Sulfate Radical-based Advanced Oxidation Processes Research Articles

Degradation of phenol by coal-based carbon membrane integrating sulfate radicals-based advanced oxidation processes

Phenol, as a representative organic pollutant in aquatic environments, has posed a serious threat to humans and ecosystem. In this work, a novel integration system combined coal-based carbon membrane with sulfate radicals-based advanced oxidation processes (SR-AOPs) was designed for degradation of phenol. The integrated system achieved 100% removal efficiency under the optimal condition (peroxydisulfate dosage is 0.2 g/L, at alkaline condition with 2 mL/min flow velocity). The quenching experiments revealed that the efficient removal of phenol by the integrated system were attributed to the co-existence of radical and nonradical mechanisms. This study proposes a green and efficient technique for the removal of phenol.

Disposal of phenol waste water by CoFe2O4&AA activated peroxydisulfate

ABSTRACT The pathological changes caused by phenolic wastewater discharged from various industries has attracted extensive attention in recent years. In this study, a novel sulfate-radical-based advanced oxidation process (SR-AOP) was used to dispose the target pollutant – phenols. Firstly, a solid-phase active catalyst – cobalt ferrite (CoFe2O4) was prepared from a sol–gel process with the innovative addition of ascorbic acid (AA). Then the original AOP was modified by using a novel CoFe2O4/AA/PDS combined system (PDS: peroxydisulfate). CoFe2O4 was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and H-M magnetic hysteresis loops. The influence factors on degradation in the new system were determined. It was found the activated PDS () generated a strong oxidizer sulfate radical (SO4·) and the phenol removal process basically obeyed the pseudo-first-order kinetics. The phenol degradation rate maximized to 98.00% under the following optimal conditions: CoFe2O4 preparation temperature at 500°C, initial phenol concentration at 50.00 mg/L, PDS dosage of 4.20 mM, CoFe2O4 dosage of 1.00 gL−1, and AA dosage of 0.42 mM. The new system had a high phenol degradation performance in a wide range of pH 3-7. The easy oxidization of metal ion solutions in a homogeneous system and the application limitation of pH range were well solved. The synergistic effect of the novel CoFe2O4/AA/PDS combined system on activated PDS was verified. The separation and reuse of CoFe2O4 were improved owing to its magnetism. These findings will underlie the practical application of CoFe2O4 into disposal of phenol waste water.

Understanding the synergetic effect from foreign metals in bimetallic oxides for PMS activation: A common strategy to increase the stoichiometric efficiency of oxidants

Synergistic effect was commonly observed in bimetallic oxide catalysts in sulfate radical-based advanced oxidation processes by forming spinel structures. In this paper, we found the incorporation of Cu demonstrated the most remarkable promotional effect to Co oxides comparing with Fe and Mn in PMS activation, and no spinel structure of mixed metals was found. Moreover, the synergism between oxides of Cu and Co was observed on various supports including MgAl layered double hydroxides, mesoporous MnO2 and ZnO. Under conditions of 0.2 g L−1 catalysts, 2 mM PMS, and 40 ppm 4-chlorophenol (4-CP), CuCo@ZnO/PMS system demonstrated excellent performance that 96.0% 4-CP could be removed, while the removal efficiency of 4-CP in Cu@ZnO/PMS and Co@ZnO/PMS systems was only 12.1% and 45.4%, respectively. The simultaneous incorporation of Co and Cu bimetallic oxides in CuCo@ZnO led to a higher surface hydroxyl density, and this surface hydroxyl density showed a linear relationship to their first order kinetic constant in 4-CP degradation. Moreover, the results of peroxymonosulfate (PMS) decomposition, quantification of sulfate radical (SO4−), EPR, XPS, H2-TPR, and CV indicated that the synergism of Cu/Co also arose from the electron transfer between Cu(I) and Co(III), which altered the redox circle of Co(II)/Co(III) and increased the steady concentration of oxidative radicals. Due to this synergism, the degradation percentage of organic contaminants, stability of heterogeneous catalysts and the stoichiometric efficiency of PMS were all improved. These findings were highly suggestive to the further development of bimetallic heterogeneous catalysts in persulfate based advanced oxidation processes.

