means of a combined system coupling an electro-Fenton process and a conventional biological treatment: By-products monitoring and performance enhancement

Effect of Fenton process as a pretreatment in the phytoremediation of metronidazole by Scirpus lacustris

The present study evaluated the effect of the Fenton process as pretreatment for metronidazole (MNZ) removal coupled with a phytoremediation system using Scirpus lacustris as macrophyte. Initial concentrations of 0.5, 5, 10, 15, and 20 mg MNZ/L were studied in batch cultures. Results obtained in the MNZ removal by phytoremediation showed efficiencies of 93 ± 2%, 81 ± 4%, 85 ± 1%, 84 ± 2%, and 87 ± 6%, respectively. The metronidazole pretreated by the Fenton process and subsequently fed to the phytoremediation system increased the removal efficiencies up to 93 ± 3%, 99 ± 1%, 99 ± 4%, 94 ± 2%, and 94 ± 3%, respectively. Individual studies with Scirpus lacustris in touch with metronidazole displayed relative growth rates of 0.02-0.04 d-1, showing the not toxic effect of the antibiotic on the macrophyte growth. On the other hand, the BMG kinetic model best describes the removal of MNZ by phytoremediation. Finally, applying the Fenton process as a pretreatment makes the MNZ more assimilable for the phytoremediation system, converting the integration of Fenton with the phytoremediation like other attractive technology to be considered in removing emerging compounds.

Enhanced metronidazole removal in seawater using a single-chamber bioelectrochemical system

The aim of this study was to investigate the removal of metronidazole (MNZ) from seawater using a bioelectrochemical system (BES). Single-chamber BES (i.e., S-BES) and dual-chamber BES (i.e., D-BES) were constructed with carbon brush as the anode and cathode. With the inoculum of sea mud and 2 g/L of glucose as the substrate in seawater, S-BES and D-BES were acclimated to test the MNZ removal. Results showed that S-BES could remove almost 100 % of 200 mg/L MNZ within 120 h and remain stable within 10 cycles of operation (∼50 d) under the applied voltage of 0.8 V. The MNZ removal reached ∼100 % and 60.2 % in the cathodic and anodic chambers of D-BES fed by 100 mg/L MNZ under 0.8 V, respectively. The MNZ concentration of 200 mg/L significantly inhibited the sulfur metabolism, decreased the ratio of live to dead cells in the electrode biofilms, and thus reduced the SO42- removal in the S-BES. The MNZ degradation and S2- oxidation was mainly attributed to the cathodic and anodic biofilms of S-BES, respectively. Three degradation pathways of MNZ were proposed based on the identified intermediates and results of density functional theory calculations. The synergies among different genus species in the bacterial communities of biofilms, and between anodic and cathodic reactions could be responsible for the high performance of S-BES. Results from this study should be not only useful for the MNZ removal but also for effective MNZ inhibition of sulfate-reducing bacteria induced microbiologically influenced corrosion in seawater.

Long-term stable and efficient degradation of ornidazole with minimized by-product formation by a biological sulfidogenic process based on elemental sulfur

Conventional biological treatment processes cannot efficiently and completely degrade nitroimidazole antibiotics, due to the formation of highly antibacterial and carcinogenic nitroreduction by-products. This study investigated the removal of a typical nitroimidazole antibiotic (ornidazole) during wastewater treatment by a biological sulfidogenic process based on elemental sulfur (S0-BSP). Efficient and stable ornidazole degradation and organic carbon mineralization were simultaneously achieved by the S0-BSP in a 798-day bench-scale trial. Over 99.8 % of ornidazole (200‒500 μg/L) was removed with the removal rates of up to 0.59 g/(m3·d). Meanwhile, the efficiencies of organic carbon mineralization and sulfide production were hardly impacted by the dosed ornidazole, and their rates were maintained at 0.15 kg C/(m3·d) and 0.49 kg S/(m3·d), respectively. The genera associated with ornidazole degradation were identified (e.g., Sedimentibacter, Trichococcus, and Longilinea), and their abundances increased significantly. Microbial degradation of ornidazole proceeded by several functional genes, such as dehalogenases, cysteine synthase, and dioxygenases, mainly through dechlorination, denitration, N-heterocyclic ring cleavage, and oxidation. More importantly, the nucleophilic substitution of nitro group mediated by in-situ formed reducing sulfur species (e.g., sulfide, polysulfides, and cysteine hydropolysulfides), instead of nitroreduction, enhanced the complete ornidazole degradation and minimized the formation of carcinogenic and antibacterial nitroreduction by-products. The findings suggest that S0-BSP can be a promising approach to treat wastewater containing multiple contaminants, such as emerging organic pollutants, organic carbon, nitrate, and heavy metals.

