Activation of peracetic acid with zero-valent iron for tetracycline abatement: The role of Fe(II) complexation with tetracycline

Organic radicals driving polycyclic aromatic hydrocarbon polymerization with peracetic acid activation in soil

The use of peracetic acid (PAA) in advanced oxidation processes has gained significant attention recently, but the knowledge of activating PAA to degrade polycyclic aromatic hydrocarbons (PAHs) is limited due to the variety and selectivity of reactive substances in PAA oxidation system. This paper presented the first systemically study on the degradation of PAHs by PAA activation in soil. It was found that heat-activated peracetic acid (heat/PAA) was capable of degrading phenanthrene (PHE) efficiently with degradation efficiency > 90 % within 30 min. Experimental results demonstrated that a series of reactive oxygen species (ROS) including organic radicals (RO•), hydroxyl radicals (HO•) and singlet oxygen (1O2) were generated, while acetylperoxyl (CH3C(O)OO•) and acetyloxyl (CH3C(O)O•) radicals were primarily responsible for PHE degradation in soil. Further analysis shows that polymerization products such as diphenic acid, 2'-formyl-2-biphenylcarboxylic acid and other macromolecules were dominant products of PHE degradation, suggesting polymerization driving PHE degradation instead of the conventional mineralization process. Toxicity analysis shows that most of the polymerization products had less toxicity than that of PHE. These results indicate that PAA activation was a highly effective remediation method for PAHs contaminated soil, which also provided a novel mechanism for pollutant degradation with the PAA activation process for environmental remediation.

Insights into the pH-dependent mechanism of peracetic acid activation by biochar-supported zero-valent iron/cobalt bimetallic nanoparticles: The shift of reactive sites and the dual role of hydrogen peroxide

The peracetic acid (PAA)-based water purification process is often controlled by the solution pH. Herein, we explored the usage of biochar (BC) supported zero-valent iron/cobalt nanoparticles (Fe/Co@BC) for triggering PAA oxidation of sulfamethazine (SMT), and discovered the PAA activation mechanisms at different pHs. Fe/Co@BC exhibited extraordinary PAA activation efficiency over the pH range of 3.0-8.2, effectively broadening the working pH of the zero-valent iron nanoparticles (NZVI)-PAA process. Specifically, the SMT removal efficiency increased by 8.3 times in Fe/Co@BC-PAA system compared to the NZVI-PAA system at pH 8.2. Besides, the leaching and recycling experiments indicated the improved stability and reusability of the materials. For the mechanism study, the main reactive species was •OH under acidic conditions and R-O•/Fe(IV) under neutral/alkaline conditions. More interestingly, the reactive sites on Fe/Co@BC shifted from Fe species to Co species as pH increased, and the role of H2O2 in this reaction system also shifted from a radical precursor to a radical scavenger with increasing pH. This study highlights the distinct mechanism of PAA activation by bimetallic composites under different pH conditions and provides a new efficient approach for PAA activation to degrade organic contaminants.

Peracetic acid (PAA)-based pretreatment effectively improves medium-chain fatty acids (MCFAs) production from sewage sludge

Peracetic acid (PAA), known for its environmentally friendly properties as a oxidant and bactericide, is gaining prominence in decontamination and disinfection applications. The primary product of PAA oxidation is acetate that can serve as an electron acceptor (EA) for the biosynthesis of medium-chain fatty acids (MCFAs) via chain elongation (CE) reactions. Hence, PAA-based pretreatment is supposed to be beneficial for MCFAs production from anaerobic sludge fermentation, as it could enhance organic matter availability, suppress competing microorganisms and furnish EA by providing acetate. However, such a hypothesis has rarely been proved. Here we reveal that PAA-based pretreatment leads to significant exfoliation of extracellular polymeric substances (EPS) from sludge flocs and disruption of proteinic secondary structures, through inducing highly active free radicals and singlet oxygen. The production of MCFAs increases substantially to 11,265.6 mg COD L-1, while the undesired byproducts, specifically long-chain alcohols (LCAs), decrease to 723.5 mg COD L-1. Microbial activity tests further demonstrate that PAA pretreatment stimulates the CE process, attributed to the up-regulation of functional genes involved in fatty acid biosynthesis pathway. These comprehensive findings provide insights into the effectiveness and mechanisms behind enhanced MCFAs production through PAA-based technology, advancing our understanding of sustainable resource recovery from sewage sludge.