Remarkably enhanced sulfate radical-based photo-Fenton-like degradation of levofloxacin using the reduced mesoporous MnO@MnOx microspheres

Sulfate radical-based advanced oxidation processes (SR-AOPs) are promising alternatives to conventional hydroxyl radical-AOPs for recalcitrant contaminants elimination in water treatment. Herein, the efficient and fast degradation of antibiotic levofloxacin (LEV) using mesoporous MnO@MnOx microspheres was successfully achieved with peroxymonosulfate (PMS) as an oxidant under simulated sunlight irradiation. Remarkably, MnO@MnOx catalyst achieves 98.1% degradation and 81.4% mineralization of LEV after being irradiated for 30 min, and SO4−, OH, O2− and 1O2 species play the imperative role in the SR-photo-Fenton-like oxidation process. Through the reaction intermediates identification, the LEV degradation pathways are speculated. The deterioration of performance is inconspicuous in the cyclic runs with negligible Mn-ions leaching. The excellent catalytic activity and stability of the H2-reduced MnO@MnOx microsphere are ascribed to the mesoporous structure, multivalence and oxygen vacancies, resulting in the large specific area, strong UV–vis response, effective charge separation coupling with desirable self-redox properties of Mn-ions on the catalyst surface. This study offers a useful guideline to efficiently degrade recalcitrant contaminants for water treatment.

Highly Efficient Utilization of Nano-Fe(0) Embedded in Mesoporous Carbon for Activation of Peroxydisulfate.

Nanoscale zerovalent iron (nZVI) particles have received much attention in environmental science and technology due to their unique electronic and chemical properties. However, the aggregation and oxidation of nZVI brings much difficulty in practical application of environmental remediation. In this study, we reported a composite nano-Fe(0)/mesoporous carbon by a chelation-assisted coassembly and carbothermal reduction strategy. Nano-Fe(0) particles with surface iron oxide (Fe2O3·FeO) were wrapped with graphitic layers which were uniformly dispersed in mesoporous carbon frameworks. The unique structure made the nano-Fe(0) particles stable in air for more than 20 days. It was used as a peroxydisulfate (PDS) activator for the oxidation treatment of 2,4,6-trichlorophenol (TCP). The TOF value of MCFe for TCP degradation is nearly 3 times higher than those of FeSO4 and Fe2O3·FeO and nearly 2 times than that of commercial nZVI. The reactive oxygen species (ROS) including •SO4-, HO•, and •O2-, 1O2 are efficiently generated by PDS activation with MCFe. The PDS activation process by nano-Fe(0) particles was intrinsically induced by the ferrous ions (Fe(II)) continuously generated at the solid/aqueous interface. Namely, the nano-Fe(0) particles were highly efficiently utilized in sulfate radical-based advanced oxidation processes (SR-AOP). The porous structure also assists the absorption and transfer of TCP during the degradation process.

Degradation of benzotriazole by sulfate radical-based advanced oxidation process

ABSTRACT Benzotriazole (BTA) is a recalcitrant contaminant that is widely distributed in aquatic environments. This study explored the effectiveness of sulfate radical-based advanced oxidation process in degrading BTA (SR-AOP). The sulfate radical was generated by heat activation of persulfate (PS). Our results show alkaline pH promoted the BTA degradation. The solution pH also affected the speciation of total radicals. Sulfate radical () predominated at acidic pH while hydroxyl radical (HO•) predominated at basic pH. High temperature, high PS concentration and low BTA concentration promoted the BTA degradation. Influence of water matrix constituents on the reaction kinetics was assessed. We found that ≤10 mM of Cl− promoted the reaction, but 100 mM Cl− inhibited it. was similar to Cl−. Br− and inhibited the reaction while did not affect the reaction. of ≤10 mM did not affect the reaction, but 100 mM of inhibited it. Eleven degradation intermediates were identified using ultra-high solution Orbitrap mass spectrometry. Based on the intermediates identified, possible reaction pathways were proposed. Overall, SR-AOP can effectively mineralize BTA, but water matrix constituents greatly influenced the reaction kinetics and thus should be carefully considered for its practical application. Abbreviations: BTA, benzotriazole; PS, persulfate; PMS, peroxymonosulfate; SPC, sodium percarbonate; AOP, advanced oxidation process; PS-AOP, persulfate-based advanced oxidation process; SR-AOP, sulfate radical-based advanced oxidation process; TAP, thermally activated persulfate; TOC, total organic carbon; TBA, tert-butyl alcohol

