Effect of anions on electrochemical degradation of azo dye Carmoisine (Acid Red 14) using a BDD anode and air-diffusion cathode

Bifunctional Ni@NiO catalyst supported on loofah sponge-derived carbon for electrocatalytic air oxidation of biorefractory pollutant in a coupling system

Oxygen (O₂) in the air is a green oxidant, and utilization of air for pollutant removal is highly desired. Herein, we report the preparation and utilization of a novel biomass-based three-dimensional (3D) Ni@NiO/carbon composite for the electro-activation of O₂ under room condition. The carbon-coated Ni@NiO nanoparticles are fabricated on a hierarchical 3D porous loofah sponge-derived carbon (LSC) support as the bifunctional catalyst for the activation of O₂ via both the electro-oxidation and electro-reduction reactions. An electrocatalytic air oxidation coupling system is constructed with the Ni@NiO/LSC shell-core electrodes for pollutant degradation. A variety of organic pollutants, including pharmaceutics and personal care products (PPCPs), dyes, phenolic compounds, and real waters are mineralized by more than 60% with significantly enhanced biodegradability. Notably, the coupling system obtains high mineralization efficiency of 70.2 ± 1.9% on landfill leachate with significant biodegradability enhancement. The specific energy consumptions of the coupling system are only 6.8 ± 0.7 to 60.2 ± 3.6 kWh kg-TOC^-1 in mineralizing different pollutants. The hollow structure of the LSC fibers endows the loaded Ni@NiO with superior intrinsic catalytic activity, which is associated with low reaction resistance and facile electron transfer. The Ni@NiO on LSC presents an electrocatalytic wet air oxidation (ECWAO) catalytic activity higher by 35.8% and cathodic air oxidation (CAO) catalytic activity higher by 22.7% as compared to that loaded on commercial graphite felt.

Toward efficient electrocatalytic degradation of iohexol using active anodes: A laser-made versus commercial anodes

The X-ray iodinated contrast medium iohexol is frequently detected in aquatic environments due to its high persistence and the inefficiency of its degradation by conventional wastewater treatments. Hence, the challenge faced in this study is the development of an alternative electrochemical treatment using active anodes. We investigate the oxidation of iohexol (16.42 mg L^-1) using different operating conditions, focusing on the role of different mixed metal oxide anodes in the treatment efficiency. The electrocatalytic efficiency of the Ti/RuO₂-TiO₂ anode prepared using a CO₂ laser heating and an ionic liquid is compared with Ti/RuO₂-TiO₂-IrO₂ and Ti/IrO₂-Ta₂O₅ commercial anodes. The hypochlorite ions generated by the anodes are also analyzed. The effect of the electrolyte composition (NaCl, Na₂SO₄, and NaClO₄) and current density (15, 30, and 50 mA cm^-2) on the iohexol degradation is also studied. The Ti/RuO₂-TiO₂ laser-made anode is more efficient than the commercial anodes. After optimizing experimental parameters, this anode removes 95.5% of iohexol in 60 min and displays the highest kinetic rate (0.059 min^-1) with the lowest energy consumption per order (0.21 kWh m^-3order^-1), using NaCl solution as the electrolyte and applying 15 mA cm^-2. Additionally, iohexol-intensified groundwater was used to compare the efficiency of anodes. The Ti/RuO₂-TiO₂ is also more efficient in removing the organic charge from the real water matrix (21.7% TOC) than the commercial anodes. Notably, the iohexol removal achieved is higher than all electrochemical treatments already reported using state-of-the-art non-active anodes in lower electrolysis time. Therefore, data from this study indicate that the electrochemical degradation of iohexol using the Ti/RuO₂-TiO₂ anode is efficient and has excellent cost-effectiveness; thus, it is a promising approach in the degradation of iohexol from wastewater. Furthermore, the Ti/RuO₂-TiO₂ active anode is competitive and can be an excellent option for treating effluents contaminated with recalcitrant organic compounds such as iohexol.

