Benzene oxidation by Fe(III)-catalyzed sodium percarbonate: matrix constituent effects and degradation pathways

Molecular mechanisms underlying sodium percarbonate treatment suppress the recovery and growth of Pseudanabaena sp. in early spring

Increasing frequency and intensity of cyanobacterial blooms in water sources is a growing global issue. Algicides are usually implemented in summer or autumn when blooms break out, however, the blooms will form again when algicide's concentration declines to a certain extent. Preventing the recovery and growth of cyanobacteria in early spring may be conducive to abatement of the blooms in summer or autumn. In this study solid sodium percarbonate (SPC) was used as an algicide to suppress recovery and growth of Pseudanabaena sp., a common odour-producing cyanobacterium, in early spring (12 °C). Results showed that 3.0 and 6.0 mg/L SPC were able to kill most of the algal cells after 12 h treatment at 12 °C, and the residual cells gradually died during the re-cultivation period at 25 °C. As a control, although SPC also caused most of algal cells to lyse at 25 °C, regrowth of cells was found during the period of re-cultivation at 25 °C. Transcriptomic analysis revealed that the dysregulated genes were strongly associated with translation and photosynthesis after SPC treatment. All differentially expressed unigenes related to translation and photosynthesis were down-regulated after SPC oxidation at 12 °C, whereas key genes associated with translation and photosynthesis were upregulated after SPC treatment at 25 °C.

A systematic review on percarbonate-based advanced oxidation processes in wastewater remediation: From theoretical understandings to practical applications

Percarbonate encompasses sodium percarbonate (SPC) and composite in-situ generated peroxymonocarbonate (PMC). SPC emerges as a promising alternative to hydrogen peroxide (H2O2), hailed for its superior transportation safety, stability, cost-effectiveness, and eco-friendliness, thereby becoming a staple in advanced oxidation processes for mitigating water pollution. Yet, scholarly literature scarcely explores the deployment of percarbonate-AOPs in eradicating organic contaminants from aquatic systems. Consequently, this review endeavors to demystify the formation mechanisms and challenges associated with reactive oxygen species (ROS) in percarbonate-AOPs, alongside highlighting directions for future inquiry and development. The genesis of ROS encompasses the in situ chemical oxidation of activated SPC (including iron-based activation, discharge plasma, ozone activation, photon activation, and metal-free materials activation) and composite in situ chemical oxidation via PMC (namely, H2O2/NaHCO3/Na2CO3, peroxymonosulfate/NaHCO3/Na2CO3 systems). Moreover, the ROS generated by percarbonate-AOPs, such as •OH, O2•-, CO3•-, HO2•-, 1O2, and HCO4-, can work individually or synergistically to disintegrate target pollutants. Concurrently, this review systematically addresses conceivable obstacles posing percarbonate-AOPs in real-world application from the angle of environmental conditions (pH, temperature, coexisting substances), and potential ecological toxicity. Considering the outlined challenges and advantages, we posit future research directions to amplify the applicability and efficacy of percarbonate-AOPs in tangible settings. It is anticipated that the insights provided in this review will catalyze the progression of percarbonate-AOPs in water purification endeavors and bridge the existing knowledge void.

Electron confinement promoted the electric double layer effect of BiOI/β-Bi2O3 in photocatalytic water splitting

In the realm of photocatalysis, understanding the interface issues (solid/solid and solid/liquid) inherent in heterojunction at the atomic level is the ultimate for engineering an efficient photocatalyst. Herein, an electrophoretic deposition technique is adopted to synthesize BiOI/β-Bi2O3 heterojunction, exhibiting superior photocatalytic activity and stability in H2 evolution (91.5 μmol g-1 h-1) and H2O2 production (11.3 mg L-1 h-1). Combined with the experimental and computational results, a lower free energy of hydrogen evolution reaction (252.4 meV) has been observed contrast to BiOI and β-Bi2O3 samples. A carrier transfer process of like S-scheme heterojunction is proposed based on density of states (DOS) and carrier distribution calculations. The theoretical calculations illustrate the transition dipole moment, migration and accumulation of carrier in BiOI/β-Bi2O3 heterojunction. Subsequent ab initio molecular dynamics (AIMD) results of solid/liquid interface systems (BiOI/β-Bi2O3/H2O and β-Bi2O3/H2O) unravel the interface H2O (solvent) behaviors. The local aggregation of photo-generated electrons in BiOI/β-Bi2O3/H2O leads to a large potential drop, high proton migration rate and the steady electric double layer (EDL) structure compared to the β-Bi2O3/H2O, which facilitates the occurrence of photocatalytic reactions in solution. In addition to offering new insights into the hydrogen evolution and proton transfer in the EDL model and the association between the heterojunction effect and EDL structure, this work also introduces a novel design strategy for Bi-based heterojunctions.

Hydrodynamic cavitation-enhanced activation of sodium percarbonate for estrogen removal

The present paper investigated the potential of hydrodynamic cavitation (HC) as an effective tool for activating sodium percarbonate (SPC). The method's efficiency was demonstrated by effectively removing estrogens, which are pollutants that have adverse impacts on aquatic ecosystems. The effects of the SPC concentration, temperature of solution, and cavitation time were evaluated. After SPC/HC treatment, the removal of estrogens was monitored by liquid chromatography-tandem mass spectrometry (LC -MS/MS). Already after 4 s of treatment and 24 h of reaction time, more than 97% of estrogens (initial concentration of 300 ng/L) were removed. The effect of post-treatment time is not considered in several papers, even though it seems to be crucial and is discussed here. The results were supported by the values of degradation rate constants, which fit the pseudo-first-order kinetic model. We also verified that HC alone was not effective for estrogen removal under the selected conditions. The sustainability of the SPC/HC system was evaluated based on electric energy per order calculation. The combination of SPC and HC is a promising approach for rapidly degrading micropollutants such as estrogenic compounds without the need for additional technological steps, such as pH or temperature adjustment.

Removal of Microcystis aeruginosa by manganese activated sodium percarbonate: Performance and role of the in-situ formed MnO2

Previous studies have found that pre-oxidation of manganese salts such as potassium permanganate and potassium manganate can remove algae in water, while existing problems such as excessive oxidation and appearance of chromaticity. In this study, our objective was to induce a Fenton-like reaction by activating sodium percarbonate (SPC) with divalent manganese (Mn(II)) to pre-oxidize algae-contaminated water. The optimal dosage of Mn(II)/SPC was determined by assessing the zeta potential of the algae and the residual Mn(II) in the solution. Moreover, we conducted a characterization of the cells post-reaction and assessed the levels of dissolved organic carbon (DOC). The disinfection by-products (DBPs) (sodium hypochlorite disinfection)of the algae-containing water subsequent to Mn(II)/SPC treatment were measured. Experiments show that Mn(II)/SPC pre-oxidation at optimal dosage acquired 88% removal of algae and less damage to the cell membrane. Moreover, the Mn(II) acted not only as a catalyst but also formed MnO2 which adsorbed onto the cell surface and facilitated sedimentation. Furthermore, this technology exhibits the capability to effectively manage algal organic matters present in water, thereby mitigating the formation of nitrogen-containing DBPs. These results highlight the potential of Mn(II)/SPC treatment for treating water contaminated with algae, thus ensuring the safety and quality of water resources.