Enhanced degradation of paracetamol in water using sulfate radical-based advanced oxidation processes catalyzed by 3-dimensional Co3O4 nanoflower

Paracetamol (APAP) represents a critical emerging contaminant in various water bodies and sulfate radical (SO4−)-involved Advanced Oxidation Processes (AOPs) using Oxone are proven as promising approaches for degrading APAP. While Co3O4 is the benchmark catalyst for activating Oxone, Co3O4 nanoparticles are usually found to aggregate severely, losing their catalytic activities. In this study, a facile but convenient protocol is developed to prepare a unique Co3O4 material, which exhibits a morphology of nanoflower. More importantly, the flower petals of this Co3O4 nanoflower (CNF) are needle-shaped and comprised of numerous fine Co3O4 particles which are separated, enabling this CNF to exhibit high surface areas and large pore volumes. CNF also shows significantly higher catalytic activities than the commercial Co3O4 NPs for activating Oxone to degrade APAP. APAP degradation is confirmed to involve with sulfate radicals via examining effects of radical probe reagents and EPR analysis. CNF is reusable over several continuous cycles. The APAP degradation pathway is also investigated according to the degradation products determined using LC-MS/MS. The findings of this study are valuable to advance treatments of APAP in water by sulfate-radical-based processes, and also insightful to determine catalytic characteristics of Co3O4 with such a unique morphology of nanoflower.

Enhanced removal of lomefloxacin based on peroxymonosulfate activation by Co3O4/δ-FeOOH composite

In the present study, a novel Co3O4/δ-FeOOH composite was successfully fabricated. Subsequently, we measured its crystal structure, morphology, and surface area. After this, the Co3O4/δ-FeOOH composite was applied to activate peroxymonosulfate (PMS) for lomefloxacin (LOM, a type of fluoroquinolones) degradation. Compared with pure Co3O4 and δ-FeOOH, Co3O4/δ-FeOOH composite exhibited the best efficiency towards LOM degradation, in which the removal of LOM (>82%) and first order reaction kinetic rate constant (kapp = 0.064 min−1) were achieved after 25 min reaction with 0.25 g·L−1 Co3O4/δ-FeOOH, 0.49 mM PMS, and 10 mg·L−1 (28.5 μM) LOM at initial pH 6.08. Next, we considered the concentration of catalyst, PMS and the effect of pH on LOM degradation. The results showed that the increase of PMS and catalyst was beneficial for the degradation of LOM. Moreover, the highest degradation efficiency of LOM was achieved under neutral conditions, which was due to the minimum repulsive force between the PMS and the catalyst. In addition, active radical scavenging experiment was performed and it was found that the contribution of hydroxyl radicals was greater than that of sulfate radicals. Subsequently, possible reaction mechanism was proposed. What’s more, possible degradation intermediates in Co3O4/δ-FeOOH system were determined and five decomposition pathways were proposed. Meanwhile, activated sludge inhibition experiment was carried out to evaluate the variation of toxicity of the LOM and its degradation intermediates in the oxidation process. Overall, this work provided a new strategy for the practical application of sulfate radicals-based advanced oxidation processes (SR-AOPs) in wastewater treatment.

Coupling of heterogeneous advanced oxidation processes and photocatalysis in efficient degradation of tetracycline hydrochloride by Fe-based MOFs: Synergistic effect and degradation pathway

In this work, a Fe-based metal organic frameworks (MIL-88A) has been synthesized through a hydrothermal method and adopted as a high-efficiency catalyst for photocatalysis (PC) coupled with sulfate radical-based advanced oxidation processes (SR-AOPs) to degrade tetracycline hydrochloride (TC-HCl) under visible light irradiation. The effects of MIL-88A/persulfate (PS) molar ratio, initial solution pH and catalyst dosage were studied. The results indicated that the combining of the photocatalysis and SR-AOPs could remarkably enhance TC degradation and 200 mg/L 100 mL TC could be degraded completely at 0.25 g/L MIL-88A, unadjusted pH value and 4 mM PS in 80 mins. The results of scavenging experiments and ESR analysis demonstrated that SO4−• and •O2– radicals were the predominant radicals for the TC degradation. The significant improvement of degradation rate in MIL-88A/PS/Vis process is attributed to the following two factors: (1) as a photocatalyst, MIL-88A could be excited by visible light, therefore photogenerated electrons (e−) on the conduction band (CB) of MIL-88A could be trapped by PS to generate SO4−• radicals. In this process, PS acted as an electron acceptor and the electron/hole recombination was suppressed leading to the enhanced photocatalyst efficiency; (2) The PS can be activated not only by photoelectrons but also Fe (III) in MIL-88A leads to the generation of SO4−• radicals more rapidly and easily. A possible mechanism and degradation pathway for TC was proposed based on the trapping/ESR experiments and liquid chromatography-mass spectrometry (LC-MS) analysis. This work proposed a new idea and method in combining two oxidation processes in degradation of organic pollutants thus could be potentially used in environmental purification.

