Feasibility study of ultraviolet activated persulfate oxidation of phenol

Oxidative polymerization versus degradation of organic pollutants in heterogeneous catalytic persulfate chemistry

Catalytic polymerization pathways in advanced oxidation processes (AOPs) have recently drawn much attention for organic pollutant elimination owing to the rapid removal kinetics, high selectivity, and recovery of organic carbon from wastewater. This work presents a review on the polymerization regimes in AOPs and their applications in wastewater decontamination. The review mainly highlights three critical issues in polymerization reactions induced by persulfate activation (Poly-PS-AOPs), including heterogeneous catalysts, persulfate activation pathways, and properties of organic substrates. The dominant influencing factors on the selection of catalysts, activation regimes of reactive oxygen species, and polymerization processes of organic substrates are discussed in detail. Moreover, we systematically demonstrate the merits and challenges of Poly-PS-AOPs upon pollutant degradation and polymer synthesis. We particularly highlight that Poly-PS-AOPs technology could be promising in the treatment of industrial wastewater containing heterocyclic organics and the synthesis of polymers and polymer-functionalized materials for advanced environmental and energy applications.

Carbonaceous Materials-Based Photothermal Process in Water Treatment: From Originals to Frontier Applications

The photothermal process has attracted considerable attention in water treatment due to its advantages of low energy consumption and high efficiency. In this respect, photothermal materials play a crucial role in the photothermal process. Particularly, carbonaceous materials have emerged as promising candidates for this process because of exceptional photothermal performance. While previous research on carbonaceous materials has primarily focused on photothermal evaporation and sterilization, there is now a growing interest in exploring the potential of photothermal effect-assisted advanced oxidation processes (AOPs). However, the underlying mechanism of the photothermal effect assisted by carbonaceous materials remains unclear. This review aims to provide a comprehensive review of the photothermal process of carbonaceous materials in water treatment. It begins by introducing the photothermal properties of carbonaceous materials, followed by a discussion on strategies for enhancing these properties. Then, the application of carbonaceous materials-based photothermal process for water treatment is summarized. This includes both direct photothermal processes such as photothermal evaporation and sterilization, as well as indirect photothermal processes that assisted AOPs. Meanwhile, various mechanisms assisted by the photothermal effect are summarized. Finally, the challenges and opportunities of using carbonaceous materials-based photothermal processes for water treatment are proposed.

Oxidation of 1,3-diphenylguanidine (DPG) by goethite activated persulfate: Mechanisms, products identification and reaction sites prediction

As emerging pollutants continue to be discovered, studies on the degradation behavior of emerging pollutants have proliferated, but few studies have focused on the reactivity of the new pollutants themselves. The work investigated the oxidation of a representative roadway runoff-derived organic contaminant, 1,3-diphenylguanidine (DPG) by goethite activated persulfate (PS). DPG exhibited the highest degradation rate (k_d = 0.42 h^-1) with present of PS and goethite at pH 5.0, then started to decrease with increasing pH. Chloride ion inhibited DPG degradation by scavenging HO·. Both HO· and SO₄^-· were generated in goethite activated PS system. Competitive kinetic experiments and flash photolysis experiments were conducted to investigate free radical reaction rate. The second-order reaction rate constants for DPG reacting with HO· and SO₄^-· were quantified (k_{DPG + HO·,}k_DPG + SO4-_·), which both reached above 10⁹ M^-1 s^-1. Chemical structures of five products were identified, four of them were previously detected in DPG photodegradation, bromination and chlorination processes. By density functional theory (DFT) calculations, ortho- and para- C were more easily attacked by both HO· and SO₄^-·. Abstraction of H on N by HO· and SO₄^-· were the favorable pathways, and the product TP-210 might be generated by cyclization of DPG radical from abstraction of H on N (3). The results of this study help us to better understand the reactivity of DPG with SO₄^-· and HO·.

Activation of persulfate by vanadium oxide modified carbon nanotube for 17β-estradiol degradation in soil: Mechanism, application and ecotoxicity assessment

Steroid hormones in the environment have attracted public attention because of their high endocrine-disrupting activity even at rather low exposure level. Excessive hormones in the soil from the pollutant discharge of intensive farming would pose a potential threat to the ecology and the human health. Vanadium oxide modified carbon nanotube (VO_X-CNT) was synthesized and applied as persulfate (PDS) activator to reduce17β-estrogen (17β-E2) in soil. 86.06 % 17β-E2 could be degraded within 12 h. Process of materials exchange during oxidation was interfered by soil, resulting in insufficient degradation of 17β-E2, but the active species involved in 17β-E2 degradation would also be enriched by it. 17β-E2 was adsorbed on the VO_X-CNT surface and directly degraded mainly by the active species generated on the catalyst surface, and ^•OH dominated the degradation of 17β-E2 in VO_X-CNT/PDS system. CO, defective sites and vanadium oxides on the surface of VO_X-CNT contributed to the generation of activate species. Oxidizer dosage, catalyst dosage, water-soil ratio and soil properties would affect the degradation of 17β-E2. The ecotoxicological impact on soil caused by VO_X-CNT/PDS was acceptable, and would be weakened with time. Additionally, a rapid decrease in the concentration of 17β-E2 and the promotion of maize growth were observed with VO_X-CNT/PDS in situ pilot-scale remediation. Those results reveal that VO_X-CNT/PDS is a potential technology to remove excessive steroid hormone from soil around large-scale livestock and poultry farms.

