Degradation of aqueous atrazine using persulfate activated by electrochemical plasma coupling with microbubbles: removal mechanisms and potential applications

Micro and nanobubbles-assisted advanced oxidation processes for water decontamination: The importance of interface reactions

Micro and nanobubbles (MNBs), as an efficient and convenient method, have been widely used in water treatment. Composed of gas and water, MNBs avoid directly introducing potential secondary pollutants. Notably, MNBs exhibit significant advantages through interface reactions in assisting AOPs. They overcome barriers like low mass transfer coefficients and limited reactive sites, and shorten the distance between pollutants and oxidants, achieving higher pollutant removal efficiency. However, there is a lack of systematic summary and in-depth discussion on the fundamental mechanisms of MNBs-assisted AOPs. In this critical review, the characteristics of MNBs related to water treatment are outlined first. Subsequently, the recent applications, performance, and mechanisms of MNBs-assisted AOPs including ozone, plasma, photocatalytic, and Fenton oxidation are overviewed. We conclude that MNBs can improve pollutant removal mainly by enhancing the utilization of reactive oxygen species (ROS) generated by AOPs due to the effective interface reactions. Furthermore, we calculated the electrical energy per order of reaction (EE/O) parameter of different MNBs-assisted AOPs, suggesting that MNBs can reduce the total energy consumption in most of the tested cases. Finally, future research needs/opportunities are proposed. The fundamental insights in this review are anticipated to further facilitate an in-depth understanding of the mechanisms of MNBs-assisted AOPs and supply critical guidance on developing MNBs-based technologies for water treatment.

Degradation of Atrazine in Water by Dielectric Barrier Discharge Combined with Periodate Oxidation: Enhanced Performance, Degradation Pathways, and Toxicity Assessment

The widespread occurrence of atrazine (ATZ) in water environments presents a considerable risk to human health and ecosystems. Herein, the performance of dielectric barrier discharge integrated with periodate (DBD/PI) for ATZ decomposition was evaluated. Results demonstrated that the DBD/PI system improved ATZ decomposition efficiency by 18.2-22.5% compared to the sole DBD system. After 10 min treatment, the decomposition efficiency attained 82.4% at a discharge power of 68 W, a PI dosage of 0.02 mM, and an initial ATZ concentration of 10 mg/L. As the PI dosage increased, the decomposition efficiency exhibited a trend of initially increasing, followed by a decrease. Acidic conditions were more favorable for ATZ removal compared to alkaline and neutral conditions. Electron paramagnetic resonance (EPR) was adopted for characterizing the active species produced in the DBD/PI system, and quenching experiments revealed their influence on ATZ decomposition following a sequence of 1O2 > O2-• > IO3• > OH•. The decomposition pathways were proposed based on the theoretical calculations and intermediate identification. Additionally, the toxic effects of ATZ and its intermediates were assessed. This study demonstrates that the DBD/PI treatment represents an effective strategy for the decomposition of ATZ in aquatic environments.

Efficient degradation of F-53B as PFOS alternative in water by plasma discharge: Feasibility and mechanism insights

The frequent detection of 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) in various environments has raised concerns owing to its comparable or even higher environmental persistence and toxicity than perfluorooctane sulfonate (PFOS). This study investigated the plasma degradation of F-53B for the first time using a water film plasma discharge system. The results revealed that F-53B demonstrated a higher rate constant but similar defluorination compared to PFOS, which could be ascribed to the introduction of the chlorine atom. Successful elimination (94.8-100 %) was attained at F-53B initial concentrations between 0.5 and 10 mg/L, with energy yields varying from 15.1 to 84.5 mg/kWh. The mechanistic exploration suggested that the decomposition of F-53B mainly occurred at the gas-liquid interface, where it directly reacted with reactive species generated by gas discharge. F-53B degradation pathways involving dechlorination, desulfonation, carboxylation, C-O bond cleavage, and stepwise CF2 elimination were proposed based on the identified byproducts and theoretical calculations. Furthermore, the demonstrated effectiveness in removing F-53B in various coexisting ions and water matrices highlighted the robust anti-interference ability of the treatment process. These findings provide mechanistic insights into the plasma degradation of F-53B, showcasing the potential of plasma processes for eliminating PFAS alternatives in water.