Sulfate radical induced catalytic degradation of metolachlor: Efficiency and mechanism

Efficient removal of residual metolachlor (MET), a frequently used herbicide from aquatic system is highly desirable but remains a challenge. In the present study, the emerging sulfate radical based advanced oxidation processes (SR-AOPs) is developed for the degradation of MET from aqueous solution. At the conditions of [MET] = 10 mg L−1, [Peroxymonosulfate (PMS)] = 3 mM, [Catalyst] = 0.2 g L−1, pH = 6.5, the degradation process could be accomplished within 40 min and the derived pseudo-first-order kinetic rate constant (kapp) was 0.11 min−1. The effects of reaction conditions including pH, oxidant dosage, temperature, concomitant anions and humic acid on the degradation process were comprehensively investigated. Sulfate radical was identified to be the main contributor to the degradation process through radical scavenging and electron paramagnetic resonance (EPR) analysis. The second-order rate constant for reaction of SO4− with MET was determined to be 2.17 × 109 M−1s−1 by competition kinetic method. The degradation showed a moderate pH-tolerance. Specifically, alkaline/neutral conditions were beneficial for the MET degradation whilst acidic condition exhibited a detrimental effect on the degradation. Through LC-Q-TOF-MS analysis, eleven aromatic derivatives were detected and their molecular structures were tentatively proposed. A tentative mechanism was proposed based on the detected derivatives. The toxicity test further revealed that the degradation products performed a less toxicity than MET. The results pave an avenue toward the applications of SR-AOPs for MET elimination from aquatic environment.

Synthesis of magnetite-supported catalysts for phenol oxidation in aqueous solution

One of the usual ways to degrade phenol contaminant is sulfate radical-based advanced oxidation processes (SR-AOPs). In this study, reactive sulfate radicals have been produced by Co3O4/Fe3O4@nSiO2@mSiO2 catalyst and Fe3O4 nanoparticles. It has been found that the couple of supported cobalt catalyst and peroxymonosulfate (PMS) is highly effective to produce sulfate radicals for phenol oxidation. In contrary to, Fe3O4-PMS system displays much low phenol degradation, and Co3O4/Fe3O4@nSiO2@mSiO2 catalyst shows a good catalytic performance in solution. The properties of this supported catalyst have been characterized by XRD (powder X-ray diffraction), SEM–EDS (scanning electron microscopy–energy-dispersive X-ray spectroscopy), TEM (transmission electron microscopy), and nitrogen adsorption–desorption. This magnetic catalyst is facility separated from the medium by an external magnetic field. Finally, three different methods involving annealing in the air, washing with water and applying ultrasonics was used for regenerating the deactivated catalyst. The heat treatment can recover the catalyst nearly.

Re-evaluation of sulfate radical based–advanced oxidation processes (SR-AOPs) for treatment of raw municipal landfill leachate

