Advanced Oxidation Treatment Research Articles

Enhanced removal of antibiotic-resistant bacteria and resistance genes by three-dimensional electrochemical process using MgFe2O4-loaded biochar as both particle electrode and catalyst for peroxymonosulfate activation

In this study, MgFe2O4-loaded biochar (MFBC) was used as a three-dimensional particle electrode to active peroxymonosulfate (EC/MFBC/PMS) for the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). The results demonstrated that, under the conditions of 1.0 mM PMS concentration, 0.4 g/L material dosage, 5 V voltage intensity, and MFBC preparation temperature of 600 °C, the EC/MFBC600/PMS system achieved complete inactivation of E. coli DH5α within 5 min and the intracellular sul1 was reduced by 81.5 % after 30 min of the treatment. Compared to EC and PMS alone treatments, the conjugation transfer frequency of sul1 rapidly declined by 92.9 % within 2 min. The cell membrane, proteins, lipids, as well as intracellular and extracellular ARGs in E. coli DH5α were severely damaged by free radicals in solution and intracellular reactive oxygen species (ROS). Furthermore, up-regulation was observed in genes associated with oxidative stress, SOS response and cell membrane permeability in E. coli DH5α, however, no significant changes were observed in functional genes related to gene conjugation and transfer mechanisms. This study would contribute to the underlying of PMS activation by three-dimensional particle electrode, and provide novel insights into the mechanism of ARB inactivation and ARGs degradation under PMS advanced oxidation treatment.

Theoretical investigation on the influence of H2 ${{\rm{H}}}_{2}$ additions on the He + 1% O2 ${{\rm{O}}}_{2}$ plasma reactivity for water treatment applications

AbstractPlasma‐based technologies offer environmentally friendly means of effective water purification. Here, we present a discharge system with He + 1% . Tunable amounts of were introduced to control the yield of reactive species. Detailed exploration of the system provides a deeper understanding of some of the fundamental chemical kinetics related to plasma‐based wastewater treatment. A global model was used to investigate the effect of additions on the yield of some important reactive species for advanced oxidation treatment of wastewater. Humidity leakage was considered to simulate the effect of humidified environments. The pathway analysis module provides deeper insight into chemical kinetics. It was concluded that additives can be used in tailoring plasma yield for water treatment applications.

Modeling and Optimization of Electrochemical Advanced Oxidation of Clopidogrel Using the Doehlert Experimental Design Combined with an Improved Grey Wolf Algorithm

In this research, the optimization of the electrochemical advanced oxidation treatment for the degradation of Clopidogrel was investigated. This study examined the influence of various experimental parameters including applied current, initial Clopidogrel concentration, and ferrous ion concentration by the use of the Doehlert design within a response surface methodology framework. The improved grey wolf optimizer was applied in order to define the optimum operating conditions. The monitoring of clopidogrel concentration during treatment revealed that complete disappearance of clopidogrel was achieved under an initial clopidogrel concentration of 0.02 mM, current intensity of 0.55 A, Fe2+concentration of 0.7 mM, and a reaction time of 20 min in a solution containing 50 mM Na2SO4 at pH 3. A quadratic polynomial model was developed, and its statistical significance was confirmed through the analysis of variance, demonstrating a high level of confidence in the model (R2 = 0.98 and p-value < 0.05). Furthermore, following electrolysis treatment for 480 min, the synthetic clopidogrel solutions underwent mineralization, achieving a 70.4% removal rate of total organic carbon. Subsequently, the applicability of the optimized process was tested on real pharmaceutical wastewater, and mineralization was investigated under the identified optimal conditions, resulting in a total organic carbon removal rate of 87% after 480 min of electrolysis time. The energy consumption for this system was calculated to be 1.4 kWh·kg−1 of the total organic carbon removed. These findings underscore the effectiveness and potential applicability of the electrochemical advanced oxidation for industrial wastewater treatment.

Simultaneous Oxidation of Trace Organics and Sorption of Trace Metals by Ferrate (Fe(VI))-Coated Sand in Synthetic Wastewater Effluent.