Ionic liquid coupled plasma promotes acetic acid production during anaerobic fermentation of waste activated sludge: Breaking the restrictions of low bioavailable substrates and altering the metabolic activities of anaerobes

This study explored the potential application of plasma coupling ionic liquid on disintegration of waste activated sludge and enhanced production of short-chain fatty acids (SCFAs) in anaerobic fermentation. Under optimal conditions (dosage of ionic liquid [Emim]OTf = 0.1 g/g VSS (volatile suspended solids) and discharge power of dielectric barrier discharge plasma (DBD) = 75.2 W), the [Emim]OTf/DBD pretreatment increased SCFA production by 302 % and acetic acid ratio by 53 % compared to the control. Mechanistic investigations revealed that the [Emim]OTf/DBD combination motivated the generation of various reactive species (such as H2O2, O3, •OH, 1O2, ONOO-, and •O2-) and enhanced the utilization of physical energies (such as heat). The coupling effects of [Emim]OTf/DBD synergistically improved the disintegration of sludge and biodegradability of dissolved organic matter, promoting the sludge anaerobic fermentation process. Moreover, the [Emim]OTf/DBD pretreatment enriched hydrolysis and SCFAs-forming bacteria while inhibiting SCFAs-consuming bacteria. The net effect was pronounced expression of genes encoding key enzymes (such as alpha-glucosidase, endoglucanase, beta-glucosidase, l-lactate/D-lactate dehydrogenase, and butyrate kinase) involved in the SCFA-producing pathway, enhancing the production of SCFAs from sludge anaerobic fermentation. In addition, [Emim]OTf/DBD pretreatment facilitated sludge dewatering and heavy metal removal. Therefore, [Emim]OTf/DBD pretreatment is a promising approach to advancing sludge reduction, recyclability, and valuable resource recovery.

Fabrication of lignosulfonate-derived porous carbon via pH-tunable self-assembly strategy for efficient atrazine removal

Herein, a straightforward protocol was developed for the one-pot synthesis of N-doped lignosulfonate-derived carbons (NLDCs) with a tunable porous structure using natural amino acids-templated self-assembly strategy. Specifically, histidine was employed as a template reagent, leading to the preparation of 10-NLDC-21 with remarkable characteristics, including the large specific surface area (SBET = 1844.5 m2/g), pore volume (Vmes = 1.22 cm3/g) and efficient adsorption for atrazine (ATZ) removal. The adsorption behavior of ATZ by NLDCs followed the Langmuir and pseudo-second-order models, suggesting a monolayer chemisorption nature of ATZ adsorption with the maximum adsorption capacity reached up to 265.77 mg/g. Furthermore, NLDCs exhibited excellent environmental adaptability and recycling performance. The robust affinity could be attributed to multi-interactions including pore filling, electrostatic attraction, hydrogen bonding and π-π stacking between the adsorbents and ATZ molecules. This approach offers a practical method for exploring innovative bio-carbon materials for sewage treatment.

Degradation mechanism and decomposition of sulfamethoxazole aqueous solution with persulfate activated by dielectric barrier discharge

The present study focused on the degradation of sulfamethoxazole (SMX) aqueous solution and the toxicity of processing aqueous by the dielectric barrier discharge (DBD) activated persulfate (PS). The effects of input voltage, input frequency, duty cycle, and PS dosage ratio on the SMX degradation efficiency were measured. Based on the results of the Response Surface Methodology (RSM), SMX degradation efficiency reached 83.21% which is 10.54% higher than that without PS, and the kinetic constant was 0.067 min-1 in 30 min when the input voltage at 204 V (input power at 110.6 W), the input frequency at 186 Hz, the duty cycle at 63%, and the PS dosage ratio at 5.1:1. The addition of PS can produce more active particles reached 1.756 mg/L (O3), 0.118 mg/L (H2O2), 0.154 mmol/L (·OH) in 30 min. Furthermore, the DBD plasma system effectively activated an optimal amount of PS, leading to improved removal efficiency of COD, and TOC to 30.21% and 47.21%, respectively. Subsequently, eight primary by-products were pinpointed, alongside the observation of three distinct pathways of transformation. Predictions from the ECOSAR software indicated that most of the degradation intermediates were less toxic than SMX. The biological toxicity experiments elucidated that the treatment with the DBD/PS system effectively reduced the mortality of zebrafish larvae caused by SMX from 100% to 20.13% and improved the hatching rate from 55.69% to 80.86%. In particular, it is important to note that the degradation intermediates exhibit teratogenic effects on zebrafish larvae.