Efficient activation of peracetic acid by cobalt modified nitrogen-doped carbon nanotubes for drugs degradation: Performance and mechanism insight

Peracetic acid (PAA) has garnered significant attention as a novel disinfectant owing to its remarkable oxidative capacity and minimal potential to generate byproducts. In this study, we prepared a novel catalyst, denoted as cobalt modified nitrogen-doped carbon nanotubes (Co@N-CNTs), and evaluated it for PAA activation. Modification with cobalt nanoparticles (∼4.8 nm) changed the morphology and structure of the carbon nanotubes, and greatly improved their ability to activate PAA. Co@N-CNTs/PAA catalytic system shows outstanding catalytic degradation ability of antiviral drugs. Under neutral conditions, with a dosage of 0.05 g/L Co@N-CNT-9.8 and 0.25 mM PAA, the removal efficiency of acyclovir (ACV) reached 98.3% within a mere 10 min. The primary reactive species responsible for effective pollutant degradation were identified as acetylperoxyl radicals (CH3C(O)OO•) and acetyloxyl radicals (CH3C(O)O•). In addition, density functional theory (DFT) proved that Co nanoparticles, as the main catalytic sites, were more likely to adsorb PAA and transfer more electrons than N-doped graphene. This study explored the feasibility of PAA degradation of antiviral drugs in sewage, and provided new insights for the application of heterogeneous catalytic PAA in environmental remediation.

Doped Cu0 and sulfidation induced transition from R-O• to •OH in peracetic acid activation by sulfidated nano zero-valent iron-copper

Peracetic acid (PAA) has emerged as a new effective oxidant for various contaminants degradation through advanced oxidation process (AOP). In this study, sulfidated nano zero-valent iron-copper (S-nZVIC) with low Cu doping and sulfidation was synthesized for PAA activation, resulting in more efficient degradation of sulfamethoxazole (SMX, 20 μM) and other contaminants using a low dose of catalyst (0.05 g/L) and oxidant (100 μM). The characterization results suggested that S-nZVIC presented a more uniform size and distribution with fewer metal oxides, as the agglomeration and oxidation were inhibited. More significantly, doped Cu0 and sulfidation significantly enhanced the generation and contribution of •OH but decreased that of R-O• in S-nZVIC/PAA/SMX system compared with that of nZVIC and S-nZVI, accounting for the relatively high degradation efficiency of 97.7% in S-nZVIC/PAA/SMX system compared with 85.7% and 78.9% in nZVIC/PAA/SMX and S-nZVI/PAA/SMX system, respectively. The mechanisms underlying these changes were that (i) doped Cu° could promote the regeneration of Fe(Ⅱ) for strengthened PAA activation through mediating Fe(Ⅱ)/Fe(Ⅲ) cycle by Cu(Ⅰ)/Cu(Ⅱ) cycle; (ii) S species might consume part of R-O•, resulting in a decreased contribution of R-O• in SMX degradation; (iii) sulfidation increased the electrical conductivity, thus facilitating the electron transfer from S-nZVIC to PAA. Consequently, the dominant reactive oxygen species transited from R-O• to •OH to degrade SMX more efficiently. The degradation pathways, intermediate products and toxicity were further analyzed through density functional theory (DFT) calculations, liquid chromatography-mass spectrometry (LC-MS) and T.E.S.T software analysis, which proved the environmental friendliness of this process. In addition, S-nZVIC exhibited high stability, recyclability and degradation efficiency over a wide pH range (3.0∼9.0). This work provides a new insight into the rational design and modification of nano zero-valent metals for efficient wastewater treatment through adjusting the dominant reactive oxygen species (ROS) into the more active free radicals.

Unlocking the power of activated carbon-mediated peracetic acid activation for efficient antibiotics abatement in groundwater: Coupling the processes of electron transfer, radical production, and adsorption

The activation of peracetic acid (PAA) by activated carbon (AC) is a promising approach for reducing micropollutants in groundwater. However, to harness the PAA/AC system's potential and achieve sustainable and low-impact groundwater remediation, it is crucial to quantify the individual contributions of active species. In this study, we developed a combined degradation kinetic and adsorption mass transfer model to elucidate the roles of free radicals, electron transfer processes (ETP), and adsorption on the degradation of antibiotics by PAA in groundwater. Our findings reveal that ETP predominantly facilitated the activation of PAA by modified activated carbon (AC600), contributing to ∼61% of the overall degradation of sulfamethoxazole (SMX). The carbonyl group (CO) on the surface of AC600 was identified as a probable site for the ETP. Free radicals contributed to ∼39% of the degradation, while adsorption was negligible. Thermodynamic and activation energy analyses indicate that the degradation of SMX within the PAA/AC600 system requires a relatively low energy input (27.66 kJ/mol), which is within the lower range of various heterogeneous Fenton-like reactions, thus making it easily achievable. These novel insights enhance our understanding of the AC600-mediated PAA activation mechanism and lay the groundwork for developing efficient and sustainable technologies for mitigating groundwater pollution. ENVIRONMENTAL IMPLICATION: The antibiotics in groundwater raises alarming environmental concerns. As groundwater serves as a primary source of drinking water for nearly half the global population, the development of eco-friendly technologies for antibiotic-contaminated groundwater remediation becomes imperative. The innovative PAA/AC600 system demonstrates significant efficacy in degrading micropollutants, particularly sulfonamide antibiotics. By integrating degradation kinetics and adsorption mass transfer models, this study sheds light on the intricate mechanisms involved, emphasizing the potential of carbon materials as sustainable tools in the ongoing battle for clean and safe groundwater.