The increased presence of toxic chemicals in aquatic matrices and their associated health effects raise the need for more effective treatment technologies. The application of Fe(VI), an advanced oxidation treatment agent with disinfecting and coagulating capabilities, is limited by Fe(VI) aqueous instability. Our previous study proposed an Fe(VI)-coated sand media to overcome this constraint and demonstrated that Fe(VI)-coated sand was an effective medium for the treatment of phenolic compounds. In this study, we assessed the potential of the media for treatment of acetaminophen (ACM), benzotriazole (BZT), sulfamethoxazole (SMX), copper (Cu), lead (Pb), and zinc (Zn)-common contaminants found in wastewater effluents-in ultrapure and synthetic wastewater effluent. Fe(VI)-coated sand reactivity was influenced by the solution pH and aqueous chemistry. For example, the removal of Pb improved by 39% in the presence of trace organics, indicating that trace metal removal was enhanced by Fe(III) phases formed during Fe(VI) reactions with trace organics. While oxidation of trace organic compounds increased as pH decreased, trace metal sorption was more favorable at higher pH (i.e., pH 8 and 9). The oxidation efficiency of trace organics by the media was the highest for ACM and SMX while BZT degradation was limited due to formation of Cu-BZT complexes. Batch tests in synthetic wastewater effluent revealed that the presence of divalent cations (i.e., Ca2+ and Mg2+) can catalyze Fe(VI) self-decay and promote Fe(III) production and subsequent trace metal removal; however, oxidation of trace organics was hindered in this matrix. This study highlights the potential for Fe(VI)-coated sand application for the treatment of complex matrices more representative of natural and engineered aquatic systems.

A Review on Electrochemical Advanced Oxidation Treatment of Dairy Wastewater

Dairy wastewater (DW) contains a high concentration of organic and inorganic pollutants. In recent years, extensive research has been conducted to develop more efficient techniques for the treatment of DW. Electrochemical advanced oxidation processes (EAOPs) have gained significant attention among the various treatment approaches. EAOPs rely on electrochemical generation of hydroxyl radicals (•OH) which are considered highly potent oxidizing compounds for the degradation of pollutants in DW. In this paper, we provide an overview of the treatment of DW using various EAOPs, including anodic oxidation (AO), electro-Fenton (EF), photo electro-Fenton (PEF), and solar photo electro-Fenton (SPEF) processes, both individually and in combination with other techniques. Additionally, we discuss the reactor design and operating parameters employed in EAOPs. The variation in degradation efficiency is due to different oxidizing agents produced in specific approaches and their pollutant degradation abilities. In AO process, •OH radicals generated on electrode surfaces are influenced by electrode material and current density, while EF procedures use Fe2+ to create oxidizing agents both on electrodes and in the DW solution, with degradation mechanisms being affected by Fe2+, pH, and current density; additionally, PEF and SPEF approaches enhance oxidizing component production and pollutant degradation using ultraviolet (UV) light. Integration of EAOPs with other biological processes can enhance the pollutant removal efficiency of the treatment system. There is a scope of further research to exhibit the effectiveness of EAOPs for DW treatment in large scale implementation.

Evaluation of an Electrocoagulation Process Modified by Fenton Reagent

This article is oriented to the degradation of nickel in an ionic state at laboratory level from synthetic water made with nickel sulfate, using the electrocoagulation process with aluminum cathodes and modifying this process by the addition of the Fenton reagent, which results from the combination of hydrogen peroxide (H2O2) and ferrous sulfate (FeSO4) being this reagent a catalyst and oxo-coagulant agent, The efficiency of this reagent will be compared with the typical treatment with aluminum sulfate, which is a typical process based on ion exchange/coagulation at the same percentage concentrations as the Fenton reagent. For this purpose, the optimum conditions of the advanced electrocoagulation process were determined, which consisted of determining the concentrations of Fenton’s reagent at concentrations of 150 ppm, 300 ppm, and 450 ppm, in addition to the operating variables such as pH of 8 and 10, voltage of 17.5 V and 19 V and their reaction time, which were compared with aluminum sulfate at 300 ppm, 600 ppm, and 900 ppm. The results obtained with respect to the typical treatment were 0% nickel degradation. However, with the advanced oxidation treatment, an average reduction of 97.5% was found at the conditions of 19 V, pH 10, and Fenton 150 ppm in a time of 30 min.