Sulfate radical (SO4-) -based advanced oxidation processes (SR-AOPs) have proven effective for simultaneously removing refractory dissolved organic matter (DOM) and ammonia in municipal landfill leachates. However, the knowledge on the competition of leachate DOM and ammonia for SO4-, the utilization efficiency of persulfate, as well as the reaction pathways and final products of ammonia oxidation during the SR-AOP treatment remains little known, thereby leading to a lack of a comprehensive evaluation of the emerging leachate treatment technology. The objective of this study was to further investigate the performance of a thermally activated persulfate system for treatment of a mature landfill leachate and re-evaluate the benefits and restrictions of SR-AOPs for leachate treatment. The laboratory experimental results showed that removal patterns of chemical oxygen demand (COD) and ammonia relied heavily upon the dose of persulfate that could be thermally activated to produce reactive sulfate radicals, reflecting the competition of leachate DOM, ammonia, and non-target leachate constituents for SO4-. The utilization efficiency of the added persulfate could be more efficiently utilized for removing the two target leachate pollutants at a lower persulfate dose, whereas more persulfate was wasted due to the reactions with non-target leachate constituents (e.g. Cl− and CO32−) and/or self-decomposition with the increasing persulfate dose. During the treatment, ammonia was oxidized, via the direct attack of SO4- and/or by molecular chlorine produced from the reactions of chloride and sulfate radicals, into nitrate and nitrogen gas, while nitrite was not detected. Of importance, this study highlighted three potentially negative impacts of SR-AOPs on the quality of treated leachate, including accumulation of total dissolved solids, the production of undesirable nitrate, and the pH decrease due to the continuous formation of hydrochloric acid. Therefore, the three issues should be carefully evaluated when a SR-AOP is selected for leachate treatment. Because these impacts become less pronounced with a decreasing persulfate dose, SR-AOPs as a pre-treatment, which is achieved at a relatively low persulfate dose, may be an appropriate option for the SR-AOP application to leachate treatment.

Enhanced activation of peroxymonosulfate by magnetic Co3MnFeO6 nanoparticles for removal of carbamazepine: Efficiency, synergetic mechanism and stability

To achieve complete removal of persistent organic pollutant from water system, an efficient, stable, magnetic and low-energy sulfate radical-based advanced oxidation process (SR-AOPs) is in desirable to be established. In this work, magnetic trimetallic oxides Co3MnFeO6 nanoparticles were successfully synthesized and utilized as novel heterogeneous catalysts to activate peroxymonosulfate (PMS) for the degradation of carbamazepine (CBZ), a recalcitrant organic pollutant. In the degradation tests, Co3MnFeO6/PMS system showed excellent performance that 99.2% of CBZ could be removed at a relative shorter time (30 min) and in a wider pH range from 3 to 10. More in-depth investigation found that synergistic effects between Co, Mn and Fe in Co3MnFeO6 catalyst were responsible for the efficient generation of sulfate radical from PMS activation. And the roles of Co, Mn and Fe in synergistic effect were identified as: the redox cycles of Co and Mn mainly worked for the activation of PMS, and Fe mainly provided magnetism for Co3MnFeO6 catalyst as well as the adsorption site for PMS and CBZ. Moreover, it was found that Co3MnFeO6 catalyst maintained high activity and robust magnetism during repeated batch experiments. Even in real wastewater samples (municipal wastewater, tap and river water), Co3MnFeO6/PMS system was capable of high activity for CBZ removal, indicating that Co3MnFeO6/PMS system possessed promising potential in practical applications. The possible CBZ degradation pathways were also proposed based on the detected intermediates. This Co3MnFeO6/PMS system may provide some new inspirations for the construction of multiple metal-based catalysts in AOPs.

Heterogeneous activation of peroxymonosulfate using Mn-Fe layered double hydroxide: Performance and mechanism for organic pollutant degradation

On account of high oxidation ability of sulfate radical-based advanced oxidation processes (AOPs), the eco-friendly catalysts for peroxymonosulfate (PMS) activation have received considerable attentions. Previous studies mainly focused on Cobalt-based catalyst due to its high activation efficiency, such as Co3O4/MnO2 and FeCo-layered double hydroxide (LDH), whereas Cobalt-based catalyst usually has serious risk to environment. To avoid this risk, MnFe-LDH was primarily synthesized in this research by simple co-precipitation and subsequently utilized as an effective catalyst for peroxymonosulfate (PMS) activation to degrade organic pollutants. The experimental results demonstrated that MnFe-LDH with a lower dosage (0.20 g/L) could efficiently activate PMS to achieve 97.56% removal of target organic pollutants Acid Orange 7 (AO7). The AO7 degradation process followed the pseudo-first-order kinetic well with an activation energy of 21.32 kJ/mol. The intrinsic influencing mechanism was also investigated. The quenching experiment and electron spin resonance (ESR) indicated that sulfate and hydroxyl radicals were produced by the effective activation of PMS by MnFe-LDH, resulting in a high rate of decolorization. The possible AO7 removal pathway in the constructed MnFe-LDH/PMS system was presented on the basis of UV–vis spectrum analysis and GC–MS, which suggested that the AO7 degradation was firstly initiated by breaking azo linkages, then generated phenyl and naphthalene intermediates and finally presented as ring-opening products. This effective MnFe-LDH/PMS system showed great application potential in the purification of wastewater contaminated by refractory organic pollutants.

