Electro-Fenton degradation of antimicrobials triclosan and triclocarban

Fluoxetine removal by anodic oxidation using different anode materials and graphite cathode

Fluoxetine (FLX) is a selective serotonin reuptake inhibitor (SSRI) medication commonly used to treat mental health disorders, but it can be harmful to the environment if not properly disposed of due to incomplete metabolism. In this study, electrochemical anodic oxidation with mixed metal oxide anodes was studied as a method to remove FLX from water and wastewater. Iridium dioxide-coated titanium (Ti/IrO2) and ruthenium dioxide-coated Ti (Ti/RuO2) electrodes were found to be more effective than platinum-coated Ti (Ti/Pt) electrodes, with removal efficiencies of 91.5% and 93.9%, respectively. Optimal conditions for FLX removal were determined to be an applied current of 150 mA, initial pH of 5, and oxidation time of 120 min. The rate of FLX degradation (kFLX) for the Ti/Pt, Ti/IrO2, and Ti/RuO2 electrodes were determined to be 0.0081 min-1 (R2:0,8161), 0.0163 min-1 (R2:0,9823), and 0.0168 (R2:0,9901) min-1 for 25 mg/L initial FLX concentration, respectively. The kFLX values varied based on the initial FLX concentration and decreased as the initial FLX concentration increased. The specific energy consumption (SEC) after 120 min of operation was 51.0 kWh/m3 for the Ti/Pt electrode, 39.6 kWh/m3 for the Ti/IrO2 electrode, and 48.6 kWh/m3 for the Ti/RuO2 electrode under optimised conditions. Overall, electrochemical anodic oxidation is an effective method for removing FLX from water and wastewater, with Ti/IrO2 and Ti/RuO2 electrodes providing superior performance compared to Ti/Pt electrodes.

Scientific and academic contributions of professor Enric Brillas through an analysis social network analysis and data science

This work describes the scientific and academic contributions of Professor Enric Brillas through the analysis of Social Network Analysis and data science. The study examines the research collaborations and co-authorship networks of Professor Brillas, indicating his active engagement and up-to-date collaborations with key co-authors, including Ignasi Sirés and Pere.L. Cabot. The analysis also reveals Professor Brillas' significant research focus on water treatment and related concepts such as oxidation-reduction, Fenton reactions, photoelectro-Fenton, and electrocatalysis. Furthermore, the most cited and recent articles by Professor Brillas are identified and discusses. Overall, the research demonstrates Professor Brillas' notable contributions to the field of electrochemical water treatment and highlights his ongoing research and collaborations in this area.

Removal of pharmaceuticals and personal care products from wastewater via anodic oxidation and electro-Fenton processes: current status and needs regarding their application

This review provides a current opinion on the most recent works that have been published toward the application of electrochemical advance oxidation processes (EAOPs) for the degradation of pharmaceutical and personal care products (PPCPs) in water streams. Advances in the application of anodic oxidation (AO)- and electro-Fenton (EF)-based processes are reported, including operational conditions, electrode performance, and removal. Although AO- and EF-based processes can easily reach 100% removal of PPCPs, mineralization is desirable to avoid the generation of potential toxic byproducts. The following section exploring some techno-economic aspects of the application of EAOPs is based on electrode selection, operational costs as well as their use as cotreatments, and their synergistic effects. Finally, this short review ends with perspectives about the emerging topics that are faced by these technologies applied for the degradation of PPCPs in research and practice.

Extraction of iron from laterite soil and green synthesis of laterite nano iron catalyst (GLaNICs) for its application as Fenton's catalyst in the degradation of triclosan

Laterite based nano iron particles were synthesized using natural laterite extract as a precursor and Psidium guajava plant extract for its application as Fenton's catalyst in the degradation of triclosan. Chemical digestion method was used for the extraction of iron from laterite soil. Synthesized nano iron catalyst was characterized using SEM-EDS, XRD and FTIR and evaluated for its catalytic application in the Fenton's oxidation of triclosan. Maximum triclosan degradation of 69.5% was observed with nano iron catalyst dosage of 0.1 g/L and hydrogen peroxide dosage of 200 mg/L at acidic pH of 3. Hydrogen peroxide influence on the process was observed with Fenton's oxidation. Role of iron in the process has been accessed by control experiment with no nano catalyst addition in which degradation is considerably low. Fenton's oxidation was compared with conventional Fenton's oxidation driven by a green nano iron catalyst. Study claims the usage of natural laterite iron as a replacement for commercial iron in Fenton's degradation of triclosan. Regeneration and reusability studies on catalyst were studied and synthesized catalyst was observed to be reusable in three consecutive cycles. Degradation of triclosan in Fenton's oxidation follows pseudo-second order reaction with linear fit.