Recent progress in treatment of dyes wastewater using microbial-electro-Fenton technology

Globally, textile dyeing and manufacturing are one of the largest industrial units releasing huge amount of wastewater (WW) with refractory compounds such as dyes and pigments. Currently, wastewater treatment has been viewed as an industrial opportunity for rejuvenating fresh water resources and it is highly required in water stressed countries. This comprehensive review highlights an overall concept and in-depth knowledge on integrated, cost-effective cross-disciplinary solutions for domestic and industrial (textile dyes) WW and for harnessing renewable energy. This basic concept entails parallel or sequential modes of treating two chemically different WW i.e., domestic and industrial in the same system. In this case, contemporary advancement in MFC/MEC (METs) based systems towards Microbial-Electro-Fenton Technology (MEFT) revealed a substantial emerging scope and opportunity. Principally the said technology is based upon previously established anaerobic digestion and electro-chemical (photo/UV/Fenton) processes in the disciplines of microbial biotechnology and electro-chemistry. It holds an added advantage to all previously establish technologies in terms of treatment and energy efficiency, minimal toxicity and sludge waste, and environmental sustainable. This review typically described different dyes and their ultimate fate in environment and recently developed hierarchy of MEFS. It revealed detail mechanisms and degradation rate of dyes typically in cathodic Fenton system under batch and continuous modes of different MEF reactors. Moreover, it described cost-effectiveness of the said technology in terms of energy budget (production and consumption), and the limitations related to reactor fabrication cost and design for future upgradation to large scale application.

Tannery wastewater treatment: conventional and promising processes, an updated 20-year review

Mismanagement of various wastes especially waste water produced by tanning processes has caused serious environmental problems and ultimately impaired human health. Constant efforts have been making to alleviate the pollution of tannery wastewater (TWW), yet terminal treatment still takes dominance. In this review, research on TWW treatment from 2000 to 2021 was summarized, and main methods such as coagulation and flocculation, adsorption, biological treatment, membrane filtration, advanced oxidation process were briefly discussed. More detailed introduction was given to the method of electrochemical treatment since it has excellent performance such as environmental friendliness and high efficiency, hence attracting more and more research attention in recent years. In view of the harsh physi-chemical conditions of TWW, integrated or combined treatment methods are accordingly recommended with better performance and multi-function, however comprehensive studies on optimization of methods combination and cost-effectiveness are needed. The certain issues that the residue Cr in treatment sludge and high salinity in effluent still remain were put forward in this work and potential solutions were provided. Moreover, this review proposed the perspective that realizing multi-function, recycling, and intensification should be the developing direction for future TWW treatment. This review is expected to provide a general guide for researchers who aspire to ameliorate TWW pollution problems and understand various methods utilized in this field.

Graphical abstract

Comparative study of the removal of direct red 23 by anodic oxidation, electro-Fenton, photo-anodic oxidation and photoelectro-Fenton in chloride and sulfate media

This study aims to compare the efficiency of anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF), and their association with UV irradiation (photo anodic oxidation (PAO), and photo electro-Fenton (PEF) for the removal of Direct Red 23 from wastewater using a BDD/carbon felt cell in chloride and sulfate medium and in their combination. The effect of the supporting electrolyte was investigated in AO-H₂O₂ and EF processes. High discoloration efficiency was obtained in chloride media while a higher mineralization rate was achieved in sulfate media. The EF process reached higher total organic carbon (TOC) removal efficiency than AO-H₂O₂. 90% TOC removal rate was achieved by the EF against 82% by AO-H₂O₂ in sulfate media. The influence of using the mixt supporting electrolyte formed of 75% Na₂SO₄ + 25% NaCl was found to have beneficial effect on TOC removal, achieving 89% and 97% by AO-H₂O₂ and EF, respectively. High currents led to higher mineralization rates while low currents yielded to a higher mineralization current efficiency (MCE%) and lower energy consumption (EC). UV irradiation enhanced process efficiency. Mineralization efficiency followed the sequence: AO-H₂O₂ < PAO < EF < PEF. The PEF process was able to remove TOC completely at 5 mA cm^-2 current density and 6 h of electrolysis with a MCE% value of 16.57% and EC value of 1.29 kWh g^-1 TOC removed.

Electrochemical degradation of vanillin using lead dioxide electrode: influencing factors and reaction pathways

In this study, a novel PbO₂-CeO₂ composite electrode was applied it to the electrocatalytic degradation of vanillin. The operating parameters such as applied current density, initial vanillin concentration, supporting electrolyte concentration and pH value were investigated and optimised. After 120 min, in a 0.10 mol L^-1 Na₂SO₄ solution with a current density of 50 mA cm^-2 and a pH value of 5.0 containing 30 mg L^-1 vanillin, the vanillin removal efficiency can reach 98.03%, the COD removal efficiency is up to 73.28%. The results indicate that electrochemical degradation has a high ability to remove vanillin in aqueous solution. The reaction follows a pseudo-first-order reaction kinetics model with rate constants of 0.03036 min^-1. In the process of electrochemical degradation, up to eight hydroxylated or polyhydroxylated oxidation by-products were identified through hydroxylation, dealkylation and substitution reactions. Furthermore, the degradation pathways were proposed, which eventually mineralised into inorganic water and carbon dioxide.

