Electro-oxidation of methyl paraben on DSA®-Cl2: UV irradiation, mechanistic aspects and energy consumption

Exploring electrochemical mechanisms for clindamycin degradation targeted at the efficient treatment of contaminated water

Numerous studies reveal pollutants like clindamycin (CLD) in the environment, posing environmental and health risks. Conventional water treatment methods are ineffective at removing these contaminants, typically found in low concentrations. An innovative treatment approach is introduced through pre-concentration via adsorption, which is highly efficient, energy-saving, and reusable. The innovation uses solvents like methanol or ethanol to desorb pollutants, creating concentrated CLD solutions for more effective electrochemical degradation than conventional methods. Thus, this study explores, for the first time, the behavior of CLD electro-oxidation in different media-water, methanol, and ethanol-using a Dimensionally Stable Anode (DSA®-Cl₂). The study reveals distinct degradation mechanisms and offers new insights into solvent-assisted electrochemical treatments. After 30 min of electrolysis, all the current densities evaluated promoted significant degradation, ranging from 90 to 92%. The energy consumption was 2.9 Wh m⁻³ per percentage point at current densities of 2 and 3.5 mA cm⁻2. This demonstrates that using higher current densities over shorter electrolysis times is feasible, achieving removal rates of approximately 90%.The performance of chloride-based electrolytes was superior to that of sulfate-based electrolytes due to the ability of DSA®-Cl2 electrodes to generate reactive chlorine species more efficiently. A higher concentration of supporting electrolytes initially improved CLD removal, but no significant changes were observed after 1 h. Neutral pH conditions optimized CLD degradation, achieving up to 91% removal. Higher pollutant concentrations were associated with lower kinetic constants and decreased removal percentages. Methanol and ethanol enhanced removal rates to 98.3% and 92.3%, respectively, by generating oxidizing species such as methoxy, hydroxymethyl, and ethoxy radicals. The degradation by-products differed across the three media, with each solvent exhibiting distinct oxidation mechanisms. These findings highlight the potential of using methanol or ethanol as an electrolytic medium with efficiency comparable to water.

Enhanced oxidation of parabens in an aqueous solution by air-assisted cold plasma

Various contaminants of emerging concern (CECs) including pharmaceuticals and personal care products (PPCPs) have been known to threaten the aquatic ecosystem and human health even at low levels in surface water. Among them, the wide variety use of parabens as preservatives may pose potential threat to human because parabens may present estrogenic activity. Various advanced oxidation processes have been attempted to reduce parabens, but challenges using cold plasma (CP) are very rare. CP is worth paying attention to in reducing parabens because it has the advantage of generating radical ions, including reactive oxygen/nitrogen species and various ions. Accordingly, this study demonstrates how CP can be utilized and how CP competes with other advanced oxidation processes in energy requirements. Quantified ethyl-, propyl-, and butyl-paraben indicate that CP can effectively degrade them up to 99.1% within 3 h. Regression reveals that the kinetic coefficients of degradation can be increased to as high as 0.0328 min-1, comparable to other advanced oxidation processes. Many by-products generated from the oxidation of parabens provide evidence of the potential degradation pathway through CP treatment. In addition, we found that the electrical energy consumption per order of CP (39-95 kWh/m3/order) is superior to other advanced oxidation processes (69∼31,716 kWh/m3/order). Overall, these results suggest that CP may be a viable option to prevent adverse health-related consequences associated with parabens in receiving water.