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.

Nano and micro architectured cues as smart materials to mitigate recalcitrant pharmaceutical pollutants from wastewater

Pharmaceuticals have been recognized for saving billions of lives, but they also appear as a novel group of environmental pollutants. The presence of pharmaceutically active residues in seawater, surface water, wastewater treatment plants, sludges, and soils has been widely reported. Their persistence in the environment for extended durations exerts various adverse consequences, such as gene toxicity, hormonal interference, antibiotic resistance, sex organs imposition, and many others. Various methodologies have been envisioned for their removal from the aqueous media. Different processes have been restricted due to high cost, inefficient removal, generation of toxic materials, and high capital requirement. The employment of nanostructured materials to mitigate pharmaceutical contaminants has been increasing during the last decades. The adsorptive nanomaterials have a high surface area, low cost, eco-friendliness, and high affinity for inorganic and organic molecules. In this review, we have documented the rising concerns of environmental pharmaceutical contamination and their remediation by applications of nanomaterials. Nanomaterials could be a robust candidate for the removal of an array of environmental contaminants in water.

Degradation of triclosan by anodic oxidation/in-situ peroxone process: Kinetics, pathway and reaction mechanism

Triclosan (TCS) is an emerging contaminant that threatens the environment and human health. This study was conducted to investigate TCS abatement by a novel electro-oxidation (EO) process, which used a Ti-based nickel and antimony doped tin oxide (NATO/Ti) anode and a carbon nanotubes (CNTs) doped carbon/PTFE (CNTs-C/PTFE) gas diffusion electrode (GDE) for oxygen reduction reaction (ORR). A comparative study was also performed for TCS degradation by using a traditional EO with a nickel foam cathode, termed as HER-EO. The optimal initial TCS concentration, current density and solution pH for TCS degradation during the ORR-EO and HER-EO were investigated. Results showed that ORR-EO removed more than 98% of TCS in 10-60 min under the concentration of 5-50 mg/L. The TCS degradation followed pseudo-first-order kinetics and its main intermediates were observed during the ORR-EO and HER-EO using liquid chromatography combined mass (LC-MS). The results of FED analysis and toxicity prediction by ECOSAR software showed that less intermediates accumulated during the ORR-EO and the residues were less harmful. The ORR-EO degradation mechanism for TCS was attacking on the ether bond and the benzene ring by ^•OH. This novel ORR-EO process exhibits a great merit in the field of emerging contaminants abatement.

Synthesis and characterization of Ag0(NPs)/TiO2 nanocomposite: insight studies of triclosan removal from aqueous solutions

Nanocomposite mesoporous Ag⁰(NPs)/TiO₂ thin film materials were synthesized and assessed for its efficient application in the elimination of potentially important drug triclosan from aqueous solutions. A template synthesis using the polyethylene glycol was enabled to obtain Ag⁰(NPs)/TiO₂ nanocomposite materials where zerovalent Ag was in situ doped to the titania network. The nanocomposite materials were characterized by the scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), EDX elemental mapping, X-ray diffraction (XRD) analyses and Brunauer-Emmett-Teller (BET) methods. Further, the diffuse reflectance spectroscopy (DRS) was introduced to estimate the band gap of these solids. The thin film materials were subjected to the remediation of water contaminated with triclosan using the UV-A light. The oxidative elimination of triclosan was demonstrated as a function of pH, concentration of triclosan and presence of several co-existing ions. Increase in pH (4.0-10.0) and triclosan concentrations (0.5-15.0 mg/L) had decreased significantly the percentage degradation of triclosan. The pseudo-first-order kinetics was shown in the degradation of triclosan and rate constant was significantly decreased with the increase in pollutant concentration (0.5-15.0 mg/L) and pH (4.0-10.0). The 1000 times presence of scavengers showed that ^•OH were, predominantly, caused the oxidation of triclosan. Moreover, multiple application of nanocomposite Ag⁰(NPs)/TiO₂(B) revealed that the thin film was fairly intact since the photocatalytic efficiency of triclosan removal was almost unaffected.