Chalcopyrite as an oxidants activator for organic pollutant remediation: A review of mechanisms, parameters, and future perspectives

Advanced oxidation processes (AOPs) based on oxidants have attracted attention for the degradation of organic pollutants. The combination of chalcopyrite with oxidants such as persulfate, peroxide, percarbonate, and others shows promise as a system due to its ability to activate through various pathways, leading to the formation of numerous radical and non-radical species. In this review, the generation of sulfate radical (SR) and hydroxyl radical (HR) in AOPs were summarized. The significance of chalcopyrite in various approaches including Fenton, photo-Fenton, and photo/Fenton-like methods, as well as its involvement in electrochemical Fenton-based processes was discussed. The stability and reusability, toxicity, catalyst mechanism, and effects of operational parameters (pH, catalyst dosage, and oxidant concentration) are evaluated in detail. The review also discusses the role of Fe2+/3+, Cu1+/2+, S2- and Sn2- present in CuFeS2 in the generation of free radicals. Finally, guidelines for future research are presented in terms of future perspectives.

Hydroxyl radical dominated ibuprofen degradation by UV/percarbonate process: Response surface methodology optimization, toxicity, and cost evaluation

Ibuprofen (IBP) is a typical nonsteroidal anti-inflammatory drug with a wide range of applications, large dosages, and environmental durability. Therefore, ultraviolet-activated sodium percarbonate (UV/SPC) technology was developed for IBP degradation. The results showed that IBP could be efficiently removed using UV/SPC. The IBP degradation was enhanced with prolonged UV irradiation time, with the decreasing IBP concentration and the increasing SPC dosage. The UV/SPC degradation of IBP was highly adaptable to pH ranging from 4.05 to 8.03. The degradation rate of IBP reached 100% within 30 min. The optimal experimental conditions for IBP degradation were further optimized using response surface methodology. IBP degradation rate reached 97.3% under the optimal experimental conditions: 5 μM of IBP, 40 μM of SPC, 7.60 pH, and UV irradiation for 20 min. Humic acid, fulvic acid, inorganic anions, and natural water matrix inhibited the IBP degradation to varying degrees. Scavenging experiments of reactive oxygen species indicated that hydroxyl radical played a major role in the UV/SPC degradation of IBP, while carbonate radical played a minor role. Six IBP degradation intermediates were detected, and hydroxylation and decarboxylation were proposed as the primary degradation pathways. An acute toxicity test, based on the inhibition of luminescence in Vibrio fischeri, indicated that the toxicity of IBP during UV/SPC degradation decreased by 11%. An electrical energy per order value of 3.57 kWh m^-3 indicated that the UV/SPC process was cost-effective in IBP decomposition. These results provide new insights into the degradation performance and mechanisms of the UV/SPC process, which can potentially be used for practical water treatment in the future.

The performance and mechanism of iron-mediated chemical oxidation: Advances in hydrogen peroxide, persulfate and percarbonate oxidation

Many studies have successfully built iron-mediated materials to activate or catalyze Fenton-like reactions, with applications in water and wastewater treatment being investigated. However, the developed materials are rarely compared with each other regarding their performance of organic contaminant removal. In this review, the recent advances of Fenton-like processes in homogeneous and heterogeneous ways are summarized, especially the performance and mechanism of activators including ferrous iron, zero valent iron, iron oxides, iron-loaded carbon, zeolite, and metal organic framework materials. Also, this work mainly compares three O-O bond containing oxidants including hydrogen dioxide, persulfate, and percarbonate, which are environmental-friendly oxidants and feasible for in-situ chemical oxidation. The influence of reaction conditions, catalyst properties and benefits are analyzed and compared. In addition, the challenges and strategies of these oxidants in applications and the major mechanisms of the oxidation process have been discussed. This work can help understand the mechanistic insights of variable Fenton-like reactions, the role of emerging iron-based materials, and provide guidance for choosing appropriate technologies when facing real-world water and wastewater applications.

Mechanism and security of UV driven sodium percarbonate for sulfamethoxazole degradation using DFT and metabolomic analysis

Recently, sodium percarbonate (SPC) as a solid substitute for H₂O₂ has aroused extensive attention in advanced oxidation processes. In current work, the degradation kinetics and mechanisms of antibiotic sulfamethoxazole (SMX) by ultraviolet (UV) driven SPC system were explored. The removal efficiency of SMX was enhanced as the increasing dosage of SPC. Moreover, hydroxyl radical (•OH), carbonate radical (CO₃^•-) and superoxide radical (O₂^•-) were verified to be presented by scavenger experiments and •OH, CO₃^•- exhibited a significant role in SMX degradation. Reactions mediated by these radicals were affected by anions and natural organic matters, implying that an incomplete mineralization of SMX would be ubiquitous. The screening four intermediates and transformation patterns of SMX were verified by DFT analysis. Metabolomic analysis demonstrated that a decreasing negative effect in E. coli after 24 h exposure was induced by intermediates products. In detail, SMX interfered in some key functional metabolic pathways including carbohydrate metabolism, pentose and glucuronate metabolism, nucleotide metabolism, arginine and proline metabolism, sphingolipid metabolism, which were mitigated after UV/SPC oxidation treatment, suggesting a declining environmental risk of SMX. This work provided new insights into biological impacts of SMX and its transformation products and vital guidance for SMX pollution control using UV/SPC technology.

New insight into the activation mechanism of hydrogen peroxide by greigite (Fe3S4) for benzene removal: The combined action of dissolved and surface bounded ferrous iron

Iron sulfides have attracted growing concern in heterogeneous Fenton reaction. However, the structure of iron sulfides is different from that of iron oxides and how the structures affect the activation property of hydrogen peroxide (H₂O₂) remains unclear. This study investigated benzene removal through the activation of H₂O₂ by the synthesized magnetite (Fe₃O₄) and greigite (Fe₃S₄). The structures of Fe₃O₄ and Fe₃S₄ were characterized by XRD and EPR, the electron transfer properties of Fe₃O₄ and Fe₃S₄ were analyzed by electrochemical workstation, XPS and DFT. It is revealed that the effective benzene removal rate of 88.86％ in the Fe₃S₄/H₂O₂ was achieved, which compared to 15.58％ obtainable from the Fe₃O₄/H₂O₂, with the apparent rate constant in the Fe₃S₄/H₂O₂ being approximately 65 times over that in the Fe₃O₄/H₂O₂. The better H₂O₂ activation by Fe₃S₄ was attributed to the significant roles of S (-II) and S vacancies in regulating the dissolution of ferrous iron ions, thus generating abundant free •OH radical. In addition, surface bounded ferrous iron of Fe₃S₄ could transfer more electrons to H₂O₂ and O₂ to generate more surface bounded •OH and •O₂^-. This study revealed the combined action of dissolved and surface bounded ferrous iron of greigite on H₂O₂ activation, and provides an efficient heterogeneous H₂O₂ activator for the remediation of organic contaminants in groundwater.

