Electrochemical incineration of omeprazole in neutral aqueous medium using a platinum or boron-doped diamond anode: degradation kinetics and oxidation products

Efficient removal of 2,4,6-trinitrotoluene (TNT) from industrial/military wastewater using anodic oxidation on boron-doped diamond electrodes

With growing public concern about water quality particular focus should be placed on organic micropollutants, which are harmful to the environment and people. Hence, the objective of this research is to enhance the security and resilience of water resources by developing an efficient system for reclaiming industrial/military wastewater and protecting recipients from the toxic and cancerogenic explosive compound-2,4,6-trinitrotoluene (TNT), which has been widely distributed in the environment. This research used an anodic oxidation (AO) process on a boron-doped diamond (BDD) electrode for the TNT removal from artificial and real-life matrices: marine water and treated wastewater. During experiments, TNT concentrations were significantly decreased, reaching the anodic degradation efficiency of above 92% within two hours and > 99.9% after six hours of environmental sample treatment. The presented results show the great potential of AO performed on BDD anodes for full-scale application in the industry and military sectors for TNT removal.

Decolorization, COD and turbidity removal of the raw vinasse effluent by a one-step electro-oxidation process on a Pb/PbO2 anode

In this research, and for the first time, the application of anode Pb/PbO2 (prepared from combined thermal oxidation and electrochemical oxidation method) and steel cathode in a flow sample electrochemical treatment process of vinasse and in the wastewater of alcohol factories, has been investigated. The combination of electrodes of Pb/PbO2 as an anode, steel, and/or graphite as a cathode was used in the proposed electrochemical treatment setup. The efficiency of the proposed electrochemical treatment was determined by the removal percentage of chemical oxygen demand (COD), turbidity and color of vinasse samples. The response surface method (RSM) by Minitab 18 was used to determine the effect of the studied factors as well as to detect the relationship between variables. The results showed that under optimum conditions (Pb/PbO2 electrode as the anode and steel electrode as the cathode, a voltage of 30 V, pH 6.5, and reaction time of 45 min), the percentage reduction values of COD, turbidity and color were 97.7, 77.3 and 92.7%, respectively.

Simultaneous Carbamazepine and Phosphate Removal from a Moving-Bed Membrane Bioreactor Effluent by the Electrochemical Process: Treatment Optimization by Factorial Design

Pharmaceutical and personal care products are frequently used in various fields and released into water bodies from the outlets of wastewater treatment plants. These products can harm the environment and human health even at low concentrations. Carbamazepine (CBZ), the most persistent pharmaceutical, has frequently been found in surface waters that bypassed the secondary treatments of conventional activated sludge. In addition, the treatment of phosphate in wastewater by the electrochemical process has recently attracted much attention because of its ability to remove, recover, and prevent environmental problems associated with eutrophication. This study proposes using the electrochemical process as an advanced oxidation process to simultaneously treat CBZ and phosphate from the moving-bed membrane bioreactor effluent. The study includes a long-term survey of CBZ treatment efficiency and common parameters of synthetic wastewater in the moving-bed membrane bioreactor system. Afterward, the electrochemical process is applied as an advanced oxidation process for the simultaneous removal of CBZ and phosphate from the moving-bed membrane bioreactor. Under the investigated conditions, CBZ has proven not to be an inhibitor of microbial activity, as evidenced by the high extent of chemical oxygen demand and nutrient removal. Using a factorial design, the electrochemical process using Pt/Ti as anode and cathode under optimal conditions (reaction time-80 min, bias potential-3 V, and electrode distance-1 cm) resulted in as high as 56.94% CBZ and 95.95% phosphate removal, respectively. The results demonstrated the ability to combine an electrochemical and a moving-bed membrane bioreactor process to simultaneously remove CBZ and phosphate in wastewater.

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.

Efficient removal of micropollutants from low-conductance surface water using an electrochemical Janus ceramic membrane filtration system

Electrochemical membrane filtration (EMF) technology is effective to remove the micropollutant in the wastewater but its efficacy is drastically compromised in treating the surface water having a typically low conductivity. In this work, a Janus Fe-Pt electrochemical ceramic membrane (ECM) was fabricated by depositing a thin Fe layer on the side of a ceramic membrane facing feed (cathode) and Pt layer on the other side facing permeate (anode). The low Fe-Pt electrode distance (∼1 mm) ensured a decent conductance of the EMF system even in the low-salinity surface water and thereby maintained the removal efficiency of the micropollutant. It was identified that hydroxyl radicals (•OH) generated via anodic water oxidation and cathodic heterogenous Fenton process on bilateral sides of ECM were the dominant reactive oxygen species. The EMF system not only achieved 74% removal of atrazine (ATZ) from the low-conductance synthetic surface water with a low energy consumption (3.6 Wh per gATZ or 7.2 Wh m ^- 3), but also realized a stable removal of ATZ from real surface water over a continuous filtration experiment of 168 h. The theoretical computations and experimental analysis identified the degradation pathway, i.e., the dechlorination and dealkylation of ATZ in the EMF system. This study highlights the great potential of the Janus ECM in removing micropollutants from low-conductance surface water and wastewater.