Characterizing Hydroxyl Radical Formation from the Light-Driven Fe(II)-Peracetic Acid Reaction, a Key Process for Aerosol-Cloud Chemistry

The reaction of peracetic acid (PAA) and Fe(II) has recently gained attention due to its utility in wastewater treatment and its role in cloud chemistry. Aerosol-cloud interactions, partly mediated by aqueous hydroxyl radical (OH) chemistry, represent one of the largest uncertainties in the climate system. Ambiguities remain regarding the sources of OH in the cloud droplets. Our research group recently proposed that the dark and light-driven reaction of Fe(II) with peracids may be a key contributor to OH formation, producing a large burst of OH when aerosol particles take up water as they grow to become cloud droplets, in which reactants are consumed within 2 min. In this work, we quantify the OH production from the reaction of Fe(II) and PAA across a range of physical and chemical conditions. We show a strong dependence of OH formation on ultraviolet (UV) wavelength, with maximum OH formation at λ = 304 ± 5 nm, and demonstrate that the OH burst phenomenon is unique to Fe(II) and peracids. Using kinetics modeling and density functional theory calculations, we suggest the reaction proceeds through the formation of an [Fe(II)-(PAA)2(H2O)2] complex, followed by the formation of a Fe(IV) complex, which can also be photoactivated to produce additional OH. Determining the characteristics of OH production from this reaction advances our knowledge of the sources of OH in cloudwater and provides a framework to optimize this reaction for OH output for wastewater treatment purposes.

Effect of interaction between dissolved organic matter and iron/manganese (hydrogen) oxides on the degradation of organic pollutants by in-situ advanced oxidation techniques

Iron and manganese (hydrogen) oxides (IMHOs) exhibit excellent redox capabilities for environmental pollutants and are commonly used in situ chemical oxidation (ISCO) technologies for the degradation of organic pollutants. However, the coexisting dissolved organic matter (DOMs) in surface environments would influence the degradation behavior and fate of organic pollutants in IMHOs-based ISCO. This review has summarized the interactions and mechanisms between DOMs and IMHOs, as well as the properties of DOM-IMHOs complexes. Importantly, the promotion or inhibition impact of DOM was discussed from three perspectives. First, the presence of DOMs may hinder the accessibility of active sites on IMHOs, thus reducing their efficiency in degrading organic pollutants. The formation of compounds between DOMs and IMHOs alters their stability and activity in the degradation process. Second, the presence of DOMs may also affect the generation and transport of active species, thereby influencing the oxidative degradation process of organic pollutants. Third, specific components within DOMs also participate and affect the degradation pathways and rates. A comprehensive understanding of the interaction between DOMs and IMHOs helps to better understand and predict the degradation process of organic pollutants mediated by IMHOs in real environmental conditions and contributes to the further development and application of IMHO-mediated ISCO technology.

Infancy of peracetic acid activation by iron, a new Fenton-based process: A review

The exacerbated global water scarcity and stricter water directives are leading to an increment in the recycled water use, requiring the development of new cost-effective advanced water treatments to provide safe water to the population. In this sense, peracetic acid (PAA, CH3C(O)OOH) is an environmentally friendly disinfectant with the potential to challenge the dominance of chlorine in large wastewater treatment plants in the near future. PAA can be used as an alternative oxidant to H2O2 to carry out the Fenton reaction, and it has recently been proven as more effective than H2O2 towards emerging pollutants degradation at circumneutral pH values and in the presence of anions. PAA activation by homogeneous and heterogeneous iron-based materials generates - besides HO• and FeO2+ - more selective CH3C(O)O• and CH3C(O)OO• radicals, slightly scavenged by typical HO• quenchers (e.g., bicarbonates), which extends PAA use to complex water matrices. This is reflected in an exponential progress of iron-PAA publications during the last few years. Although some reviews of PAA general properties and uses in water treatment were recently published, there is no account on the research and environmental applications of PAA activation by Fe-based materials, in spite of its gratifying progress. In view of these statements, here we provide a holistic review of the types of iron-based PAA activation systems and analyse the diverse iron compounds employed to date (e.g., ferrous and ferric salts, ferrate(VI), spinel ferrites), the use of external ferric reducing/chelating agents (e.g., picolinic acid, l-cysteine, boron) and of UV-visible irradiation systems, analysing the mechanisms involved in each case. Comparison of PAA activation by iron vs. other transition metals (particularly cobalt) is also discussed. This work aims at providing a thorough understanding of the Fe/PAA-based processes, facilitating useful insights into its advantages and limitations, overlooked issues, and prospects, leading to its popularisation and know-how increment.