Recent developments on advanced oxidation processes for degradation of pollutants from wastewater with focus on antibiotics and organic dyes

The existence of various pollutants in water environment contributes to global pollution and poses significant threats to humans, wildlife, and other living beings. The emergence of an effective, realistic, cost-effective, and environmentally acceptable technique to treat wastewater generated from different sectors is critical for reducing pollutant accumulation in the environment. The electrochemical advanced oxidation method is a productive technology for treating hazardous effluents because of its potential benefits such as lack of secondary pollutant and high oxidation efficiency. Recent researches on advanced oxidation processes (AOPs) in the period of 2018-2022 are highlighted in this paper. This review emphasizes on recent advances in electro-oxidation (EO), ozone oxidation, sonolysis, radiation, electro-Fenton (EF), photolysis and photocatalysis targeted at treating pharmaceuticals, dyes and pesticides polluted effluents. In the first half of the review, the concept of the AOPs are discussed briefly. Later, the influence of increasing current density, pH, electrode, electrolyte and initial concentration of effluents on degradation are discussed. Lastly, previously reported designs of electrochemical reactors, as well as data on intermediates generated and energy consumption during the electro oxidation and Fenton processes are discussed. According to the literature study, the electro-oxidation technique is more appropriate for organic compounds, whilst the electro-Fenton technique appear to be more appropriate for more complex molecules.

The utility of ultraviolet beam in advanced oxidation-reduction processes: a review on the mechanism of processes and possible production free radicals

Advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) are a set of chemical treatment procedures designed to eliminate organic (sometimes inorganic) contamination in water and wastewater by producing free reactive radicals (FRR). UV irradiation is one of the factors that are effectively used in oxidation-reduction processes. Not only does the UV beam cause the photolysis of contamination, but it also leads to the product of FRR by affecting oxidants-reductant, and the pollutant decomposition occurs by FRR. UV rays produce active radical species indirectly in an advanced redox process by affecting an oxidant (O3, H2O2), persulfate (PS), or reducer (dithionite, sulfite, sulfide, iodide, ferrous). Produced FRR with high redox potential (including oxidized or reduced radicals) causes detoxification and degradation of target contaminants by attacking them. In this review, it was found that ultraviolet radiation is one of the important and practical parameters in redox processes, which can be used to control a wide range of impurities.

Bimetal-oxide (Fe/Co) modified bagasse-waste carbon coated on lead oxide-battery electrode for metronidazole removal