Pharmaceuticals and personal care products in water streams: Occurrence, detection, and removal by electrochemical advanced oxidation processes

Pharmaceutical and personal care products (PPCPs) are part of the emerging contaminants (ECs) in the environment due to their known or suspected adverse effects in aquatic and terrestrial organisms, as well as in human health. Presence of PPCPs in aquatic and terrestrial ecosystems has been mainly attributed to the effluents of wastewater treatment plants (WWTPs). Although several PPCPs have been detected in wastewater, their removal from wastewater via biological processes is limited. Removal of PPCPs depends on their chemical structure, concentration, solubility, and technology used to treat the wastewater. Electrochemical Advanced Oxidation Processes (EAOPs) are some of the most sought-after methods for dealing with organic pollutants in water including PPCPs, due to generation of strong oxidants such as •OH, H₂O₂ and O₃^- by using directly or indirectly electrochemical technology. This review is focused on the removal of main PPCPs via EAOPs such as, anodic oxidation, electro-Fenton, photoelectron-Fenton, solar photoelectron-Fenton, photoelectrocatalysis and sonoelectrochemical processes. Although more than 40 PPCPs have been identified through different analytical approaches, antibiotics, anti-inflammatory and antifungal are the main categories of PPCPs detected in different water matrices. Application of EAOPs has been centered in the removal of antibiotics and analgesics of high consumption by using model media, e.g. Na₂SO_4. Photoelectrocatalysis and Electro-Fenton processes have been the most versatile EAOPs applied for PPCPs removal under a wide range of operating conditions and a variety of electrodes. Although EAOPs have gained significant scientific interest due to their effectiveness, low environmental impact, and simplicity, further research about the removal of PPCPs and their by-products under realistic concentrations and media is needed. Moreover, mid-, and long-term experiments that evaluate EAOPs performance will provide knowledge about key parameters that allow these technologies to be scaled and reduce the potential risk of PPCPs in aquatic and terrestrial ecosystem.

Electrochemical degradation of amoxicillin in acidic aqueous medium using TiO2-based electrodes modified by oxides of transition metals

One of the most widely used antibiotics is amoxicillin (AMX), which is the most widely used in humans and animals, but it is discharged metabolically due to its indigestibility. Conventional biological and physicochemical methods for removing AMX from water are not enough to mineralize it; it is only concentrated and transferred to produce new residues that require further processing to remove the new residues. In this research, naked and modified surfaces with TiO₂ nanotubes (TiO_2,nt) electrophoretically modified with PbO₂, IrO₂, RuO₂, and Ta₂O₅ were used to evaluate their efficiency in the electrochemical degradation of AMX in acid media (0.1 mol L^-1 H₂SO₄). After their comparison, Pb-Ta 50:50|TiO_2,nt|Ti showed the highest removal efficiency of AMX (44.71%) with the lowest specific energy consumption (8.69 ± 0.78 kWh Kg COD^-1) and the average instant current efficiency of 26.67 ± 9.19%, in comparison with the others naked and modified surfaces of TiO_2,nt∣Ti.

Recent Trends in Pharmaceuticals Removal from Water Using Electrochemical Oxidation Processes

Nowadays, the research on the environmental applications of electrochemistry to remove recalcitrant and priority pollutants and, in particular, drugs from the aqueous phase has increased dramatically. This literature review summarizes the applications of electrochemical oxidation in recent years to decompose pharmaceuticals that are often detected in environmental samples such as carbamazapine, sulfamethoxazole, tetracycline, diclofenac, ibuprofen, ceftazidime, ciprofloxacin, etc. Similar to most physicochemical processes, efficiency depends on many operating parameters, while the combination with either biological or other physicochemical methods seems particularly attractive. In addition, various strategies such as using three-dimensional electrodes or the electrosynthesis of hydrogen peroxide have been proposed to overcome the disadvantages of electrochemical oxidation. Finally, some guidelines are proposed for future research into the applications of environmental electrochemistry for the degradation of xenobiotic compounds and micropollutants from environmental matrices. The main goal of the present review paper is to facilitate future researchers to design their experiments concerning the electrochemical oxidation processes for the degradation of micropollutants/emerging contaminants, especially, some specific drugs considering, also, the existing limitations of each process.