Simultaneous purification of salt and condensate by collaborated evaporation-peroxodisulfate treatment of high salinity organic wastewater

High salinity organic wastewater is commonly treated by evaporation, which produces a large amount of waste salts and condensed water containing organic compounds. The waste salts are typical classified as hazardous waste and the condensed water often requires advanced oxidation treatment before it can be biochemically treated. In this study, a synergistic treatment process combining evaporation with thermal activation of peroxodisulfate (PDS) was developed for the treatment of wastewater containing tetrabromobisphenol S (TBBPS) and Na2SO4 to reduce the content of organics in the crystal salt and condensed water. Compared with evaporation alone, the synergistic treatment process allows the complete removal of TBBPS from the crystal salt with an increase of TOC removal from 4.48 % to 94.44 %. Meanwhile, in the condensed water, TBBPS can also be completely removed with a decrease of the average TOC content from 25.56 mg/L to 4.97 mg/L. EPR detection reveals that the dominant reactive species are •OH, SO4-•, and 1O2. Moreover, the presence of SO42- can enhance the conversion of •OH to SO4-•, thereby improving the utilization of reactive species by increasing the contribution of SO4-•. The degradation intermediates of TBBPS were detected by IC and LC-MS, based on which the possible degradation mechanism of TBBPS was proposed. The synergistic treatment process can not only promote the resource utilization of waste salt and reduce the difficulty of condensed water treatment but also improve the stability of the evaporation system.

Research progress and perspective on sludge anaerobic digestion technology: A bibliometric analysis.

Rational disposal of sludge is an ongoing concern. This work is the first attempt for in-depth statistical analysis of anaerobic digestion (AD) research in recent three decades (1986-2022) using both quantitative and qualitative approaches in bibliometrics to investigate the research progress, trends and hot spots. All publications in the Web of Science Core Collection database from 1986 to April 4, 2022 were analyzed. Results showed that the research on AD started in 1999 and the number of papers significantly increased since 2012. The research about the disposal of sewage sludge mainly focuses on energy recovery (e.g. methane and short chain volatile organic acids) by AD. Besides, different pretreatment technologies were studied in this study to eliminate the negative effects on the disposal of sludge caused by hydrolysis (rate-limiting step of AD), water content (increasing the costs) and heavy metal (toxic to the environment) of sludge. Of those, the treatment technologies related to direct interspecies electron transfer were worth further studied in the future. Towards that end, iron conductive material, iron-based advanced oxidation and biological treatment were concluded as the prospective technologies and worth to further study.

Cyanide-Isolated Cobalt Catalyst for Ultraefficient Advanced Oxidation Treatment.

Catalyst design with a "Co-N-C" structure at the atomic level has shown great interest for peroxymonosulfate (PMS) activation toward advanced oxidation water treatment. Here, we present an innovative way of producing cobalt hexacyanocobaltate (Co-HCC) with an abundance of atomically isolated CoII-NC sites at the outer surface. This material allows ultraefficient PMS activation to generate plenty of sulfate and hydroxyl radicals, with a turnover frequency much higher than those of most cobalt-based catalysts reported so far and even the homogeneous catalysis by Co2+ ions. We gained fundamental insights on its unprecedently high catalytic performance based on experimental results and computational study. Then, we controlled the growth of Co-HCC on a ceramic membrane to form a confined oxidation environment that utilizes the extended surface area and maximal exposure of short-lived radicals for a fast removal of organic pollutants that enter the pores. As a result, this catalytic membrane achieves complete disruption of micropollutants under a water flux up to 10,000 LMH (merely 0.2 s retention time) and further >90% mineralization of organic pollutants in complex industrial wastewater matrices (<100 s retention time), together with the merits of operational simplicity and great longevity (2 weeks continuous run). Our study elicits a new milestone in "Co-N-C" catalyst structure design for PMS activation and highlights the great interest of producing catalytic membranes for a confined treatment of organic pollutants from partial oxidation to complete mineralization as a new benchmark.

Synthesis of Integrated Material with Activation and Oxidation Functions by Mechanical Milling of Activated Carbon and Persulfate for Enhanced Tetracycline Degradation over Non-Radical Mechanism