Degradation performance and mechanism of microcystins in aquaculture water using low-temperature plasma technology

The eutrophication of aquaculture water bodies seriously restricts the healthy development of the aquaculture industry. Among them, microcystins are particularly harmful. Therefore, the development of technologies for degrading microcystins is of great significance for maintaining the healthy development of the aquaculture industry. The feasibility and mechanism of removing microcystins-LR by dielectric barrier discharge (DBD) plasma were studied. DBD discharge power of 49.6 W and a treatment time of 40 min were selected as the more suitable DBD parameters, resulting in microcystin-LR removal efficiency of 90.4%. Meanwhile, the effects of initial microcystin-LR concentration, initial pH value, turbidity, anions on the degradation effect of microcystin-LR were investigated. The removal efficiency of microcystin-LR decreased with the increase of initial microcystin-LR concentration and turbidity. The degradation efficiency of microcystin-LR at pH 4.5 and 6.5 is significantly higher than that at pH 8.5 and 3.5. HCO3- can inhibit the removal efficiency of microcystin-LR. Furthermore, five intermediates products (m/z = 1029.5, 835.3, 829.3, 815.4, 642.1) were identified in this study, and the toxicity analysis of these degradation intermediates indicated that DBD treatment can reduce the toxicity of microcystin-LR. e－aq, •OH, H2O2, and O3 have been shown to play a major role in the degradation of microcystin-LR, and the contribution ranking of these active species is e－aq > •OH > H2O2 > O3. The application of DBD plasma technology in microcystin-LR removal and detoxification has certain development potential.

Cold plasma turns mixed-dye-contaminated wastewater bio-safe

The excessive and uncontrollable discharge of diverse organic pollutants into the environment has emerged as a significant concern, presenting a substantial risk to human health. Among the advanced oxidation processes used for the purification of wastewater, cold plasma technology is superior in fast and effective decontamination but often fails facing mixed pollutants. To address these issues, here we develop the new conceptual approach, plasma process, and proprietary reactor that ensure, for the first time, that the efficiency of treatment (114.7%) of two mixed organic dyes, methylene blue (MB) and methyl orange (MO), is higher than when the two dyes are treated separately. We further reveal the underlying mechanisms for the energy-efficient complete degradation of the mixed dyes. The contribution of plasma-induced ROS and the distinct degradation characteristics and mechanism of pollutants in mixed treatment are discussed. The electron transfer pathway revealed for the first time suggest that the mixed pollutants reduce the overall redox potentials and facilitate electron transfer during the plasma treatment, promoting synergistic degradation effects. The integrated frameworks including both direct and indirect mechanisms provide new insights into the high-efficiency mixed-contaminant treatment. The degradation products for mixed degradation are revealed based on the identification of intermediate species. The plasma-treated water is proven safe for living creatures in waterways and sustainable fishery applications, using in vivo zebrafish model bio-toxicity assay. Overall, these findings offer a feasible approach and new insights into the mechanisms for the development of highly-effective, energy-efficient technologies for wastewater treatment and reuse in agriculture, industry, and potentially in urban water networks.

Iron-doped bismuth oxybromides as visible-light-responsive Fenton catalysts for the degradation of atrazine in aqueous phases

Pesticides and its degradation products, being well-known residues in soil, have recently been detected in many water bodies as pollutants of emerging concerns, and thus there is a contemporary demand to develop viable and cost-effective techniques for the removal of related organic pollutants in aqueous phases. Herein, a visible-light-responsive Fenton system was constructed with iron-doped bismuth oxybromides (Fe-BiOBr) as the catalysts. Taking the advantage of sustainable Fe(III)/Fe(II) conversion and optimized H2O2 utilization, the optimal Fe-BiOBr-2 catalyst showed an excellent atrazine removal efficiency of 97.61% in 120 min, which is superior than the traditional homogeneous Fenton and the majority of heterogeneous processes documented in the literature. In this photo-Fenton system, hydroxyl (·OH) and superoxide (·O2-) radicals were dominant active species contributed to the oxidative degradation of atrazine. Due to the production of various active radicals, five degradation pathways were proposed based on the identification of intermediates and degradation products. Overall, this work not only demonstrates a fundamental insight into creating highly efficient and atom economic photo-Fenton systems, but also provides a complementary strategy for the treatment of organic pollutants in water.

Synergistic degradation of Congo Red by hybrid advanced oxidation via ultraviolet light, persulfate, and hydrodynamic cavitation

In the present study, hybrid activation of sodium peroxydisulfate (PS) by hydrodynamic cavitation and ultraviolet radiation was investigated for Congo Red (CR) degradation. Experiments were conducted using the Box-Benken design on inlet pressure (2-6 bar), PS concentration (0-50 mg. L-1) and UV radiation power (0-32 W). According to the results, at the optimum point where the pressure, PS concentration and UV radiation power were equal to 4.5 bar, 30 mg. L-1 and 16 W respectively, 92.01% of decolorization was achieved. Among the investigated processes, HC/UV/PS was the best process with the rate constant and synergetic coefficient of 38.6 × 10-3 min-1 and 2.76, respectively. At the optimum conditions, increasing the pollutant concentration from 20 mg. L-1 to 80 mg. L-1 decrease degradation rate from 92.01 to 45.21. Presence of natural organic mater (NOM) in all concentrations inhibited the CR degradation. Quenching experiments revealed that in the HC/UV/PS hybrid AOP free radicals accounted for 63.4% of the CR degradation, while the contribution of sulfate (SRs) and hydroxyl radicals (HRs) was 53.1% and 46.9%, respectively.