Microbial fuel cell coupled Fenton oxidation for the cathodic degradation of emerging contaminants from wastewater: Applications and challenges

Urbanization and industrialization have resulted in the escalation of the occurrence of emerging contaminants (EC) in the wastewater and ultimately to the receiving water bodies due to their bio-refractory nature. The presence of ECs in the water bodies adversely affects all three domains of life, viz. bacteria, archaea and eukaryotes, and eventually the ecosystem. Fenton oxidation is one of the most suitable method that is capable of degrading a variety of ECs by employing a strong oxidizing agent in the form of •OH. The coupling of Fenton oxidation with microbial fuel cell (MFC) offers benefits, such as low-cost, minimal requirement of external energy, and in-situ generation of oxidizing agents. The resulting system, termed as bio-electro-Fenton MFC (BEF-MFC), is capable of degrading the ECs in the cathodic chamber, while harvesting bioelectricity and simultaneously removing oxidizable organic matter from wastewater in the anodic chamber. This review discusses the applications of BEF-MFC for the treatment of dyes, pharmaceuticals, pesticides, and real complex wastewaters. Additionally, the effect of operating conditions on the performance of BEF-MFC are elaborated and emphasis is also given on possible future direction of research that can be adopted in BEF-MFC in the purview of up-scaling.

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.

Electrochemical degradation of psychotropic pharmaceutical compounds from municipal wastewater and neurotoxicity evaluations

Contaminants of emerging concern (CECs) are released daily into surface water, and their recalcitrant properties often require tertiary treatment. Electrochemical oxidation (EO) is often used as an alternative way to eliminate these compounds from water, although the literature barely addresses the neurotoxic effects of residual by-products. Therefore, this study investigated the performance of EO in the removal of five CECs (alprazolam, clonazepam, diazepam, lorazepam, and carbamazepine) and performed neurotoxicity evaluations of residual EO by-products in Wistar rat brain hippocampal slices. Platinum-coated titanium (Ti/Pt) and boron-doped diamond (BDD) electrodes were studied as anodes. Different current densities (13-75 A m^-2), pH values (3-10), electrolyte dosages (NaCl), and matrix effects were assessed using municipal wastewater (MWW). The drugs were successfully degraded after 5 min of reaction for both the Ti/Pt and BDD electrodes when a current density of 75 A m^-2 was applied. For Ti/Pt and BDD, neutral and acidic pH demonstrated better CEC removal performance, respectively. Compound degradation using MWW achieved 40% removal after 120 min for Ti/Pt and ranged between 33 and 52% for the BDD anode. For Ti/Pt, neurotoxicity studies using MWW indicated a decrease in reactive oxygen species (ROS) signals. However, when an artificial cerebrospinal fluid (ACSF) medium was reapplied, the signal recovered and increased to a value above the baseline, indicating that cells recovered part of their normal activity but remained in a different condition. For the BDD anode, the treated MWW did not cause significant ROS production variations, suggesting that he EO was effective in eliminating the toxicity of the treated solution.

Treatment of tannery effluent by chemical coagulation combined with batch-recirculated electro-oxidation at different anode materials

The aim of this work was to evaluate the pollutant load from tannery effluents treated by chemical coagulation (CC) followed by electro-oxidation (EO), performed in two different experimental batch-recirculated setups, one with a BDD anode and the other with Ti/Pt/PbO₂ and Ti/Pt/SnO₂-Sb₂O₄ anodes (PS). Results were compared with those obtained from EO of the raw sample. CC was performed with a Fe³⁺ concentration of 0.25 g L^-1, and the applied current densities for EO in each setup were 60 mA cm^-2 for BDD and, in the PS setup, 20 and 40 mA cm^-2 for Ti/Pt/SnO₂-Sb₂O₄ and Ti/Pt/PbO₂, respectively. During CC, removals of 27% in chemical oxygen demand (COD), 14% in total nitrogen, 100% in sulfide, and 73% in Cr(VI) were observed. COD removal in the EO of the raw sample was higher than that obtained for the combined CC + EO, for both setups, showing that the organic compounds removed by CC are mainly those that would be more easily removed by EO. For most of the other parameters related with carbon and nitrogen, the removals for CC + EO were higher than for EO alone. During EO, sulfide is converted to sulfate, especially with BDD. Concerning Cr(VI) concentration, it increases during EO, in particular for PS setup. Combined treatment, with both setups, proved to be an effective choice to treat tannery effluents.