Waste coconut shell-derived carbon monolith as an efficient binder-free cathode for electrochemical advanced oxidation treatment of endocrine-disrupting compounds

Discharge of endocrine-disrupting compounds such as methylparaben (MePa) into natural water bodies deteriorates the aquatic ecosystem. In this regard, electrochemical oxidation (EO) and electro-Fenton (EF) processes are acknowledged as effective methods to eliminate biorecalcitrant compounds from different wastewater matrices. In these systems, the H2O2-producing ability of carbon-based cathodes is put to advantage for producing homogenous hydroxyl radicals by simulating Fenton's reaction, which dramatically augments the contaminant removal efficiency. However, commercial carbon based cathodes are not economically affordable, especially for voluminous treatment. Hence in the present work, waste-derived carbonised coconut shell (CCS) monolith was employed as a cathode in EO and EF treatment of MePa. Almost the entire MePa with initial concentration of 10 mg/L was removed in 60 min by EO and 45 min by EF process at neutral pH, applied current density of 7.5 mA/cm2, NaCl concentration of 1.0 g/L and 10 mg/L of Fe2O3 dosing. The MePa removal efficiency of the CCS cathode-fitted system after 60 min was better than the commercial graphite plate and Ti-based mixed metal oxide employing system due to higher H2O2 electrosynthesis (H2O2 = 9.0 ± 0.6 mg/L after 60 min). Moreover, the same setup was used for treating 10 mg/L of MePa-spiked real sewage and demonstrated MePa and total organic carbon removal efficiency of 80.16 ± 2.31% and 37.42 ± 3.50%, respectively, in 45 min. Further, the CCS-mediated EF treatment achieved >90% removal of MePa for eight continuous batch cycles and recorded a current density drop of just 0.23% per cycle. The degradation pathway and toxicity assessment of the intermediates using the Ecological Structure Activity Relationships (ECOSAR) tool supported the eco-friendliness of the current treatment scheme.

Decentralized approach toward organic pollutants removal using UV radiation in combination with H2O2-based electrochemical water technologies

The current literature lacks a comprehensive discussion on the trade-off between pollutant degradation/mineralization and treatment time costs in utilizing UV light in combination with H2O2-based electrochemical advanced oxidation processes (EAOPs). The present study sheds light on the benefits of using the photoelectro-Fenton (PEF) process with UVA or UVC for methylparaben (MetP) degradation in real drinking water. Although light boosts the photodegradation of refractory Fe(III) complexes and the photolysis of H2O2 (with UVC only), the energy-intensive nature of light-based treatments is acknowledged. To help tackle the high energy consumption issue, a novel approach was employed: partial application of UVA or UVC light after a predetermined electro-Fenton electrolysis time. The proposed treatment approach yielded satisfactory comparable results to those obtained from the application of PEF/UVA or PEF/UVC in terms of total organic carbon removal (ca. 100%), with notably lower energy consumption (ca. 50%). The study delves into the combined method's feasibility, analyzing pollutant degradation/mineralization process and overall energy consumption. The research identifies possible degradation routes based on intermediate detection and radical quenching experiments. Finally, toxicological assessments evaluate the toxicity levels of MetP and its intermediates. The findings of this study bring meaningful contributions to the fore and point to the highly promising potential of the proposed approach, in terms of sustainability and cost-effectiveness, when applied for decentralized water treatment.

Assessing the electrochemical degradation of reactive orange 84 with Ti/IrO2-SnO2-Sb2O5 anode using electrochemical oxidation, electro-Fenton, and photoelectro-Fenton under UVA irradiation

Today, water shortage problems around the world have forced the search for new treatment alternatives, in this context, electrochemical oxidation technology is a hopeful process for wastewater treatment, although it is still needed exploration of new efficient and economically viable electrode materials. In this way, mixed metal oxide anodes look like promising alternatives but their preparation is still a significant point to study, searching for finding low-cost materials to improve electrocatalytic efficiencies. In an exploration of this kind of highly efficient materials, this work presents the results obtained using an MMO Ti/IrO2-SnO2-Sb2O5 anode. All the prepared anodes exhibited excellent physical and electrochemical properties. The electrochemical oxidation of 100 mL and 200 mg L-1 Reactive Orange 84 (RO 84) diazo dye was studied using 3 cm2 of such synthesized anodes by applying current densities of 25, 50, and 100 mA cm-2. Faster and more efficient electrochemical oxidation occurred at 100 mA cm-2 with 50 mM of Na2SO4 + 10 mM NaCl as supporting electrolyte at pH 3.0. The degradation and mineralization processes of the above solution were enhanced with the electro-Fenton process with 0.05 mM Fe2+ and upgraded using photoelectron-Fenton with UVA light. This process yielded 91% COD decay with a low energy consumption of 0.1137 kWh (g COD)-1 at 60 min. The evolution of a final carboxylic acid like oxalic was followed by HPLC analysis. The Ti/IrO2-SnO2-Sb2O5 is then an efficient and low-cost anode for the photoelectro-Fenton treatment of RO 84 in a chloride and sulfate media.