Current study covers the preparation and application of a commercial modified lead oxide battery electrode (LBE) in electrochemical oxidation (ECO) of metronidazole (MNZ) in an aqueous phase. Modified electrode is prepared by doping of bimetal-oxide (Fe and Zn) nanoparticles (NPs) & single metal-oxide (Fe/Zn) on bagasse-waste carbon (bwc) which is further coated on LBE. The modified LBE electrode surface was examined for metal-oxide NPs through X-ray diffraction analysis (XRD). Different electrodes are prepared by varying combinations of two metal-oxide based on molar ratio and tested for electrochemical characterization and MNZ removal test. Based on large oxygen evolution potential in a linear sweep volumetry (LSV) analysis and high MNZ removal rate, the best electrode has been represented as Fe1:Co2-bwc/LBE which contains Fe & Co molar ratio of 1:2. Moreover, equilibrium attained at faster rate in degradation process of MNZ, where pseudo first order kinetics of 2.29 × 10-2 min-1 was obtained under optimized condition of (MNZ:100 mg/L, pH:7, CD: 30 mA/cm2 and electrolyte: 0.05 M Na2SO4). Maximum MNZ removal, total organic carbon removal (TOC), mineralization current efficiency (MCE) & energy consumption (EC) of 98.7%, 85.3%, 62.2% & 96.143 kW h/kg-TOC removed are found in 180 min of treatment time for Fe1:Co2-bwc/LBE electrode. Accelerated service life test confirms that the stability of modified electrode is enhanced by 1.5 times compared to pristine LBE. Repeatability test confirms that modified LBE (Fe1:Co2-bwc/LBE) can be utilized up to 3 times.

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.

Exceptional photo-elimination of antibiotic by a novel Z-scheme heterojunction catalyst composed of nanoscale zero valent iron embedded with carbon quantum dots (CQDs)-black TiO2

Passivation of nanoscale zero valent iron (nZVI, Fe0) impaired its longevity while black TiO2 (b-TiO2) suffered from restricted optical properties. Using a facile approach, a novel Z-scheme heterojunction catalyst (Fe0@CQDs-TiO2(b)) of nZVI decorated with carbon quantum dots (CQDs) implanted into b-TiO2 was designed. Characterization results revealed the optical potential of the passivation coating of nZVI. The incorporation of CQDs stimulated the creation of active •OH during the dark reaction, and led to an accelerated mobility of photo-excited carriers of b-TiO2 and optimized its band gap (narrowing from 2.36 eV to 2.15 eV) during the light reaction. The photo-elimination capacity of metronidazole (MNZ) on Fe0@CQDs-TiO2(b) (99.36%) was 2.64, 8.25 and 1.34 fold beyond that on nZVI, b-TiO2 and Fe0@b-TiO2, respectively. The assembled material offered excellent adaptability to environmental substrates, in addition to being virtually unaffected by tap (95.62%) and river water (92.62%). The mechanism of MNZ degradation was elaborated, and the combination of density functional theory (DFT) calculations and LC-MS discerned 12 intermediates and 3 routes. Toxicity assessment of these products was conducted to ensure no inadvertent negative environmental impacts arose. This work proposed an original direction and mechanism for the application of passivation layers in nZVI-based materials for environmental restoration.

Biological treatment of triclosan using a novel strain of Enterobacter cloacae and introducing naphthalene dioxygenase as an effective enzyme

In recent years, triclosan (TCS) has been widely used as an antibacterial agent in personal care products due to the spread of the Coronavirus. TSC is an emerging contaminant, and due to its stability and toxicity, it cannot be completely degraded through traditional wastewater treatment methods. In this study, a novel strain of Enterobacter cloacae was isolated and identified that can grow in high TCS concentrations. Also, we introduced naphthalene dioxygenase as an effective enzyme in TCS biodegradation, and its role during the removal process was investigated along with the laccase enzyme. The change of cell surface hydrophobicity during TCS removal revealed that a glycolipid biosurfactant called rhamnolipid was involved in TCS removal, leading to enhanced biodegradation of TCS. The independent variables, such as initial TCS concentration, pH, removal duration, and temperature, were optimized using the response surface method (RSM). As a result, the maximum TCS removal (97%) was detected at a pH value of 7 and a temperature of 32 °C after 9 days and 12 h of treatment. Gas chromatography-mass spectrometry (GC/MS) analysis showed five intermediate products and a newly proposed pathway for TCS degradation. Finally, the phytotoxicity experiment conducted on Cucumis sativus and Lens culinaris seeds demonstrated an increase in germination power and growth of stems and roots in comparison to untreated water. These results indicate that the final treated water was less toxic.

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.

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.

