Persulfate Activation Methods Research Articles

Heterogeneous activation of persulfate by FeS – Surface influence on selectivity

Recently, several studies have been published on sulfate radicals as strong oxidants and methods of their generation. A shift from homogeneous to heterogeneous methods can be observed for persulfate activation as a means of generating sulfate radicals. However, to date, the influence of the surface on the radical chemistry has not been examined in detail.In the present study, homogeneous persulfate activation methods (elevated temperature and dissolved iron(II)) are compared with heterogeneous activation by FeS. The selectivity patterns for the oxidation of chlorinated ethenes, ethanes and benzenes differ notably depending on the persulfate activation method. The obtained kinetic data are in conformity with the hypothesis that sulfate radicals generated at the FeS surface have different selectivities than freely dissolved radicals. The assumption of different reactive species is further confirmed by the determination of hydrogen kinetic isotope effects (H-KIEs) for the oxidation of methanol isotopologues with sulfate radicals using the set of activation methods. The H-KIE obtained in the heterogeneous system (H-KIEFeS = 3.0 ± 0.3) is significantly higher than for the homogeneous system (H-KIEhom = 2.3 ± 0.1). This leads us to the conclusion that sulfate radicals generated on the FeS surface react as surface-associated radicals, which show a different selectivity pattern than freely dissolved radicals.Furthermore, the apparent second-order rate constants in homogenous solution at ambient temperature, ranging from 5 · 107 to 1.7 · 109 M−1 s−1, were determined for the reaction of sulfate radicals with various chlorinated hydrocarbons under study.

Comparing the efficacy of various methods for sulfate radical generation for antibiotics degradation in synthetic wastewater: degradation mechanism, kinetics study, and toxicity assessment.

In the present study the aim was to investigate and compare various activation processes for amoxicillin degradation. UV radiation, ultrasound, heat, and hydrogen peroxide were selected as the persulfate activation methods. The effects of various parameters such as pH, persulfate concentration, reaction time, AMX concentration, radical scavengers, and anions were thoroughly investigated. The results showed that AMX degradation was following the pseudo-first order kinetic model. The reaction rate of 0.114 min−1 was calculated for the UV/PS process, which was higher than that of the other investigated processes. The AMX degradation mechanism and pathway investigations revealed that sulfate and hydroxyl radicals were responsible for the degradation of AMX by two degradation pathways of hydroxylation and the opening of the β-lactam ring. Competition kinetic analysis showed that the second-order rate constant of AMX with sulfate radicals was 8.56 × 109 L mol−1 s−1 in the UV/PS process. Cost analysis was conducted for the four investigated processes and it was found that 1.9 $m−3 per order is required in the UV/PS process for the complete destruction of AMX. Finally, cytotoxic assessment of the treated effluent on human embryonic kidney cells showed a considerable reduction in AMX-induced cell cytotoxicity, proving that the investigated process is sufficiently capable of completely destroying AMX molecules to nontoxic compounds. Therefore, it can be concluded that UV radiation is much more effective than other methods for persulfate activation and can be considered as a reliable technique for antibiotic removal.

Persulfate enhanced visible light photocatalytic degradation of iohexol by surface-loaded perylene diimide/acidified biochar

Persulfate (PS) is extensively employed as an oxidant to develop the sulfate radical-based advanced oxidation processes for removing organic pollutants and various PS activation methods have been explored. Iohexol (IOH), as a typical iodinated X-ray contrast media, poses a threat to human health and ecological environment, which is difficult to be removed by conventional treatment methods. In our work, a photocatalytic coupling persulfate system was constructed for efficient IOH degradation. A novel binary photocatalyst of biochar loaded with perylene diimide (PDI/BC, PB) was successfully prepared via a one-pot water bath heating method, which achieved BC acidification and PDI self-assembly simultaneously. Different mass ratios of BC and PDI lead to variance in average particle size, electronegativity, bandgap width and electron/hole separation efficiency. The optimized efficiency of 10 mg/L IOH on PB-9 (PDI:BC = 1:9, w/w) reached 100% in 2 h with 1.5 mM sodium persulfate under visible light irradiation. Based on the results of trapping experiments and electron paramagnetic resonance, holes and hydroxyl radicals were the dominant active species and the free radical chain reaction and mutual conversion reaction of active species occurred. The amide hydrolysis, amine and C-OH oxidation, hydrogen extraction, deiodination and OH addition were observed during the degradation process. Density functional theory calculation was conducted to confirm the free radical attack sites. The findings of this work demonstrate that metal-free supramolecular loaded photocatalyst has the potential for application in the removal of organic pollutants for water remediation.