Study of degradation of amitriptyline antidepressant by different electrochemical advanced oxidation processes

Amitriptyline (AMT) is the most widely used tricyclic antidepressant and is classified as a recalcitrant emergent contaminant because it has been detected in different sources of water. Its accumulation in water and soil represents a risk for different living creatures. To remove amitriptyline from wastewater, the Advanced Oxidation Processes (AOPs) stands up as an interesting option since generate highly oxidized species as hydroxyl radicals (OH) by environmentally friendly mechanism. In this work, the oxidation and mineralization of AMT solution have been comparatively studied by 3 Electrochemical AOPs (EAOPs) where the OH is produced by anodic oxidation of H₂O (AO-H₂O₂), or by electro-Fenton (EF) or photoelectro-Fenton (PEF). PEF process with a BDD anode showed the best performance for degradation and mineralization of this drug due to the synergistic action of highly reactive physiosorbed BDD (OH), homogeneous OH and UVA radiation. This process achieved total degradation of AMT at 50 min of electrolysis and 95% of mineralization after 360 min of treatment with 0.5 mmol L^-1 Fe²⁺ at 100 mA cm^-2. Six aromatic intermediates for the drug mineralization were identified in short time of electrolysis by GC-MS, including a chloroaromatic by-product formed from the attack of active chlorine. Short-chain carboxylic acids like succinic, malic, oxalic and formic acid were quantified by ion-exclusion HPLC. Furthermore, the formation of NO₃^- ions was monitored. Finally, the organic intermediates identified by chromatographic techniques were used to propose the reaction sequence for the total mineralization of AMT.

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.

Gas diffusion electrodes for H2O2 production and their applications for electrochemical degradation of organic pollutants in water: A review

Nowadays, it is a great challenge to minimize the negative impact of hazardous organic compounds in the environment. Highly efficient hydrogen peroxide (H₂O₂) production through electrochemical methods with gas diffusion electrodes (GDEs) is greatly demand for degradation of organic pollutants that present in drinking water and industrial wastewater. The GDEs as cathodic electrocatalyst manifest more cost-effective, lower energy consumption and higher oxygen utilization efficiency for H₂O₂ production as compared to other carbonaceous cathodes due to its worthy chemical and physical characteristics. In recent years, the crucial research and practical application of GDE for degradation of organic pollutants have been well developed. In this review, we focus on the novel design, fundamental aspects, influence factors, and electrochemical properties of GDEs. Furthermore, we investigate the generation of H₂O₂ through electrocatalytic processes and degradation mechanisms of refractory organic pollutants on GDEs. We describe the advanced methodologies towards electrochemical kinetics, which include the enhancement of GDEs electrochemical catalytic activity and mass transfer process. More importantly, we also highlight the other technologies assisted electrochemical process with GDEs to enlarge the practical application for water treatment. In addition, the developmental prospective and the existing research challenges of GDE-based electrocatalytic materials for real applications in H₂O₂ production and wastewater treatment are forecasted. According to our best knowledge, only few review articles have discussed GDEs in detail for H₂O₂ production and their applications for degradation of organic pollutants in water.

Overview of recent developments of resource recovery from wastewater via electrochemistry-based technologies

As the rapid increase of the worldwide population, recovering valuable resources from wastewater have attracted more and more attention by governments and academia. Electrochemical technologies have been extensively investigated over the past three decades to purify wastewater. However, the application of these technologies for resource recovery from wastewater has just attracted limited attention. In this review, the recent (2010-2020) electrochemical technologies for resource recovery from wastewater are summarized and discussed for the first time. Fundamentals of typical electrochemical technologies are firstly summarized and analyzed, followed by the specific examples of electrochemical resource recovery technologies for different purposes. Based on the fundamentals of electrochemical reactions and without the addition of chemical agents, metallic ions, nutrients, sulfur, hydrogen and chemical compounds can be effectively recovered by means of electrochemical reduction, electrochemical induced precipitation, electrochemical stripping, electrochemical oxidation and membrane-based electrochemical processes, etc. Pros and cons of each electrochemical technology in practical applications are discussed and analyzed. Single-step electrochemical process seems ineffectively to recover valuable resources from the wastewater with complicated constituents. Multiple-step processes or integrated with biological and membrane-based technologies are essential to improve the performance and purity of products. Consequently, this review attempts to offer in-depth insights into the developments of next-generation of electrochemical technologies to minimize energy consumption, boost recovery efficiency and realize the commercial application.