Feasibility and mechanism of removing Microcystis aeruginosa and degrading microcystin-LR by dielectric barrier discharge plasma

Harmful cyanobacterial bloom is one of the serious environmental problems worldwide. Microcystis aeruginosa is a representative harmful alga in cyanobacteria bloom. It is of great significance to develop new technologies for the removal of Microcystis aeruginosa and microcystins. The feasibility and mechanism of removing microcystis aeruginosa and degrading microcystins by dielectric barrier discharge (DBD) plasma were studied. The suitable DBD parameters obtained in this study are DBD (41.5 W, 40 min) and DBD (41.5 W, 50 min), resulting in algae removal efficiency of 77.4% and 80.4%, respectively; scanning electron microscope and LIVE-DEATH analysis demonstrate that DBD treatment can disrupt cell structure and lead to cell death; analysis of elemental composition and chemical state indicated that there are traces of oxidation of organic nitrogen and organic carbon in microcystis aeruginosa; further intracellular ROS concentration and antioxidant enzyme activity analysis confirm that DBD damage microcystis aeruginosa through oxidation. Meanwhile, DBD can effectively degrade the microcystin-LR released after cell lysis, the extracellular microcystin-LR concentration in the DBD (41.5 W) group decreased by 88.7% at 60 min compared to the highest concentration at 20 min; further toxicity analysis of degradation intermediates indicated that DBD can reduce the toxicity of microcystin-LR. The contribution of active substances to the inactivation of microcystis aeruginosa is eaq- > •OH > H2O2 > O3 > 1O2 > •O2- > ONOO-, while on the degradation of microcystin-LR is eaq- > •OH > H2O2 > O3 > •O2- > 1O2 > ONOO-. The application of DBD plasma technology in microcystis aeruginosa algae removal and detoxification has certain prospects for promotion and application.

Feasibility and mechanism of recycling carbon resources from waste cyanobacteria and reducing microcystin toxicity by dielectric barrier discharge plasma

Recycling carbon resources from discarded cyanobacteria is a worthwhile research topic. This study focuses on the use of dielectric barrier discharge (DBD) plasma technology as a pretreatment for anaerobic fermentation of cyanobacteria. The DBD group (58.5 W, 45 min) accumulated the most short chain fatty acids (SCFAs) along with acetate, which were 3.0 and 3.3 times higher than the control. The DBD oxidation system can effectively collapse cyanobacteria extracellular polymer substances and cellular structure, improve the biodegradability of dissolved organic matter, enrich microorganisms produced by hydrolysis and SCFAs, reduce the abundance of SCFAs consumers, thereby promoting the accumulation of SCFAs and accelerating the fermentation process. The microcystin-LR removal rate of 39.8% was obtained in DBD group (58.5 W, 45 min) on day 6 of anaerobic fermentation. The toxicity analysis using the ECOSAR program showed that compared to microcystin-LR, the toxicity of degradation intermediates was reduced. The contribution order of functional active substances to cyanobacteria cracking was obtained as eaq- > •OH > 1O2 > •O2- > ONOO-, while the contribution order to microcystin-LR degradation was eaq- > •OH > •O2- > 1O2 > ONOO-. DBD has the potential to be a revolutionary pretreatment method for cyanobacteria anaerobic fermentation.

Insight into Chinese medicine residue biochar combined with ultrasound for persulfate activation in atrazine degradation: Acanthopanax senticosus precursors, synergistic effects and toxicity assessment

The synergistic activation of persulfate by multiple factors could degrade pollutants more efficiently. However, the co-activation method based on metal ions has the risk of leakage. The non-metallic coupling method could achieve the same efficiency as the metal activation and meanwhile release environmental stress. In this study, the original biochar (BC) was prepared through using Chinese medicinal residue of Acanthopanax senticosus as the precursor. Compared with other biochar, the pore size structure was higher and toxicity risk was lower. The ultrasonic (US)/Acanthopanax senticosus biochar (ASBC)/persulfate oxidation system was established for Atrazine (ATZ). Results showed that 45KHz in middle and low frequency band cooperated with ASBC600 to degrade nearly 70 % of ATZ within 50 min, and US promoted the formation of SO₄^- and OH. Meanwhile, the synergy index of US and ASBC was calculated to be 1.18, which showed positive synergistic effect. Finally, the potential toxicity was examined by using Toxicity Characteristic Leaching Procedure (TCLP) and luminescent bacteria. This study provides a promising way for the activation of persulfate, which is expected to bring a new idea for the win-win situation of pollutant degradation and solid waste resource utilization.