Electro-oxidation of secondary effluents from various wastewater plants for the removal of acetaminophen and dissolved organic matter

Electro-oxidation of acetaminophen (ACT) in three different doped secondary effluents collected from a conventional Municipal Waste Water Treatment Plant (MWWTP), a MWWTP using a membrane bioreactor (WWTP MBR) and a lab-scale MBR treating source-separated urine (Urine MBR) was investigated by electro-Fenton (EF) coupled with anodic oxidation (AO) using sub-stoichiometric titanium oxide anode (Ti₄O₇). After 8 h of treatment, 90 ± 15%, 76 ± 3.8% and 46 ± 1.3% of total organic carbon removal was obtained for MWWTP, MWWTP-MBR and Urine-MBR respectively, at a current intensity of 250 mA, pH of 3 and [Fe²⁺] = 0.2 mM. Faster degradation of ACT was observed in the WWTP MBR because of the lower amount of competitive organic matter, however, >99% degradation of ACT was obtained after 20 min for all effluents. The acute toxicity of the treated effluent was measured using Microtox® tests. Results showed an initial increase in toxicity, which could be assigned to formation of more toxic by-products than parent compounds. From 3D excitation and emission matrix fluorescence (3DEEM), different reactivity was observed according to the nature of the organic matter. Particularly, an increase of low molecular weight organic compounds fluorescence was observed during Urine MBR treatment. This could be linked to the slow decrease of the acute toxicity during Urine MBR treatment and ascribed to the formation and recalcitrance of toxic organic nitrogen and chlorinated organic by-products. By comparison, the acute toxicity of other effluents decreased much more rapidly. Finally, energy consumption was calculated according to the objective to achieve (degradation, absence of toxicity, mineralization).

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

Combination of the electro-Fenton process with a post-biological treatment could represent a cost-effective solution for application of electrochemical advanced oxidation processes. The objective of this study was to assess this treatment strategy in the case of a complex pharmaceutical mixture. First, main operating parameters ([Fe²⁺] and current) of the electro-Fenton process were optimized. An optimal concentration of 0.2 mM of Fe²⁺ was obtained for mineralization of the pharmaceutical mixture. An optimal current of 400 mA was also obtained for degradation of caffeine and 5-fluorouracil in the mixture. However, mineralization of the effluent was continuously improved when increasing the current owing to the promotion of mineralization of organic compounds at the BDD anode. Besides, energy efficiency was decreased at prolonged treatment time because of mass transport limitation. Interestingly, it was observed a strong biodegradability enhancement of the solution after short treatment times (<3 h) at 500 and 1000 mA, which can be related to the degradation of parent compounds into more biodegradable by-products. The need for an acclimation time of the biomass to the pre-treated effluent was also emphasized, most probably because of the formation of some toxic by-products as observed during acute toxicity tests. Therefore, a biological post-treatment could represent a cost-effective solution for the removal of biodegradable residual organic compounds as well as for the removal of nitrogen released from mineralization of organic compounds under the form of NO₃^- and NH₄⁺ during electro-Fenton pre-treatment.

Emerging organic contaminants in wastewater: Understanding electrochemical reactors for triclosan and its by-products degradation

Degradation technologies applied to emerging organic contaminants from human activities are one of the major water challenges in the contamination legacy. Triclosan is an emerging contaminant, commonly used as antibacterial agent in personal care products. Triclosan is stable, lipophilic and it is proved to have ecotoxicologic effects in organics. This induces great concern since its elimination in wastewater treatment plants is not efficient and its by-products (e.g. methyl-triclosan, 2,4-dichlorophenol or 2,4,6-trichlorophenol) are even more hazardous to several environmental compartments. This work provides understanding of two different electrochemical reactors for the degradation of triclosan and its derivative by-products in effluent. A batch reactor and a flow reactor (mimicking a secondary settling tank in a wastewater treatment plant) were tested with two different working anodes: Ti/MMO and Nb/BDD. The degradation efficiency and kinetics were evaluated to find the best combination of current density, electrodes and set-up design. For both reactors the best electrode combination was achieved with Ti/MMO as anode. The batch reactor at 7 mA/cm² during 4 h attained degradation rates below the detection limit for triclosan and 2,4,6-trichlorophenol and, 94% and 43% for 2,4-dichlorophenol and methyl triclosan, respectively. The flow reactor obtained, in approximately 1 h, degradation efficiencies between 41% and 87% for the four contaminants. This study suggests an alternative technology for emerging organic contaminants degradation, since the combination of a low current density with the flow and matrix induced disturbance increases and speeds up the compounds' elimination in a real environmental matrix.

Critical review on the mechanistic photolytic and photocatalytic degradation of triclosan

The environmentally extended presence of triclosan, TCS, component of many pharmaceutical and personal care products, and its known persistent character have awoke the scientific and social concern leading to the study of effective remediation techniques. Advanced oxidation techniques stand out for the effectiveness in degrading many persistent compounds, and as a result, they have been addressed by many researchers. However, the powerful oxidation media might lead to the formation of undesirable by-products, concern that has also been widely addressed. With regard to the presence of TCS, photolytic and photocatalytic processes provide a very effective degradation yield and rate, with a large number of reports addressing its removal from different environmental matrices. But currently, there is no clear understanding of the mechanisms involved and the routes responsible for the formation of degradation products. Thus, this work presents an exhaustive and critical analysis of the state of the art related to the photo-degradation of TCS, with special focus on the formation of oxidation by-products, on the phenomena responsible and on the influence of operation variables. This report aims at offering valuable information to researchers dealing with this environmentally relevant problem.