Activating peroxymonosulfate using carbon from cyanobacteria as support for zero-valent iron

In the present study, the cyanobacterial char (ACC) prepared from Chaohu cyanobacteria was used as a nanoscale carrier for zero-valent iron (NZVI) to synthesize a highly efficient activation material designated as cyanobacterial char-supported nanoscale zero-valent iron (NZVI@ACC), which was subsequently used for activating peroxymonosulfate (PMS) to degrade the orange II (OII) dye. The XRD and XPS results revealed that NZVI was anchored onto the ACC through coordination bonding, forming a stable structure. The SEM and TEM observations revealed that the NZVI was embedded in the sheet structure of the ACC. The NZVI@ACC had a larger specific surface area (42.249 m²/g) and also magnetism, due to which its components could be separated through an externally applied magnetic field. Using this NZVI@ACC/PMS system, the rate of degradation of OII (100 mg/L) reached 98.32% within 14 min. The OII degradation reaction using the NZVI@ACC/PMS system followed first-order kinetics. The activation energy of this degradation reaction was 17.34 kJ/(mol·K). Quenching and EPR experiments revealed that various free radicals (SO₄·^-, ·OH) were produced, with SO₄·^- playing the major role in the reaction. The theoretical calculations revealed that SO₄·^- attacked the 12 (N) of OII, thereby destroying and degrading both azo and hydrogenated azo structures of OII. The presence of halogen ions in the actual dye-containing wastewater samples inhibited the OII degradation by the NZVI@ACC system to different degrees, and the inhibition effect followed the order I^-  > Br^-  > Cl^-.

Treatment of contaminants by a cathode/FeIII/peroxydisulfate process: Formation of suspended solid organic-polymers

Treatment of highly contaminated wastewaters containing refractory or toxic organic contaminants (e.g. industrial wastewaters) is becoming a global challenge. Most technologies focus on efficient degradation of organic contaminants. Here we improve the cathode/Fe^III/peroxydisulfate (PDS) technology by turning down the current density and develop an innovative mechanism for organic contaminants abatement, namely polymerization rather than degradation, which allows simultaneous contaminants removal and resource recovery from wastewater. This polymerization leads to organic-particles (suspended solid organic-polymers) formation in bulk solution, which is demonstrated by eight kinds of representative organic contaminants. Taking phenol as a representative, 83% of PDS is saved compared to degradation process, with 87.2% of DOC removal. The formed suspended solid organic-polymers occupy 59.2% of COD of the original organics in solution, and can be easily separated from aqueous solution by sedimentation or filtration. The separated organic-polymers are a series of polymers coupled by phenolic monomers, as confirmed by FTIR and ESI-MS analyzes. The energy contained in the recovered organic polymers (4.76 × 10^-5 kWh for 100 mL of 1 mM phenol solution in this study) can fully compensate the consumed electrical energy (2.8 × 10^-5 kWh) in the treatment process. A representative polymerization model for this process is established, in which the SO₄^•- and HO^• generated from PDS activation initiate the polymerization and improve the polymerization degree by the production of oligomer intermediates. A practical coking wastewater treatment is carried out to verify the research results and get positive feedback, with 56.0% of DOC abatement and the suspended solid organic-polymers accounts for 42.5% of the total COD in the raw wastewater. The energy consumption (47 kWh/kg COD, including electricity and PDS cost) is lower than the values in previous reports. This study provides a novel method for industrial wastewater treatment based on polymerization mechanism, which is expected to recover resources while removing pollutants with low consumption.

Degradation of Acyclovir by Zero-valent Iron Activated Persulfate Oxidation: Kinetics and Pathways Research

Acyclovir (ACV) is a commonly used antiviral drug; however, its poor bioavailability can lead to at least ng/L level residue in natural water. Sulfate radical, produced from persulfate (PS) by zero-valent iron (ZVI) activation, was demonstrated to effectively degrade ACV in this study. Influencing parameters, including ZVI dose, PS usage, initial ACV concentration, solution pH, and temperature, were evaluated to find the optimal degradation conditions. Intermediates were identified and main degradation pathways were proposed. Experiments showed that ACV degradation by ZVI/PS oxidation followed a pseudo zero-order reaction well (R² > 0.99). At pH ≦ 9, the optimal combination was 0.4 mM PS with 1.2 mM ZVI, in order to completely remove 10 μM ACV during 60-min reaction. Heat activation of PS would hinder the effect of ZVI if temperature was 45 °C or above. ACV could be oxidized to four major degradation products, including methoxyacetic acid (P1, C₃H₆O₃, m/z = 91), 1,1,2-trinitroethane (P2, C₂H₃N₃O₆, m/z = 165), trinitromethane (P3, CHN₃O₆, m/z = 151), and dinitromethane (P4, CH₂N₂O₄, m/z = 105). Though the mineralization rate was not high (about 24.0%), ZVI/PS oxidation was proved to be an available treatment method for ACV-induced water pollution.

Recent advances on inactivation of waterborne pathogenic microorganisms by (photo) electrochemical oxidation processes: Design and application strategies

Compared with other conventional water disinfection processes, (photo) electrochemical oxidation (P/ECO) processes have the characteristics of environmental friendliness, convenient installation and operation, easy control and high efficiency of inactivating waterborne pathogenic microorganisms (PMs), so that more and more research work has been focused on this topic, but there is still a huge gap between the research and practical application. Here, the research network of inactivating PMs by P/ECO processes has been comprehensively summarized, and the electrode/reactor/process design strategies based on strengthening direct and indirect oxidation, enhancing mass transfer efficiency and electron transfer efficiency, and improving the effective dose of electrogenerated oxidants are discussed. Furthermore, the factors affecting the inactivation of PMs and the issues regarding to stability and lifetime of the electrode are discussed respectively. Finally, the important research priorities and possible research challenges of P/ECO processes are put forward to make significant progress of this technology.