Study on the Electrochemical Removal Mechanism of Oxytetracycline by a Ti/IrO2-Ta2O5 Plate

In this study, a Ti/IrO₂-Ta₂O₅ anode was prepared by a hydrothermal method, and the prepared electrode was characterized by techniques such as scanning electron microscopy, X-ray diffraction, and electron dispersive spectroscopy. At the same time, the anode characteristics before and after electrochemical experiments were analyzed. The electrode gradation mechanism of oxytetracycline is discussed. In the whole experimental process, the range of electrolysis conditions was determined by single factor experiment, and then the optimal removal condition of oxytetracycline was determined by orthogonal experiments. The removal rate of oxytetracycline reached 99.02% after 20 min of electrolysis under the following optimal conditions: a current of 0.500 A, plate spacing of 2 cm, Na₂SO₄ electrolyte concentration of 4 g/L, and solution pH of 3. Additionally, the mechanism of oxytetracycline removal was explored, free radical scavenging experiments were performed, and the degradation mechanism was inferred based on the changes in the ultraviolet absorption of the oxytetracycline solution before and after electrolysis. Then, based on the liquid chromatography-mass spectrometry data, seven possible compounds and five possible removal pathways were proposed.

Electro-catalytic membrane reactors for the degradation of organic pollutants – a review

Electro-catalytic membrane reactor exhibiting electro-oxidation degradation of organic pollutants on anodic membrane.

A critical review on advanced oxidation processes for the removal of trace organic contaminants: A voyage from individual to integrated processes

Advanced oxidation processes (AOPs), such as photolysis, photocatalysis, ozonation, Fenton process, anodic oxidation, sonolysis, and wet air oxidation, have been investigated extensively for the removal of a wide range of trace organic contaminants (TrOCs). A standalone AOP may not achieve complete removal of a broad group of TrOCs. When combined, AOPs produce more hydroxyl radicals, thus performing better degradation of the TrOCs. A number of studies have reported significant improvement in TrOC degradation efficiency by using a combination of AOPs. This review briefly discusses the individual AOPs and their limitations towards the degradation of TrOCs containing different functional groups. It also classifies integrated AOPs and comprehensively explains their effectiveness for the degradation of a wide range of TrOCs. Integrated AOPs are categorized as UV irradiation based AOPs, ozonation/Fenton process-based AOPs, and electrochemical AOPs. Under appropriate conditions, combined AOPs not only initiate degradation but may also lead to complete mineralization. Various factors can affect the efficiency of integrated processes including water chemistry, the molecular structure of TrCOs, and ions co-occurring in water. For example, the presence of organic ions (e.g., humic acid and fulvic acid) and inorganic ions (e.g., halide, carbonate, and nitrate ions) in water can have a significant impact. In general, these ions either convert to high redox potential radicals upon collision with other reactive species and increase the reaction rates, or may act as radical scavengers and decrease the process efficiency.

Photoelectro-Fenton system including electromagnetic induction electrodeless lamp and black carbon poly tetra fluoro ethylene air-diffusion cathode: Degradation kinetics, intermediates and pathway for azo dye

The role of illumination and cathode is important to improve the efficiency of photoelectro-Fenton (PEF) system. In this study, cathodes with black carbon-poly tetra fluoro ethylene (BC-PTFE) for increase the concentration of hydrogen peroxide in PEF. A new PEF system using EIEL and BC-PTFE air-diffusion cathode was established. The electrode performance was tested and the influence factors, degradation kinetics, intermediates, pathway and mechanism of the model compound methyl orange (MO) were studied. The capacities of concentration decays and total organic carbon (TOC) removals were compared between different electrochemical advanced oxidation processes. The experimental conditions were optimized for a current density of 20 mA cm^-2 with 0.5 mM Fe²⁺ and 100 mg L^-1 MO at 20 °C and pH 3.0 in an 8 L reservoir. The higher MO concentration was, the smaller pseudo-first-order kinetic constants of concentration decays and TOC removals were. Intermediate products were identified by gas chromatography-mass spectrometry and ion-exclusion high performance liquid chromatograph in EIEL-PEF. Combined with frontier electron density, the degradation pathway was deduced as follows: destruction of azo bond, substitution of ^•OH, dehydrogenation and oxidation, opening-ring and mineralization. In EIEL-PEF, the concentration of oxalic acid and oxamic acid reached the maximum value 9.2 and 1.5 mg L^-1 at 60 and 90 min, respectively. The photolysis of N-intermediates produced NH₄⁺-N was released in more proportion than NO₃^--N and oxamic acid-N. The study indicated that PEF system has the potential to remove organic pollutants in aquatic environments.