Unveiling the mechanisms of peracetic acid activation by iron-rich sludge biochar for sulfamethoxazole degradation with wide adaptability

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) has been extensively concerned for the degradation of organic pollutants. In this study, metallic iron-modified sludge biochar (Fe-SBC) was employed to activate PAA for the removal of sulfamethoxazole (SMX). The characterization results indicated that FeO and Fe2O3 were successfully loaded on the surface of the sludge biochar (SBC). Fe-SBC/PAA system achieved 92% SMX removal after 30 min. The pseudo-first-order kinetic reaction constant of the Fe-SBC/PAA system was 7.34 × 10-2 min-1, which was 2.4 times higher than the SBC/PAA system. The degradation of SMX was enhanced with increasing the Fe-SBC dosage and PAA concentration. Apart from Cl-, NO3- and SO42- had a negligible influence on the degradation of SMX. Quenching experiments and electron paramagnetic resonance (EPR) techniques identified the existence of reactive species, of which CH3C(O)OO•, 1O2, and O2•- were dominant reactive species in Fe-SBC/PAA system. The effect of different water matrices on the removal of SMX was investigated. The removal of SMX in tap water and lake water were 79% and 69%, respectively. Four possible pathways for the decay of SMX were presented according to the identification of oxidation products. In addition, following the ecological structure-activity relationship model (ECOSAR) procedure and the germination experiments with lettuce seeds to predict the toxicity of the intermediates. The acute and chronic ecotoxicity of SMX solution was dramatically diminished by processing with Fe-SBC/PAA system. In general, this study offered a prospective strategy for the degradation of organic pollutants.

Recent Advances in Nanoscale Zero-Valent Iron (nZVI)-Based Advanced Oxidation Processes (AOPs): Applications, Mechanisms, and Future Prospects

The fast rise of organic pollution has posed severe health risks to human beings and toxic issues to ecosystems. Proper disposal toward these organic contaminants is significant to maintain a green and sustainable development. Among various techniques for environmental remediation, advanced oxidation processes (AOPs) can non-selectively oxidize and mineralize organic contaminants into CO2, H2O, and inorganic salts using free radicals that are generated from the activation of oxidants, such as persulfate, H2O2, O2, peracetic acid, periodate, percarbonate, etc., while the activation of oxidants using catalysts via Fenton-type reactions is crucial for the production of reactive oxygen species (ROS), i.e., •OH, •SO4-, •O2-, •O3CCH3, •O2CCH3, •IO3, •CO3-, and 1O2. Nanoscale zero-valent iron (nZVI), with a core of Fe0 that performs a sustained activation effect in AOPs by gradually releasing ferrous ions, has been demonstrated as a cost-effective, high reactivity, easy recovery, easy recycling, and environmentally friendly heterogeneous catalyst of AOPs. The combination of nZVI and AOPs, providing an appropriate way for the complete degradation of organic pollutants via indiscriminate oxidation of ROS, is emerging as an important technique for environmental remediation and has received considerable attention in the last decade. The following review comprises a short survey of the most recent reports in the applications of nZVI participating AOPs, their mechanisms, and future prospects. It contains six sections, an introduction into the theme, applications of persulfate, hydrogen peroxide, oxygen, and other oxidants-based AOPs catalyzed with nZVI, and conclusions about the reported research with perspectives for future developments. Elucidation of the applications and mechanisms of nZVI-based AOPs with various oxidants may not only pave the way to more affordable AOP protocols, but may also promote exploration and fabrication of more effective and sustainable nZVI materials applicable in practical applications.

Co-generation of hydroxyl and sulfate radicals via homogeneous and heterogeneous bi-catalysis with the EO-PS-EF tri-coupling system for efficient removal of refractory organic pollutants

Advanced oxidation processes are commonly considered one of the most effective techniques to degrade refractory organic pollutants, but the limitation of a single process usually makes it insufficient to achieve the desired treatment. This work introduces, for the first time, a highly-efficient coupled advanced oxidation process, namely Electro-Oxidation-Persulfate-Electro-Fenton (EO-PS-EF). Leveraging the EO-PS-EF tri-coupling system, diverse contaminants can be highly efficiently removed with the help of reactive hydroxyl and sulfate radicals generated via homogeneous and heterogeneous bi-catalysis, as certified by radical quenching and electron spin resonance. Concerning degradation of tetracycline (TC), the EO-PS-EF system witnessed a fast pseudo-first-order reaction kinetic constant of 2.54 × 10-3 s-1, ten times that of a single EO system and three-to-four times that of a binary system (EO-PS or EO-EF). In addition, critical parameters (e.g., electrolyte, pH and temperature) are systematically investigated. Surprisingly, after 100 repetitive trials TC removal can still reach 100% within 30 min and no apparent morphological changes to electrode materials were observed, demonstrating its long-term stability. Finally, its universality was demonstrated with effective degradation of diverse refractory contaminants (i.e., antibiotics, dyes and pesticides).