Hydrogen atom abstraction mechanism for organic compound oxidation by acetylperoxyl radical in Co(II)/peracetic acid activation system

Peracetic acid (PAA) has been widely used as an alternative disinfectant in wastewater treatment, and PAA-based advanced oxidation processes (AOPs) have drawn increasing attention recently. Among the generated reactive species after PAA activation, acetylperoxyl radical (CH₃CO₃•) plays an important role in organic compounds degradation. However, little is known about the reaction mechanism on CH₃CO₃• attack due to the challenging of experimental analysis. In this study, a homogeneous PAA activation system was built up using Co(II) as an activator at neutral pH to generate CH₃CO₃• for phenol degradation. More importantly, reaction mechanism on CH₃CO₃•-driven oxidation of phenol is elucidated at the molecular level. CH₃CO₃• with lower electrophilicity index but much larger Waals molecular volume holds different phenol oxidation route compared with the conventional •OH. Direct evidences on CH₃CO₃• formation and attack mechanism are provided through integrated experimental and theoretical results, indicating that hydrogen atom abstraction (HAA) is the most favorable route in the initial step of CH₃CO₃•-driven phenol oxidation. HAA reaction step is found to produce phenoxy radicals with a low energy barrier of 4.78 kcal mol^-1 and free energy change of -12.21 kcal mol^-1. The generated phenoxy radicals will undergo further dimerization to form 4-phenoxyphenol and corresponding hydroxylated products, or react with CH₃CO₃• to generate catechol and hydroquinone. These results significantly promote the understanding of CH₃CO₃•-driven organic pollutant degradation and are useful for further development of PAA-based AOPs in environmental applications.

Activation of Na2S2O8 by α-Fe2O3/CuS composite oxides for the degradation of Orange II under visible light irradiation

Layered α-Fe2O3/CuS nanoflowers with abundant active sites were synthesized by a hydrothermal method.

Optimization and mechanism of oily sludge treatment by a novel combined surfactants with activated-persulfate method

Recently, the extensive discharge of oily sludge, due to excessive use of fossil oil, has become a serious worldwide concern, as it leads to serious environmental pollution and even threat human health. However, the complex properties and compositions of oily sludge make it difficult for the treatment of oily sludge. This study proposed a novel method of combined degradation of oily sludge by surfactants with activated-persulfate, and analyzed the degradation efficiency and degradation pathway. The organics in oil sludge were eluted by surfactant, and the residual oil difficult to be eluted was further oxidized by activated persulfate. The combined method significantly improved the degradation efficiency of oily sludge, and the removal rate reached 94.6 ± 2.8%, and the oil content of the residual oily sludge was 0.57%, which had reached the discharge standard. The mechanism analysis indicated that surfactant could increase the solubility of oil by reducing the surface tension, and the hydroxyl radical and sulfate radical generated by activated persulfate could degrade the complex organic matters into small molecule matters, achieving efficient degradation of oil sludge. This work demonstrated a new avenue for the efficient and cost-effective treatment of oily sludge, opening an environmentally friendly treatment concept.

Cavitation based treatment of industrial wastewater: A critical review focusing on mechanisms, design aspects, operating conditions and application to real effluents

Acoustic cavitation (AC) and hydrodynamic cavitation (HC) coupled with advanced oxidation processes (AOPs) are prominent techniques used for industrial wastewater treatment though most studies have focused on simulated effluents. The present review mainly focuses on the analysis of studies related to real industrial effluent treatment using acoustic and hydrodynamic cavitation operated individually and coupled with H₂O₂, ozone, ultraviolet, Fenton, persulfate and peroxymonosulfate, and other emerging AOPs. The necessity of using optimum loadings of oxidants in the various AOPs for obtaining maximum COD reduction of industrial effluent have been demonstrated. The review also presents critical analysis of designs of various HCRs that have been or can be used for the treatment of industrial effluents. The impact of operating conditions such as dilution, inlet pressure, ultrasonic power, pH, and operating temperature have been also discussed. The economic aspects of the industrial effluent treatment have been analyzed. HC can be considered as cost-efficient approach compared to AC on the basis of the lower operating costs and better transfer efficiencies. Overall, HC combined with AOPs appears to be an effective treatment strategy that can be successfully implemented at industrial-scale of operation.

Efficient decomposition of lignocellulose and improved composting performances driven by thermally activated persulfate based on metagenomics analysis

In this study, fresh dairy manure and bagasse pith were used as raw materials to study the effect of potassium persulfate in the aerobic composting process. The influence of sulfate radical anion (SO₄^-·) generated by thermally activated persulfate on physicochemical parameters, lignocellulose degradation, humic substance (HS) formation, microbial community succession, and carbohydrate-active enzymes (CAZymes) composition were assessed during composting. Experimental results showed that the degradation rates of cellulose, hemicellulose and lignin in the treatment group with potassium persulfate (PS) (61.47%, 74.63%, 73.1%) were higher than that in blank control group (CK) (59.98%, 71.47%, 70.89%), respectively. Additionally, persulfate additive promoted dynamic variation of dissolved organic matter (DOM) and accelerated the formation of HS. Furthermore, metagenomics analysis revealed that persulfate changed the structure of the microbial community, and the relative abundances of Actinobacteria and Proteobacteria increased by 17.64% and 34.09% in PS, whereas 12.09% and 29.96% in CK. Glycoside hydrolases (GHs) and auxiliary activities (AAs) families were crucial to degrade lignocellulose, and their abundances were more in PS. Redundancy analysis (RDA) manifested that Actinobacteria and Proteobacteria were closely associated with lignocellulosic degradation. In brief, persulfate could accelerate the degradation of organic components, promote the formation of HS, optimize the structure of microbial community, and improve the compost quality.