Comparison of Manganese Dioxide and Permanganate as Amendments with Persulfate for Aqueous 1,4-Dioxane Oxidation

Persulfate (PS) is widely used to degrade emerging organic contaminants in groundwater and soil systems, and various PS activation methods (e.g., energy or chemical inputs) have been considered to increase oxidation strength. This study investigates PS activation through manganese amendment in the form of potassium permanganate (KMnO4) and manganese dioxide (MnO2) to subsequently degrade the emerging and recalcitrant groundwater contaminant 1,4-dioxane (1,4-D). The activation of PS by MnO2 was confirmed by radical trap and by product formation. The degradation kinetics of 1,4-D by PS was also compared with varying amendments of KMnO4 and MnO2. The results showed that MnO2 activated PS, which increased the degradation rate constant of 1,4-D. KMnO4 activation of PS was not observed even though the binary oxidant mixture did enhance the degradation of 1,4-D. These results have implications for applying in situ chemical oxidation in subsurface systems, especially for conditions wherein manganese exists naturally in groundwater or aquifer minerals to support possible PS activation.

Modification of nZVI with a bio-conjugate containing amine and carbonyl functional groups for catalytic activation of persulfate

Although the catalytic activation of persulfate by iron is now common in environmental sciences, there are still several obstacles, including the non-selectiveness and high cost of the production of the iron catalyst. Therefore, it is essential to develop fast and easy methods for producing an iron catalyst that exhibits high surface area properties and rapid catalytic activation of persulfate. In the present work, a chitosan-poly(3–hydroxybutyrate) conjugate (CS-PHB) was used to improve the synthesis of nanoscale zero-valent iron (nZVI). CS-PHB possesses among others two functional groups (carbonyl and amine) that are desirable for catalytic applications, including heterogeneous persulfate activation. The produced CS-PHB-nZVI particles showed an extensive surface area (113 m2/g) and, at the same time, superior activity in heterogeneous catalysis, which was tested and compared with others persulfate activation methods (heat, Fe2+, commercial nZVI). The most suitable activation conditions for complete degradation of 0.15 mM of the model pollutant (methyl orange; MO) were determined (i.e., a pH of 7, persulfate and CS-PHB-nZVI concentrations of 2 mM and 50 mg/L, respectively). The role of temperature in MO oxidation was evaluated by the Arrhenius equation, and the results showed that the estimated activation energy (Ea) was 27.1 kJ/mol. The MO degradation may be attributed to the generation of SO4− in the system as a result of scavenging tests. A magnet can be used to easily separate the remaining catalyst. It is believed that due to it having several advantages over traditionally used nZVI, CS-PHB-nZVI may be successfully applied for catalytic remediation of contaminants that are reactive towards sulfate radicals.

Highly efficient degradation of rhodamine B by carbon nanotubes-activated persulfate

Recently, sulfate radical SO4∙-(E0 = 2.60 V) generated by the activation of persulfate (PS) has been reported to be effective in destructing recalcitrant organic contaminants. However, conventional PS activation methods (e.g., via heat, UV or carbon-base materials) need high energy input or may cause secondary contamination (due to the use of transition metals). In the present study, a novel system with PS activated by metal-free carbon-nanotubes (CNTs) was developed. Results indicate that CNTs could efficiently activate PS for degradation of RhB (e.g., 100% removal with 150 min) with low concentrations of PS at the initial pH range of 3–9. The removal efficiency of RhB increased with an increase in CNTs dosage and PS concentration. The coexistence of natural organic matter (NOM) in the natural environment significantly promoted the degradation of RhB. Both radical and non-radical pathway could activate PS by CNTs, but non-radical pathway was dominated. PS can be activated by the oxygen-containing groups on the surface of CNTs to generate hydroxyl radical (OH∙) and sulfate radical(SO4∙-).Meanwhile, the electron transfer process among PS, RhB and CNTs was confirmed by PS decomposition and linear sweep voltammetry (LSV) experiments. Furthermore, the possible degradation pathway of RhB was proposed according to the analytical results. These findings provides a new strategy for high efficiency treatment of RhB wastewater without using high energy input or introducing any secondary contamination associated with metal pollution.

Removal of polycyclic aromatic hydrocarbons (PAHs) and the response of indigenous bacteria in highly contaminated aged soil after persulfate oxidation.