Influence of ruthenium doping on UV- and visible-light photoelectrocatalytic color removal from dye solutions using a TiO2 nanotube array photoanode

The photocatalytic activity of TiO₂ anodes was enhanced by synthesizing Ru-doped Ti|TiO₂ nanotube arrays. Such photoanodes were fabricated via Ti anodization followed by Ru impregnation and annealing. The X-ray diffractograms revealed that anatase was the main TiO₂ phase, while rutile was slightly present in all samples. Scanning electron microscopy evidenced a uniform morphology in all samples, with nanotube diameter ranging from 60 to 120 nm. The bias potential for the photoelectrochemical (PEC) treatment was selected from the electrochemical characterization of each electrode, made via linear sweep voltammetry. All the Ru-doped TiO₂ nanotube array photoanodes showed a peak photocurrent (PP) and a saturation photocurrent (SP) upon their illumination with UV or visible light. In contrast, the undoped TiO₂ nanotubes only showed the SP, which was higher than that reached with the Ru-doped photoanodes using UV light. An exception was the Ru(0.15 wt%)-doped TiO₂, whose SP was comparable under visible light. Using that anode, the activity enhancement during the PEC treatment of a Terasil Blue dye solution at E_bias(PP) was much higher than that attained at E_bias(SP). The percentage of color removal at 120 min with the Ru(0.15 wt%)-doped TiO₂ was 98% and 55% in PEC with UV and visible light, respectively, being much greater than 82% and 28% achieved in photocatalysis. The moderate visible-light photoactivity of the Ru-doped TiO₂ nanotube arrays suggests their convenience to work under solar PEC conditions, aiming at using a large portion of the solar spectrum.

Removal of bisphenol A from acidic sulfate medium and urban wastewater using persulfate activated with electroregenerated Fe2

Model solutions of bisphenol A (BPA) in 0.050 M Na₂SO₄ at pH 3.0 have been treated by the electro/Fe²⁺/persulfate process. The activation of 5.0 mM persulfate with 0.20 mM Fe²⁺ yielded a mixture of sulfate radical anion (SO₄^-) and OH, although quenching tests revealed the prevalence of the former species as the main oxidizing agent. In trials run in an IrO₂/carbon-felt cell, 98.4% degradation was achieved alongside 61.8% mineralization. The energy consumption was 253.9 kWh (kg TOC)^-1, becoming more cost-effective as compared to cells with boron-doped diamond and Pt anodes. Carbon felt outperformed stainless steel as cathode because of the faster Fe²⁺ regeneration. All BPA concentration decays agreed with a pseudo-fist-order kinetics. The effect of persulfate, Fe²⁺ and BPA concentrations as well as of the applied current on the degradation process was assessed. Two dehydroxylated and three hydroxylated monobenzenic by-products appeared upon SO₄^- and OH attack, respectively. The analogous treatment of BPA spiked into urban wastewater yielded a faster degradation and mineralization due to the co-generation of HClO and the larger OH production as SO₄^- reacted with Cl^-.

Electrochemical oxidative degradation of X-6G dye by boron-doped diamond anodes: Effect of operating parameters

Boron-doped diamond (BDD) is an excellent electrode material. As the anode in an electrochemical degradation tank, BDD has been receiving widespread attention for the treatment of azo dye wastewater. In this study, electrochemical oxidation (EO) was applied to electrolyze reactive brilliant yellow X-6G (X-6G) using BDD as the anode and Pt as the cathode. To balance the degradative effects and power consumption in the electrolysis process, the effects of a series of operating parameters, including current density, supporting electrolyte, initial pH, reaction temperature and initial dye concentration, were systematically studied. The oxidative process was analyzed by color removal rate, and the degree of mineralization was evaluated by TOC. The optimal experimental parameters were finally determined: 100 mA cm^-2, 0.05 M Na₂SO₄ electrolyte, pH 3.03, 60 °C, and an initial X-6G concentration of 100 mg L^-1. As a result, color completely disappeared after 0.75 h of electrolysis, and TOC was removed by 72.8% after 2 h of electrolysis. In conclusion, the EO of a BDD electrode as an anode can be a potent treatment method for X-6G synthetic wastewater.