Synergistic chromium(VI) reduction and phenol oxidative degradation by FeS2/Fe0 and persulfate

It is a challenge to simultaneously treat the combined pollutants of chromium(VI) (Cr(VI)) and organics (such as phenol) in wastewater. Here, a stable and efficient redox system based on FeS₂ sulfidated zero valent iron (FeS₂/Fe⁰) and persulfate (PS) was developed to synchronously remove Cr(VI) and phenol. 100% of phenol (10 mg/L) was oxidized in 10 min and Cr(VI) (20 mg/L) was completely reduced to Cr(III) in 90 min in the FeS₂/Fe⁰+PS system with a pH range of 3.0-9.0, respectively. phenol was selectively oxidized without re-oxidizing Cr(III) in such system. The surface-bound Fe²⁺ was the major reactive species to synchronously reduce Cr(VI) and oxidize phenol. The mechanisms were elucidated that the phenol degradation was accelerated by the generated Cr(III) complexing with its products, and that SO₄^2-, whose production speed was accelerated by the PS activation to oxidize phenol and FeS₂, was conductive to corrode Fe⁰ to regenerate the surface-bound Fe²⁺ for reducing Cr(VI) and oxidizing phenol. It is potential to develop a high-performance and large-scaled FeS₂/Fe⁰-based redox platform to remediate the complex pollution of Cr(VI) and organics.

Advanced oxidation of 4-chlorophenol via combined pulsed light and sulfate radicals methods: Effect of co-existing anions

Pulsed light (PL) technology, which is based on photonic technology involves the application of broadband emission of light with short and high-power pulses is beginning to emerge for the treatment of wastes via advanced oxidation processes (AOP). The present work investigates the efficiency of PL as a light source for persulfate (PS) activation (PL/PS) and 4-chlorophenol)4-CP) degradation, an organic model pollutant. The influencing parameters on 4-CP degradation such as solution pH, reaction time, initial concentration of 4-CP, PS dose, pulse intensity and frequency, and distance from PL source are systematically investigated. With increasing pH from 3 to 9, the 4-CP degradation decreased from 49.79 ± 2.49 to 33.12 ± 1.66%. The 4-CP degradation followed the first order kinetics that was improved with increasing reaction time, PS dose, pulse intensity, frequency of pulse, and decreasing pH, initial 4-CP concentration and distance from the PL source. The presence of sulfate, chloride, and carbonate anions in the solution has the inhibitory effects on 4-CP degradation, while nitrate anion improved the performance of PL/PS system. In addition, presence of humic acid had an inhibitory effect on the PL/PS system, which led to a decrease of reaction rate constant and 4-CP degradation was performed in PL/PS system with OH, SO₄^-, O₂^- and ₁O² radicals. The contributions of OH and SO₄^- radicals were 46% and 51%, respectively for the 4-CP degradation and synergistic effect of PL/PS system showed a significant influence on 4-CP degradation while using a combination of PL and PS, suggesting that PL is an effective activator of PS.

Uncertainty and misinterpretation over identification, quantification and transformation of reactive species generated in catalytic oxidation processes: A review

The identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests has attracted extensive attention, but some mistakes or misinterpretations are often present in recent literature. This review aims to clarify the corresponding issues through surveying literature, including the uncertainty about the identity of radicals in the bulk solution or adsorbed on the catalyst surface in quenching tests, selection of proper scavengers, data explanation for incomplete inhibition, the inconsistent results between quenching and EPR tests (e.g., SO₄^•- is predominant in quenching test while the signal of ^•OH predominates in EPR test), and the incorrect identification of EPR signals (e.g., SO₄^•- is identified by indiscernible or incorrect signals). In addition, this review outlines the transformation of radicals for better tracing the origin of radicals. It is anticipated that this review can help in avoiding mistakes while investigating catalytic oxidative mechanism with quenching and EPR tests.

Degradation of aniline by ferrous ions activated persulfate: Impacts, mechanisms, and by-products

Wastewater contains a large number of anions and organics which can scavenge reactive radicals and limit the application of sulfate radical-based advanced oxidation processes (SR-AOPs) in practical engineering. Here, we studied the removal rate and mechanism of aniline by SR-AOPs in different influencing factors, such as sodium persulfate dosage, ferrous ions dosage, solution pH, Cl^-, HCO₃^-, NO₃^-, and other organic matter. By recognizing and analyzing free radicals, we concluded that SO₄^•- plays a major role in aniline degradation. The aniline removal rate increased with the initial concentrations of persulfate and ferrous ions, but aniline degradation was inhibited by excessive dosage. The aniline removal rate by ferrous-ions-catalyzed persulfate was higher under acidic conditions and could be improved under alkaline conditions if no ferrous ions were added. The addition of bicarbonate ions inhibited aniline removal, and the addition of nitrate ions barely caused the effect. While the addition of chloride ions promoted aniline degradation, which was confirmed that HClO generated from the reacting of Cl^- and persulfate played a key role. However, TOC indicated that aniline was not completely mineralized in the process. Further analysis of the products from GC-MS demonstrated that chloride-ion additions produced some harmful halogenated by-products. Our results can act as a basis for developing processes for the aniline degradation in wastewater.

Degradation of basic violet 16 dye by electro-activated persulfate process from aqueous solutions and toxicity assessment using microorganisms: determination of by-products, reaction kinetic and optimization using Box–Behnken design