Fabrication of boron-doped diamond films electrode for efficient electrocatalytic degradation of cresols

The choice of anode materials has a significant influence on the electrocatalytic degradation of organics. Accordingly, the electrocatalytic activity of several active anodes (Ti/Ru-Ir, Ti/Ir-Ta, Ti/Pt) and non-active anodes (Ti/PbO₂, Ti/SnO₂, Si/BDD (boron-doped diamond)) was compared by electrocatalytic degradation of m-cresol. The results indicated Si/BDD electrode had the strongest mineralization ability and the lowest energy consumption. And the order of the activity of m-cresol degradation was as follows: Si/BDD > Ti/SnO₂>Ti/PbO₂>Ti/Pt > Ti/Ir-Ta > Ti/Ru-Ir. Also their intermediate products were compared. The effects of experimental parameters on electrocatalytic degradation of m-cresol with Si/BDD electrode showed m-cresol conversion was affected slightly by the electrode spacing and electrolyte concentration, but affected greatly by the temperature and current density. And smaller electrode spacing and current density, higher electrolyte concentration and temperature were beneficial to reduce energy consumption. Their degradation processes were all accord with the pseudo-first-order reaction kinetics completely. In addition, the results of electrocatalytic degradation of m, o, p-cresol indicated there was almost no significant difference on conversion rate between cresols isomers with the current density of 30 mA cm^-2. However, the influence of group position was shown when the current density was reduced to 10 mA cm^-2 and cresols conversion followed the sequence of m-cresol ≈ o-cresol > p-cresol.

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.

Recent Trends in Removal Pharmaceuticals and Personal Care Products by Electrochemical Oxidation and Combined Systems

Due to various potential toxicological threats to living organisms even at low concentrations, pharmaceuticals and personal care products in natural water are seen as an emerging environmental issue. The low efficiency of removal of pharmaceuticals and personal care products by conventional wastewater treatment plants calls for more efficient technology. Research on advanced oxidation processes has recently become a hot topic as it has been shown that these technologies can effectively oxidize most organic contaminants to inorganic carbon through mineralization. Among the advanced oxidation processes, the electrochemical advanced oxidation processes and, in general, electrochemical oxidation or anodic oxidation have shown good prospects at the lab-scale for the elimination of contamination caused by the presence of residual pharmaceuticals and personal care products in aqueous systems. This paper reviewed the effectiveness of electrochemical oxidation in removing pharmaceuticals and personal care products from liquid solutions, alone or in combination with other treatment processes, in the last 10 years. Reactor designs and configurations, electrode materials, operational factors (initial concentration, supporting electrolytes, current density, temperature, pH, stirring rate, electrode spacing, and fluid velocity) were also investigated.

Advanced Oxidation Processes for the Removal of Antibiotics from Water. An Overview

In this work, the application of advanced oxidation processes (AOPs) for the removal of antibiotics from water has been reviewed. The present concern about water has been exposed, and the main problems derived from the presence of emerging pollutants have been analyzed. Photolysis processes, ozone-based AOPs including ozonation, O3/UV, O3/H2O2, and O3/H2O2/UV, hydrogen peroxide-based methods (i.e., H2O2/UV, Fenton, Fenton-like, hetero-Fenton, and photo-Fenton), heterogeneous photocatalysis (TiO2/UV and TiO2/H2O2/UV systems), and sonochemical and electrooxidative AOPs have been reviewed. The main challenges and prospects of AOPs, as well as some recommendations for the improvement of AOPs aimed at the removal of antibiotics from wastewaters, are pointed out.