Reduction of metronidazole in municipal wastewater and protection of activated sludge system using a novel immobilized Aspergillus tabacinus LZ-M

Metronidazole (MNZ) accumulation inhibits municipal wastewater treatment bio-systems, and an effective solution to augment anaerobic activated sludge (AAS) is required. This research discovered that Aspergillus tabacinus LZ-M could degrade 77.39% of MNZ at 5 mg/L. MNZ was metabolized into urea, and the enzymes involved in its degradation were aminotransferase, methyltransferase, monooxygenase, and CN cleavage hydrolase. The strain was immobilized in polyurethane foam and used in AAS for the treatment of MNZ-containing municipal wastewater. The results showed that, using immobilized LZ-M, MNZ was completely removed, and the degradation efficiency of wastewater's chemical oxygen demand (COD) was increased from 11.7% to 83.31%. The extracellular polymer and ROS levels indicated that MNZ's toxicity on AAS was reduced. Furthermore, bioaugmentation stabilized its microbial community, and decreased MNZ resistance genes. These observations confirm that the immobilized fungi are effective in protecting AAS against antibiotic contamination in the treatment process of municipal wastewater.

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.

Fast and Complete Destruction of the Anti-Cancer Drug Cytarabine from Water by Electrocatalytic Oxidation Using Electro-Fenton Process

The fast and complete removal of the anti-cancer drug cytarabine (CYT) from water was studied, for the first time, by the electro-Fenton process using a BDD anode and carbon felt cathode. A catalytic amount (10−4 M) of ferrous iron was initially added to the solution as catalyst and it was electrochemically regenerated in the process. Complete degradation of 0.1 mM (24.3 mg L−1) CYT was achieved quickly in 15 min at 300 mA constant current electrolysis by hydroxyl radicals (●OH) electrocatalytically generated in the system. Almost complete mineralization (91.14% TOC removal) of the solution was obtained after 4 h of treatment. The mineralization current efficiency (MCE) and energy consumption (EC) during the mineralization process were evaluated. The absolute (second order) rate constant for the hydroxylation reaction of CYT by hydroxyl radicals was assessed by applying the competition kinetics method and found to be 5.35 × 109 M−1 s−1. The formation and evolution of oxidation reaction intermediates, short-chain carboxylic acids and inorganic ions were identified by gas chromatography-mass spectrometry, high performance liquid chromatography and ion chromatography analyses, respectively. Based on the identified intermediate and end-products, a plausible mineralization pathway for the oxidation of CYT by hydroxyl radicals is proposed.

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.

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.

Influence of metronidazole on activated sludge activity

Metronidazole is potentially carcinogenic to humans and it has been detected in wastewaters. The Wastewater Treatment Plants using biological processes have been highly impacted by the emergent compounds of recalcitrant type, and the knowledge about that issue is quite relevant. Therefore, this paper was focused on how metronidazole influences the kinetics and metabolic behaviour of nitrification and heterotrophic activity on activated sludge in batch cultures. Eight concentrations of metronidazole in the range of 5-100 mg/L were evaluated, in the presence of 2109 ± 129 mg VSS/L. The increment of initial metronidazole concentration caused a decline on COD and ammonium removal efficiencies, nitrate production yields, as well as in the substrate-specific consumption rates. Metronidazole (MDZ) had a greater impact on heterotrophic activity than nitrifying activity; also, it had a greater inhibitory effect on nitrite oxidation than ammonium oxidation. The activated sludge was not able to biotransform metronidazole; however, the azole compound significantly affected the physiology of it. The inhibition of ammonium oxidation was non-competitive (q_max= 120 mg NH₄⁺-N consumed/gVSS-d, and K_i = 41.5 mg MDZ/L) and the initial metronidazole concentration that inhibited 50% of nitrifying activity (IC₅₀) was 43 mg MDZ/L.

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.