Plasma-microbubble treatment and sustainable agriculture application of diclofenac-contaminated wastewater

The demand for efficient wastewater treatment is becoming increasingly urgent due to the rising threat of pharmaceutical residues in water. As a sustainable advanced oxidation process, cold plasma technology is a promising approach for water treatment. However, the adoption of the technology encounters several challenges, including the low treatment efficiency and the potentially unknown environmental impact. Here, microbubble generation was integrated with cold plasma system to enhance treatment of wastewater contaminated with diclofenac (DCF). The degradation efficiency depended on the discharge voltage, gas flow, initial concentration, and pH value. The best degradation efficiency was 90.9% after 45 min plasma-bubble treatment under the optimum process parameters. The hybrid plasma-bubble system exhibited strongly synergistic performance heralded by up to seven-times higher DCF removal rates than the two systems operated separately. The plasma-bubble treatment remains effective even after addition of SO₄^2-, Cl^-, CO₃^2-, HCO₃^-, and humic acid (HA) as interfering background substances. The contributions of •O₂^-, O₃, •OH, and H₂O₂ reactive species to the DCF degradation process were specified. The synergistic mechanisms for DCF degradation were deduced through the analysis of the degradation intermediates. Further, the plasma-bubble treated water was proven safe and effective to stimulate seed germination and plant growth for sustainable agriculture applications. Overall, these findings provide new insights and a feasible approach with a highly synergistic removal effect for the plasma-enhanced microbubble wastewater treatment, without generating secondary contaminants.

An in-depth insight into the simultaneous oxidation of sulfamethoxazole and reduction of Cr (VI) by one system of water film DBD plasma: The interaction effect, role of active species, and their dominant to pathways

This study aims to deeply investigate the simultaneous elimination of sulfamethoxazole (SMZ) and Cr (VI) through one system of water film dielectric barrier discharge (WFDBD) plasma. The interaction effect of SMZ degradation and Cr (VI) reduction and dominant effect of active species were highlighted. Results showed that the oxidation of SMZ and the reduction of Cr (VI) directly promote each other. When the concentration of Cr (VI) raised from 0 to 2 mg L^-1, the degradation rate of SMZ enhanced from 75.6% to 88.6%, respectively. Similarly, when the concentration of SMZ improved from 0 to 15 mg L^-1, the removal efficiency of Cr (VI) improved from 70.8% to 84.3%, respectively. ·OH, ¹O₂ and ·O₂^- play crical roles for SMZ degradation, and e^-, ·O₂^-, ·H and H₂O₂ dominated to the Cr (VI) reduction. The variations of pH, conductivity and TOC during the removal process were also explored. The removal process was studied by UV-vis spectroscopy and a three-dimensional excitation-emission matrix. Based on DFT calculation and LC-MS analysis, free radicals dominated SMZ degradation pathways in the WFDBD plasma system were clarified. Besides, the influence of Cr (VI) on SMZ degradation pathway was clarified. The ecotoxicity of SMZ and the toxicity of Cr (VI) into Cr (III) were greatly reduced. This study provides a significant reference value for the application and mechanism of plasma simultaneous removal of organic pollutants and heavy metals in wastewater.

Synergistic catalysis induced by a multi-component system constructed by DBD plasma combined with α-Fe2O3/FeVO4/HCP and peroxymonosulfate for gatifloxacin removal

The dielectric barrier discharge (DBD) multi-component system containing plasma, α-Fe₂O₃/FeVO₄, and peroxymonosulfate (PMS) with high catalytic activity was successfully constructed. Thereinto, α-Fe₂O₃/FeVO₄ was loaded on the honeycomb ceramic plate (HCP) surface (α-Fe₂O₃/FeVO₄/HCP) and placed under the water surface below the discharge area. The catalytic activity was evaluated by the removal rate of gatifloxacin (GAT), and the DBD+α-Fe₂O₃/FeVO₄+PMS system exhibited the optimal catalytic activity. The enhanced catalytic activity can be attributed to the fact that the occurrence of synergistic catalysis that simultaneously includes plasma oxidation, photocatalysis, PMS oxidation, O₃ catalysis, and Fenton reaction. The effect of various initial degradation parameters including input power, PMS dosage, pH, etc. On GAT removal was investigated. DBD+α-Fe₂O₃/FeVO₄+PMS system has a significant increase in the concentration of H₂O₂ and O₃, and the role played in the multi-component system was analyzed. The identification and analysis of organic matters during GAT degradation were visualized with the help of 3D EEMs. HPLC-MS and theoretical calculations identified the major intermediates and further deduced the possible GAT degradation pathways. Additionally, the acute toxicity of the major intermediates was predicted by the QSAR model. Finally, the possible mechanisms of synergistic catalysis to enhance catalytic activity were discussed based on the characteristics of several advanced oxidation processes (AOPs) and the results of experimental and characterization. This work provides a feasible technical route and theoretical basis for wastewater treatment by plasma combined with other AOPs.