Advanced oxidation processes for the removal of mono and polycyclic aromatic hydrocarbons - A review

Aromatic hydrocarbons (AHs) are toxic environmental contaminants presented in most of the environmental matrices. Advanced oxidation processes (AOPs) for the removal of AHs in the account of complete mineralization from various environmental matrices have been reviewed in this paper. An in-depth discussion on various AOPs for mono (BTEX) and polyaromatic hydrocarbons (PAHs) and their derivatives is presented. Most of the AOPs were effective in the removal of AHs from the aquatic environment. A comparative study on the degradation of various AHs revealed that the oxidation of the AHs is strongly dependent on the number of aromatic rings and the functional groups attached to the ring. The formation of halogenated and nitrated derivatives of AHs in the real contaminated water containing chloride, nitrite, and nitrate ions seems to be a challenge in using the AOPs in real systems. The phenolic compounds, quinone, alcohols, and aliphatic acids are the important byproducts formed during the oxidation of AHs, initiated by the attack of reactive oxygen species (ROS) on their electron-rich center. In conclusion, AOPs are the adaptable method for the removal of AHs from different environmental matrices. The persulfate-based AOPs were applied in the soil phase removal as an in situ chemical oxidation of AHs. Moreover, the combination of AOPs will be a conclusive solution to avoid or minimize unexpected or other toxic intermediate products and to obtain rapid oxidation of AHs.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), carbonate radicals (CO₃^•-), and peroxymonocarbonate (HCO₄^-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Peracetic acid activation by mechanochemically sulfidated zero valent iron for micropollutants degradation: Enhancement mechanism and strategy for extending applicability

In this study, mechanically sulfidated microscale zero valent iron (S-ZVI) was found to effectively activate the peracetic acid (PAA) with a result of almost complete degradation of six micropollutants within 10 min under neutral conditions, and > 95% sulfamethoxazole (SMX) removal after six cycles. Reactive oxidized species (ROS) including HO•, carbon-centered radicals, and Fe(IV) were generated in the S-ZVI/PAA system, while HO• was the main contributor towards micropollutants degradation. This study clearly revealed that enhancement of the electron donating ability of ZVI by the formed conductive iron sulfides was crucial for promoted Fe(II) generation and subsequent PAA activation over several cycles, rather than the ability of sulfides to reduce Fe(III) for Fe(II) regeneration as reported previously. Interestingly, it's discovered that co-existence of Fe(III) would dramatically improve the contaminants removal efficiency of the S-ZVI/PAA system; transform the surfaced Fe(II) dominated ROS generation process to aqueous Fe(II) one; enhance the tolerance of the proposed system to water matrix. The promoting effect of predosed Fe(III) on PAA activation by S-ZVI should be mainly associated with: the greater ability of Fe(III) than H₂O to accept electron from Fe⁰ for obtaining more active sites; slower Fe⁰ consumption and solid sulfur species release for elevated electron utilization efficiency and PAA activation. Considering the convenient and cost-effective access of Fe(III), the decrease of acute toxicity of treated SMX, excellent stability and good removal of various micropollutants fully demonstrate the superiority of S-ZVI/PAA system for practical application.

Recent progress on in-situ chemical oxidation for the remediation of petroleum contaminated soil and groundwater

Accidental oil leaks and spills can often result in severe soil and groundwater pollution. In situ chemical oxidation (ISCO) is a powerful and efficient remediation technology. In this review, the applications and recent advances of three commonly applied in-situ oxidants (hydrogen peroxide, persulfate, and permanganate), and the gap in remediation efficiency between lab-scale and field-scale applications is critically assessed. Feasible improvements for these measures, especially solutions for the 'rebound effect', are discussed. The removal efficiencies reported in 108 research articles related to petroleum-contaminated soil and groundwater were analyzed. The average remediation efficiency of groundwater (82.7%) by the three oxidants was higher than that of soil (65.8%). A number of factors, including non-aqueous phase liquids, adsorption effect, the aging process of contaminants, low-permeability zones, and vapor migration resulted in a decrease in the remediation efficiency and caused the residual contaminants to rebound from 19.1% of the original content to 57.7%. However, the average remediation efficiency of ISCO can be increased from 40.9% to 75.5% when combined with other techniques. In the future, improving the utilization efficiency of reactive species and enhancing the contact efficiency between oxidants and petroleum contaminants will be worthy of attention. Multi-technical combinations, such as the ISCO coupled with phase-transfer, viscosity control, controlled release or natural attenuation, can be effective methods to solve the rebound problem.

Remediation of PAHs contaminated industrial soils by hypochlorous acid: performance and mechanisms

Polycyclic aromatic hydrocarbons (PAHs) mainly originate from incomplete combustion of organic substances and are carcinogenic, mutagenic and teratogenetic, posing a high risk to the ecosystem and human health. The remediation of soils contaminated with PAHs has aroused wide public concern. In this study, hypochlorous acid (HOCl) was applied to realize PAHs removal from industrial contaminated soil with an extremely high degradation efficiency of 93.33% when the initial chlorine concentration was 5000 mg L⁻¹. The degradation behavior of PAHs by HOCl oxidation was investigated in detail. Parameters including chlorine dosage, pH and temperature that had effects on the degradation process were evaluated systematically. The removal of PAHs was followed well with the pseudo-first-order kinetic model. It is found that HOCl and OH˙ were major contributors to the degradation products of chlorinated and oxygenated PAHs. This research provided an easy-operating and energy-saving way to realize the remediation of PAHs contaminated industrial soil practically with high efficiency.

An extremely high degradation efficiency of 93.3% was realized for PAHs in contaminated industrial soil by HOCl oxidation.

Insights into naphthalene degradation in aqueous solution and soil slurry medium: Performance and mechanisms

The performance of naphthalene (NAP) degradation in peroxodisulfate (PDS) and peroxymonosulfate (PMS) oxidation systems by nano zero valent iron (nZVI) combined with citric acid (CA) activation was reported in aqueous solution and soil slurry medium. The results in aqueous solution tests indicated that 98.1% and 98.9% of NAP were individually degraded in PDS/nZVI/CA and PMS/nZVI/CA systems within 2 h when the dosages of PDS, PMS, nZVI and CA were 1.0 mM, 0.1 mM, 0.2 mM and 0.1 mM, respectively. The consequences of scavenging tests and electron paramagnetic resonance detection demonstrated that HO• and SO₄^-• were the key factors on NAP removal. The presence of surfactants could consume ROSs and inhibit NAP removal. In addition, GC-MS was applied for the determination of NAP degradation intermediates, and three possible NAP degradation pathways were proposed in PDS oxidation process and two pathways in PMS oxidation process, respectively. The results in soil slurry medium showed that the presence of CA could promote the dissolution of soil minerals and the desorption of NAP from soil medium. 93.5% and 96.8% degradation of NAP were obtained in PDS/nZVI/CA and PMS/nZVI/CA systems within 24 h. Besides, the existence of DOM in soil could promote Fe(II)/Fe(III) cycle and NAP degradation through electron transfer. Based on the NAP degradation performance in the actual groundwater and soil medium, the above findings could provide basis and strong support for the potential application of PDS/nZVI/CA and PMS/nZVI/CA systems in the remediation of NAP contaminated sites.