Continuous flow pulsed power plasma reactor for the treatment of aqueous solution containing volatile organic compounds and real pharmaceutical wastewater

The degradation of four recalcitrant and toxic VOCs (volatile organic compounds) present in pharmaceutical wastewater was studied using a continuous flow plasma reactor, along with evaluating its potential for real effluent treatment. The wastewater was sprayed into the plasma zone of the reactor, and it was re-circulated for better performance. The effect of different HRTs (hydraulic retention time) and initial concentrations of VOCs on the degradation efficiency were evaluated. In continuous reactor, complete removal of 200 mg/L of chloroform, chlorobenzene, and toluene was achieved at a HRT of 33.3 min, with an energy consumption of 22.4 kWh/m³. The study on the effect of different inlet loading rates of VOCs on elimination capacity showed that, the removal was limited initially by diffusion of reactive species and at higher loads, it was limited by insufficient amount of reactive species produced. During degradation of VOC mixture, more than 90% removal of chloroform, chlorobenzene and toluene was achieved at HRT of 33.3 min, and the TOC removal was 78.3%. The degradation efficiency of VOC mixture reduced slightly compared to that of individual compounds, due to insufficient amount of reactive species produced. The COD and BOD removal achieved after 140 min of direct plasma treatment of real pharmaceutical wastewater in batch reactor was 92.7% and 95.2%, respectively. Coagulation pre-treatment did not have a significant effect on the plasma treatment of real wastewater. When pharmaceutical effluent treatment was carried out in continuous flow reactor, 91.8% COD removal, 90.9% BOD removal and more than 90% degradation of all VOCs were achieved at a HRT of 150 min. Plasma treatment alone was capable of effectively treating the real pharmaceutical wastewater without any pre-treatment.

Structured photocatalytic systems: photocatalytic coatings on low-cost structures for treatment of water contaminated with micropollutants-a short review

The persistence of many micropollutants in water and wastewater is of great concern to the contemporary scientific community. Several types of advanced techniques such as heterogeneous photocatalysis are being used for the degradation of micropollutants in waters from domestic, industrial, and agricultural activities. Thus, structured photocatalytic systems are a great alternative in the development of photocatalytic reactors and continuous water treatment systems, as they present good autonomy during the treatment process. Many aspects such as type and geometry of the catalytic structure to be developed must be carefully chosen for the proper functioning of the system, as well as the best routes by which the photocatalysts will be immobilized. In this sense, this work brings the main photocatalytic coating techniques in low-cost structures for the treatment of water and wastewater contaminated with micropollutants. The methodologies and synthesis parameters that can influence the final result of the coating were highlighted, as well as the ability to reuse photocatalysts and methods for pretreating the structural surface. The dip-coating technique was the most reported among the current works due to its simplicity and, predominantly, the pretreatment techniques of the structure are still cleaning the surface with water, soap, and also some alcohols.

Artificial neural network modeling of cefixime photodegradation by synthesized CoBi2O4 nanoparticles

CoBi₂O₄ (CBO) nanoparticles were synthesized by sol-gel method using polyvinylpyrrolidone (PVP) as a complexing reagent. For a single phase with the spinel structure, the formed gel was dried and calcined at four temperatures stages. Various methods were used to identify and characterize the obtained spinel, such as X-ray diffraction (XRD), scanning electron micrograph (SEM-EDX), transmission electron microscope (TEM), Fourier transform infrared (FT-IR), X-ray fluorescence (XRF), Raman, and UV-Vis spectroscopies. The photocatalytic activity of CBO was examined for the degradation of a pharmaceutical product cefixime (CFX). Furthermore, for the prediction of the CFX degradation rate, an artificial neural network model was used. The network was trained using the experimental data obtained at different pH with different CBO doses and initial CFX concentrations. To optimize the network, various algorithms and transfer functions for the hidden layer were tested. By calculating the mean square error (MSE), 13 neurons were found to be the optimal number of neurons and produced the highest coefficient of correlation R² of 99.6%. The relative significance of the input variables was calculated, and the most impacting input was proved to be the initial CFX concentration. The effects of some scavenging agents were also studied. The results confirmed the dominant role of hydroxyl radical OH^• in the degradation process. With the novel CoBi₂O₄/ZnO hetero-system, the photocatalytic performance has been enhanced, giving an 80% degradation yield of CFX (10 mg/L) at neutral pH in only 3 h.