New insights into the mechanism of Fered-Fenton treatment of industrial wastewater with high chloride content: Role of multiple reactive species

Hydroxyl radical (OH) is considered the dominant reactive species in the electro-Fenton (EF) and Fered-Fenton (EF-Fere) processes for wastewater treatment. However, in chloride-rich media, this is arguable due to the obscure mechanisms for the oxidant speciation and pollutant degradation. Herein, the role of active chlorine and Fe(IV)-oxo species (Fe^IVO²⁺) as primary oxidizing agents in HClO-mediated Fered-Fenton (EF-Fere-HClO) process is discussed, along with the dependence of their contribution on the pollutant structure. HClO generated from anodic oxidation of Cl^- can be consumed by added H₂O₂ to form singlet oxygen (¹O₂), which is detrimental because this species is quickly deactivated by water. The reaction between HClO and Fe²⁺ was proved to generate Fe^IVO²⁺, rather than OH or Cl suggested in the literature. The yield of Fe^IVO²⁺ species was proportional to the Cl^- concentration and barely affected by solution pH. The long-lived HClO and Fe^IVO²⁺ can selectively react with electron-rich compounds, which occurs simultaneously to the non-selective attack of OH formed from Fenton's reaction. The Fe^IVO²⁺ and OH concentration profiles were successfully modelled. Although the accumulation of toxic chlorinated by-products from HClO-mediated oxidation might cause new environmental concerns, the toxicity of pesticide wastewater with 508 mM Cl^- was halved upon EF-Fere-HClO treatment.

Electro-oxidation of tetracycline in ethanol-water mixture using DSA-Cl2 anode and stimulating/monitoring the formation of organic radicals

Recent studies reported a new strategy of electro-oxidation of organic compounds using methanol as solvent. Considering its well-known toxicity, this work sought to evaluate the use of ethanol as an alternative solvent for pollutants degradation. Therefore, thorough analyses were performed in order to evaluate tetracycline (TC) electro-oxidation using DSA-Cl₂ anode in ethanol-H₂O solutions. The effects of solvent mixture, pH and current density on the degradation efficiency were evaluated. TC degradation in methanol-water and ethanol-water media resulted in very close removals of 95% and 90%, respectively, after 15 min of electrolysis at 10 mA cm^-2. In ethanol medium, the increase in current densities from 10 to 25 mA cm^-2 did not lead to significant changes in removal efficiency. The variation of the initial pH of the solution showed that the best removal efficiencies were obtained at neutral pH resulting in TC removals up to 90%, which is actually related to the molecular structure of TC. Through analysis using electron paramagnetic resonance (EPR), the formation of radicals such as hydroxyethyl (CH₃^●CHOH), hydroxyl (^●OH) and ethoxy (CH₃CH₂O^●) were detected, which effectively contributed toward the pollutant oxidation.

Ultrasound-assisted electrochemical treatment of cosmetic industry wastewater: Mechanistic and detoxification analysis