Mineralization of Acid Red 1 azo dye by solar photoelectro-Fenton-like process using electrogenerated HClO and photoregenerated Fe(II)

The degradation of Acid Red 1 (AR1) azo dye by solar photoelectro-Fenton-like (SPEF-like) process involving continuously electrogenerated hypochlorous acid (HClO) and photoregenerated Fe(II) to yield hydroxyl radicals, has been studied. The assays were made in a flow plant that included a filter-press cell equipped with a Ti|Ir-Sn-Sb oxide anode, to oxidize Cl^- ion to HClO, and a stainless-steel cathode. The cell was coupled to a compound parabolic collector (CPC) photoreactor, in series with a reservoir containing 6 L of solution. The influence of the added Fe²⁺ concentration, current density and initial AR1 content over the performance of the SPEF-like process was systematically studied. The best treatment for 0.196 mM AR1 solutions in 35 mM NaCl and 25 mM Na₂SO₄ at pH 3.0 was achieved in the presence of 0.40 mM Fe²⁺ under a current density of 15 mA cm^-2, which yielded total color removal at 120 min and 74% COD decay at 480 min, with 25% of average current efficiency and 0.076 kW h (g COD)^-1 of energy consumption. The SPEF-like process was compared with anodic oxidation with electrogenerated active chlorine (AO-HClO), electro Fenton-like (EF-like) and photoelectro-Fenton-like (PEF-like) processes, and it was found that the oxidation power decreased in the sequence: SFEF-like > PEF-like > EF-like > AO-HClO. Ion-exclusion HPLC analysis of electrolyzed solutions revealed the formation of maleic and oxalic acid as final short-chain linear carboxylic acids.

Electro-Oxidation-Plasma Treatment for Azo Dye Carmoisine (Acid Red 14) in an Aqueous Solution

Currently, azo dye Carmoisine is an additive that is widely used in the food processing industry sector. However, limited biodegradability in the environment has become a major concern regarding the removal of azo dye. In this study, the degradation of azo dye Carmoisine (acid red 14) in an aqueous solution was studied by using a sequenced process of electro-oxidation–plasma at atmospheric pressure (EO–PAP). Both the efficiency and effectiveness of the process were compared individually. To ascertain the behavior of azo dye Carmoisine over the degradation process, the variations in its physical characteristics were analyzed with a voltage–current relationship, optical emission spectra (OES) and temperature. On the other hand, chemical variables were analyzed by finding out pH, electrical conductivity, absorbance (UV/VIS Spectrophotometry), chemical oxygen demand (COD), cyclic voltammetry (CV), energy consumption and cost. The sequenced process (EO–PAP) increased degradation efficiency, reaching 100% for azo dye Carmoisine (acid red 14) in 60 min. It was observed that the introduction of small quantities of iron metal ions (Fe²⁺/Fe³⁺) as catalysts into the plasma process and the hydrogen peroxide formed in plasma electrical discharge led to the formation of larger amounts of hydroxyl radicals, thus promoting a better performance in the degradation of azo dye. This sequenced process increased the decolorization process.

Performance evaluation of photolytic and electrochemical oxidation processes for enhanced degradation of food dyes laden wastewater

Wastewater containing dyes is considered as the top-priority pollutant when discharged into the environment. Herein, we report for the applicability of 254 nm ultraviolet light and electrochemical process using a titanium ruthenium oxide anode for the degradation of Allura red and erythrosine dyes. During the photolytic process, 95% of Allura red dye (50 ppm) was removed after 1 h at pH 12 and 35 °C, whereas 90% color removal of erythrosine dye (50 ppm) was achieved after 6 h of treatment at pH 6.0 and 30 °C. On the other hand, 99.60% of Allura red dye (200 ppm) was removed within 5 min by the electrochemical process applying a current density (5 mA cm^-2) at pH 5.0 and 0.1 mol L^-1 sodium chloride (NaCl) electrolytic medium. Similarly, 99.61% of erythrosine dye (50 ppm) degradation was achieved after 10 min at a current density of 8 mA cm^-2, pH 6.0, and 0.1 mol L^-1 of NaCl electrolyte. The minimum energy consumption value for Allura red and erythrosine dyes (0.196 and 0.941 kWh m^-3, respectively) was calculated at optimum current densities of 5 and 8 mA cm^-2. The results demonstrated that the electrochemical process is more efficient at removing dyes in a shorter time than the photolytic process since it generates powerful oxidants like the chlorine molecule, hypochlorous acid, and hypochlorite on the surface of the anode and initiates a chain reaction to oxidize the dyes molecules.