Fabrication and optimization of paper chips from calcinated Fe-MOFs for rapid and in situ visual detection of tetracyclines in water environments

Antibiotics such as tetracyclines (TCs) have become a major threat to ecosystem safety and human health, as their abuse has caused the occurrence and proliferation of antibiotic-resistant bacteria and genes. Currently, there is still a lack of convenient in situ methods for the detection and monitoring of TC pollution in actual water systems. This research reports a paper chip based on the complexation of iron-based metal organic frameworks (Fe-MOFs) and TCs for rapid and in situ visual detection of representative oxytetracycline (OTC) pollution in water environments. The optimized complexation sample NH₂-MIL-101(Fe)- 350 obtained by calcination at 350 °C exhibited the highest catalytic activity and was then used for paper chip fabrication by printing and surface modification. Notably, the paper chip demonstrated a detection limit as low as 17.11 nmol L^-1 and good practicability in reclaimed water, aquaculture wastewater, and surface water systems, with OTC recovery rates of 90.6-111.4%. More importantly, the presence of dissolved oxygen (9.13-12.7 mg L^-1), chemical oxygen demand (0.52-12.1 mg L^-1), humic acid (< 10 mg L^-1), Ca²⁺, Cl^-, and HPO₄^2- (< 0.5 mol L^-1) had negligible interference on the detection of TCs by the paper chip. Therefore, this work has developed a promising method for rapid and in situ visual monitoring of TC pollution in actual water environments.

Vitamin C promoted refractory organic contaminant elimination in the zero-valent iron/peracetic acid system: Efficiency, mechanism and effects of various parameters

The conventional zero-valent iron/peracetic acid (ZVI/PAA) system is severely limited owing to the passivation of ZVI and the low recovery of Fe²⁺. In this study, a reducing agent, vitamin C (H₂A), was used for the first time to enhance the ZVI/PAA system as a way to improve its degradation performance. Under optimal conditions, the removal efficiency of the H₂A/ZVI/PAA system was 82.9%, while that of the H₂A/PAA and ZVI/PAA systems were only 19.0% and 25.6%. Free radical quenching and electron paramagnetic experiments (EPR) confirmed that CH₃C(O)O•, •OH and CH₃C(O)OO• were the major active species for acid orange 7 (AO7) degradation with contributions of 9.7%, 75% and 14.4%, respectively. The degradation mechanism was proposed through UV-vis full-wavelength scanning and chemical oxygen demand (COD) experiments. The removal of AO7 was not affected in the presence of Cl^-, SO₄^2- and HCO₃^-, while inhibition occurred with humic acid. ZVI exhibited excellent catalytic properties and stability, and the removal efficiency of AO7 exceeded 70% after three cycles. Additionally, the H₂A/ZVI/PAA system showed good ability to remove AO7 in well water, lake water, river water and reservoir water, and the elimination efficiency of MO, DCF and ACE also exceeded 70%. Overall, this study contributes new cognition for enhancing the ZVI/PAA system to degrade contaminants, which is expected to achieve a cleaner water environment.

Enhanced tetracycline abatement by peracetic acid activation with sulfidation of nanoscale zerovalent iron

Iron-based heterogeneous catalysts due to the environmental friendliness have been widely studied for activation of peracetic acid (PAA) for abatement of organic contaminants in the water and wastewater treatment. However, the slow reduction from Fe(III) to Fe(II) of the iron-based catalysts as the rate-limiting step results in the low PAA activation efficiency. With regard to the excellent electron-donating capability of the reductive sulfur species, sulfidized nanoscale zerovalent iron is proposed for PAA activation (simplified as the S-nZVI/PAA process) and the tetracycline (TC) abatement efficacy and mechanism of this process are elucidated. The optimal sulfidation ratio (S/Fe) of S-nZVI is 0.07, which exhibits superior performance in PAA activation for TC abatement with the efficiency of 80-100% in the pH range of 4.0-10.0. The radical quenching experiments and oxygen release measurements confirm that acetyl(per)oxygen radicals (CH₃C(O)OO•) are the main radical contributing to TC abatement. The influence of sulfidation on the crystalline structure, hydrophobicity, corrosion potential, and electron transfer resistance of S-nZVI is evaluated. The main sulfur species on the S-nZVI surface are identified as ferrous sulfide (FeS) and ferrous disulfide (FeS₂). The analysis by X-ray photoelectron spectroscopy (XPS) and Fe(II) dissolution suggest that the reductive sulfur species can accelerate the conversion from Fe(III) to Fe(II). In summary, the S-nZVI/PAA process exhibits application prospects for the abatement of antibiotics in the aquatic environments.