Fate, risk and removal of triclocarban: A critical review

The halogenated antimicrobial triclocarban (TCC) has large production and consumption over last decades. Its extensive utilization in personal care products and insufficient treatment in conventional wastewater treatment plants (WWTPs) has led to its listing as one of emerging organic contaminants (EOCs). Due to the hydrophobicity and chemical stability of TCC, it has been omnipresent detected in terrestrial and aquatic environments, and its prolonged exposure has thrown potential pernicious threat to ecosystem and human health. Considering its recalcitrance, especially under anoxic conditions, both biological and non-biological methods have been exploited for its removal. The efficiency of advanced oxidation processes was optimistic, but complete removal can rarely be realized through a single method. The biodegradation of TCC either with microbial community or pure culture is feasible but efficient bacterial degraders and the molecular mechanism of degradation need to be further explored. This review provides comprehensive information of the occurrence, potential ecological and health effects, and biological and non-biological removal of TCC, and outlines future prospects for the risk evaluation and enhanced bioremediation of TCC in various environments.

Photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri: Pathway and toxic mechanism

Pyraclostrobin is a fungicide used widely across the world. However, its photolysis pathway and toxic mechanism is unclear. In this study, photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri were determined. The results showed that direct photolysis dominated the degradation of pyraclostrobin. Gas Chromatography-Mass spectrometry and quantum chemical calculation revealed that the pyraclostrobin was firstly photo-degraded into Methyl N-phenyl-carbamate and 1-(4-chlorophenyl)-3-hydroxy-1H-pyrzole, synthetic intermediates of pyraclostrobin, then into aniline, benzoquinone and acids. Toxicity assay showed that bioluminescent inhibition rate to V. fischeri fluctuated with radiation/illumination time and the toxicity curve can be classified into three phases (Phase I: 0-10 min, incline; Phase II: 10-60 min, decline; Phase III: 60-120 min, incline). The up-and-down curve indicates the change of parent compound during the photolysis. Simulation of molecular docking showed that the CDOCKER interaction energy of pyraclostrobin (-44.71) lower than other intermediate products (>-30.00), indicating that the parent compound is more toxic than its intermediates. An increased toxicity observed in the toxicity curve was attributed to the generation of benzoquinone with log1/EC₅₀ of 6.73, which can greatly change structure of target luciferase in Vibrio fischeri. In addition, the addition of radical scavengers can inhibit the bioluminescence of the tested solutions, indicating the involvement of radicals in the transformation of intermediates. This paper reveals that one of photochemical transformation products of pyraclostrobin can cause more toxic than its parent compound to bacteria. Environmental risk assessment should consider not only the parent compound, but also its metabolites.

Electronic Tongue Coupled to an Electrochemical Flow Reactor for Emerging Organic Contaminants Real Time Monitoring

Triclosan, which is a bacteriostatic used in household items, has raised health concerns, because it might lead to antimicrobial resistance and endocrine disorders in organisms. The detection, identification, and monitoring of triclosan and its by-products (methyl triclosan, 2,4-Dichlorophenol and 2,4,6-Trichlorophenol) are a growing need in order to update current water treatments and enable the continuous supervision of the contamination plume. This work presents a customized electronic tongue prototype coupled to an electrochemical flow reactor, which aims to access the monitoring of triclosan and its derivative by-products in a real secondary effluent. An electronic tongue device, based on impedance measurements and polyethylenimine/poly(sodium 4-styrenesulfonate) layer-by-layer and TiO₂, ZnO and TiO₂/ZnO sputtering thin films, was developed and tested to track analyte degradation and allow for analyte detection and semi-quantification. A degradation pathway trend was observable by means of principal component analysis, being the sample separation, according to sampling time, explained by 77% the total variance in the first two components. A semi-quantitative electronic tongue was attained for triclosan and methyl-triclosan. For 2,4-Dichlorophenol and 2,4,6-Trichlorophenol, the best results were achieved with only a single sensor. Finally, working as multi-analyte quantification devices, the electronic tongues could provide information regarding the degradation kinetic and concentrations ranges in a dynamic removal treatment.