This study was performed to determine the efficiency of the electro/persulfate process to remove basic violet 16 (BV16) dye and COD from aqueous solutions. The present study was experimentally performed on a laboratory scale. The effect of pH on the process was investigated independently, and after performing the experiments, the effect of voltage (volts), the dose of persulfate (g/L), initial concentration of BV16 dye, and electrolysis time was investigated with the model presented by Box Behnken design, and optimal conditions for BV16 dye removal was obtained. Under optimal conditions, COD removal efficiency and toxicity changes during the process were calculated, and the effect of distance between electrodes and surface of electrodes on process efficiency was investigated. By-products of oxidative degradation were determined with LS-MS. The amount of electrical energy consumed by the process was investigated by voltage changes and then the kinetics of the process was investigated by a pseudo-first-order model. The results showed that the electro/persulfate process in optimal conditions including pH of 5, a voltage of 11.43 V, persulfate dose of 0.09 g/L, initial BV16 concentration of 45 mg/L, and electrolysis time of 48.5 min could provide BV16 dye removal efficiency of 95% and COD removal efficiency of 57.14%. Findings of electrical energy consumption showed that with increasing voltage, the efficiency of the process increased, but the amount of energy consumption also increased. Under optimal conditions, increasing distance between the electrodes was led to a decrease in removal efficiency, but the removal efficiency increased with the increasing surface of the electrodes. Based on the kinetic results, the electro/persulfate process followed pseudo-first-order kinetics with R 2 = 0.9956. The present study showed that the electro/persulfate process as a useful technique has high efficiency in removing BV16 dye and its toxicity from aqueous solutions and can be effective and useful in removing the COD of solution.

Synergistic heat/UV activated persulfate for the treatment of nanofiltration concentrated leachate

Nanofiltration concentration leachate is a high concentration organic wastewater with low biodegradability and high toxicity. To explore the feasibility of a combined Heat/UV activated persulfate process on nanofiltration concentrated leachate, the effects of persulfate concentration, initial solution pH before reaction, UV-lamp power and reaction temperature on the removal of organic pollutant were systematically investigated. Results indicated that the maximum rate of chemical oxygen demand (COD), ammonia-nitrogen (NH₃-N) and absorbance of organic matter under UV light at 254 nm (UV₂₅₄) removal from the leachate were 65.4%, 51.4% and 98.1%, respectively, at a persulfate concentration of 18 g L^-1, initial solution pH before reaction of 9.0, UV-lamp power of 60 W and temperature of 80 °C. The results of three-dimensional fluorescence and UV₂₅₄ showed that the removal rates of humic substances contained in the nanofiltration concentrated leachate were over 98%. In addition, the results of free radical scavenging showed that hydroxyl radicals were dominant under alkaline conditions. The results of this study demonstrated that coupling heat and ultraviolet activated persulfate oxidation is a promising technique for the treatment of nanofiltration concentrated leachate.

Simultaneous removal of chromium(VI) and tetracycline hydrochloride from simulated wastewater by nanoscale zero-valent iron/copper-activated persulfate

In this paper, metallic copper (Cu) was supported on nanoscale zero-valent iron (nZVI) to form a nanoscale bimetallic composite (nZVI-Cu), which was used to activate persulfate (PS) to simultaneously remove the compound contaminants Cr(VI) and tetracycline hydrochloride (TCH) in simulated wastewater. nZVI, nZVI-Cu, and nZVI-Cu-activated PS (nZVI-Cu/PS) were characterized by SEM, TEM, XRD, and XPS. The effects of the bimetallic composite on Cr(VI) and TCH removal were compared in the nZVI, nZVI-activated PS (nZVI/PS), nZVI-Cu, and nZVI-Cu/PS systems. The results showed that nZVI and Cu can form a nanobimetallic system, which can create galvanic cells; thus, the galvanic corrosion of nZVI and the transfer of electrons are accelerated. For a single contaminant, the removal efficiency of Cr(VI) and TCH is the highest when nZVI is loaded with 3 wt% and 1 wt% Cu, respectively. The ratio of nZVI-Cu with 3 wt% Cu to PS is 7:1, and the removal efficiency of Cr(VI) and TCH compound contaminants is ~ 100% after 60 min under acidic conditions, which indicates that the Cr(VI) reduction and TCH oxidation were complete in the nZVI-Cu/PS system. The mechanisms of simultaneous removal of Cr(VI) and TCH in the nZVI-Cu/PS system are proposed. The removal of Cr is because of the adsorption-reduction effects of the nZVI-Cu bimetallic material. The degradation of TCH is mainly due to the action of oxidative free radicals generated by Fe²⁺-activated PS. The free radical capture experiments showed that SO- 4· plays a major role in the process of TCH degradation.

Photo-assisted peroxymonosulfate activation via 2D/2D heterostructure of Ti3C2/g-C3N4 for degradation of diclofenac

In this paper, a two dimensional/two dimensional (2D/2D) heterostructure of Ti₃C₂/g-C₃N₄ (T/CN) was constructed and used to activate peroxymonosulfate (PMS) for the degradation of diclofenac (DCF) in water in the presence of light illumination. Compared with single photocatalytic process by T/CN (0.040/min) and with pure g-C₃N₄ nanosheets in PMS system (0.071/min), 5.0 and 3.0 times enhanced activities were achieved in the T/CN-PMS system at optimum Ti₃C₂ (1.0 wt%) loading under light illumination (0.21/min). Moreover, the decomposing processes of DCF in T/CN-PMS system were applicable in a wide initial pH range (3∼14), therefore, overcoming the limitation of pH dependence in traditional PMS system. Based on the synergistic effect of photocatalysis and PMS oxidation processes, the ¹O₂ was generated as primary reactive species for the removal of DCF in T/CN-PMS system. The DCF degradation mechanism was further proposed through the results of liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculations.

Application of a microbial siderophore desferrioxamine B in sunlight/Fe3+/persulfate system: from the radical formation to the degradation of atenolol at neutral pH

The present work reported a modified persulfate activation process with a microbial siderophore named desferrioxamine B (DFOB). DFOB was a natural complexing agent and could complex with Fe³⁺ strongly. The photochemical reactivity of Fe(III)-DFOB was studied. Fe²⁺ and HO^• were produced from Fe(III)-DFOB photolysis. Furthermore, the degradation of atenolol (ATL) was followed in light/persulfate (PS)/Fe(III)-DFOB system. The main oxidative radicals were SO₄^•- in this system. The results of pH effect showed that there was no obviously fluctuation on ATL degradation efficiency with the pH increased from 2.5 to 8.4. Moreover, k_SO4•-,DFOB was determined by laser flash photolysis (LFP) experiments. DFOB had positive effect on Fe²⁺ formation but negative effect on ATL degradation due to the high react rate constant between DFOB and SO₄^•-. The effects of chloride and carbonate ion were also investigated. The results in this study proposed the reaction mechanism of the modified persulfate activation process, and it could be applied in neutral and weak-alkaline pH range.