Biodegradability improvement of composting leachate by sulfate radical-advanced oxidation process followed by aerobic and anaerobic treatmentcomparison of biodegradability improvement of composting leachate by sulfate radical-advanced oxidation process for aerobic and anaerobic treatment

Aims: Comparing to strong traditional oxidation, the persulfate and sulfate radicals was characterized by relatively low cost and easy application. The present study aimed to investigate the performance of sulfate radical-based advanced oxidation process (SR-AOP) for pretreatment of compost leachate in order to improvement of its biodegradability. Materials and Methods: The sulfate radicals was used for pretreatment of compost leachate in the batch reactor followed by aerobic and anaerobic biological reactors. Results: the results of combination of SR-AOP with biological treatment showed that BOD5/COD ratio was increase. However, the different trend was observed in COD removal by sequencing batch reactor (SBR) and anaerobic sequencing batch reactor (ASBR). Comparing to SR-AOP with ASBR, the SR-AOP with SBR substantially improved final COD removal efficiency up to 70%. Although pretreatment of compost leachate with the SR-AOP clearly improved the BOD5/COD ratio of entering raw leachate into ASBR (from 0.4 to 0.65), but, the COD removal efficiency was ranging between 25% and 27%. Conclusion: Based on the results, it can be concluded that the BOD5/COD ratio cannot be suggested as biodegradability improvement indicator without considerations of changing of substrate nature during pretreatment.

Highly flexible, mesoporous structured, and metallic Cu-doped C/SiO2 nanofibrous membranes for efficient catalytic oxidative elimination of antibiotic pollutants.

The development of inorganic membranous catalysts with both large mesopores and superb flexibility is extremely favorable for the enhancement of their catalytic oxidation activity for the degradation of antibiotic pollutants in wastewater via sulfate radical-based advanced oxidation processes; however, there still exists a huge challenge for inorganic materials to simultaneously realize these two properties. Herein, metallic copper-doped carbon/silica nanofibrous membranes (Cu@C/SiO2 NFMs) with large mesopores, superb flexibility, and robust mechanical strength were fabricated through a sol-gel electrospinning and subsequent in situ carbonization reduction method. The synthesized Cu nanoparticles were homogeneously distributed throughout the mesoporous C/SiO2 nanofiber matrix, which enabled the resultant Cu@C/SiO2 NFMs to be applied as heterogeneous catalysts, and their catalytic performance was systematically assessed through activating persulfate for the elimination of tetracycline hydrochloride (TCH) in water. The fabricated Cu@C/SiO2 NFMs provided outstanding catalytic performance towards TCH with a high removal efficiency of 95% in 40 min and a rapid removal speed of 0.054 min-1. Moreover, the membranes could be facilely recycled through being directly separated from water without any post-processing. Such a facile strategy for preparing mesoporous and flexible metal-doped inorganic nanofibrous membranes may offer novel insights for designing new types of heterogeneous catalysts for antibiotic-containing wastewater treatment or other potential applications.

Quantum chemical investigations of the decomposition of the peroxydisulfate ion to sulfate radicals

Decomposition of the peroxydisulfate ion (S2O82−, PS) to sulfate radicals (SO4−) is a key step in sulfate radical-based advanced oxidation processes (SR-AOPs). In this study, quantum chemical investigations and calculation of activation energy were performed to reveal the decomposition process of S2O82− at the atomic level. Furthermore, the impacts of several main co-existing components (CCs), including inorganic cations, inorganic anions and organic molecules in wastewater, on the activation energy were evaluated. The results revealed that 3 steps were involved in the S2O82− decomposition: 1) the distance between two subgroups of the ground state of S2O82− (PSS0) increases from ∼0.15 to ∼0.215 nm driven by exogenous energy; 2) a transition occurs for S2O82− from PSS0 to the lowest triplet state (PST1); and 3) two subgroups of PST1 separate from each other spontaneously. The energy needed in the first step was demonstrated to be the activation energy. Moreover, two possible routes by which CCs affect the transition from PSS0 to PST1 were proposed. After ascertaining which route would be taken by different types of CCs, various methods of calculation were used to determine their impacts on S2O82− decomposition, i.e. promotion effect for H+, NH4+, Ca2+, Cl− and Br−, and inhibition effect for Na+, K+, Mg2+, NO3−, CO32−, SO42−, and all studied organic molecules, including acetic acid, benzene, bromoethane, 1-propanol and 4-chlorotoluene. The present study provided novel insights into the decomposition of S2O82− to SO4−, and emphasized the effects of main co-existing inorganic ions and organic molecules in wastewater on SR-AOPs.