As an alternative to the traditional advanced oxidation process of adding potassium persulfate (PS) and its activator to the solution separately, in this study, M(AC-PS), an integrated activator and catalyst, was synthesized by vacuum ball milling of PS and activated carbon (AC) to improve the PS’s utilization efficiency. The joint mechanical milling caused a change in the preferentially exposed crystal surface of the PS and the generation of more π-π* structures on the AC, leading to successful and stable connection of the PS onto the surface of the AC. Within 40 min, the M(AC-PS) achieved a degradation rate of 97.3% for tetracycline (TC, 20 mg/L), while the mixed system where AC and PS were separately ball milled achieved only a 53.1% removal of TC. Reactive oxygen species and electrochemical tests showed that M(AC-PS) mainly oxidized TC through non-free radical mechanisms. In M(AC-PS), AC provided oxygen-containing functional groups (e.g., C=O) to activate the PS and electron holes as an electron transfer medium, generating 1O2 and promoting electron donation from the TC to enhance the oxidation of the TC. Almost no catalytic components were detected in the solution, indicating that the obtained solid composite material avoids the limitations of solid–liquid interface contact and mass transfer, and then improves the efficiency of activation and catalysis. This study presents a simple and feasible method for obtaining efficient and convenient material for the advanced oxidation treatment of wastewater.

Highly efficient peroxymonosulfate activation by CoFe2O4@attapulgite–biochar composites: Degradation properties and mechanism insights

Sulfate radical-based advanced oxidation processes (SR-AOPs) have been considered as a promising approach for degrading organic pollutants. Herein, CoFe2O4 anchored on attapulgite-biochar composites (CoFe2O4@ATP–BC) were synthesized by a sol-gel co-pyrolysis method and showed excellent catalytic performance, reusability and stability in activating peroxymonosulfate (PMS) for the degradation of Rhodamine B (RhB). The effects of PMS concentration, catalyst dosage, temperature, initial pH, NOM and inorganic ions on the removal of RhB were investigated. The radical quenching experiments and electron paramagnetic resonance (EPR) measurement confirmed that 1O2, O2∙− and surface-bound ∙OH and SO4∙− were major reactive oxygen species (ROS) in the RhB degradation by CoFe2O4@ATP–BC/PMS system, indicating that radical and non-radical degradation pathways were both involved. The possible catalytic mechanism of PMS by CoFe2O4@ATP–BC was proposed including the interface reaction and bulk reaction. The main degradation intermediates were identified by liquid chromatograph-mass spectrometry (LC-MS), and three possible degradation pathways of RhB were deduced accordingly. In general, the CoFe2O4@ATP–BC/PMS system provided fundamentals of theoretical and applied research to further develop supported bimetallic oxides for advanced oxidation treatment of organic wastewater.

Enhanced advanced oxidation treatment through the synergy of chloride ion activation and electro-Fenton process

A photoelectrocatalytic system has been developed utilizing the WO3@BiVO4 photoanode and the oxidized carbon black (CB) cathode, enabling the synergistic advanced oxidation treatment by combining chlorine radicals and hydroxyl radicals. The WO3@BiVO4 heterojunction is prepared through hydrothermal growth of BiVO4 onto the surface of WO3 synaptic structure. The as-prepared WO3@BiVO4|Pt system demonstrates a remarkable degradation efficiency of organic pollutants with 97.1 % in 30 min under visible light irradiation with a 1.2 V bias, which is 1.24 times higher compared to the WO3|Pt system. Furthermore, even when utilizing actual seawater as the electrolyte, the treatment efficacy remains high at 92.8 % within 20 min. The oxidized CB cathode is obtained by calcining commercial CB in the air atmosphere. The WO3@BiVO4|CB system achieves the degradation efficiency of 85.9 % within 10 min in simulated seawater, utilizing the electro-Fenton process at 0.2 V. The WO3@BiVO4|CB system effectively removes organic pollutants through the synergistic effect of combining the WO3@BiVO4 photoanode with CB-A cathode. Additionally, impressive degradation efficiency of 97.8 % is achieved in 15 min when using simulated seawater as the electrolyte. The •OH, •Cl, and •Cl2− play the key role in the WB|CB-A synergistic system. The combined action of anodic active chlorine radicals and cathodic electro-Fenton process in the WO3@BiVO4|CB system demonstrates effective microorganism sterilization, resulting in a 92.5 % reduction within 15 min

Comparative study of advanced oxidation treatment of tannery effluent in Multi-orifice Oscillatory Baffled Column with sono-catalytic treatment using Titanium Dioxide