Degradation of atrazine in river sediment by dielectric barrier discharge plasma (DBDP) combined with a persulfate (PS) oxidation system: response surface methodology, degradation mechanisms, and pathways

Single degradation systems based on dielectric barrier discharge plasma (DBDP) or persulfate (PS) oxidation cannot achieve the desired goals (high degradation efficiency, high mineralization rate, and low product toxicity) of degrading atrazine (ATZ) in river sediment. In this study, DBDP was combined with a PS oxidation system (DBDP/PS synergistic system) to degrade ATZ in river sediment. A Box-Behnken design (BBD) including five factors (discharge voltage, air flow, initial concentration, oxidizer dose, and activator dose) and three levels (- 1, 0, and 1) was established to test a mathematical model by response surface methodology (RSM). The results confirmed that the degradation efficiency of ATZ in river sediment was 96.5% in the DBDP/PS synergistic system after 10 min of degradation. The experimental total organic carbon (TOC) removal efficiency results indicated that 85.3% of ATZ is mineralized into CO₂, H₂O, and NH₄⁺, which effectively reduces the possible biological toxicity of the intermediate products. Active species (sulfate (SO₄•^-), hydroxy (•OH), and superoxide (•O₂^-) radicals) were found to exert positive effects in the DBDP/PS synergistic system and illustrated the degradation mechanism of ATZ. The ATZ degradation pathway, composed of 7 main intermediates, was clarified by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). This study indicates that the DBDP/PS synergistic system is a highly efficient, environmentally friendly, novel method for the remediation of river sediment containing ATZ pollution.

Enhancement of peroxymonosulfate activation for 2,4-dichlorophenoxyacetic acid removal by MoSe2 induced Fe redox cycles

The limited regeneration of Fe2+ in the Fe-catalyzed advanced oxidation processes (AOPs) constrained its application for the removal of organic pollutants. Herein, MoSe2 was introduced to promote the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the Fe2+/PMS system. Compared with Fe2+/PMS processes, the 2,4-D degradation efficiency and PMS decomposition rate respectively increased by 73.8% and 84.2% in the MoSe2/Fe2+/PMS system. DFT simulation results suggested that Se atoms acted smoothly as the bridge supporting the charge transfer from Mo to adjacent Fe atoms, which led to the reduction of Fe3+. The rapid regeneration of Fe2+ boosted the activation of PMS and the degradation of pollutants. Additionally, the electron paramagnetic resonance (EPR) and quenching experiments results indicated that SO4∙-, ∙OH, and 1O2 accounted for 2,4-D degradation, and SO4∙- and 1O2 predominated the reaction. The Mo based co-catalysts showed better co-catalytic effect than the W counterparts, and the moderate adsorption for PMS and lower electron transfer electron transfer resistance accounted for the more excellent co-catalytic performance of MoSe2 than that of WSe2. In addition, the degradation efficiency of 2,4-D was up to 95.5% after five cycles of MoSe2 in the co-catalytic system. The coexistent humic acid (HA) and Cl- showed ignorant negative effect on the degradation, while HCO3- would depress the oxidation reaction. The acidic etching wastewater can be applied as the Fe ions source in this co-catalytic process to remove 2,4-D effectively.

Real-Time Monitoring of the Atrazine Degradation by Liquid Chromatography and High-Resolution Mass Spectrometry: Effect of Fenton Process and Ultrasound Treatment

High resolution mass spectrometry (HRMS) was coupled with ultra-high-performance liquid chromatography (uHPLC) to monitor atrazine (ATZ) degradation process of Fenton/ultrasound (US) treatment in real time. Samples were automatically taken through a peristaltic pump, and then analysed by HPLC-HRMS. The injection in the mass spectrometer was performed every 4 min for 2 h. ATZ and its degradation metabolites were sampled and identified. Online Fenton experiments in different equivalents of Fenton reagents, online US experiments with/without Fe²⁺ and offline Fenton experiments were conducted. Higher equivalents of Fenton reagents promoted the degradation rate of ATZ and the generation of the late-products such as Ammeline (AM). Besides, adding Fe²⁺ accelerated ATZ degradation in US treatment. In offline Fenton, the degradation rate of ATZ was higher than that of online Fenton, suggesting the offline samples were still reacting in the vial. The online analysis precisely controls the effect of reagents over time through automatic sampling and rapid detection, which greatly improves the measurement accuracy. The experimental set up proposed here both prevents the degradation of potentially unstable metabolites and provides a good way to track each metabolite.