Integrated chemical-biological treatment is a promising alternative to remove PAHs from contaminated soil, wherein indigenous bacteria is the key factor for the biodegradation of residual PAHs after the application of chemical oxidation. However, systematical study on the impact of persulfate (PS) oxidation on indigenous bacteria as well as PAHs removal is still scarce. In this study, the influences of different PS dosages (1%, 3%, 6%, and 10% [w/w]), as well as various activation methods (native iron, H2O2, alkaline, ferrous iron, and heat) on PAHs removal and indigenous bacteria in highly contaminated aged soil were investigated. Apparent degradation of PAHs in the soil treated with PS oxidation was observed, and the removal efficiency of total PAHs in the soil ranged from 38.28% to 79.97%. The removal efficiency of total PAHs in the soil increased with increasing consumption of PS. However, the bacterial abundance in soil was negatively affected following oxidation for all of the treatments added with PS, with bacterial abundance in the soil decreased by 0.89-2.93 orders of magnitude compared to the untreated soil. Moreover, the number of total bacteria in the soil decreased as PS consumption increased. Different PS activation methods and PS dosages exhibited different influences on the bacterial community composition. Bacteria capable of degrading PAHs under anoxic conditions were composed predominantly by Proteobacteria and Firmicutes. The total amount of Proteobacteria and Firmicutes also decreased with increasing consumption of PS. The results of this study provide important insight for the design of PAHs contaminated soil remediation projects.

A potential novel approach for in situ chemical oxidation based on the combination of persulfate and dithionite

Although persulfate (PS) activation has been commonly applied to remove organic contaminants on the subsurface, it is valuable to further explore PS activation methods. In this study, a novel combined process based on PS coupled with dithionite was investigated using trichloroethene (TCE) as a typical organic contaminant. PS/dithionite was demonstrated to be an effective system for TCE degradation depending on the operating parameters such as the initial PS and dithionite dosages. The optimal molar ratio of PS/dithionite/TCE was 5/5/1. Sulfate radicals (SO4•−) were the dominant reactive species responsible for TCE degradation in the PS/dithionite system. Two pathways for SO4•− generation were proposed in the PS/dithionite system. The generation of SO4•− increased in the presence of oxygen but was still effective in an anaerobic environment. This study is the first to report a novel combined process based on PS coupled with dithionite, which is expected to be an efficient and environmentally friendly approach for in situ chemical oxidation (ISCO) remediation of contaminated soil and groundwater, whether in aerobic or anaerobic environments.

Remediating Potentially Toxic Metal and Organic Co-Contamination of Soil by Combining In Situ Solidification/Stabilization and Chemical Oxidation: Efficacy, Mechanism, and Evaluation.

Most soil remediation studies investigated single contaminants or multiple contaminants of the same type. However, in field conditions, soils are often contaminated with potentially both toxic metals and organic pollutants, posing a serious technical challenge. Here, batch experiments were conducted to evaluate the performance of combining in situ solidification/stabilization (ISS) and in situ chemical oxidation (ISCO) for the simultaneous removal of aniline (1000 mg/kg) and Cd (10 mg/kg). All four tested ISS amendments, especially quick lime and Portland cement, promoted in situ chemical oxidation with activated persulfate in contaminated soil. Combined ISS/ISCO remediation effectively removed aniline and reduced the bioavailable Cd content at optimal initial persulfate and ISS amendment concentrations of 1.08 mol/kg and 30 wt% with a seven-day curing time, and significantly reduced leaching. Persulfate inhibited the reduction of the bioavailable Cd content, and ISS amendment with persulfate did not synergistically remediate Cd in co-contaminated soil. Strong alkalinity and high temperature were the main mechanisms driving rapid pollutant removal and immobilization. The reaction of CaO with water released heat, and Ca(OH)2 formation increased the pH. The relative contributions of heat vs. alkaline activation, as well as the contaminant removal efficiency, increased with ISS amendment CaO content. Combined treatment altered the soil physicochemical properties, and significantly increased Ca and S contents. Activated persulfate-related reactions did not negatively impact unconfined compressive strength and hydraulic conductivity. This work improves the selection of persulfate activation methods for the treatment of soils co-contaminated with both potentially toxic metals and organic pollutants.

Catalytic oxidation of aqueous organic contaminants by persulfate activated with sulfur-doped hierarchically porous carbon derived from thiophene