Electrochemical degradation of triclosan in aqueous solution. A study of the performance of an electro-Fenton reactor

The electro-Fenton degradation of Triclosan in aqueous solution was studied using a cylindrical reactor in which polarized carbon cloth electrodes and a cation exchange resin were employed. Using a factorial design of experiments approach, the effect of four variables (considering two levels for each one), was measured on four response parameters that reflect the electrooxidation efficiency of the electrochemical reactor. The results revealed that in all cases triclosan degradation was very efficient (above 95%) and that while there is a reasonable effect of all variables and their interactions, the one with the strongest influence on the process is the nature and magnitude of the ionic strength of the electrolytic solution. In this way, while the presence of a buffer species in this solution can keep the pH in a value that affects the generation of ^•OH radicals from the Fenton mixture, a high ionic strength solution can promote the elimination of Fe ionic species from the reactor by decreasing resin Fe retention due to competition effects of other ions for the binding sites of the substrate. HPLC experiments of the effluent solutions, also revealed that the degradation by-products of triclosan were dependent on the nature and ionic strength of the electrolytic solution in the electro-Fenton process under study. Finally, comparison of the different operation modes, also suggested that electro-adsorption of Fe cationic species in the negatively polarized cathode surface, is the main factor that controls Fe ion retention within the reactor.

High-efficiency electrochemical degradation of antiviral drug abacavir using a penetration flux porous Ti/SnO2-Sb anode

Electrochemical degradation of antiviral drug abacavir was investigated by using a penetration flux porous Ti/SnO₂-Sb anode prepared by sol-gel method. The effects of applied current density, initial pH, and inorganic anions on the degradation kinetics were systematically studied. Degradation efficiency more than 97% was performed in only 10 min at a current density of 0.2 mA cm^-2. The corresponding degradation rate constant and the lowest electrical energy per order were calculated to be 0.36 min^-1 and 6.5 mWh L^-1, respectively. Extending the reaction duration to 5 h, 53.3% of TOC removal was observed. The results indicated that effective degradation of abacavir appeared in the penetration flux porous Ti/SnO₂-Sb anode with a very low energy consumption. Furthermore, the electrochemical intermediate products and the reaction site during abacavir degradation were detected and recognized. The quantitative structure-activity relationship model revealed that the potential risks of abacavir to the aquatic organism, such as fish, greatly decreased after flowing through the penetration flux porous Ti/SnO₂-Sb anode.

PCDD/Fs traceability during triclosan electrochemical oxidation

5-Chloro-2-(2,4-dichlorophenoxy)phenol (TCS) is a persistent organic pollutant (POP) widely used in different consumer goods. Its recalcitrant nature demands the application of effective remediation technologies in order to avoid the negative environmental impact associated to the discharge of contaminated waters. Although advanced oxidation technologies have been considered the best alternative to destroy bio-recalcitrant compounds, the likely formation of high toxicity byproducts must be analysed before large-scale deployment. In this work, we aim to trace the presence of chlorinated compounds during the electro-oxidation of aqueous TCS samples. First, we analyze the influence of the initial concentration of TCS on the toxicity of the oxidation medium expressed by the International-Toxicity Equivalency Factor (I-TEF); second, we have detected the formation of intermediate organo-chlorinated compounds by GC-MS supported by HPLC and finally, we have quantified the concentration of highly-polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) by HRGC-HRMS within the oxidation treatment. In those samples where TCS had been completely degraded the concentration of PCDD/Fs showed a high increase, especially when NaCl was used as electrolyte, with the initial concentration of TCS. Under these conditions the I-TEF achieved values up to 3.8 × 10² pg L^-1.

Sonochemical degradation of triclosan in water in a multifrequency reactor

Degradation of triclosan (TCS) by multifrequency ultrasound (US) was studied at high and low frequencies. Frequency effect on initial degradation rates was analyzed, and an optimum frequency was found. Power density always has a positive effect on degradation rates over the whole equipment work range. A reaction mechanism similar to that proposed by Serpone resulted in a pseudo-linear model that fitted statistically better than the nonlinear model proposed by Okitsu. Pulsed US showed a positive effect on degradation rates; however, simultaneous analysis of the effect of power, frequency, pulse time, and silent time did not show a clear trend for degradation as a function of pulse US variables. According to these results and those for degradation in the presence of radical scavengers, it was concluded that US TCS degradation was taking place in the bubble/liquid interface. A toxicity test was conducted by Microtox®, showing a decrease in toxicity as TCS concentration decreased and increase in toxicity after total depletion of TCS. Eight possible degradation by-products were identified by GC-MS analysis, and a degradation pathway was proposed.