Removal of antibiotic resistant microbes by Fe(II)-activated persulfate oxidation

Sewage in WWTPs is one of main way to spread antibiotic resistant microbes (ARMs), and beach bay water is in direct contact with human skin. It is necessary to pay attention to remove the ARMs in WWTP sewage and bay water. Our results showed that ARMs and total microbes (TMs) can be effectively removed by S₂O₈^2-/Fe²⁺ in the effluent stage of WWTPs and bay water. Quenching experiments using tert-butyl alcohol, dimethyl sulfoxide and Al₂O₃ as scavengers confirmed that the primary reactive oxidants responsible for microbes removal during the Fe(II)-activated persulfate oxidation process might be SO₄^•- and Fe(IV), rather than •OH. The bacterial community shifted and the alpha diversity significantly reduced after treatment. In WWTP group, relative abundance of Firmicutes increased to 8.56%, and potential pathogens such as genus Vibrio decreased to 0.03% in bay water after treatment. The ecological toxicity to the environment of S₂O₈^2-/Fe²⁺ further illustrated that the mortality of indicator species Oryzias latipes did not increase after treatment, and the dosage of 60/30 μM can be potentially ideal dosage of S₂O₈^2-/Fe²⁺. This study revealed Fe(II)-activated persulfate oxidation as an eco-friendly and economical method could reduce TMs and ARMs in WWTP sewage and bay water.

Synergistic degradation of 4-chlorophenol by persulfate and oxalic acid mixture with heterogeneous Fenton like system for wastewater treatment: Adaptive neuro-fuzzy inference systems modeling

The 4-chlorophenol (4-CP) is known to be a highly toxic compound having harmful effects on human health and the environment. Due to adverse effect of 4-CP, a new combination of persulfate (PS) and oxalic acid (OA) with heterogeneous Fenton like (HFL) system was developed and applied for 4-CP degradation as an emerging contaminant from synthetic wastewater. The individual (OA, PS, and HFL) and combined (HFL/OA, HFL/PS, and HFL/OA/PS) systems were investigated under various conditions to synergistic effects verification and determination of degradation mechanism of 4-CP. Compared to individual and combined systems, significant synergetic of 4-CP degradation efficiency was observed by HFL/OA/PS system. The highest 4-CP degradation efficiency by HFL/OA/PS system under optimal conditions (solution pH: 6, H₂O₂ dose: 275 mg/L, goethite dose: 125 mg/L, OA dose: 50 mg/L and PS dose: 100 mg/L) with an initial 4-CP concentration of 30 mg/L was 99.6 ± 4.9% after 35 min reaction time. 4-CP degradation by HFL/OA/PS system was followed with the first-order kinetic. The application of radical scavengers including ethanol (EtOH) and tert-butyl alcohol (TBA) revealed that the SO₄^•- radical was determined as primary produced radical species. The Cl- ions release was measured during degradation reaction at various 4-CP concentrations and indicating the complete 4-CP degradation. The developing of the adaptive neuro-fuzzy inference system (ANFIS) for 4-CP degradation efficiency prediction was revealed. These results show that prediction of 4-CP degradation efficiency using HFL/OA/PS system is possible by the ANFIS model with a high accuracy (R²: 0.98).

Degradation of azo dye Acid Red 14 (AR14) from aqueous solution using H2 O2 /nZVI and S2 O8 2- /nZVI processes in the presence of UV irradiation

Azo dyes are mostly toxic and carcinogenic and cause harm to humans and the environment. This study was conducted to investigate the degradation of azo dye acid red 14 (AR14) from aqueous solution using hydrogen peroxide (H₂ O₂₎ /nano zerovalent iron (nZVI) and persulfate (S₂ O₈ ^2- )/nZVI processes in the presence of ultraviolet (UV) irradiation. This experimental study was carried out in a laboratory-scale batch photoreactor with a useful volume of 1 L. The nZVI was synthesized by the sodium borohydride (NaBH₄ ) reduction method. In these processes, the effects of parameters including initial pH, H₂ O₂ concentration, S₂ O₈ ^2- concentration, nZVI dose, concentration of AR14 dye, and reaction time were studied. The results showed that decolorization increased by increasing the nZVI dosage, H₂ O₂ and S₂ O₄ ^2- concentrations, and reaction time, or decreasing dye concentration and pH. However, a too high oxidant concentration (H₂ O₂ and S₂ O₄ ^2- ) could inhibit the degradation. The experimental conditions for degradation of AR14 by UV/S₂ O₈ ^2- /nZVI and UV/H₂ O₂ /nZVI processes were as follows: [H₂ O₂ ] = 10 mM, [S₂ O₈ ^2- ] = 8 mM, AB14 dye = 100 mg/L, pH = 3, and nZVI dose = 0.05 g. Under these conditions, the highest removal efficiencies of AR14, chemical oxygen demand (COD), and total organic carbon (TOC) for the UV/S₂ O₈ ^2- /nZVI process were 93.94%, 86.5%, and 81.6%, respectively, while these values were 89.3%, 79.57%, and 72.9% for the UV/H₂ O₂ /nZVI, respectively. Also, the average oxidation state (AOS) was decreased from 2.93 to 2.14 in the effluent of the UV/S₂ O₈ ^2- /nZVI process and from 2.93 to 2.2 for the UV/H₂ O₂ /nZVI process. The results showed that the ratio of biochemical oxygen demand (BOD₅ ) to COD in the effluents of the UV/S₂ O₈ ² /nZVI and UV/H₂ O₂ /nZVI processes after 90 min was 0.63 and 0.74, respectively. These findings suggest biodegradability improvement. PRACTITIONER POINTS: Photocatalytic degradation of azo dye Acid Red 14 (AR14) was achieved using H₂ O₂ /nZVI and S₂ O₈ ^2- /nZVI processes in the presence of UV irradiation. Effects of operating parameters on photocatalytic degradation AR14 dye were evaluated in the UV/H₂ O₂ /nZVI and UV/S₂ O₈ ^2- /nZVI processes. Biodegradability and mineralization studies of AR14 dye photocatalytic degradation were performed for the UV/H₂ O₂ /nZVI and UV/S₂ O₈ ^2- /nZVI processes.