Synergistic improvement of short-chain fatty acid production from waste activated sludge via anaerobic fermentation by combined plasma-calcium peroxide process

In this study, the combination of dielectric barrier discharge plasma (DBD) with calcium peroxide (CaO₂) achieved significant synergistic effects in promoting hydrolysis of waste activated sludge (WAS) and short-chain fatty acid (SCFA) production during anaerobic fermentation. Compared with the control, DBD/CaO₂ pretreatment increased SCFA production by 116 %, acetic acid ratio by 39 %, and sludge reduction by 30 % under the optimal conditions (discharge power = 76.5 W, CaO₂ dosage = 0.05 g/g VSS). Mechanism investigations elucidated that DBD/CaO₂ enhanced the generation of •OH, ¹O₂, and •O₂^-, synergistically promoted decomposing extracellular polymeric substances (EPS), lysing cells, releasing biodegradable substances, and enhancing acetic acid-enriched SCFA accumulation from fermentation. Meanwhile, Illumina MiSeq sequencing analysis revealed that the enrichment of hydrolytic and SCFAs-forming bacteria and the decrease in SCFAs-consuming bacteria by DBD/CaO₂ treatment also contributed. This work provides an effective method to boost the SCFA production from WAS fermentation.

Effect of dielectric barrier discharge plasma on persulfate activation for rapid degradation of atrazine: Optimization, mechanism and energy consumption

Dielectric barrier discharge plasma (DBDP) is an emerging and promising advanced oxidation process (AOP) for wastewater treatment. After investigating the effect of input voltage, O₃ (generated by dielectric barrier discharge), and peroxydisulfate (PDS) dosage, the DBDP_O3/PDS system was established. With the assistance of PDS, the atrazine (ATZ) removal efficiency increased from 69.67% to 82.46% within 25 min. Synergistic effect calculation suggests that there were markedly synergies between DBDP, O_3, and PDS. Under the effect of SO₄^-•, the total organic carbon (TOC) removal and dechlorination efficiency were significantly improved. In addition, the DBDP_O3/PDS system maintained the ATZ removal efficiency at a high level over a wide range of initial pH values. According to quenching experiments and electron paramagnetic resonance (EPR) detection, the dominant radical for ATZ degradation in the DBDP_O3/PDS system was HO^•. A possible degradation pathway of ATZ was proposed based on density functional theory (DFT) analysis, quadrupole-time of flight-liquid chromatography/mass spectrometry (Q-TOF-LC/MS) results, and related literature. The acute toxicity to aquatic minnows and the developmental toxicity of intermediate products prediction confirmed that the DBDP_O3/PDS system could effectively reduce ATZ toxicity. The electrical energy per order (E_EO) was 7.10 kWh m^-3 order^-1 illustrating that the DBDP_O3/PDS was a more energy-economic system than other energy-intensive processing technologies.

Application of perovskite oxides and their composites for degrading organic pollutants from wastewater using advanced oxidation processes: Review of the recent progress

In the recent years, perovskite oxides are gaining an increasing amount of attention owing to their unique traits such as tunable electronic structures, flexible composition, and eco-friendly properties. In contrast, their catalytic performance is not satisfactory, which hinders real wastewater remediation. To overcome this shortcoming, various strategies are developed to design new perovskite oxide-based materials to enhance their catalytic activities in advanced oxidation process (AOPs). This review article is to provide overview of basic principle and different methods of AOPs, while the strategies to design novel perovskite oxide-based composites for enhancing the catalytic activities in AOPs have been highlighted. Moreover, the recent progress of their synthesis and applications in wastewater remediation (pertaining to the period 2016-2022) was described, and the related mechanisms were thoroughly discussed. This review article helps scientists to have a clear outlook on the selection and design of new effective perovskite oxide-based materials for the application of AOPs. At the end of the review, perspective on the challenges and future research directions are discussed.

Degradation of Residual Herbicide Atrazine in Agri-Food and Washing Water

Atrazine, an herbicide used to control grassy and broadleaf weed, has become an essential part of agricultural crop protection tools. It is widely sprayed on corn, sorghum and sugar cane, with the attendant problems of its residues in agri-food and washing water. If ingested into humans, this residual atrazine can cause reproductive harm, developmental toxicity and carcinogenicity. It is therefore important to find clean and economical degradation processes for atrazine. In recent years, many physical, chemical and biological methods have been proposed to remove atrazine from the aquatic environment. This review introduces the research works of atrazine degradation in aqueous solutions by method classification. These methods are then compared by their advantages, disadvantages, and different degradation pathways of atrazine. Moreover, the existing toxicological experimental data for atrazine and its metabolites are summarized. Finally, the review concludes with directions for future research and major challenges to be addressed.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.