Toward Selective Oxidation of Contaminants in Aqueous Systems

The presence of diverse pollutants in water has been threating human health and aquatic ecosystems on a global scale. For more than a century, chemical oxidation using strongly oxidizing species was one of the most effective technologies to destruct pollutants and to ensure a safe and clean water supply. However, the removal of increasing amount of pollutants with higher structural complexity, especially the emerging micropollutants with trace concentrations in the complicated water matrix, requires excessive dosage of oxidant and/or energy input, resulting in a low cost-effectiveness and possible secondary pollution. Consequently, it is of practical significance but scientifically challenging to achieve selective oxidation of pollutants of interest for water decontamination. Currently, there are a variety of examples concerning selective oxidation of pollutants in aqueous systems. However, a systematic understanding of the relationship between the origin of selectivity and its applicable water treatment scenarios, as well as the rational design of catalyst for selective catalytic oxidation, is still lacking. In this critical review, we summarize the state-of-the-art selective oxidation strategies in water decontamination and probe the origins of selectivity, that is, the selectivity resulting from the reactivity of either oxidants or target pollutants, the selectivity arising from the accessibility of pollutants to oxidants via adsorption and size exclusion, as well as the selectivity due to the interfacial electron transfer process and enzymatic oxidation. Finally, the challenges and perspectives are briefly outlined to stimulate future discussion and interest on selective oxidation for water decontamination, particularly toward application in real scenarios.

Coupling sodium percarbonate (SPC) oxidation and coagulation for membrane fouling mitigation in algae-laden water treatment

To alleviate algal fouling in membrane water treatment processes, conventional technologies such as coagulation with poly aluminum chloride (PACl) has been widely adopted by many drinking water treatment plants. However, coagulation alone exhibited relatively weak removal effect for algal pollutants, and the coagulant residues due to the excess dosage also raised concerns. Thus, a novel process of coupling sodium percarbonate (SPC) oxidation and PACl coagulation was proposed, integrated with membrane filtration for algae-laden water treatment. The dosages of PACl and SPC were optimized, and the SPC dosing strategies were systematically compared. The changes in the characteristics of algal pollutants were investigated, and the results revealed that the resistance of algal foulants to aggregation was decreased, and the particle size of algal foulants became larger. With the synergism of coagulation and oxidation, the degradation of fluorescent organics was strengthened, and macromolecular biopolymers were decomposed into low molecular weight organics. The fouling control efficiency was further explored, and the results indicated that both irreversible and reversible fouling were effectively controlled, among which PACl/SPC (simultaneous treatment) performed best with the irreversible fouling reduced by 90.5%, while the efficiency of SPC-PACl (SPC followed by PACl) was relatively lower (57.3%). The fouling mechanism was altered by slowing the formation of cake filtration, and the reduction of algal cells played a more important role for the fouling alleviation. The interface properties of contaminated membranes (i.e., functional groups, images, and micromorphology) were characterized, and the efficiency of the proposed strategy was further verified. The proposed strategy exhibits great application values for improving membrane performance during algae-laden water treatment.

A review on percarbonate-based advanced oxidation processes for remediation of organic compounds in water

Sodium percarbonate (SPC) is considered a potential alternative to liquid hydrogen peroxide (H₂O₂) in organic compounds contaminated water/soil remediation due to its regularly, transportable, economical, and eco-friendly features. The solid state of SPC makes it more suitable to remediate actual soil and water with a milder H₂O₂ release rate. Apart from its good oxidative capacity, alkaline SPC can simultaneously remediate acidized solution and soil to the neutral condition. Conventionally, percarbonate-based advanced oxidation process (P-AOPs) system proceed through the catalysis under ultraviolet ray, transition metal ions (i.e., Fe²⁺, Fe³⁺, and V⁴⁺), and nanoscale zero-valent metals (iron, zinc, copper, and nickel). The hydroxyl radical (^•OH), superoxide radical (^•O₂^-), and carbonate radical anion (^•CO₃^-) generated from sodium percarbonate could attack the organic pollutant structure. In this review, we present the advances of P-AOPs in heterogeneous and homogeneous catalytic processes through a wide range of activation methods. This review aims to give an overview of the catalysis and application of P-AOPs for emerging contaminants degradation and act as a guideline of the field advances. Various activation methods of percarbonate are summarized, and the influence factors in the solution matrix such as pH, anions, and cations are thoroughly discussed. Moreover, this review helps to clarify the advantages and shortcomings of P-AOPs in current scientific progress and guide the future practical direction of P-AOPs in sustainable carbon catalysis and green chemistry.

Roles of hydroxyl and carbonate radicals in bisphenol a degradation via a nanoscale zero-valent iron/percarbonate system: influencing factors and mechanisms

In this work, nanoscale-zero-valent iron (nZVI) was applied to activate sodium percarbonate (SPC) to eliminate bisphenol A (BPA), which poses a risk to ecological and human health as a typical endocrine disruptor. The influence of nZVI loading, SPC dosing, initial pH, and the presence of inorganic anions (including Cl-, HPO4 2-, NO3 - and NO2 -) and humic acid on BPA removal by the nZVI/SPC system were investigated. Based on the scavenger test results, ˙OH and CO3˙- participated in the degradation of BPA, and ˙OH was illustrated to be the dominant radical. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggested that surface iron oxide generation, electron transfer and Fe2+ release were the main processes of the SPC activation by nZVI. Moreover, BPA transformation products were detected by LC-MS allowing the proposal of a possible degradation pathway of BPA. Along with the degradation of the parent compound BPA, the total organic carbon (TOC) gradually decreased, while the bio-toxicity increased at the initial stage of the reaction (0-3 min) and then decreased to a lower level rapidly at 20 min. Overall, this study evidenced the feasibility of the nZVI/SPC system to efficiently degrade BPA, broadening the applications of nZVI in wastewater treatment.

The performance of chlorobenzene degradation in groundwater: comparison of hydrogen peroxide, nanoscale calcium peroxide and sodium percarbonate activated with ferrous iron

The chlorobenzene (CB) degradation performances by various oxidants, including hydrogen peroxide (H₂O₂), nanoscale calcium peroxide (nCaO₂) and sodium percarbonate (SPC), activated with ferrous iron (Fe(II)) were investigated and thoroughly compared. The results showed that all tested systems had strong abilities to degrade CB. The CB removal rate increased with increasing dosages of oxidants or Fe(II) because the generation of reactive oxygen species could be promoted with the chemical dosages' increase. Response surface and contour plots showed that CB could achieve a better removal performance at the same H₂O₂ and Fe(II) molar content, but the Fe(II) dosage was higher than that of oxidants in the nCaO₂ and SPC systems. The optimal molar ratios of H₂O₂/Fe(II)/CB, nCaO₂/Fe(II)/CB and SPC /Fe(II)/CB were 5.2/7.6/1, 8/8/1, and 4.5/8/1, respectively, in which 98.1%, 98%, and 96.4% CB removals could be obtained in 30 min reaction. The optimal pH condition was around 3, while CB removal rates were less than 20% in all three systems when the initial pH was adjusted to 9. The oxidative hydroxyl radicals (HO•) and singlet oxygen (¹O₂) had been detected by the electron paramagnetic resonance test. Based upon the results of liquid chromatograph-mass spectrometer analysis, the pathways of CB degradation were proposed, in which ¹O₂ roles were elaborated innovatively in the CB degradation mechanism. The CB degradation performance was significantly affected in actual groundwater, while increasing the molar ratio of oxidant/Fe(II)/CB was an effective way to overcome the adverse effects caused by the complex of actual groundwater matrix.