This study aims to investigate the mineralization of cosmetics producing industrial wastewater (CW) using sono-electrochemical (US-EC) treatments. The influence of operating parameters such as current density (j), electrolyte (Na₂SO₄) concentration (m), initial pH (pH_o), and ultrasonic power was investigated using Ti/RuO₂ dimensionally stable electrodes. The results demonstrated 80.9% chemical oxygen demand (COD) removal efficiency, 433.5 kWh (kg COD removed)^-1 of specific energy consumption at the optimum conditions of P = 100 W, j = 213 A m^-2, pH_o= 7.6 (natural pH), and m = 1.5 g L^-1. With the application of ultrasound, COD removal efficiency increases from 60.2% to 80.9%, with a synergistic effect of 1.1. Kinetics study analysis confirms that mineralization follows the n^th order kinetics model. In the presence of ultrasound, the performance of electrochemical treatment gets enhanced due to higher electron transfer, the enhanced production of ^•OH radicals, and sulfate radicals (SO₄^•-). The pathway for the degradation of the compound was suggested by quadrupole time of flight mass spectroscopy (QToF-MS). The operating cost of the process was also evaluated to establish the applicability of the US-EC process at the industrial scale.

Electrochemical degradation of a methyl paraben and propylene glycol mixture: Interference effect of competitive oxidation and pH stability

Endocrine disrupting compounds (EDCs) are one of the many classes of harmful pollutants frequently found in water resources. Even at low concentrations, EDCs might accumulate in the organisms and interfere on numerous processes controlled by hormones. Parabens, for example, are preservatives widely used in pharmaceutical and cosmetic industries, but several studies related them to human breast cancer. It is well-known that electrochemical technologies are an efficient alternative for wastewater treatment, promoting the appropriate destruction of EDCs. However, most studies are applied to single target contaminant solutions, which may neglect the impact from co-exited inorganic/organic pollutants. Based on that, this study aimed to elucidate the interfering effects of two target organic contaminants of very different nature during electrochemical mediated process. For that, methyl paraben (MeP) and propylene glycol (PG) were selected as models of aromatic/phenolic and carboxylate compounds versus low-molecular aliphatic alcohols. These two compounds are often together used in preservative blends and cosmetic/pharmaceutical formulations. PG is not a harmful chemical, but it is present in several types of effluents in relatively high concentrations. Thus, it may interfere on the degradation of numerous pollutants of low concentrations. The electrochemical treatment of a mixture containing 100 mg L^-1 MeP +1000 mg L^-1 PG showed that both contaminants suffered interfering effects. The presence of MeP negatively interfered on PG degradation; the carboxylate compound is more easily oxidized even at lower molecular concentration. On the other hand, the presence of PG showed an unexpected positive effect on MeP degradation, that was not reflected on its mineralization. The results indicate that in addition to the expected effect of anodic competition, polymerization and copolymerization reactions may also occur in the studied system. The use of an acidic buffer medium increased the removal of both contaminants and favored the oxidation pathway over the polymerization. In this case, the increase in the removal was reflected in the mineralization process, which increased up to 6 times when the mixture was treated in the buffered medium.

Toxicity and removal of parabens from water: A critical review

Parabens are biocides used as preservatives in food, cosmetics and pharmaceuticals. They possess antibacterial and antifungal activity due to their ability to disrupt cell membrane and intracellular proteins, and cause changes in enzymatic activity of microbial cells. Water, one of our most valuable natural resource, has become a huge reservoir for parabens. Halogenated parabens from chlorination/ozonation of water contaminated with parabens have shown to be even more persistent in water than other types of parabens. Unfortunately, there is dearth of data on their (halogenated parabens) presence and fate in groundwater which serves as a major source of drinking water for a huge population in developing countries. An attempt to neglect the presence of parabens in water will expose man to it through ingestion of contaminated food and water. Although there are reviews on the occurrence, fate and behaviour of parabens in the environment, they largely omit toxicity and removal aspects. This review therefore, presents recent reports on the acute and chronic toxicity of parabens, their estrogenic agonistic and antagonistic activity and also their relationship with antimicrobial resistance. This article further X-rays several techniques that have been employed for the removal of parabens in water and their drawbacks including adsorption, biodegradation, membrane technology and advanced oxidation processes (AOPs). The heterogeneous photocatalytic process (one of the AOPs) appears to be more favoured for removal of parabens due to its ability to mineralize parabens in water. However, more work is needed to improve this ability of heterogeneous photocatalysts. Perspectives that will be relevant for future scientific studies and which will drive policy shift towards the presence of parabens in our drinking waters are also offered. It is hoped that this review will elicit some spontaneous actions from water professionals, scientists and policy makers alike that will provide more data, effective technologies, and adaptive policies that will address the growing threat of the presence of parabens in our environment with respect to human health.