Comparison of Ag and AgI-Modified ZnO as Heterogeneous Photocatalysts for Simulated Sunlight Driven Photodegradation of Metronidazole

Ag and AgI-modified ZnO composites (Ag/ZnO and AgI/ZnO) were synthesized in facile ways. The photocatalysts were used for the photodegradation of metronidazole (MNZ) under the irradiation of simulated sunlight. The results of experiments showed that both Ag/ZnO and AgI/ZnO had a specific molar ratio to reach the best performance. Ag/ZnO performed better in the photodegradation of MNZ than AgI/ZnO under the same conditions. The reaction rate constant of AgI/ZnO was less affected by the variation of initial concentration of MNZ or pH values. The main reactive oxygen species of the photocatalytic process are OH, O2− and h+, but the free radicals which play the most critical part differ in Ag/ZnO and AgI/ZnO. Several intermediates were revealed by LC–MS/MS analysis. The stability of the photocatalysts was evaluated by a series of repeated MNZ photodegradation experiments. The results showed that AgI/ZnO had better stability than Ag/ZnO.

Application of response surface methodology for optimization of electrochemical process in metronidazole (MNZ) removal from aqueous solutions using stainless steel 316 (SS316) and lead (Pb) anodes

Pharmaceutical compounds in drinking water sources, in addition to threatening environmental health, increase bacterial resistance in aquatic environments. The purpose of this study was to investigate the application of response surface methodology for the optimization of the electrochemical process in the removal of metronidazole (MNZ) aqueous solutions using stainless steel 316 (SS316) and Lead (Pb) anodes. In this experimental study, the effect of different parameters including pH (4–10), electrolysis time (40–120 min), MNZ antibiotic concentration (30–150 mg/L), and current density (2–10 mA/cm2) on Antibiotic removal efficiency was evaluated by a central composite design method using Design-Expert software. Data were analyzed using ANOVA and p-Value tests. Hence, central composite design (CCD) established a reduced quadratic polynomial model with P-value < 0.0001 and R2 = 0.98. The optimal values for the solution pH initial, electrolysis time, current density, and MNZ antibiotic concentration were 5.5, 100.0 min, 8.0 mA/cm2, and 50 mg/L, respectively. By employing the optimum conditions obtained, the maximum experimental removal efficiencies by SS316 and Pb anodes were 67.85 and 78.66%, respectively. The Chemical Oxygen Demand/total organic carbon (COD/TOC) ratio was decreased from 1.67 at the inlet to 1.53 at the outlet for SS316 and from 1.7 to 1.42 for Pb. Moreover, average oxidation state (AOS) was increased from 1.45 to 1.7 for SS316 and from 1.45 to 1.86 for Pb, which indicates the biodegradability of MNZ antibiotics by the electrochemical process. The electrochemical degradation process was identified as an effective method for the removal of MNZ from aquatic solutions, and it has an outstanding potential in removing other refractory pollutants from the environment.

Degradation of ronidazole by electrochemically simultaneously generated persulfate and ferrous ions

Nitroimidazoles are found in pharmaceuticals and personal care products (PPCPs) and, when discharged into the environment, have adverse effects on human health and survival. Advanced oxidation technologies (AOTs) based on persulfate (PS) can rapidly and efficiently degrade organic pollutants via strong oxidizing radicals under activation conditions. This study investigated the degradation of ronidazole (RNZ) by indirect electrolytic generation of PS and its activator, ferrous ion (Fe²⁺). An electrochemical system was developed, with a high concentration of PS generated at the anode while the activator Fe²⁺ was produced at the cathode. It showed that ammonium polyphosphate (APP) could effectively promote the electrolysis of PS. A high current efficiency (88%) at the anode could be obtained after 180 min at a high current density (300 mA cm^-2). However, Fe²⁺ was inhibited at the cathode due to material control. The degradation of RNZ in the Fe²⁺/PS system generated from the electrochemical system was also explored. Increasing PS concentration and Fe²⁺/PS ratio were beneficial to the RNZ degradation. In homogeneous reactions, the degradation efficiency of RNZ could be improved by decreasing the Fe²⁺ addition rate through a peristaltic pump. Five intermediates were also detected and the degradation pathways were proposed. These findings provide a new method and mechanism for rapid and efficient degradation of RNZ.