Trichloroethylene degradation by PVA-coated calcium peroxide nanoparticles in Fe(II)-based catalytic systems: enhanced performance by citric acid and nanoscale iron sulfide

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative study was performed with optimum usages of chemical reagents in both PVA@nCP/Fe(II)/CA and PVA@nCP/Fe(II)/nFeS systems. Further, the probe compounds tests and electron paramagnetic resonance (EPR) analysis confirmed the generation of reactive oxygen species. The scavenging experiments elucidated the dominant role of HO• to TCE degradation, particularly in PVA@nCP/Fe(II)/nFeS system. Both CA and nFeS strengthened PVA@nCP/Fe(II) system, but displayed completely different mechanisms in the enhancement of active radicals generation; hence, their different contribution to TCE degradation. The acidic environment was favorable for TCE degradation, and a high concentration of HCO₃^- inhibited TCE removal in both systems. Conclusively, compared to PVA@nCP/Fe(II)/nFeS system, PVA@nCP/Fe(II)/CA system resulted in encouraging TCE degradation outcomes in actual groundwater, showing great potential for prolonged benefits in the remediation of TCE polluted groundwater. Graphical abstract.

Ferrous-activated sodium percarbonate pre-oxidation for membrane fouling control during ultrafiltration of algae-laden water

Membrane technology has been shown to be promising for the treatment of algae-laden water, but membrane fouling is still an obstacle influencing the purification efficiency and effluent quality. To mitigate ultrafiltration membrane fouling during Microcystis aeruginosa-laden water treatment, a strategy of sodium percarbonate pre-oxidation activated with ferrous ion (Fe²⁺/SPC) was put forward in this study. Due to the synergistic effect of Fe²⁺ and SPC, this process was significantly more efficient with the terminal specific flux increased from 0.097 to 0.397, and the reversible fouling resistance reduced by approximately 80%. It was also found that subsequent sedimentation followed by Fe²⁺/SPC could further improve the fouling control efficiency. The model fitting results indicated that Fe²⁺/SPC pre-oxidation delayed the transition from standard blocking to cake filtration. Extracellular organic matter and algal cells were extracted from algal foulants to explore the contribution of each component, and the fouling control efficiencies were systematically studied. The characteristics of the algal foulants were determined with fluorescence excitation-emission matrix spectrum, and the results suggested that macromolecular proteinaceous substances were more efficiently removed by Fe²⁺/SPC, in comparison with humic-like matters. The alleviation of membrane fouling was also verified by the characterization methods of scanning electron microscopy and attenuated total reflection-Fourier infrared spectroscopy. Overall, the proposed strategy of Fe²⁺/SPC has an application prospect for membrane fouling control in algal-laden water treatment.

Activation of percarbonate by water treatment sludge-derived biochar for the remediation of PAH-contaminated sediments

Sludge from a groundwater treatment plant was used to prepare biochar by pyrolysis. The Fe-Mn rich biochar was used to activate percarbonate for the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated aquatic sediments. Results showed that the sludge-derived biochar (SBC) produced at a pyrolysis temperature of 700 °C was the most effective in activating percarbonate, which exhibited significant oxidative removal of PAHs. PAHs degradation took place via a Fenton-like oxidation manners, contributed from the Fe³⁺/Fe²⁺ and Mn³⁺/Mn²⁺ redox pairs, and achieved the highest degradation efficiency of 87% at pH₀ 6.0. Reactions between oxygenated functional groups of biochar and H₂O₂ generated of O₂^•- and HO• radicals in abundance under neutral and alkaline pH was responsible for the catalytic degradation of PAHs. Our results provided new insights into the environmental applications of SBC for the green sustainable remediation of organics-contaminated sediments and aided in reduction of associated environmental and health risk.

Oxidative degradation and mineralization of bentazone from water

Bentazone degradation efficiency and mineralization in water solutions using chlorine dioxide treatment were evaluated. Double distilled water and a river water sample spiked with bentazone were studied and compared after chlorine dioxide treatment. Degradation efficiency was determined using high-performance liquid chromatography (HPLC). Daphnia magna toxicity testing and total organic carbon (TOC) analysis were used to ascertain the toxicity of the degraded solutions and mineralization degree. Bentazone degradation products were identified using gas chromatography with a triple quadrupole mass detector (GC-MS-MS). A simple mechanistic scheme for oxidative degradation of bentazone was proposed based on the degradation products that were identified. Decrease in D. magna mortality, high degradation efficiency and partial bentazone mineralization were achieved by waters containing bentazone degradation products, which indicate the formation of less toxic compounds than the parent bentazone and effective removal of bentazone from the waters. Bentazone degraded into four main degradation products. Humic acid from Sava River water influenced bentazone degradation, resulting in a lower degradation efficiency in this matrix (about 10% lower than in distilled water). Chlorine dioxide treatment of water to degrade bentazone is efficient and offers a novel approach in the development of new technology for removal of this herbicide from contaminated water.

Modeling and optimization of imidacloprid degradation by catalytic percarbonate oxidation using artificial neural network and Box-Behnken experimental design

Due to its toxicity and persistence, pesticide pollution poses a serious threat to human health and the environment. Imidacloprid or IMD is an archetypal neonicotinoid insecticide commonly used to protect a variety of crops worldwide. The present study examines the applicability of two numerical tools -- artificial neural network (ANN) and response surface methodology - Box Behnken design (RSM-BBD) -- to model and optimize oxidative IMD degradation by sodium percarbonate (SPC). The influences of SPC dose, Fe²⁺ catalyst dosage, and solution pH on IMD removal were evaluated. An ANN composed of an input layer with three neurons, a hidden layer with eight optimum neurons, and an output layer with one neuron was developed to map the complex non-linear process at different levels. Seventeen designed runs of different experimental conditions were derived from RSM-BBD. These experimental conditions and their response values showed to be best fitted in a reduced cubic model equation. Sensitivity analyses revealed the relative importance of the various components: Fe²⁺ (40.4%) > pH (31.1%) > SPC dose (28.5%). The two model were highly predictive with overall coefficients of determination and root-mean-square errors of 0.9983 and 0.31 for ANN, while 0.9996 and 0.20 for RSM-BBD. Overall, the present study established ANN and RSM-BBD as valuable and effective tools for catalytic SPC oxidation of IMD contaminants. SPC is a cleaner alternative to other oxidants for pesticide degradation as it is non-toxic, safe to handle, and produces by-products that inherently exist in the natural water matrix.

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

Chlorine dioxide (ClO₂) degradation of the organophosphorus pesticides azamethiphos (AZA) and dimethoate (DM) (10 mg/L) in deionized water and in Sava River water was investigated for the first time. Pesticide degradation was studied in terms of ClO₂ level (5 and 10 mg/L), degradation duration (0.5, 1, 2, 3, 6, and 24 h), pH (3.00, 7.00, and 9.00), and under light/dark conditions in deionized water. Degradation was monitored using high-performance liquid chromatography. Gas chromatography coupled with triple quadrupole mass detector was used to identify degradation products of pesticides. Total organic carbon was measured to determine the extent of mineralization after pesticide degradation. Real river water was used under recommended conditions to study the influence of organic matter on pesticide degradation. High degradation efficiency (88-100% for AZA and 85-98% for DM) was achieved in deionized water under various conditions, proving the flexibility of ClO₂ degradation for the examined organophosphorus pesticides. In Sava River water, however, extended treatment duration achieved lower degradation efficiency, so ClO₂ oxidized both the pesticides and dissolved organic matter in parallel. After degradation, AZA produced four identified products (6-chlorooxazolo[4,5-b]pyridin-2(3H)-one; O,O,S-trimethyl phosphorothioate; 6-chloro-3-(hydroxymethyl)oxazolo[4,5-b]pyridin-2(3H)-one; O,O-dimethyl S-hydrogen phosphorothioate) and DM produced three (O,O-dimethyl S-(2-(methylamino)-2-oxoethyl) phosphorothioate; e.g., omethoate; S-(2-(methylamino)-2-oxoethyl) O,O-dihydrogen phosphorothioate; O,O,S-trimethyl phosphorodithioate). Simple pesticide degradation mechanisms were deduced. Daphnia magna toxicity tests showed degradation products were less toxic than parent compounds. These results contribute to our understanding of the multiple influences that organophosphorus pesticides and their degradation products have on environmental ecosystems and to improving pesticide removal processes from water.