Combined electrochemical processes for the efficient degradation of non-polar organochlorine pesticides

This study deals with the development of efficient and economic electrochemical treatment processes to confront the treatment of liquid wastes containing non-polar organochlorine pesticides. In previous works, it was demonstrated that it is possible to use electrocoagulation (EC) as a concentration technique for a model organochlorine pesticide (oxyfluorfen). Within this framework, the present work describes a process for the degradation of wastes containing non-polar organochlorines (oxyfluorfen or lindane) in two consecutive stages: 1) a first stage of concentration by electrocoagulation; 2) a second stage of electrochemical degradation by electro-oxidation (EO) or electro-Fenton (EF). The first result reached in the present work is that it is possible to remove close to 50% of both pollutants using EO and more that 94% using EF. Additionally, it was proved that the addition of a pre-concentration stage decreases by a factor of 20 the power consumption needed to deplete by EO the same amount of the initial pollutant. Moreover, when EF process is performed to the concentrated stream, the power consumption is further reduced, getting values (for 1-log removal) as low as 14.51 kWh m^-3 for oxyfluorfen decrease and 49.7 kWh m^-3 for lindane. These results strengthen the fact that the removal efficiency increases with the concentration of the pollutant and demonstrate that the combination of concentration steps and electrochemical degradation technologies is an efficient and promising alternative for the degradation of non-polar organochlorines.

Electro-transformation of mefenamic acid drug: a case study of kinetics, transformation products, and toxicity

Poor removal of many pharmaceuticals and personal care products in sewage treatment plants leads to their discharge into the receiving waters, where they may cause negative effects for aquatic environment and organisms. In this study, electrochemical removal process has been used as alternative method for removal of mefenamic acid (MEF). For our knowledge, removal of MEF using electrochemical process has not been reported yet. Effects of initial concentration of mefenamic acid, sodium chloride (NaCl), and applied voltage were evaluated for improvement of the efficiency of electrochemical treatment process and to understand how much electric energy was consumed in this process. Removal percentage (R%) was ranged between 44 and 97%, depending on the operating parameters except for 0.1 g NaCl which was 9.1%. Consumption energy was 0.224 Wh/mg after 50 min at 2 mg/L of mefenamic acid, 0.5 g NaCl, and 5 V. High consumption energy (0.433 Wh/mg) was observed using high applied voltage of 7 V. Investigation and elucidation of the transformation products were provided by Bruker software dataAnalysis using liquid chromatography-time of flight mass spectrometry. Seven chlorinated and two non-chlorinated transformation products were investigated after 20 min of electrochemical treatment. However, all transformation products (TPs) were eliminated after 140 min. For the assessment of the toxicity, it was impacted by the formation of transformation products especially between 20 and 60 min then the inhibition percentage of E. coli bacteria was decreased after 80 min to be the lowest value.

Electrochemical advanced oxidation processes (EAOPs) as alternative treatment techniques for carwash wastewater reclamation

Electrochemical advanced oxidation processes such as electrooxidation (EO), electrooxidation with hydrogen peroxide generation (EO-H₂O₂) and electro-Fenton process (EF) have been investigated as alternative treatment techniques for complete removal of anionic surfactants and organic matters from real carwash wastewater. The electrochemical processes were performed with acidified real carwash wastewater using boron doped anode and carbon felt cathode. In all cases, the chemical oxygen demand (COD) removal efficiency was always increased with rise in applied current and complete organic matter decay was achieved at applied current of 500 mA or above after 6 h of electrolysis. Faster and higher COD decay was observed with EF compared to either EO or EO-H₂O₂ treatment, at all currents and electrolysis time. Besides, complete degradation of anionic surfactants - the major organic content of the wastewater could be achieved at all applied currents studied irrespective of the process used, indicating the efficacy of processes for total remediation of real carwash wastewater. The short-chain carboxylic acids formed as the final organic byproducts were identified and quantified by ion-exclusion chromatography. More so, lower energy consumption and higher current efficiency were achieved with EF compared to EO-H₂O₂. Electrochemical treatment was found to be a powerful technology for the complete abatement of organic matter in carwash wastewater for possible reuse.

Electrochemical treatment of flutriafol wastewater using a novel 3D macroporous PbO2 filter: Operating parameters, mechanism and toxicity assessment

In order to break the high operating cost bottleneck of electrochemical treatment of aqueous flutriafol (FTF), an emerging fungicide, a novel three-dimensional ordered macroporous PbO₂ (3DOM-PbO₂) filter was designed to facilitate mass transfer. The effects of operating parameters, including current density, flow rate and initial concentration on FTF electrooxidation performance were investigated using conventional flat Ti/PbO₂ (F-Ti/PbO₂) and 3DOM-PbO₂ filters, with primary objective being the development of appropriate parameters for FTF treatment. The results indicated that the FTF removal efficiency on 3DOM-PbO₂ filter was improved by 2.8 times compared to that on F-Ti/PbO₂ at 5 mA cm^-2, 10 ml s^-1 and 100 mg L^-1 FTF. The corresponding electrical energy consumption was reduced by 2.7 times, ` TOC removal and mineralization current efficiency were enhanced by 4.9 and 4.8 times, respectively. Furthermore, aromatic intermediates, nitrogenous compounds and carboxylic acids were identified as main byproducts using experimental method combined with quantum chemical calculations. Then, a possible pathway of FTF degradation on 3DOM-PbO₂ was proposed. Finally, the acute toxicity results showed that toxicity of the byproducts first increases and then decreases through the proposed route. LC_50,48 h value of FTF wastewater increased 35%-70% on the 3DOM-PbO₂ filter, indicating a significant biodegradability enhancement.