UV-C-activated persulfate oxidation of a commercially important fungicide: case study with iprodione in pure water and simulated tertiary treated urban wastewater

Recently, the European Food Safety Authority (EFSA) has banned the use of iprodione (IPR), a common hydantoin fungicide and nematicide that was frequently used for the protective treatment of crops and vegetables. In the present study, the treatment of 2 mg/L (6.06 μM) aqueous IPR solution through ultraviolet-C (UV-C)-activated persulfate (PS) advanced oxidation process (UV-C/PS) was investigated. Baseline experiments conducted in distilled water (DW) indicated that complete IPR removal was achieved in 20 min with UV-C/PS treatment at an initial PS concentration of 0.03 mM at pH = 6.2. IPR degradation was accompanied with rapid dechlorination (followed as Cl^- release) and PS consumption. UV-C/PS treatment was also effective in IPR mineralization; 78% dissolved organic carbon (DOC) was removed after 120-min UV-C/PS treatment (PS = 0.30 mM) compared with UV-C at 0.5 W/L photolysis where no DOC removal occurred. LC analysis confirmed the formation of dichloroaniline, hydroquinone, and acetic and formic acids as the major aromatic and aliphatic degradation products of IPR during UV-C/PS treatment whereas only dichloroaniline was observed for UV-C photolysis under the same reaction conditions. IPR was also subjected to UV-C/PS treatment in simulated tertiary treated urban wastewater (SWW) to examine its oxidation performance and ecotoxicological behavior in a more complex aquatic environment. In SWW, IPR and DOC removal rates were inhibited and PS consumption rates decreased. The originally low acute toxicity (9% relative inhibition towards the photobacterium Vibrio fischeri) decreased to practically non-detectable levels (4%) during UV-C/PS treatment of IPR in SWW.

Comparing biochar- and bentonite-supported Fe-based catalysts for selective degradation of antibiotics: Mechanisms and pathway

The selective degradation of recalcitrant antibiotics into byproducts with low toxicity and high biodegradability has been increasingly popular using peroxymonosulfate (PMS) based advanced oxidation processes (AOPs). In this paper, two Fe-based heterogeneous catalysts, bentonite supported Fe-Ni composite (BNF) and biochar-supported Fe composite (Fe/C), were tailored and comprehensively characterized for distinctive physicochemical properties, crystalline structures, and interfacial behaviors. Two widely used antibiotics, sulfapyridine (SPY) and oxytetracycline (OTCs) at their common concentrations in pharmaceutical wastewaters (250 and 10 mg L^-1) were tested for degradation in three PMS-based oxidation processes, i.e., PMS, PMS-BNF, and PMS-Fe/C, respectively. Results demonstrated that a large amount of PMS (10 and 1 mM) could effectively remove SPY (0.385 min^-1, 100% removal) and OTC (2.737 min^-1, 100% removal) via¹O₂ derived from PMS self-decomposition and non-radical pathway, respectively. Additional Fe-based catalysts (0.5 g L^-1 Fe/C and BNF) significantly reduced the PMS consumption (1 and 0.25 mM) and accelerated the reaction rate (1.08 and 5.05 min^-1) of SPY and OTC removal. Moreover, the supplementary catalysts shifted the degradation route. The biochar matrix in Fe/C composite contributed to predominant interaction with PMS forming ¹O₂, which preferably attacked SPY via hydroxylation. In contrast, the redox-active Fe-Ni pairs induced SO₄^- formation, which could selectively degrade OTC through decarboxylation. Thus, these results are conducive to tailoring advanced yet low-cost heterogeneous catalysts for eco-friendly treatment of antibiotics-rich industrial wastewaters.

Effects of Persulfate Activation with Pyrite and Zero-Valent Iron for Phthalate Acid Ester Degradation

Phthalic acid esters (PAEs) are often detected in remediated groundwater using appropriate oxidant materials by in situ groundwater treatment. The study compares zero-valent iron–persulfate with a pyrite–persulfate system to degrade three PAEs—di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and dimethyl phthalate (DMP). Column experiments were conducted, and rapid oxidation occurred in a pyrite–persulfate system due to sulfate radical generation. DMP concentration was found at about 60.0% and 53.0% with zero-valent iron (ZVI) and pyrite activation of persulfate, respectively. DBP concentration was measured as 25.0–17.2% and 23.2–16.0% using ZVI–persulfate and pyrite–persulfate systems, respectively. However, DEHP was not detected. The total organic carbon concentration lagged behind the Ʃ3 PAEs. Persulfate consumption with ZVI activation was half of the consumption with pyrite activation. Both systems showed a steady release of iron ions. Overall, the oxidation–reduction potential was higher with pyrite activation. The surface morphologies of ZVI and pyrite were investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and XPS. Intensive corrosion occurs on the pyrite surface, whereas the ZVI surface is covered by a netting of iron oxides. The pyrite surface showed more oxidation and less passivation in comparison with ZVI, which results in more availability of Fe 2 + for persulfate activation. The pyrite–persulfate system is relatively preferred for rapid PAE degradation for contamination.