The performance of nCaO2 for BTEX removal: Hydroxyl radical generation pattern and the influences of co-existing environmental pollutants

In this study, nano-CaO₂ (nCaO₂ ) was successfully synthesized and constituted the nCaO₂ /Fe(II) system applying to remediate BTEX, which are typical mixed pollutants in contaminated groundwater. The particle size of the synthesized nCaO₂ was 108.91 nm, and it displayed better BTEX remediation performance than that of commercial CaO₂ . The innovative generation pattern of hydroxyl radicals ( HO · ) in the nCaO₂ /Fe(II) system has been investigated using benzoic acid as the HO · probe, and the proper molar ratio of nCaO₂ /Fe(II) was optimized as 1/1. Over 90% of BTEX was removed in 180 min with the nCaO₂ /Fe(II)/BTEX molar ratio of 40/40/1. Further experiments evaluated the influence of co-existence of mixed pollutants chlorinated hydrocarbon compounds (CHCs) or surfactant constituents on BTEX remediation performance. The experimental results suggested that CHCs have limited influence on BTEX removal rate and surfactants have negative effects on BTEX remediation performance in the experimental conditions. In conclusion, the findings in this study could give some inspirations to apply the nCaO₂ /Fe(II) process in remediating co-existing pollutants in contaminated groundwater. PRACTITIONER POINTS: nCaO₂ /Fe(II) system applied to remediate mixed contaminants. HO · generation pattern of the nCaO₂ /Fe(II) system has been investigated. The influence of chloride hydrocarbon compounds have been studied. The effects of surfactants were evaluated.

Degradation and transformation of bisphenol A in UV/Sodium percarbonate: Dual role of carbonate radical anion

The bicarbonate and carbonate ions (HCO₃^- &CO₃^2-) will consume hydroxyl radical (HO^•) to generate carbonate radical anion (CO₃^•-) in hydroxyl radical based advanced oxidation processes (HO^•-AOPs) resulting in reduced oxidation efficiencies of the systems. However, despite the HO^• quenching effect of carbonate species, the contribution of CO₃^•- to the degradation of bisphenol A (BPA) was observed in UV/sodium percarbonate (UV/SPC). In order to study the performance of UV/SPC for BPA degradation and the role of CO₃^•- in this process, the degradation kinetics and mechanisms of BPA in UV/SPC and in UV/hydrogen peroxide (UV/H₂O₂) were compared at equivalent concentration of H₂O₂. In this study, the observed degradation rates of BPA by UV/SPC and by UV/H₂O₂ in Milli-Q water were similar. Variation of the BPA degradation rates in the presence of radical quenchers, tert-butanol and phenol, suggested that both CO₃^•- and HO^• contributed to the degradation of BPA in UV/SPC. Second order rate constant of CO₃^•- towards BPA ( [Formula: see text]  = 2.23 × 10⁸ M^-1 s^-1) and steady state concentrations of CO₃^•- ( [Formula: see text]  = 2.3 × 10^-12 M) and HO^• ( [Formula: see text]  = 1.82 × 10^-14 M) in UV/SPC were determined with competition kinetics at 1 mM SPC and pH 8.5. The high [Formula: see text] observed in UV/SPC compensated for the smaller [Formula: see text] compared to [Formula: see text] and the consumption of HO^• making the degradation rate of BPA in UV/SPC comparable to that in UV/H₂O₂. Detailed studies on identification of transformation products (TPs) of BPA in UV/SPC revealed that phenol ring and isopropylidene bridge were the main reactive sites of BPA. Degradation pathways were proposed accordingly. The results of kinetic and mechanistic studies provide better fundamental understanding of the degradation of BPA in UV/SPC and HCO₃^-&CO₃^2- impact on BPA degradation by HO^•-AOPs. This also demonstrates potential for CO₃^•- based water purification technologies.

Degradation of trichloroethylene in aqueous solution by nanoscale calcium peroxide in the Fe(II)-based catalytic environments

In this study, nCaO₂ was synthesized successfully and applied in the Fe(II)-based catalytic environments in investigating trichloroethylene (TCE) removal performance. nCaO₂ with the particle sizes in the range of 50-200 nm was prepared, and it performed better for TCE removal when compared to the conventional CaO₂. Further experimental results showed that 70.4% of TCE could be removed in 180 min at the nCaO₂/Fe(II)/TCE molar ratio of 1/2/1, while this data was elevated to 86.1% in the presence of citric acid (CA) at the nCaO₂/Fe(II)/CA/TCE molar ratio of 1/2/2/1 in the same test period. Probe compound tests, specifically designed for free radicals confirmation, demonstrated the presence of HO• and O₂ ^-•. Moreover, scavenging tests indicated that HO• was the major radical responsible for TCE degradation but O₂ ^-• promoted the removal of TCE in both nCaO₂/Fe(II) and nCaO₂/Fe(II)-CA system. In addition, the effects of initial solution pH and anions (Cl^-, HCO₃ ^-) were also evaluated. The performance of TCE degradation in actual groundwater demonstrated that both nCaO₂/Fe(II) and nCaO₂/Fe(II)-CA systems can be applicable for TCE removal in ISCO practice and the nCaO₂/Fe(II)-CA system is much promising technique. These fundamental data strongly confirmed the feasibility and potential of nCaO₂ based technique in the remediation of TCE contaminated groundwater.

Fast degradation of phthalate acid esters by polyoxometalate nanocatalysts through adsorption, esterolysis and oxidation

A novel route was created to facilitate the degradation of diethyl phthalate (DEP) upon micellar polyoxometalate (POM) catalysts and H₂O₂. The best catalytic activity was obtained using [C₁₆H₃₃N(CH₃)₃]H₄PMo₁₀V₂O₄₀ (N-hexadecyl-N,N,N-trimethylammonium tetrahydrogen decamolybdo-divanadophosphate, abbreviated as (CTA)H₄PMoV) with 90.2% degradation efficiency within 30 min, while the chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency were about 77.7% and 74.3% within 40 min. The highest efficiency was attributed to the concentration of DEP by amphiphilic POM catalyst, coupling with its strong Brønsted acidity and higher redox potential to catalyze esterolysis and oxidation of DEP. This allowed the phthalate acid esters (PAEs) with long carbon chains in super low concentration of 0.03 μM to be efficiently decomposed. The above synergistic effects explored DEP being degraded into ethanol, lactic acid and CO₂, which were non-toxic to the water surroundings. And the reaction activation energy (Ea) of 12.49 kJ/mol was obtained upon the degradation of DEP with (CTA)H₄PMoV followed first-order kinetics. Meanwhile, (CTA)H₄PMoV acted as a heterogeneous catalyst, which showed long duration and higher stability with only 3.7% loss amount during ten recycles.