&lt;p&gt;Treatment of tannery effluent is a key issue that requires novel research. The presented work is an attempt to carry out advanced oxidation process in a Multi-orifice Oscillatory Baffled Column using ozone as oxidizer and compare the extent of treatment with sono-catalytic treatment with TiO2 as catalyst. Studies have been carried out to understand the effect of treatment time, concentration of effluent and oscillation frequency upon ozonation and the effect of power of ultrasound, time of treatment and catalyst loading for sono-catalytic treatment. For ozonation the COD, BOD and TDS reduction obtained are 88.8%, 84.01%, 90.73% respectively and for sono-TiO2 treatment the reduction of COD, BOD and TDS obtained are 91.2%, 91.5%, 94%. Optimization and analysis of variables is carried out to identify the effective factors for treatment.&lt;/p&gt;&#x0D;

Advanced oxidation treatment of aqueous atrazine by fixed-bed reactor packed with carbon-supported molybdenum disulfide

MoS2/carbon composites were prepared by affixing MoS2 onto carbon particulates and used as packing materials to establish persulfate advanced oxidation fixed-bed reactors (PS-FBR) for effective continuous-flow degradation of organic pollutants. Since MoS2 was a co-catalyst in accelerating the conversion of Fe3+ to Fe2+, an improved degradation performance against organic pollutants such as atrazine (ATZ) was achieved in this PS/Fe2+/MoS2-FBR. Cost-effective materials of granular carbon, needle carbon, quartz particles, and MoS2 with different morphologies were compared during the preparation of MoS2/carrier composites. The results indicated that a higher adsorption capacity of both carriers and MoS2 was more plausible for ATZ degradation in FBR. After the systematic investigation of reaction conditions, a removal efficiency of 99 % for ATZ was achieved at pH 3–7, 2 mg/L Fe2, 2 mM PS, flow rate of 2 mL/min (cross-sectional area of 1.33 cm2). Meanwhile, this PS/Fe2+/MoS2-FBR could be continuously operated for over 5 days with removal efficiency above 90 %. Importantly, a low Fe2+ concentration of 2 mg/L was sufficient in this system, which could limit the formation of iron sludge and ensure long-term operation.

Advanced oxidation of recalcitrant chromophores in full-scale MBR effluent for non-potable reuse of leachate co-treated municipal wastewater

Wastewater non-potable reuse involves further processing of secondary effluent to a quality level acceptable for reuse and is a promising solution to combating water scarcity. Recalcitrant chromophores in landfill leachate challenge the water quality for non-potable reuse when leachate is co-treated with municipal wastewater. In this study, we first use multivariate statistical analysis to reveal that leachate is an important source (with a Pearson's coefficient of 0.82) of recalcitrant chromophores in the full-scale membrane bioreactor (MBR) effluent. We then evaluate the removal efficacies of chromophores by chlorination, breakpoint chlorination, and the chlorination-UV/chlorine advanced oxidation treatment. Conventional chlorination and breakpoint chlorination only partially remove chromophores, leaving a colour level exceeding the standards for non-potable reuse (>20 Hazen units). We demonstrate that pre-chlorination (with an initial chlorine dosing of 20 mg/L as Cl2) followed by UV radiation (with a UV fluence of 500 mJ/cm2) effectively degraded recalcitrant chromophores (>90%). By quantifying the electron donating capacity (EDC) and radical scavenging capacity (RSC) of the reclaimed water, we demonstrate that pre-chlorination reduces EDC and RSC by up to 64%, increases UV transmittance by 32%, and increases radical yields from UV photolysis of chlorine by 1.7–2.2 times. The findings advance fundamental understanding of the alteration of dissolved coloured substances by (photo)chlorination treatment and provide implications for applying advanced oxidation processes in treating wastewater effluents towards sustainable non-potable reuse.

Control de la resistencia antibiótica microbiana mediante procesos de oxidación avanzada, Manta -Ecuador

Effluent water from oxidation ponds in Manta, Ecuador, and its subsequent treatment by advanced oxidation were evaluated. The objective was to determine the effectiveness of activated carbon treatments to inhibit antibiotic-resistant microorganisms (ARM) in these effluents. The physical-chemical parameters of the effluent from the oxidation pond were characterized before and after the treatments, such as pH, turbidity, total dissolved solids (STD) and electrical conductivity (EC). Three advanced oxidation treatments were used at time intervals and ozone equipment was used that provided a final O3 concentration of 3.0 grams per hour. All ozone treatments were effective in inhibiting the growth of total coliforms. The use of activated (CA) and modified carbon (CAM) with iron during the 2-h ozonation showed remarkable efficiency in this regard. These findings highlight the potential of ozone treatments in combination with the use of activated carbon for disinfection and control of microbiological contamination in water. Theisolated microorganisms were resistant to the drugs bacitracin and ampicillin, without the treatments modifying this resistance. However, sensitivity effects were observed at all stages of treatment for the drugs amikacin and levofloxacin. This study highlights the effectiveness of activated carbon and ozone treatments in improving water quality, removing turbidity, and inhibiting total coliforms, providing information to address contamination and conservation of water resource.