Electro Fenton removal of clopyralid in soil washing effluents

The removal of a commercial herbicide, based on clopyralid, by means of Electro-Fenton (EF) was studied using a soil washing effluent obtained using synthetic ground water as washing fluid. From the results, it was observed that the degradation and mineralization yields of clopyralid were high, even without the addition of supporting electrolyte. The groundwater could be then used as a sustainable supporting electrolyte. The influence of the minerals constituents, the current and the ferrous ions regeneration was evaluated. The highest hydrogen peroxide production was achieved working at 200 mA but regeneration of ferrous ions was not efficient at this current. Iodide ions were one of the main responsible in the EF efficiency decrease due to their reaction with the produced hydrogen peroxide. Electrochemical study proved that clopyralid was not electroactive and that its degradation was mainly due to radical oxidation. Long duration electrolysis carried out at 200 mA in groundwater provided an improvement of the solution biodegradability after 480 min that can be linked to a significant increase in the carboxylic acids production. These results support the feasibility of applying an EF process in order to carry out a subsequent biological mineralization.

Electrospun spongy zero-valent iron as excellent electro-Fenton catalyst for enhanced sulfathiazole removal by a combination of adsorption and electro-catalytic oxidation

In this study, a highly active electro-Fenton catalyst, spongy zero-valent iron (ZVI), has been developed at first via in-situ synthesis of ZVI nanoparticles (NPs) on an electrospun three-dimensional (3D) nanofiber network. The spongy ZVI effectively overcame the defects of easy aggregation of ZVI NPs and ferric sludge accumulation during the electro-catalytic process. Then, a three-dimensional electro-Fenton (3D-EF) system using the as-fabricated spongy ZVI as particle catalytic electrodes was designed, which presented a significant synergistic effect of adsorption and electro-catalytic oxidation on the enhanced removal of a widely used antibiotic, sulfathiazole (STZ) from water. Adsorption experiments demonstrated that the spongy ZVI had a relative high adsorption affinity towards STZ with about 50% of the total removal within 240 min, and the adsorption equilibrium was reached in 570 min. Hydroxyl radical (OH) was produced in the 3D-EF system with spongy ZVI catalyst, and almost 100% STZ was removed within 5 min. Reactive oxygen species analysis verified that OH was mainly responsible for the STZ degradation. Based on intermediates identified by a liquid chromatography-tandem mass spectrometry (LC-MS/MS), three pathways for the electro-Fenton oxidative degradation of STZ were proposed.

Experimental data on the removal of phenol by electro-H2O2 in presence of UV with response surface methodology

Phenol is classified as priority pollutant. Phenol and its derivatives are stable in water, environmental contamination, and health concerns that are used as raw material in many chemical industries. This study investigated the removal of phenol by electro-H₂O₂/UV system.

The response surface methodology (RSM) using central composite design (CCD) was used to modeling and optimization of experimental parameters such as pH, contact time, initial concentration of phenol, concentration of hydrogen peroxide, and current density.

The obtained results demonstrated that the efficiency of the electro-H₂O₂/UV system was maximum (>99%) under the optimal conditions for the phenol removal from aqueous solutions, 2 mM of hydrogen peroxide concentration, 50 mg/L of initial phenol concentration, pH of 5, 10 mA/cm² of current density, reaction time of 25 min and 2.1 kW h/m³ of energy consumption. Therefore, the electro-H₂O₂/UV system is an efficient method for the removal of organic compounds from industrial wastewater.