Simultaneous adsorption of Cd(II) and degradation of OTC by activated biochar with ferrate: Efficiency and mechanism

Biochar-supported zero-valent iron nanocomposites have received much attention due to their application potential in environmental pollution remediation. However, in many occasions, zero-valent iron loading improves the electron transfer efficiency and catalytic oxidation capacity of biochar while blocking the original pore structure of biochar, limiting its application potential. In this study, a zero-valent iron composites with large SSA (865.86 m²/g) was prepared in one step using pre-pyrolysis of biochar powder and K₂FeO₄ grinding for co-pyrolysis. The processes of ZVI generation and SSA expansion during the pyrolysis were investigated. The factors affecting the removal process of Cd and OTC in water by the composites were investigated. The mechanisms of Cd fixation and OTC degradation by the composites were explored by experiments, characterization, and DFT calculations. The OTC degradation pathway was proposed by theoretical predication and LC-MS spectrometry. The results indicate that ion exchange, complexation with oxygen-containing functional groups, electrostatic attraction, and interaction with π-electrons are the main mechanisms of Cd immobilization. The degradation pathways of OTC mainly include dehydroxylation, deamination and dealkylation.

New insights into the degradation of micro-pollutants in the hydroxylamine enhanced Fe(II)/peracetic acid process: Contribution of reactive species and effects of pH

The hydroxylamine-enhanced Fe(II)/peracetic acid (PAA) process is a promising advanced oxidation process (AOP) with the generation of reactive species (RS) including RO•, •OH and Fe(IV). Nevertheless, it is still challenging to identify which RS is the major intermediate oxidant, and the reasons why the optimal condition is pH 4.5 rather than 3.0 are also unclear. Herein, the generation of RS and their contribution to the degradation of three micro-pollutants were explored. The quenching experiments and pseudo first-order kinetic model demonstrated that RO• rather than the other two RS were predominant. Then the overall generation and evolution pathways of RS were depicted. The elevation of pH (3.0-4.5) would accelerate the Fe(II)/Fe(III) redox cycle through the enhanced reduction of Fe(III) by hydroxylamine and induce the conversion of Fe(IV) to RO•, which benefited naproxen degradation. While the adverse Fe(III) precipitation would dominate the reduced degradation performance with the solution pH higher than 4.5. The elevation of PAA and Fe(II) dosages sped up the PAA activation, while excess hydroxylamine could consume the formed RS and exhibited an inhibitory effect. This study helps further understand the role of HA and differentiate the contribution of RS in the emerging PAA-based AOPs.

Graphene shell-encapsulated copper-based nanoparticles (G@Cu-NPs) effectively activate peracetic acid for elimination of sulfamethazine in water under neutral condition

In this study, a graphene shell-encapsulated copper-based nanoparticles (G@Cu-NPs) was prepared and employed for peracetic acid (PAA) activation. The characterization of G@Cu-NPs confirmed that the as-prepared material was composed of Cu⁰ and Cu₂O inside and encapsulated by a graphene shell. Experimental results suggested that the synthesized G@Cu-NPs could activate PAA to generate free radicals for efficiently removing sulfamethazine (SMT) under neutral condition. The formation of graphene shells could strongly facilitated electron transfer from the core to the surface. Radical quenching experiments and electron spin resonance (ESR) analysis confirmed that organic radicals (R-O•) and hydroxyl radicals (•OH) were generated in the G@Cu-NPs/PAA system, and R-O• (including CH₃CO₃• and CH₃CO₂•) was the main contributor to the elimination of SMT. The possible SMT degradation pathways and mechanisms were proposed, and the toxicity of SMT and its intermediates was predicted with the quantitative structure-activity relationship (QSAR) analysis. Besides, the effects of some key parameters, common anions, and humic acid (HA) on the removal of SMT in the G@Cu-NPs/PAA system were also investigated. Finally, the applicability of G@Cu-NPs/PAA system was explored, showing that the G@Cu-NPs/PAA system possessed satisfactory adaptability to treat different water bodies with admirable reusability and stability.