Effect of MoS2 on phenol decomposition in water after high-voltage pulse discharge treatment

Molybdenum disulfide (MoS₂) was added to the system after being treated with high-voltage pulse discharge plasma to improve the degradation efficiency of pollutants and reduce energy consumption. The discharge plasma-treated solution contains hydrogen peroxide and metal iron ions, and MoS₂ addition can cause co-catalytic Fenton reaction. The effects of discharge time, initial pH, phenol concentration, MoS₂ dosage, discharge voltage, and gas type on phenol removal and aqueous H₂O₂ concentration were mainly investigated. Results showed that the addition of MoS₂ after plasma treatment can reduce the plasma treatment time by 70% and maintain or even increase the degradation efficiency of phenol from 40% (after 20 min of discharge plasma) to 92% (after turning off the discharge and dosing with MoS₂ for 30 min). Acidic conditions (pH = 3-4) and oxygen were beneficial to phenol removal. MoS₂ addition greatly improved the catalytic oxidation of discharge plasma. This study provides a promising direction for water treatment based on plasma technology.

Recent Advances of Emerging Organic Pollutants Degradation in Environment by Non-Thermal Plasma Technology: A Review

Emerging organic pollutants (EOPs), including endocrine disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs), and persistent organic pollutants (POPs), constitute a problem in the environmental field as they are difficult to completely degrade by conventional treatment methods. Non-thermal plasma technology is a novel advanced oxidation process, which combines the effects of free radical oxidation, ozone oxidation, ultraviolet radiation, shockwave, etc. This paper summarized and discussed the research progress of non-thermal plasma remediation of EOPs-contaminated water and soil. In addition, the reactive species in the process of non-thermal plasma degradation of EOPs were summarized, and the degradation pathways and degradation mechanisms of EOPs were evaluated of selected EOPs for different study cases. At the same time, the effect of non-thermal plasma in synergy with other techniques on the degradation of EOPs in the environment was evaluated. Finally, the bottleneck problems of non-thermal plasma technology are summarized, and some suggestions for the future development of non-thermal plasma technology in the environmental remediation were presented. This review contributes to our better understanding of non-thermal plasma technology for remediation of EOPs-contaminated water and soil, hoping to provide reference for relevant practitioners.

Insights into the mechanism of redox pairs and oxygen vacancies of Fe2O3@CoFe2O4 hybrids for efficient refractory organic pollutants degradation

The core-shell Fe₂O₃@CoFe₂O₄ hybrids microspheres with abundant oxygen vacancies were synthesized through in-situ ion exchange-calcination method and employed to induce peroxymonosulfate (PMS) to eliminate organic pollutants. The superior catalytic activity and stability of Fe₂O₃@CoFe₂O₄ were attributed to the synergistic effects of M²⁺/M³⁺ (M denotes Co or Fe) redox cycles. SO₄^·-, ·OH, O₂^·- and ¹O₂ were proved to be the main reactive oxygen species (ROS) involved in the phenol degradation process through quenching experiments and EPR measurements, while the surface-bound SO₄^·- played a dominant role. Trace metal ions leached during the reaction enhanced the PMS activation, and the oxygen vacancies electron transfer process played a critical role in the formation of O₂^·-/¹O₂ and the cycle of M²⁺/M³⁺ redox pairs. The formation of ROS and function of ¹O₂ were also revealed from bulk reaction and interface reaction. This study highlighted the simultaneous evolution of PMS reduction and oxidation to generate ROS, which provided an insight into the efficient catalytic degradation of persistent organic pollutants (POPs).

High-efficiency electrochemical degradation of phenol in aqueous solutions using Ni-PPy and Cu-PPy composite materials

Conductive crystalline polypyrrole (Cryst-PPy), Nickel-polypyrrole (Ni-PPy), and copper- polypyrole (Cu-PPy) hybrid materials were prepared using a chemical polymerization method in an aqueous solution. Part I was focused on the Chemical synthesis of Cryst-PPy powder from an organic medium. Cryst-PPy powder was successfully synthesized by chemical route from an organic medium of acetonitrile with polyethylene oxide as a stabilizing agent and oxidizing agent like potassium peroxydisulfate. The morphological study was showed the presence of spherical nanoparticles and cubic microparticles giving rise to a denser structure of PPy. In the second part, the based electrodes composites were examined in the oxidation of phenol by an electrochemical process in an alkaline medium. To follow the yield of phenol degradation at the alkaline solution, UV-visible analysis was performed at the following operating conditions: current density of 0.58 mA cm^-2, phenol initial concentration of 0.150 M and for 3 h processing; the rate of phenol elimination was 56%, 38% and 28% for Cu-PPy, Ni-PPy, and pure PPy electrodes respectively. Thus, can be found that the doped Cu-PPy electrodes electrode is a new material with high electrochemical oxidation ability for phenol degradation in aqueous solutions.