Mechanism of carbon tetrachloride reduction in ferrous ion activated calcium peroxide system in the presence of methanol

This study investigated the reductive initiation for the depletion of highly oxidized/perhalogenated pollutants, specifically the degradation of carbon tetrachloride (CT) was induced by adding methanol (MeOH) into a ferrous ion (Fe(II)) activated calcium peroxide (CaO₂) system. The results indicated that CT could be completely degraded within 20 min at CaO₂/Fe(II)/MeOH/CT molar ratio of 30/40/10/1 in this system. Scavenging tests suggested that both superoxide radical anion (O₂ ^•-) and carbon dioxide radical anion (CO₂ ^•-) were predominant reactive species responsible for CT destruction. Hydroxymethyl radicals (^•CH₂OH), an intermediate in the transformation of MeOH, could also initiate CT degradation by reducing C-Cl bond. GC/MS analysis identified CHCl₃, C₂Cl₄, and C₂Cl₆ as the intermediates accompanied by CT destruction, and a reduction mechanism for CT degradation was proposed accordingly. In addition, the impact of solution matrix and initial solution pH were evaluated, and the results showed that Cl^-, NO₃ ^-, and HCO₃ ^- had adverse effects on CT degradation. Moreover, the alkaline condition was unfavorable to CT depletion. In conclusion, the results obtained in the actual groundwater tests encouragingly demonstrated that the CaO2/Fe(II)/MeOH process is a highly promising technique for the remediation of CT-contaminated groundwater.

Insight into CaO2-based Fenton and Fenton-like systems: strategy for CaO2-based oxidation of organic contaminants

This study conducted a comparison of the CaO₂-based Fenton (CaO₂/Fe(II)) and Fenton-like (CaO₂/Fe(III)) systems on their benzene degradation performance. The H₂O₂, Fe(II), Fe(III), and HO^● variations were investigated during the benzene degradation. Although benzene has been totally removed in the two systems, the variation patterns of the investigated parameters were different, leading to the different benzene degradation patterns. In terms of the Fe(II)/Fe(III) conversion, the CaO₂/Fe(II) and CaO₂/Fe(III) systems were actually inseparable and had the inherent mechanism relationships. For the CaO₂/Fe(III) system, the initial Fe(III) must be converted to Fe(II), and then the consequent Fenton reaction could be later developed with the regenerated Fe(II). Moreover, some benzene degradation intermediates could have the ability to facilitate the transformation of the Fe(III) to Fe(II) without the classic H₂O₂-associated propagation reactions. By varying the Fe(II) dosing method, an effective degradation strategy has been developed to take advantage of the two CaO₂-based oxidation systems. The proposed strategy was further successfully tested in TCE degradation, therefore extending the potential for the application of this technique.

Percarbonate promoted antibiotic decomposition in dielectric barrier discharge plasma

A coupling technique introducing sodium percarbonate (SPC) into a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of antibiotic tetracycline (TC) in aqueous. The dominant effects of SPC addition amount and discharge voltage were evaluated firstly. The experiments indicated that the moderate SPC dosages in the DBD presented an obvious synergistic effect, improving the TC decomposition efficiency and kinetics. Elevating the voltage was conducive for the promotion of antibiotic abatement. After 5 min treatment, the removal reached 94.3% at the SPC of 52.0 μmol/L and voltage of 4.8 kV for 20 mg/L TC. Especially the defined synergy factors were greater than one since the SPC being added, and the energy yield was increased by 155%. Besides, the function mechanism was explained by the hydrogen peroxide and ozone quantitative determinations and radical scavenger test, and the results confirmed that the collaborative method could increase the generation of reactive species, and the produced hydroxyl and superoxide radicals both played the significant roles for the TC elimination. Furthermore, the decomposition and mineralization of the synergism were verified by UV-vis spectroscopy, TOC and COD analyses, and the degradation byproducts and transformation pathways were identified based on the analysis of HPLC-MS finally.

Effective degradation of Orange G and Rhodamine B by alkali-activated hydrogen peroxide: roles of HO2- and O2·

Advanced oxidation processes offer effective solutions in treating wastewater from various industries. The process of alkali-activated hydrogen peroxide (H₂O₂) was superior for the treatment of alkaline dye wastewater because no additional reagents were required except H₂O₂. However, an important and interesting phenomenon had been observed that the primary reactive species were found different for degrading organic pollutants with the process of alkali-activated H₂O₂. Azo dye of Orange G (OG) and triphenylmethane dye of Rhodamine B (RhB) were chosen as the target organic pollutants. The influences of various parameters on OG and RhB degradation by alkali-activated H₂O₂ were evaluated. Furthermore, different scavengers, including ascorbic acid, methanol, t-butanol, isopropyl alcohol, furfuryl alcohol, and nitro blue tetrazolium, have been tested to identify the active species involved in dye degradation, and it was found that O₂^·- was mainly responsible for degrading OG, while HO₂^- anion was the primary oxidant for degrading RhB.

Activation of sodium percarbonate by vanadium for the degradation of aniline in water: Mechanism and identification of reactive species

Sodium percarbonate (SPC)-based advanced oxidation process has been applied to the wastewater treatment in recent years. In the present study, a novel catalyst utilization of vanadium(V) was investigated for the activation of SPC for aniline degradation. The mechanism of SPC activation by V(IV) was demonstrated, and the major free radicals were identified through scavenging tests and electron paramagnetic resonance (EPR) analysis. The performance of aniline degradation was evaluated in the V(IV)/H₂O₂ and V(IV)/H₂O₂/Na₂CO₃ systems and compared with that of the V(IV)/SPC system. The influences of initial pH and effects of inorganic anions were also studied. The results show that aniline could be decomposed efficiently by SPC activated with V(IV) and the degradation efficiency increased with the increase in V(IV) and SPC dosage. O₂^-, CO₃^-, and OH were found to participate in aniline degradation, and O₂^- and CO₃^- were confirmed to be the predominant species. The decomposition of aniline was enhanced when equal amount of H₂O₂ was utilized instead of SPC under acidic condition while a comparative behavior was achieved in the V(IV)/H₂O₂/Na₂CO₃ system. Furthermore, aniline degradation was not impacted significantly by the initial pH and addition of Cl^-, SO₄^2- and NO₃^-, while HCO₃^- led to a betterment of aniline removal. These results indicate that the V(IV)/SPC system is an effective and promising approach for the removal of aniline from water for its feasibility and stability, which achieves eliminating contaminants by another waste.

Elucidation of the oxidation mechanisms and pathways of sulfamethoxazole degradation under Fe(II) activated percarbonate treatment

Fe(II) activated sodium percarbonate (SPC) process (SPC/Fe(II)) could efficiently remove sulfamethoxazole (SMX) in the aqueous phase, and has the potential in groundwater remediation. However, the degradation mechanisms, especially the degradation products and pathways till now have remained unclear. In the present study, intermediate products were identified using high resolution liquid chromatography coupled with ion trap and time-of-flight mass spectrometry (LCMS-IT-TOF). Nine intermediate products were identified, six of which have not yet been reported during the oxidation of SMX. The oxidation mechanisms involved hydroxyl substitution, the cleavage of sulfonamide bond, isoxazole ring opening and a rearrangement following the loss of the SO₂-group. Based on the identified intermediate products, the degradation pathways of SMX by SPC/Fe(II) process were illustrated. Fenton's reaction after the dissolution of SPC was proposed as the main reaction mechanisms, which was checked and confirmed by radical species detection tests and radical species scavenging studies. The results showed that although both O₂^- and HO were present in SPC/Fe(II) system, HO was dominant in the system while O₂^- was seldom involved in the degradation of SMX. These findings provided useful information and supported the application of this advanced oxidation process for antibiotics elimination in the groundwater.