The degradation of phthalate esters in marine sediments by persulfate over iron-cerium oxide catalyst

This study investigated the degradation of phthalate esters (PAEs) in marine sediments by sodium persulfate (Na₂S₂O₈, PS) activated by a series of iron-cerium (Fe-Ce) bimetallic catalysts (FCBCs). The surface structure and chemistry of the FCBCs were characterized by TEM, HRTEM, XRD, FTIR, BET and XPS. Results show successful synthesis of FCBC catalysts. Factors such as PS concentration, Fe to Ce molar ratio, catalyst dosage, and initial pH that might affect PAEs degradation were investigated. Results revealed that PAEs was degraded more effectively over FCBC with a Fe-Ce molar ratio of 1.5:1. Increase in Ce improved the catalytic activity of FCBC due to increase in oxygen storage capacity (OSC). Acidic conditions enhanced PAEs degradation with a maximum degradation of 86% at pH 2 and rate constant (k_obs) of 1.5 × 10^-1 h^-1 when the PS and FCBC concentrations were to 1.0 × 10^-5 M and 1.67 g/L, respectively. Di-(2-ethylhexyl) phthalate (DEHP) was a salient marker of PAE contamination in sediments. Dimethyl phthalate (DMP) and diethyl phthalate (DEP) were easier to degrade than DEHP, diisononyl phthalate (DINP), dioctyl phthalate (DnOP) and diisononyl phthalate (DIDP). The synergistic catalytic effect of Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ redox couples, in addition to electron transfer of oxygen vacancies, activated S₂O₈^2- to generate SO₄^- and HO radicals, which played the major role of PAEs degradation. 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trapping EPR studies verified the crucial role of SO₄^- and HO in the oxidative degradation process. FCBC/PS oxidation exhibited high-performance for the remediation of PAEs-contaminated marine sediments.

Carbon Materials Inhibit Formation of Nitrated Aromatic Products in Treatment of Phenolic Compounds by Thermal Activation of Peroxydisulfate in the Presence of Nitrite

Recent studies have reported that toxic nitrated aromatic products are generated during treatment of phenolic compounds by thermally activated peroxydisulfate (thermal/PDS) in the presence of nitrite (NO₂^-). This work explored the potential of carbon materials on controlling the formation of nitrated aromatic products using phenol as a model compound. In the presence of selected carbon materials including diverse carbon nanotubes (CNT) and powdered activated carbon (PAC), the transformation kinetics of phenol was significantly enhanced, primarily attributed to nonradical activation of PDS by carbon materials. Nitrophenols (NPs) including 2-NP and 4-NP were formed in phenol oxidation by the thermal/PDS/NO₂^- process, due to the reaction of phenol with reactive nitrogen species generated from NO₂^- oxidation. The addition of carbon materials obviously inhibited NPs formation under various experimental conditions. The bonding of nitro groups on the CNT surface was clearly confirmed by means of various characterizations, probably resulting from the competitive reaction of reactive nitrogen species with CNT vs phenol. The controlling effect of carbon materials was also verified in the cases of other phenolic compounds. Therefore, the addition of carbon materials may be a promising approach to control the formation of undesirable nitrated byproducts by the thermal/PDS process in the presence of NO₂^-.

Evaluation of urea removal by persulfate with UV irradiation in an ultrapure water production system

The removal of urea by persulfate with UV irradiation in an ultrapure water (UPW) production system was examined using a continuously operated column reactor. Urea is a substance that is not properly removed by the unit processes in UPW production systems. Based on our monitoring of urea concentration over 1 year of the operation of a UPW production facility, a relatively high concentration of urea was introduced between February and May in 2016 and the total organic carbon (TOC) concentration of the UPW was increased in that period. Approximately 50% of the urea in the raw water was removed by the UPW production process, for which double-pass reverse osmosis units were instrumental. The addition of persulfate to the TOC reduction UV unit in the UPW production process was examined to improve the efficiency of urea removal. As a result, supplying over 20 μmol/L persulfate to the TOC reduction UV reactor improved the efficiency of urea removal from 9% to 90%. UV dose was an important factor of urea removal. In the ion analysis, nitrate and sulfate were detected in the effluent, and the ratio of produced nitrate to the removed urea was approximately 2.

Thermochemical degradation of furfural by sulfate radicals in aqueous solution: optimization and synergistic effect studies

In this study, thermochemical degradation of furfural by sulfate radical has been investigated to find the best-operating conditions. For this purpose, the response surface methodology (RSM) based on central composite design (CCD) was applied to optimize the five independent variables of thermally activated persulfate (TAP)/nZVI oxidation process including pH, PS concentration, furfural concentration, nZVI dosage, and heat. The ANOVA results ("P > F value" < 0.0001 and [Formula: see text] = 0.9701) showed the obtained quadratic model is acceptable to predict furfural removal. Based on the reduced quadratic model PS concentration, nZVI dosage, and heat revealed the positive effects on removal efficiency, while pH and furfural concentration had a negative effect. Accordingly, 98.4% of furfural could be removed within 60 min of reaction under the optimum conditions: pH 5.26, PS concentration of 20.52 mM, furfural concentration of 84.32 mg/L, nZVI dosage of 1.15 mg/L, and a temperature of 79 °C. In such circumstances, the furfural removal efficiency for TAP, PS/nZVI, PS, and nZVI was 94.5, 9, 3, and 2%, respectively. Therefore, based on the synergy index (SI) values, the combination of PS, nZVI, and heat can lead to a synergistic effect in the performance of the thermochemical process.