Applying analytical decision methods for determination of the best treatment alternative to remove emerging micropollutants from drinking water and wastewater: triclosan example

Increasing human activities have not only substantially altered the natural material cycle but also created new synthetic chemicals flows. Some of these chemicals, which are described as micropollutants (MPs), may result in adverse effects on human health, aquatic organisms, and ecosystems. MPs can be transported to the environment and water resources in a variety ways including domestic and industrial wastewater. Unfortunately, most MPs are only partially removed in existing conventional treatment plants. Therefore, conventional treatment plants should be modernized by advanced treatment technologies to protect the environment and human health. However, there are various mysteries about best treatment techniques, evaluation criteria, and decision-making methods. In this study, it was aimed to determine the best treatment alternatives for triclosan (TCS) which is one of the priority MPs. A total of 18 evaluation criteria were identified and prioritized by employing analytical hierarchy process (AHP) and entropy methods. Treatment alternatives were identified and their performance was assessed through a comprehensive literature investigation. In decision-making processes of determining these alternatives, "technique for order preference by similarity to ideal solution (TOPSIS)," "preference ranking organization method for enrichment evaluation (PROMETHEE)," and "Višekriterijumsko kompromisno rangiranje (VIKOR)" analytical decision-making methods were employed, and priority rankings were determined according to each decision method. The final priority ranking was found as adsorption > membrane filtration > hybrid processes > advanced oxidation processes > constructed wetlands > conventional treatment processes > biological treatment > other treatment processes. Although the obtained results are specific to TCS, the employed analytical decision methods can be also used to decide the best treatment alternatives for other MPs.

Nanocomposite Au NP/TiO2 thin film in the efficient remediation of aqueous solutions contaminated with emerging micro-pollutants

The present communication specifically aims to synthesize novel nanocomposite material Au NPs/TiO₂ in a simple template process using the polyethylene glycol as filler media. The thin film of the nanocomposite material was characterized by the advanced analytical tools. The surface morphology was obtained by the scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images of solids. Similarly, the surface topography and roughness of solid were obtained by the atomic force microscopic (AFM) image of thin film. X-ray diffraction (XRD) data enabled to confirm that the TiO₂ was predominantly present with its anatase phase. The specific surface area and pore size of the solid were obtained using the N₂ adsorption/desorption data. Nanocomposite Au NP/TiO₂ thin film was employed in the photocatalytic removal of sulfamethoxazole and triclosan from aqueous solutions using less harmful UV-A light (λ_max = 330 nm). Various physicochemical parametric studies enabled to deduce the mechanism involved in the degradation process. The degradation kinetics as a function of pH (pH 4.0-10.0) and micro-pollutant concentrations (0.5-15.0 mg/L) was extensively studied. The mineralization of these pollutants was obtained using the non-purgeable organic carbon (NPOC) data. The stability of thin film was assessed by the repeated operations, and presence of several co-existing ions simulates the studies to real matrix treatment. Further, the presence of scavengers enabled to pin point the radical-induced degradation of sulfamethoxazole and triclosan from aqueous solutions.

Fate and hazard of the electrochemical oxidation of triclosan. Evaluation of polychlorodibenzo‑p‑dioxins and polychlorodibenzofurans (PCDD/Fs) formation

Triclosan (TCS) is widely used as antiseptic or preservative in many personal care products (PCPs), such as cosmetics, hand wash, toothpaste and deodorant soaps, among others. It is characterized by acute toxicity, resistance to biodegradation, environmental persistence and relatively high lipophilicity. In order to protect the environment and natural resources from the negative effects of the discharge of polluted wastewater with TCS, the application of efficient remediation technologies able to degrade the pollutant to harmless levels becomes crucial. Electrochemical oxidation, among all advanced oxidation processes (AOPs), has been reported as very effective in the complete degradation of a number of persistent pollutants; therefore, its performance using boron-doped diamond (BDD) anodes, and response to operation variables, has been studied in this work. As expected, complete degradation of TCS was achieved in all the studied conditions; however, going a step further and knowing that TCS is a precursor of polychlorinated dibenzo‑p‑dioxins and dibenzofurans (PCDD/Fs), their quantitative presence in the oxidation media has been assessed. Results showed the dominance of dichlorinated (DCDD) and trichlorinated (TrCDD/Fs) in the homologue profile of total PCDD/Fs, reaching values up to 1.48 × 10⁵ pg L^-1 in samples with initial concentration of TCS of 100 mg L^-1 and NaCl as electrolyte. Under these conditions, the International Toxicity Equivalency Factor (I-TEF) achieved values up to 2.76 × 10² pg L^-1. Nevertheless, the presence of copper in the oxidation medium tends to reduce I-TEF values. Finally, considering the information reported in literature, a mechanism describing the formation of low chlorinated PCDD/Fs from TCS oxidation reactions is proposed.