Dual function Mg-doped binary metal ferrite: Photocatalytic degradation of trichlorophenol, bactericidal activity and molecular docking analysis

A new Mg-doped Zn_0.5Ni_0.5Fe₂O₄ (Mg-FZN) photocatalyst was synthesised using a simple co-precipitation-doping technique to develop a dual-function material with the ability to degrade hazardous and refractory pollutants and inactivate bacterial strains. The characterization results revealed that Mg-FZN is an n-type semiconductor with a conduction band of -0.413 eV, an average pore width of 2.32 nm, and a crystal size of 31.45 nm. The photocatalytic activity of Mg-FZN was assessed based on the degradation of 2,4,5-trichlorophenol and achieved 83.8% degradation efficiency under optimised conditions. The radical quenching results revealed that h⁺ significantly contributed to the photodegradation process while ^•OH, and ^•O₂^- played key roles. Additionally, within 60 min, 25 mg of Mg-FZN had bactericidal effects on the bacteria E. coli and S. aureus in both the presence and absence of UV light. Mg-FZN showed H-bonding, electrostatic, and metal-contact interactions with the amino acid residues of the bacterial protein with high binding scores (-4.711 kcal/mol and -5.872 kcal/mol), according to molecular docking.

A comparison of oxidation and re-flocculation behaviors of Fe2+/PAA and Fe2+/H2O2 treatments for enhancing sludge dewatering: A mechanism study

In this study, Fe²⁺ activated-PAA was developed as a novel technology to enhance sludge dewatering. The result showed that the filterability (CST₀/CST) enhanced by 4.20 ± 0.14 times more than the control, and the SRF and bound water content decreased from 4.58 ± 0.07 × 10¹³ m/kg and 2.11 ± 0.28 g/g dry sludge to 9.47 ± 0.05 × 10¹² m/kg and 1.27 ± 0.18 g/g dry sludge, respectively after the sludge was conditioned by 1.20 mM/g VSS Fe²⁺ and 1.20 mM/g VSS PAA. The dewatering performance, physicochemical properties, aggregation behaviors, and EPS fractions of sludge were compared before and after Fe²⁺/PAA and Fe²⁺/H₂O₂ conditionings. The results showed that Fe²⁺/PAA treatment was more competitive in enhancing dewaterability under neutral and alkaline conditions than Fe²⁺/H₂O₂ treatment but slightly weaker under acid conditions. Besides, it was found that the oxidation and re-flocculation behaviors were different in those two enhanced dewatering technologies due to the difference in the generated ROS. R-O was the primary radical in the Fe²⁺/PAA system, while OH was the major one in the Fe²⁺/H₂O₂ system. The mechanism analysis found that the Fe²⁺/PAA process caused harsher disintegration of sludge flocs, meaning more generation of fine particles. However, it exhibited less effect on reducing the energy barrier between sludge particles. Therefore, the Fe²⁺/PAA treated sludge presented weaker aggregation behaviors. The weaker aggregation was unfavorable for sludge dewatering because the weaker aggregated flocs were more easily fragmented, which hampered the consolidation of sludge cakes and removal of bound water. Moreover, loosely-bound extracellular polymeric substances, particularly tightly-bound extracellular polymeric substances, governed the sludge dewaterability.

Oxidation of sulfamethazine by peracetic acid activated with biochar: Reactive oxygen species contribution and toxicity change

Peracetic acid (PAA) as an emerging oxidative has been concerned increasingly due to its high oxidation capacity and low byproducts formation potential. This study was to investigate the oxidation of sulfamethazine (SMZ) by PAA activated with activated biochar (ABC) after thermal modification. The results demonstrated that PAA could be effectively activated by ABC to degrade SMZ in a wide pH range (3-9), which followed the pseudo-second-order kinetics (R² > 0.99). Both non-radicals (singlet oxygen) and free radicals (alkoxy radicals, hydroxyl radicals) existed in the ABC/PAA system, and the degradation of SMZ was dominated by singlet oxygen. Humic acid (HA), SO₄^2- and HCO₃^- slightly inhibited the degradation of SMZ in the ABC/PAA process, while Cl^- and Br^- promoted the degradation of SMZ. The cleavage of S-N, S-C bond, and SO₂ extraction reaction rearrangement was the main oxidation process of SMZ. Meanwhile, the results of the ECOSAR program showed that the acute toxicity of most by-products was significantly reduced compared to SMZ, which revealed the potential applicability of the ABC/PAA process in the treatment of antibiotics pollution and their detoxification.