Electro-oxidation of tetracycline in methanol media on DSA®-Cl2

The electro-oxidation of tetracycline (TeC) in methanol medium containing chloride or sulfate ions was evaluated using a DSA®-Cl₂ in a flow reactor and compared with BDD. The results show that after 30 min of electrolysis no TeC is detected by liquid chromatography when chloride is used as supporting electrolyte. On the other hand, after 90 min of electrolysis using a BDD anode only 61% of TeC was removed from solutions with chloride, but in the presence of sulfate the removal reaches 94%. This evidences that the oxidizing species generated during electrochemical oxidation control the process and the mechanism of degradation of the TeC. Besides that, it was possible to infer that only a small amount of methanol might convert to formaldehyde or formic acid, although they were not detected according to the nil changes in the FTIR spectra or in the HPLC chromatograms recorded.

Paraben Compounds—Part II: An Overview of Advanced Oxidation Processes for Their Degradation

Water scarcity represents a problem for billions of people and is expected to get worse in the future. To guarantee people’s water needs, the use of “first-hand water” or the reuse of wastewater must be done. Wastewater treatment and reuse are favorable for this purpose, since first-hand water is scarce and the economic needs for the exploration of this type of water are increasing. In wastewater treatment, it is important to remove contaminants of emerging concern, as well as pathogenic agents. Parabens are used in daily products as preservatives and are detected in different water sources. These compounds are related to different human health problems due to their endocrine-disrupting behavior, as well as several problems in animals. Thus, their removal from water streams is essential to achieve safe reusable water. Advanced Oxidation Processes (AOPs) are considered very promising technologies for wastewater treatment and can be used as alternatives or as complements of the conventional wastewater treatments that are inefficient in the removal of such contaminants. Different AOP technologies such as ozonation, catalytic ozonation, photocatalytic ozonation, Fenton’s, and photocatalysis, among others, have already been used for parabens abatement. This manuscript critically overviews several AOP technologies used in parabens abatement. These treatments were evaluated in terms of ecotoxicological assessment since the resulting by-products of parabens abatement can be more toxic than the parent compounds. The economic aspect was also analyzed to evaluate and compare the considered technologies.

High chlorine evolution performance of electrochemically reduced TiO2 nanotube array coated with a thin RuO2 layer by the self-synthetic method

Recently, reduced TiO2 nanotube arrays via electrochemical self-doping (r-TiO2) are emerging as a good alternative to conventional dimensionally stable anodes (DSAs) due to their comparable performance and low-cost. However, compared with conventional DSAs, they suffer from poor stability, low current efficiency, and high energy consumption. Therefore, this study aims to advance the electrochemical performances in the chlorine evolution of r-TiO2 with a thin RuO2 layer coating on the nanotube structure (RuO2@r-TiO2). The RuO2 thin layer was successfully coated on the surface of r-TiO2. This was accomplished with a self-synthesized layer of ruthenium precursor originating from a spontaneous redox reaction between Ti3+ and metal ions on the r-TiO2 surface and thermal treatment. The thickness of the thin RuO2 layer was approximately 30 nm on the nanotube surface of RuO2@r-TiO2 without severe pore blocking. In chlorine production, RuO2@r-TiO2 exhibited higher current efficiency (∼81.0%) and lower energy consumption (∼3.0 W h g-1) than the r-TiO2 (current efficiency of ∼64.7% of and energy consumption of ∼5.2 W h g-1). In addition, the stability (ca. 22 h) was around 20-fold enhancement in RuO2@r-TiO2 compared with r-TiO2 (ca. 1.2 h). The results suggest a new route to provide a thin layer coating on r-TiO2 and to synthesize a high performance oxidant-generating anode.