Insight into the application of micro-nano bubbles combined with heat-activated persulfate oxidation for removing dissolved organic matter from printing and dying wastewater

The effluent quality of printing and dyeing wastewater after secondary treatment does not meet industry discharge standards, which poses serious environmental risks. In this work, micro-nano bubbles and a heat-activated persulfate advanced oxidation process were innovatively combined to thoroughly treat industrial printing and dyeing wastewater. Under the optimal reaction conditions (a reaction time of 60 min, persulfate concentration of 20 mM, and temperature of 40 °C), the effluent quality met the discharge standards. Furthermore, the degradation and transformation mechanisms of dissolved organic matter during the wastewater treatment process were investigated by three-dimensional fluorescence spectroscopy and Fourier ion transform spin resonance mass spectrometry. The results showed that organic compounds in the wastewater were clearly degraded by the treatment process, and this was accompanied by a significant increase in molecular diversity. In summary, this work provides insight into the practical application of micro-nano bubbles in the advanced oxidation treatment of industrial wastewater as well as the degradation mechanism responsible for removing pollutants from this wastewater.

Ultrasonication-flotation-advanced oxidation tertiary treatment of oil-based drilling cuttings

The treatment of oil-based drilling cuttings (OBDCs) with high oil content is difficult. In this study, a tertiary treatment of ultrasonication–flotation–advanced oxidation for treating OBDCs with a high oil content of 20.10 wt% was proposed for the first time. All stages of the treatment processes were optimised. The recommended parameters for ultrasonication at room temperature were a mass ratio of OBDCs to the degreaser of 1:8, an ultrasonication power of 600 W and treatment time of 30 min. After the ultrasonication treatment, the oil content of the OBDCs decreased from 20.10 wt% to 5.00 wt%. Flotation was performed at room temperature with a mass ratio of OBDCs to the degreaser of 1:10, a stirring speed of 400 rpm, an aeration head aperture of 3 μm and airflow rate of 400 mL/min under N2 injection for 60 min. After the flotation treatment, the oil content of the OBDCs decreased from 5.00 wt% to 2.01 wt%. Advanced oxidation was performed at room temperature with a mass ratio of OBDCs to water of 1:10, 3.57 wt% sodium persulphate in water, 4.17 wt% ferrous sulphate heptahydrate in water and ultrasonication power of 1000 W for 100 min. Following the advanced oxidation treatment, the oil content of the OBDCs decreased from 2.01 wt% to 0.58 wt%. The results of this study provide a new method and idea for treating OBDCs with high oil content.

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.

Subnanoscale spatially confined heterogeneous Fenton reaction enables mineralization of perfluorooctanoic acid

Superoxide radical (•O2−) is capable of degrading perfluorinated compounds that are persistent in nature and cannot be removed by biological or advanced oxidation treatments, but the inherent drawback is the negligible reactivity of •O2−in aqueous phases due to the hydration effect. Here, we explored an innovative way to make use of •O2− by modulating a partial hydration state through spatial confinement control. We demonstrated this idea by conducting heterogeneous Fenton reaction with layered iron oxychloride (FeOCl) catalyst, wherein •O2−radicals produced and confined within the catalyst structure (interlayer spacing of 7.92 Å) showed defluorination effect dealing with perfluorooctanoic acid (PFOA) as model compound. The defluorination combined with advanced oxidation achieved mineralization. Mechanism study revealed that the confinement frustrated the hydration shell of •O2−with coordination number reduced from 3.3 (for bulk phase) to 1.89, and thereby changed its orbital electron properties and enhanced the nucleophilic ability. We further demonstrated a compact FeOCl membrane reactor with highly efficient degradation of PFOA (kobs up to 1.2 min−1) and cost-effective mineralization (2 × 10−6 $ per mgC), operated under ultrafiltration reaction mode. Our findings highlight the great interest of developing spatial confinement technology to modulate •O2−-based reactions, as well as the feasibility of combining confinement catalyst structures with heterogeneous Fenton reaction to achieve the mineralization treatment goal.