Mechanistic insights into the efficient activation of peracetic acid by pyrite for the tetracycline abatement

Recently, iron-based heterogenous catalysts have received much attention in the activation of peracetic acid (PAA) for generating reactive radicals to degrade organic pollutants, yet the PAA activation efficiency is compromised by the slow transformation from Fe(III) to Fe(II). Herein, considering the electron-donating ability of reducing sulfur species, a novel advanced oxidation process by combining pyrite and PAA (simplified as pyrite/PAA) for the abatement of tetracycline (TC) is proposed in this study. In the pyrite/PAA process, TC can be completely removed within 30 min under neutral conditions by the synergy of homogeneous and heterogenous Fe(II) species. CH₃C(O)OO• is the main radical generated from the pyrite/PAA process responsible for TC abatement. The excellent activation properties of pyrite can be attributed to the superior electron-donating ability of reducing sulfur species to facilitate the reduction of Fe(III). Meanwhile, the complexation of leached Fe²⁺ with TC favors PAA activation and concomitant TC abatement. In addition, the degradation pathways of TC and the toxicity of the degradation intermediates are analyzed. The pyrite/PAA process shows an excellent TC abatement efficacy in the pH range of 4.0∼10.0. The coexistence of Cl^-, HCO₃^-, and HPO₄^2- exhibits negligible effect on TC abatement, while the HA slightly inhibits the abatement rate of TC. This study highlights the efficient activation of PAA by pyrite and the important role of sulfur in promoting the conversion of Fe(III) to Fe(II) in the pyrite/PAA process.

Mechanisms and product toxicity of activated carbon/peracetic acid for degradation of sulfamethoxazole: implications for groundwater remediation

Carbon-based materials activated peracetic acid (PAA) to repair groundwater is an environmentally friendly and low-cost technology to overcome secondary pollution problems. In this study, thermally modified activated carbon (AC600) was applied to activate PAA to degrade sulfamethoxazole (SMX). And the effect of groundwater pH, chloride ion (Cl^-), bicarbonate (HCO₃^-), sulfate ion (SO₄^2-), and natural organic matter (NOM) on SMX removal by AC600/PAA process was studied in detail. PAA could be effectively activated by AC600. Increasing AC600 dose (10-100mg/L) or PAA dosages (0.065-0.39 mM) generally enhanced the SMX removal, the excellent performance in SMX removal was achieved at 50 mg/L AC600 and 0.26 mM PAA. The removal of SMX was well-described by second-order kinetic, with the rate constant (k_obs) of 10.79 M^-1s^-1, both much greater than the removal constants of PAA alone (0.034 M^-1s^-1) and AC600 alone (1.774 M^-1s^-1). R-O·(CH₃C(O)OO·, CH₃C(O)O·) and electron-transfer process were proved to be responsible for the removal of SMX while HO· and ¹O₂ made little to no contribution to the novel PAA/AC600 system, which differs from typical advanced oxidation processes. The SMX can be removed effectively over a wide pH range (3-9), exhibiting a remarkable pH-tolerant performance. Sulfate ion (SO₄^2-), dissolved oxygen (DO), NOM displayed negligible influence on the SMX removal. Bicarbonate (HCO₃^-) exerted an inhibitory effect on SMX abatement, while chloride ion (Cl^-) promoted the removal of SMX. This showed excellent anti-interference capacity and satisfactory decontamination performance under actual groundwater conditions. Furthermore, the degradation pathways of SMX were proposed, there was no obvious difference in the acute toxicity of the mixed products during the degradation process. It will facilitate further research of metal-free catalyst/PAA system as a new strategy for groundwater in-situ remediation technology.

Effective inactivation of fungal spores by the combined UV/PAA: Synergistic effect and mechanisms

Peracetic acid (PAA) can effectively inactivate fungi in water, while may pose a potential risk of regrowth after disinfection. The inactivation kinetic and mechanism of fungal spores by combined UV and PAA (UV/PAA) was investigated in this study. The results showed that synergistic factor of the inactivation of A. niger and A. flavus was 1.44 and 1.37, which indicated significant synergistic effect of UV/PAA. The k of A. niger and A. flavus was similar at pH 5.0 and 7.0, while decreased 60.00% and 39.13% at pH 9.0 compared with that at pH 7.0. The effect of HA concentration on the inactivation efficiency of fungal spores by UV/PAA was negative, while the effect of PAA concentration was positive. The membrane permeabilized cell of A. niger and A. flavus caused by UV/PAA was 17.0% and 31.7%, which was higher than that caused by PAA and UV alone. The changes of morphology of fungal spores and the leakage of intracellular material indicated that the damage of cell structure caused by UV/PAA system was more serious than that of UV or PAA alone. In addition, the four parts that contributed in UV/PAA system was in the following order: UV > radical > PAA > synergistic effect. The inactivation efficiency of combined UV and chlorine (UV/Cl₂) was higher than that of UV/PAA. Furthermore, the typical order of the inactivation efficiency in different matrix was: phosphate buffer solution > surface water > secondary effluent. The regrowth potential of fungal spores after UV/PAA treatment was significantly lower than that by PAA alone, indicating that UV/PAA could decrease the microbial regrowth potential after PAA disinfection alone.