Degradation of tetracycline by medium pressure UV-activated peroxymonosulfate process: Influencing factors, degradation pathways, and toxicity evaluation

This study employed the medium pressure UV/peroxymonosulfate (MPUV/PMS), a new sulfate radical-based advanced oxidation process, to eliminate tetracycline (TTC) in water. At pH = 3.7, initial TTC concentration of 11.25 μM, PMS dosage of 0.2 mM and UV dose of 250 mJ cm−2, 82% of TTC was degraded by MPUV/PMS. The second-order reaction rate constants of TTC with SO4− and OH were found to be 1.4 × 1010 M−1 s−1 and 6.0 × 109 M−1 s−1, respectively. Radical quenching experiments indicated that OH played the major role in the degradation of TTC. Higher PMS dosage (0.1–1.0 mM) and higher pH (3–11) could accelerate the TTC removal. Besides, the presence of Cl− (0.1–5.0 mM) and CO32− (0.05–0.5 mM) could also promote the reaction. Eight transformation products (TPs) were identified, and the potential degradation pathways mainly involved hydroxylation, demethylation and decarbonylation processes. The variation in the genotoxicity was investigated using the umu-test, and the results indicate that the genotoxicity of TTC after the MPUV/PMS treatment significantly increased during the initial stage. In addition, the ecotoxicity and mutagenicity of TTC and its TPs were predicted using quantitative structure-activity relationship (QSAR) analysis, and the results revealed that some TPs could have equivalent and even higher toxicity than TTC. MPUV/PMS showed better performance in TTC degradation in real waters than in Milli-Q water. MPUV/PMS is concluded to be an efficient method for removing TTC, but more attention should be paid to the changes of toxicity during this process.

Assessment of Sulfate Radical-Based Advanced Oxidation Processes for Water and Wastewater Treatment: A Review

High oxidation potential as well as other advantages over other tertiary wastewater treatments have led in recent years to a focus on the development of advanced oxidation processes based on sulfate radicals (SR-AOPs). These radicals can be generated from peroxymonosulfate (PMS) and persulfate (PS) through various activation methods such as catalytic, radiation or thermal activation. This review manuscript aims to provide a state-of-the-art overview of the different methods for PS and PMS activaton, as well as the different applications of this technology in the field of water and wastewater treatment. Although its most widespread application is the elimination of micropollutants, its use for the disinfection of wastewater is gaining increasing interest. In addition, the possibility of combining this technology with ultrafiltration membranes to improve the water quality and lifespan of the membranes has also been discussed. Finally, a brief economic analysis of this technology has been undertaken and the different attempts made to implement it at full-scale have been summarized. As a result, this review tries to be useful for all those people working in that area.

A method for removing persulfate interference in the analysis of the chemical oxygen demand in wastewater

In recent years, sulfate radical-based advanced oxidation has received increasing attention for the treatment of water and wastewater. However, the chemical oxygen demand (COD), a common measure of gross organic contamination, is subject to interference from residual persulfate in the treated water. In this study, a new method, based on addition of sodium sulfite (Na2SO3) and heating, has been developed to eliminate the interference of remaining potassium persulfate (PSk) on COD analysis. Results of batch experiments show that potassium persulfate can be efficiently removed with molar ratio of Na2SO3/potassium persulfate ≥ 2 and heating at 90 °C for 60 min. This method (Na2SO3–heating treatment) was further tested in a phenol wastewater and a coal industry wastewater. The deviation of COD values of Na2SO3–heating treatment was lower than 5%, which was much lower than the deviation of the calibration curve method, of more than 14%. This new method could be applied to water samples containing persulfate and organic substances and help researchers to accurately evaluate performance of sulfate radical-based advanced oxidation processes.