Kinetics of Acid Orange 7 oxidation by using carbon fiber and reticulated vitreous carbon in an electro-Fenton process

In this study, a micro-scale parallel plate reactor was built to electrochemically generate hydrogen peroxide (H₂O₂) and to develop the Fenton reaction in situ, for the treatment of toxic organic pollutants. Two types of carbon materials were compared and used as cathodes: unidirectional carbon fiber (CF) and reticulated vitreous carbon (RVC). As anode, a stainless steel mesh was used. The results of H₂O₂ were experimentally compared by means of electrogeneration process. RVC cathode with dimensions of 2.5 × 1 × 5 cm (170 mA and variable voltage V = 2.0-2.7) and 180 min produced 5.3 mM H₂O₂, with an H₂O₂ production efficiency of 54%. Unidirectional carbon fiber cathode produced 7.5 mM of H₂O₂ (96% of H₂O₂ production efficiency) when a voltage of 1.8 V was applied during 180 min to a total area of 480 cm² of this material. Acid Orange 7 (AO7) was degraded to a concentration of 0.16 mM during the first 40 min of the process, which represented 95% of the initial concentration. Electrolysis process removed nearly 100% of the AO7 using both cathodes at the end of these experiments (180 min).

Electrochemical treatment of 2, 4-dichlorophenol using a nanostructured 3D-porous Ti/Sb-SnO2-Gr anode: Reaction kinetics, mechanism, and continuous operation

2, 4-dichlorophenol (2, 4-DCP) is considered to be a highly toxic, mutagenic, and possibly carcinogenic pollutant. This study is focused on the electrochemical oxidation of 2, 4-DCP on nanostructured 3D-porous Ti/Sb-SnO₂-Gr anodes, with the aim of presenting a comprehensive elucidation of mineralization process through the investigation of influential kinetics, the reactivity of hydroxyl radical's and analysis of intermediates. High efficiency was achieved at pH of 3 using Na₂SO₄ electrolytes at a current density of 30 mA cm^-2. Under the optimized conditions, a maximum removal of 2, 4-DCP of up to 99.9% was reached, whereas a TOC removal of 81% was recorded with the lowest EC_TOC (0.49 kW h g^-1) within 40 min of electrolysis. To explore the stability of the 3D-Ti/Sb-SnO₂-Gr electrodes, a continuous electrochemical operation was established, and the consistent mineralization results indicated the effectiveness of the 3D-Ti/Sb-SnO₂-Gr system concerning its durability and practical utilization. EPR studies demonstrated the abundant generation of OH radicals on 3D-Ti/Sb-SnO₂-Gr, resulting in fast recalcitrant pollutant incineration. From dechlorination and the reactivity of the OH radicals, several intermediates including six cyclic byproducts and three aliphatic carboxylic acids were detected, and two possible degradation pathways were proposed that justify the complete mineralization of 2, 4-DCP.

Novel integrated electrodialysis/electro-oxidation process for the efficient degradation of 2,4-dichlorophenoxyacetic acid

This work presents a novel approach of wastewater treatment technology that consists of a combined electrodialysis/electro-oxidation process, specially designed to allow increasing the efficiency in the oxidation of ionic organic pollutants contained in diluted waste. Respect to conventional electrolysis, the pollutant is simultaneously concentrated and oxidized, enhancing the performance of the cell due to the higher concentration achieved in the nearness of the anode. A proof of concept is tested with the ionic pesticide 2,4-D (2,4-dichlorophenoxyacetic acid) and results show that the efficiency of this new technology overcomes that electrolysis by more than double, regardless the supporting electrolyte used (either NaCl or Na₂SO₄). Moreover, the removal rate of 2,4-D when using NaCl was found to be more efficient, due to the best performance of the electrode material selected (DSA^®) towards the formation of oxidants in chloride supporting electrolyte. These results open the way for overcoming the efficiency limitations of electrochemical treatment processes for the treatment of solutions with low concentrated ionic pollutants.