Feasibility and applicability of the scaling-up of bio-electro-Fenton system for textile wastewater treatment

Textile wastewater entering natural water bodies could cause serious environment and health issues. Bio-electro-Fenton (BEF) as an efficient and energy saving wastewater treatment technology has recently attracted widespread attention. So far, there is no research available on the scaling-up of BEF process. In this work, an innovative 20 L up-scaled BEF system was constructed for the treatment of methylene blue (MB) containing wastewater. The system was first tested in batch mode. The results showed that the system performance was majorly related to the operating parameters including initial MB concentration, catholyte pH and concentration, cathodic aeration rate, Fe²⁺ dosage, and applied voltage. At the optimal condition, 20 mg L^-1 of MB was efficiently removed following the apparent first order kinetics. The corresponding rate constants for the decolorization and mineralization were 0.68 and 0.20 h^-1, respectively. Furthermore, MB decolorization efficiency of 99% and mineralization efficiency of 74% were observed when the hydraulic retention time was 28 h in continuous mode. This work demonstrates the scaling-up potential of BEF for recalcitrant wastewater treatment.

Microbial degradation of azo dye carmoisine in aqueous medium using Saccharomyces cerevisiae ATCC 9763

Carmoisine is an azo dye widely used in many industries, and therefore frequently occurs in the effluent of many factories. To our knowledge, biological degradation of carmoisine has received little attention. The present study investigates the capability of Saccharomyces cerevisiae ATCC 9763 for degradation of carmoisine. Spectrophotometry data indicates that carmoisine (50 mg/l) was eliminated from the aqueous medium after approximately 7 h of incubation with Saccharomyces under anaerobic shaking conditions. Thin layer chromatography (TLC) revealed the removal of carmoisine as well as the appearance of aromatic amines in samples collected from the decolourized medium by S. cerevisiae and this was subsequently confirmed by Fourier transform infrared (FTIR) spectroscopy. Liquid chromatography mass spectrometry (LC/MS) was carried out on fractions from consecutive column chromatography and two-dimensional (2D) chromatography. LC/MS indicated degradation of carmoisine into its constituent aromatic amines. In addition, investigating the effect of environmental conditions on the decolourization process indicated that yeast extract could positively affect decolourization rates; shaking significantly accelerated decolourization and shortened the time required for complete biodecolourization from ≃ 8 days to ≃ 7 h; and Saccharomyces was able to consume sucrose as a carbon source and remove the carmoisine despite the presence of sunset yellow, which remained unaffected.

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

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

On the performance of electrocatalytic anodes for photoelectro-Fenton treatment of synthetic solutions and real water spiked with the herbicide chloramben

The destruction of the herbicide chloramben in 0.050 M Na₂SO₄ solutions at natural pH has been studied by photoelectro-Fenton with UVA light (PEF). The trials were carried out in a cell equipped with an air-diffusion cathode for H₂O₂ generation and different electrocatalytic anodes, namely active IrO₂-based and RuO₂-based electrodes and non-active boron-doped diamond (BDD) and PbO₂ ones. Similar removal rates were found regardless of the anode nature because the herbicide was mainly oxidized by OH formed from Fenton's reaction, which was enhanced by UVA-induced photo-Fenton reaction. The use of an IrO₂-based anode led to almost total mineralization at high current density, as also occurred with the powerful BDD anode, since photoactive intermediates originated from OH-mediated oxidation were degraded under irradiation with UVA light. The good performance of the IrO₂-based anode in PEF was confirmed at different current densities and herbicide concentrations. The presence of Cl^- in the medium caused a slight deceleration of herbicide removal as well as mineralization inhibition, owing to the production of active chlorine with consequent formation of persistent chloroderivatives. Seven aromatic products along with oxalic and oxamic acids were identified in sulfate medium. Five aromatic derivatives were detected in Cl^--containing matrix, corroborating the generation of organochlorine compounds. In secondary effluent, larger mineralization was achieved by PEF with a BDD anode due to its high oxidation ability to destroy the chloroderivatives, although an acceptable performance was also obtained using an IrO₂-based anode.