Sulfate radicals (SO4−) generated from persulfate (PS) activated by carbocatalysis is expected to provide an environmentally friendly and highly efficient catalytic oxidation process for aqueous organics degradation. Herein, a novel sulfur-doped hierarchically porous carbon with both structural and compositional modification was proposed for PS activation by using thiophene as sulfur/carbon precursor and KOH as activator. The effect of annealing temperature on its textural properties and surface chemistry was characterized by Elemental analysis, N2 sorption isotherms, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, Raman spectra and X-ray diffraction. The as-prepared sample treated at 800°C (SDAC-800) demonstrated outstanding catalytic activity for activation of PS to degrade 4-chlorophenol (4CP). Studies on the role of sulfur in the catalytic activity enhancement were carried out by comparing with a sulfur-free activated carbon and a carbon model (reduced graphene oxide (rGO)). The effects of catalyst dosage, initial 4CP concentration, and reaction temperature on 4CP degradation were comprehensively investigated. In addition, contrast tests with other conventional PS activation methods, SDAC-800 reusability and its general applicability tests were also carried out. The mechanism of PS activation and 4CP oxidation was elucidated by using quenching tests with chloridion, l-histidine and ethanol as radical scavengers. It revealed that the conventional radical pathway was not a critical role in 4CP degradation. In contrast, the process was controlled by both particle-surface interaction and non-radical pathway, and the latter played a dominant role.

Elimination of sulfaclozine from water with SO4[rad]− radicals: Evaluation of different persulfate activation methods

The evaluation of different persulfate activation methods (UV, solar light, electron, Fe(II)) on the degradation of sulfaclozine was investigated along with the effect of persulfate concentrations. UV/TiO2/K2S2O8 resulted in the highest degradation rate regardless persulfate concentrations. However, persulfate addition on the UV/TiO2 system was not as efficient as expected and the use of radical scavengers showed that pH played an important role in the distribution of dominant radicals. It was found that at pH 7, hydroxyl and sulfate radicals were involved in the degradation of sulfaclozine, whereas at pH 11 no contribution of sulfate radicals was observed.Following the formation of the six by-products of the first generation formed in UV/TiO2 system, we obtained the formation of two by-products out of six in the UV/K2S2O8 system and four in the UV/TiO2/K2S2O8 system but with different concentrations, confirming the hypothesis suggested about the intervention of O2− in the degradation mechanism of sulfaclozine.The second order rate constant of the reaction between sulfaclozine and SO4− radicals was determined by a competitive kinetics method and two values of 7.5×109M−1s−1 and 1.7×1010M−1s−1 were obtained depending on the references used, and found to be close to those obtained between sulfaclozine and OH radicals (7.2×109M−1s−1 and 5.9×109M−1s−1).

Evaluation of sulfathiazole degradation by persulfate in Milli-Q water and in effluent of a sewage treatment plant.

The presence of antibiotics and their metabolites in natural waters has raised some concern among scientists around the world because it can lead to bacterial resistance and other unknown consequences to mankind and wildlife. Persulfate (PS)-driven oxidation is a new technology that has been used successfully to remediate contaminated sites, but its use to treat wastewater, especially sewage treatment plant (STP) effluent, is still scarce. This paper describes the effect of several persulfate activation methods for degrading sulfathiazole (STZ) in Milli-Q water and in STP effluent. Some parameters, such as pH, persulfate concentration, presence of Mn2+, Zn2+, Cu2+, Fe2+, and Fe3+, as well as copper and iron organic complexes, were studied in STZ degradation. Raising the pH from 5 to 9, as well as the persulfate concentration, resulted in increased STZ degradation. Among the transition metals evaluated, only Fe2+ and Cu2+ were able to activate persulfate molecules. Copper was a better activator than iron since its effect lasts longer. Citrate was the best ligand evaluated increasing Fe(II) activation capacity at pH 7. Hydroxylamine addition to Fe(II) on persulfate system extended the Fe(II) effect. The presence of bicarbonate or humic acid did not affect PS-driven degradation of STZ. Finally, the degradation of STZ in STP effluent promoted by PS-driven oxidation (25°C) was as fast as in Milli-Q water, proving to be successful.

Effect and mechanism of persulfate activated by different methods for PAHs removal in soil

The influence of persulfate activation methods on polycyclic aromatic hydrocarbons (PAHs) degradation was investigated and included thermal, citrate chelated iron, and alkaline, and a hydrogen peroxide (H2O2)-persulfate binary mixture. Thermal activation (60°C) resulted in the highest removal of PAHs (99.1%) and persulfate consumption during thermal activation varied (0.45–1.38g/kg soil). Persulfate consumption (0.91–1.22g/kg soil) and PAHs removal (73.3–82.9%) varied using citrate chelated iron. No significant differences in oxidant consumption and PAH removal was measured in the H2O2–persulfate binary mixture and alkaline activated treatment systems, relative to the unactivated control. Greater removal of high molecular weight PAHs was measured with persulfate activation. Electron spin resonance spectra indicated the presence of hydroxyl radicals in thermally activated systems; weak hydroxyl radical activity in the H2O2–persulfate system; and superoxide radicals were predominant in alkaline activated systems. Differences in oxidative ability of the activated persulfate were related to different radicals generated during activation.