Response of environmental variables and microbial community to sodium percarbonate addition to contaminated sediment

Sodium percarbonate (SPC) is a common reagent used for in situ remediation of contaminated soil. Current studies focus on the effects of SPC on pollutant removal; however, a knowledge gap exists for the biochemical process following SPC addition. In this study, a microcosm batch experiment was conducted to investigate the residual effect caused by different doses of SPC addition on native microbial communities, as well as on the environmental variables of contaminated sediments. The obtained results showed that the more SPC was added, the more dissolved matters were generated and the oxidation-reduction potential was lowered. Furthermore, the metabolic activities of the microbial community were enhanced and the microbial community structure responded differently to different SPC doses: the microbes that increased at high SPC dose mainly belonged to the phylum Firmicutes, the class Clostridia, and the genera Petrimonas and Proteiniclasticum. The microbes that increased at medium SPC dose mainly belonged to the class Alphaproteobacteria and the genus Brevundimonas. In contrast, vulnerable microbes mainly belonged to the phylum Acidobacteria, the class Caldisericia, Holophagae, and the genus Sulfuricurvum. Microbes capable of fermentation, ureolysis, and chemohetrotrophy increased. These results indicate that SPC addition could indirectly provide both electron acceptors and donors, thus improving the metabolic activities of the microorganisms in the contaminated sediment. Furthermore, the utilized SPC dose should be considered to achieve the optimal benefit for in situ remediation. This study forms a valuable reference for the application of SPC in ecological engineering.

Dimethyl phthalate elimination from micro-polluted source water by surface discharge plasma: Performance, active species roles and mechanisms

Plasticizer pollution brought huge risks to ecological environment and human health. Surface discharge plasma (SDP) was employed to eliminate plasticizer in natural water, with dimethyl phthalate (DMP) as a typical plasticizer. Experimental results showed that DMP degradation efficiency reached 82.8% within 60 min's SDP treatment, and the elimination process fitted well the first-order kinetic model. Low initial DMP concentration, alkaline condition, and low natural organic matter content were all conducive for DMP degradation. The contributions of OH radical and O₂^- to DMP elimination were 91.9% and 78.1%, respectively. Total organic carbon (TOC), UV-vis spectroscopy, and atomic force microscopy analysis demonstrated that DMP molecular structure was destroyed after the SDP treatment, and some small molecular fractions were generated. Approximately 47.8% of TOC and 73.5% of COD were eliminated after 60 min's SDP treatment. Phthalic acid monomethyl ester, phthalic acid, o-phthalic anhydride, acetic acid, formic acid, and oxalic acid were detected as the byproducts. Carbon balance analysis among these intermediates showed that total carbon content was approximately 4.64 × 10^-2 mmol before treatment, and it was 4.578 × 10^-2 mmol after treatment, suggesting that some C-containing intermediates still existed but not detected. DMP degradation pathways in the SDP system were proposed.

Degradation of trichloroethylene in aqueous solution by rGO supported nZVI catalyst under several oxic environments

The reduced graphene oxide (rGO) supported nano zero-valent iron (nZVI) (nZVI-rGO) was synthesized successfully and applied in the several oxic environments to remove trichloroethylene (TCE). The nZVI-rGO had a better catalytic performance than bare nZVI for the TCE removal. Both aggregation of nZVI and agglomeration of rGO were in part prevented by loading the nZVI nanoparticles on the rGO sheet. Among all the oxic environments, the better removal of TCE was followed as the order of PMS > SPS > H₂O₂. Chemical scavenger tests were carried out to identify the reactive oxygen species (ROSs) generated in the removal of TCE, showing that in PMS and SPS systems, SO₄^- and HO were main radicals responsible for TCE removal, while HO and O₂^- were main radicals in H₂O₂ system. The possible mechanisms were proposed with nZVI-rGO under several oxic environments. The recyclability of nZVI-rGO, dechlorination and mineralization of TCE were investigated. These fundamental data confirmed the effectiveness of nZVI-rGO to remove TCE and could help selecting the suitable oxidants to use with nZVI-rGO in the actual field groundwater remediation.

Removal of NAPL from columns by oxidation, sparging, surfactant and thermal treatment

In this paper, four treatment techniques commonly applied to Volatile Organic Compounds (VOC) removal from soil are compared in column experiments with pure sand containing a residual Light Non-Aqueous Phase Liquid (L-NAPL) contamination. Oxidation is tested through the injection of Fenton reagent, with persulfate, and combined with sparging with the injection of ozone. Surfactant treatment was conducted at low flow rates with Tween^®80. Sparging was conducted by air injection but at a low flow rate of 1 mL min^-1. Finally several columns were thermally treated at a temperature of 80 °C. The results showed high removal (>90%) for all techniques used, although only thermal treatment on BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) reached 100% efficiency. The main limiting factors of each technique were: (i) for oxidation, the solubility of the substance limited the removal; (ii) for surfactant both the solubility in the surfactant and the type of surfactant are important; (iii) for sparging, the main factors are contaminant vapor pressure and porous media grain size; (iv) for thermal treatment, the limitation arises from the contaminant vapor pressure and the medium hydraulic conductivity. A comparison with literature data shows that the results are consistent with most of the studies conducted on one technique.

Enhanced effect of HAH on citric acid-chelated Fe(II)-catalyzed percarbonate for trichloroethene degradation

This work demonstrates the impact of hydroxylamine hydrochloride (HAH) addition on enhancing the degradation of trichloroethene (TCE) by the citric acid (CA)-chelated Fe(II)-catalyzed percarbonate (SPC) system. The results of a series of batch-reactor experiments show that TCE removal with HAH addition was increased from approximately 57 to 79% for a CA concentration of 0.1 mM and from 89 to 99.6% for a 0.5 mM concentration. Free-radical probe tests elucidated the existence of hydroxyl radical (HO^•) and superoxide anion radical (O₂^•-) in both CA/Fe(II)/SPC and HAH/CA/Fe(II)/SPC systems. However, higher removal rates of radical probe compounds were observed in the HAH/CA/Fe(II)/SPC system, indicating that HAH addition enhanced the generation of both free radicals. In addition, increased contribution of O₂^•- in the HAH/CA/Fe(II)/SPC system compared to the CA/Fe(II)/SPC system was verified by free-radical scavengers tests. Complete TCE dechlorination was confirmed based on the total mass balance of the released Cl^- species. Lower concentrations of formic acid were produced in the later stages of the reaction for the HAH/CA/Fe(II)/SPC system, suggesting that HAH addition favors complete TCE mineralization. Studies of the impact of selected groundwater matrix constituents indicate that TCE removal in the HAH/CA/Fe(II)/SPC system is slightly affected by initial solution pH, with higher removal rates under acidic and near neutral conditions. Although HCO₃^- was observed to have an adverse impact on TCE removal for the HAH/CA/Fe(II)/SPC system, the addition of HAH reduced its inhibitory effect compared to the CA/Fe(II)/SPC system. Finally, TCE removal in actual groundwater was much significant with the addition of HAH to the CA/Fe(II)/SPC system. The study results indicate that HAH amendment has potential to enhance effective remediation of TCE-contaminated groundwater.