Degradation of triclosan and its main intermediates during the combined irradiation and biological treatment

Triclosan is an extensively applied antimicrobial agent which has been frequently detected in the environment. In this paper, the degradation of triclosan and its main intermediates was investigated during the combined irradiation and biological treatment. The results showed that triclosan degradation increased with increase of absorbed dose, the removal efficiency of triclosan was 62%, 77%, 87%, 91% and 94%, respectively at 1, 2, 3, 4 and 5 kGy. The final removal efficiency of triclosan after the combined irradiation and biological process was 81%, 86%, 90%, 92% and 95%, respectively. During the irradiation process, two main intermediates, that is, 4,4'-2'-phenoxyphenol (Intermediate 1) and 4-chloro-2'-phenoxyphenol (Intermediate 2) were detected, in which Intermediate 1 dominated during the irradiation process. In the following biological treatment process, Intermediates 1 and 2 could be further degraded. In single biological treatment process, the final removal efficiency of triclosan was 54%, and Intermediates 1 and 2 were detected. Intermediate 1 could be biodegraded while Intermediate 2 could not. The concentration of Intermediate 2 increased during biological treatment process. In conclusion, irradiation as pre-treatment process can enhance the degradation of triclosan and improve the biodegradability of Intermediate 2. Combined irradiation and biological process can be promising for treating antibiotic-containing wastewater.

Photodegradation of micropollutants using V-UV/UV-C processes; Triclosan as a model compound

Non-potable reuse of treated wastewater is becoming widespread as means to address growing water scarcity. Removal of micropollutants (MPs) from such water often requires advanced oxidation processes using OH radicals. OH can be generated in-situ via water photolysis under vacuum-UV (λ<200nm) irradiation. The aim of this study was to investigate the potential of unmasking V-UV radiation from low pressure Hg lamps (emitting at 185 and 254nm), commonly used in decentralized treatment systems, for enhancing MPs removal efficiency. Triclosan, a biocide of limited biodegradability, served as a model compound for MPs that are not very biodegradable. Its degradation kinetics and identification of intermediate products were investigated under 254nm and under combined 254/185nm irradiation both in dry thin films and in aqueous solutions. In the latter, degradation was faster under combined 254/185nm radiation, although the 185nm radiation accounted for only 4% of the total UV light intensity. In contrast, triclosan photodegradation in dry film did not show significant differences between these irradiation wavelengths, suggesting that the enhanced degradation of dissolved triclosan under combined radiation is mainly due to oxidation by OH formed via water photolysis under V-UV. This conclusion was supported by slower TCS degradation in aqueous solution when methanol was added as OH scavenger. Under both irradiation types (254, 254/185nm) three transformation products (TPs) were identified: 2,8-dichlorodibenzo-p-dioxin, 5-chloro-2-(4- or 2-chlorophenoxy)phenol, and 2-hydroxy-8-chlorodibenzodioxin. In-silico QSAR toxicity assessment predicted potential toxicity and moderate-to-low biodegradability of these TPs. Removal of these TPs was faster under 254/185nm irradiation. Considering the low cost, simple operation (i.e. no chemicals addition) and small size of such low-pressure mercury lamps, this is a promising direction. Further investigation of the process in flow-through reactors and real wastewater/greywater effluent is needed for its future implementation in small on-site systems for post-treatment of persistent pollutants.

Ecotoxicological risk assessment and seasonal variation of some pharmaceuticals and personal care products in the sewage treatment plant and surface water bodies (lakes)

This paper reports the seasonal variation and environmental quality control data for five fingerprint pharmaceuticals and personal care products (PPCPs) (acetaminophen ciprofloxacin, caffeine, irgasan and benzophenone) in the influent and the effluent of the sewage treatment plant (STP) and surface water bodies (six major lakes) in and around Nagpur, one of the "A class city" in the central India over a period of 1 year. The target compounds were analysed using developed offline solid-phase extraction (SPE) coupled with reversed phase high-performance liquid chromatography (RP-HPLC-PDA) method. All the five PPCPs were found in the influent, whereas four were found in the effluent of the STP. However, in the surface water bodies, three PPCPs were detected in all the seasons. Above PPCPs were present in the concentration range of 1-174 μg L^-1 in the surface water bodies, 12-373 μg L^-1 in the influent and 11-233 μg L^-1 in the effluent of the STP. Amongst the five PPCPs, caffeine was found to be in higher concentration as compared to others. The seasonal trends indicate higher concentrations of PPCPs in summer season and lowest in the rainy season. Additionally, physico-chemical characterisations (inorganic and organic parameters) of the collected samples were performed to access the anthropogenic pollution. Ecotoxicological risk assessment was done to appraise the degree of toxicity of the targeted compounds. Hazard quotient (HQ) values were found to be < 1 indicating no adverse effect on the targeted organism.