Distribution of six anticancer drugs and a variety of other pharmaceuticals, and their sorption onto sediments, in an urban Japanese river

The distributions of 31 pharmaceuticals grouped into nine therapeutic classes, including six anticancer drugs, were investigated in the waters and sediments of an urban river in Japan. The coefficients of sorption (logK _d) to the river sediments were also determined from the results of a field survey and laboratory-scale experiment. Three anticancer drugs-bicalutamide, doxifluridine, and tamoxifen-were detected in the river sediments at maximum concentrations of 391, 392, and 250 ng/kg, respectively. In addition, the transformation products of psychotropic carbamazepine (2-hydroxy carbamazepine, acridine, and acridone) were detected in the range of 108 ng/kg (2-hydroxy carbamazepine) to 2365 ng/kg (acridine), and the phytoestrogen glycitein was detected in the range of N.D. to 821 ng/kg. The logK _d values of the targeted pharmaceuticals in river sediments in the field survey ranged from 0.5 (theophylline) to 3.3 (azithromycin). These results were in accord with those of the laboratory-scale sorption experiment. To the best of our knowledge, this is the first report of the detection of the anticancer drugs bicalutamide and tamoxifen, the transformation products of carbamazepine (2-hydroxy carbamazepine, acridine, and acridone), and the phytoestrogen genistein in river sediments.

Photochemical transformation and wastewater fate and occurrence of omeprazole: HRMS for elucidation of transformation products and target and suspect screening analysis in wastewaters

Omeprazole is one of the world-wide most frequently prescribed and administered pharmaceuticals in humans for the relief of gastro-intestinal disorders. Despite its high worldwide consumption, omeprazole is rarely detected in urban wastewaters and environmental waters. On the other hand, its human urinary metabolites and transformation products formed through abiotic processes in the environment have been recently documented. Despite these available data, however, there is still a lack of information on the extent of environmental fate and occurrence, on elimination mechanisms and efficiencies in waste water treatment plants. In this study, the relevance of photodegradation processes on the environmental persistence of omeprazole under simulated and solar irradiation was investigated. Photodegradation experiments were performed in distilled water, lake, river and seawater, and revealed that the different matrix in natural waters significantly affect the photolytic behavior of the investigated compound. Overall, the results highlight that photodegradation process by solar irradiation significantly contributes to omeprazole degradation and elimination from the aquatic environment. TPs formed through the process were identified and elucidated by using liquid chromatography high resolution mass spectrometry. In total seven TPs were identified, among of which four were also detected as hydrolysis TPs. The Microtox bioassay showed that solar photolysis is efficient to detoxify omeprazole and its TPs in aqueous solutions. Finally, a systematic investigation was conducted in order to provide information on removal efficiency and occurrence of omeprazole and its metabolites/TPs in 8 WWTPs in North West Greece by performing target and suspect screening analysis. The findings revealed the presence of both parent compound and metabolites/TPs in wastewaters. Given, however, the scarce detection of omeprazole at fairly low concentration levels, from analytical and environmental point of view, further attention should be given to metabolites/TPs instead of the parent compound.

Electrochemical destruction of trans-cinnamic acid by advanced oxidation processes: kinetics, mineralization, and degradation route

Acidic solutions of trans-cinnamic acid at pH 3.0 have been comparatively treated by anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF), and photoelectro-Fenton (PEF). The electrolytic experiments were carried out with a boron-doped diamond (BDD)/air-diffusion cell. The substrate was very slowly abated by AO-H₂O₂ because of its low reaction rate with oxidizing ^•OH produced from water discharge at the BDD anode. In contrast, its removal was very rapid and at similar rate by EF and PEF due to the additional oxidation by ^•OH in the bulk, formed from Fenton's reaction between cathodically generated H₂O₂ and added Fe²⁺. The AO-H₂O₂ treatment yielded the lowest mineralization. The EF process led to persistent final products like Fe(III) complexes, which were quickly photolyzed upon UVA irradiation in PEF to give an almost total mineralization with 98 % total organic carbon removal. The effect of current density and substrate concentration on all the mineralization processes was examined. Gas chromatography-mass spectrometry (GC-MS) analysis of electrolyzed solutions allowed identifying five primary aromatics and one heteroaromatic molecule, whereas final carboxylic acids like fumaric, acetic, and oxalic were quantified by ion exclusion high-performance liquid chromatography (HPLC). From all the products detected, a degradation route for trans-cinnamic acid is proposed.