Oxidation of indometacin by ferrate (VI): kinetics, degradation pathways, and toxicity assessment

The oxidation of indometacin (IDM) by ferrate(VI) (Fe(VI)) was investigated to determine the reaction kinetics, transformation products, and changes in toxicity. The reaction between IDM and Fe(VI) followed first-order kinetics with respect to each reactant. The apparent second-order rate constants (k _app) decreased from 9.35 to 6.52 M^-1 s^-1, as the pH of the solution increased from 7.0 to 10.0. The pH dependence of k _app might be well explained by considering the species-specific rate constants of the reactions of IDM with Fe(VI). Detailed product studies using liquid chromatography-tandem mass spectrometry (LC-MS/MS) indicated that the oxidation products were primarily derived from the hydrolysis of amide linkages, the addition of hydroxyl groups, and electrophilic oxidation. The toxicity of the oxidation products was evaluated using the Microtox test, which indicated that transformation products exhibited less toxicity to the Vibrio fischeri bacteria. Quantitative structure-activity relationship (QSAR) analysis calculated by the ecological structure activity relationship (ECOSAR) revealed that all of the identified products exhibited lower acute and chronic toxicity than the parent pharmaceutical for fish, daphnid, and green algae. Furthermore, Fe(VI) was effective in the degradation IDM in water containing carbonate ions or fulvic acid (FA), and in lake water samples; however, higher Fe(VI) dosages would be required to completely remove IDM in lake water in contrast to deionized water.

Enhanced biodegradation of triclosan by means of gamma irradiation

Triclosan is an antimicrobial agent which has been frequently detected in the environment. In this paper, the biodegradation of triclosan after radiation-induced advanced oxidation was investigated. The results show that the removal efficiency of triclosan in the combined irradiation and biological treatment process ranged from 88% to 97%, depending on the absorbed dose, while it was only 54% in the single biological treatment process. The removal efficiency of total organic carbon (TOC) was in the range of 53.1%,-59.2% at dose of 1-5 kGy in the combined irradiation and biological treatment process. In comparison, the removal efficiency of TOC in the single biological treatment process was 24.5%, suggesting that irradiation can enhance the mineralization of triclosan. The dechlorination efficiency of triclosan ranged from 48.6% to 78.4% at dose of 1-5 kGy. The intermediates of triclosan degradation were tentatively identified by LC-MS analysis and the possible degradation pathway was proposed. Based on the above results, the combined irradiation and biological treatment process could be an alternative process for treating triclosan-containing wastewater.

Removal of artificial sweetener aspartame from aqueous media by electrochemical advanced oxidation processes

The degradation and mineralization of aspartame (ASP) in aqueous solution were investigated, for the first time, by electrochemical advanced oxidation processes (EAOPs) in which hydroxyl radicals were formed concomitantly in the bulk from Fenton reaction via in situ electrogenerated Fenton's reagent and at the anode surface from the water oxidation. Experiments were performed in an undivided cylindrical glass cell with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. The effect of Fe²⁺ concentration and applied current on the degradation and mineralization kinetics of ASP was evaluated. The absolute rate constant for the reaction between ASP and OH was determined as (5.23 ± 0.02) × 10⁹ M^-1 s^-1 by using the competition kinetic method. Almost complete mineralization of ASP was achieved with BDD anode at 200 mA constant current electrolysis. The formation and generation of the formed carboxylic acids (as ultimate end products before complete mineralization) and released inorganic ion were monitored by ion-exclusion high performance liquid chromatography (HPLC) and ion chromatography techniques, respectively. The global toxicity of the treated ASP solution during treatment was assessed by the Microtox^® method using V. fischeri bacteria luminescence inhibition.

Sub-stoichiometric titanium oxide (Ti4O7) as a suitable ceramic anode for electrooxidation of organic pollutants: A case study of kinetics, mineralization and toxicity assessment of amoxicillin

Electrochemical degradation of aqueous solutions containing antibiotic amoxicillin (AMX) has been extensively studied in an undivided electrolytic cell using a sub-stoichiometric titanium oxide (Ti₄O₇) anode, elaborated by plasma deposition. Oxidative degradation of AMX by hydroxyl radicals was assessed as a function of applied current and was found to follow pseudo-first order kinetics. The use of carbon-felt cathode enhanced oxidation capacity of the process due to the generation of H₂O₂. Comparative studies at low current intensity using dimensional stable anode (DSA) and Pt anodes led to the lower mineralization efficiencies compared to Ti₄O₇ anode: 36 and 41% TOC removal for DSA and Pt respectively compared to 69% for Ti₄O₇ anode. Besides, the use of boron doped diamond (BDD) anode under similar operating conditions allowed reaching higher mineralization (94%) efficiency. Although Ti₄O₇ anode provides a lesser mineralization rate compared to BDD, it exhibits better performance compared to the classical anodes Pt and DSA and can constitutes an alternative to BDD anode for a cost effective electro-oxidation process. Moreover several aromatic and aliphatic oxidation reaction intermediates and inorganic end-products were identified and a plausible mineralization pathway of AMX involving these intermediates was proposed.