Sulfate Radical-based Oxidation Processes Research Articles

UV/persulfate processes for the removal of total organic carbon from coagulation-treated industrial wastewaters

Sulfate radical-based oxidation processes were investigated to understand the relationship between persulfate (PS) consumption and total organic carbon (TOC) removal from industrial wastewater under various PS concentrations. First, the degradation and mineralization of Bisphenol A (BPA) (initial concentration: 11 mg/L) were investigated in ultraviolet (UV)/PS systems. Complete degradation was achieved within 30 min of UV irradiation, and 41%–72% TOC removal was achieved at PS concentrations of 200 and 400 mg/L. The consumed concentration of S2O82− and generated concentration of SO42− increased gradually to similar levels. The ratio of the PS consumption to TOC removal based on the mass concentration (mg/L) was 14.5 and 23.2 at 180 min for 200 and 400 mg/L of S2O82−, respectively. Three types of coagulation-treated industrial wastewater from metal-processing, food-processing, and adhesive-producing plants were obtained, and TOC removal was analyzed using the same UV/PS systems (initial TOC concentration: 100 mg/L). The TOC removal rates ranged from 16.9% to 94.4% after 180 min of UV irradiation at PS concentrations of 1,000, 2,000, 4,000, and 8,000 mg S2O82−/L. Despite the higher TOC removal at higher PS concentrations, the PS activation efficiency decreased significantly as the PS concentration increased. Only approximately 30%–40% activation efficiency was achieved at a PS concentration of 8,000 mg/L. In this study, the ratio of PS consumption to TOC removal ranged from 20.6 to 43.9.

Escherichia coli inactivation in water by sulfate radical-based oxidation process using FeCl3-activated biochar/persulfate system

Pathogenic microbes in water present great risks to environments, water resources, and human health. In the present study, for the first time, a FeCl3-activated bermudagrass-derived biochar (FA-BC) was applied to activate persulfate (PS) for E. coli inactivation. The PS activation was ascribed to the presence of Fe0 and Fe3O4 on the surface of FA-BC, and SO4·− radicals were proved to be the main role for E. coli inactivation using FA-BC activated PS system (FA-BC/PS). Decreasing the pH (5–9) and increasing the PS concentration (50–300 mg/L), reaction temperature (20–50 °C), and FA-BC dosage (100–500 mg/L) resulted in the enhancement of disinfection efficiency of E. coli using FA-BC/PS. 6.21 log reductions of E. coli were achieved within 20 min under the optimal conditions (500 mg/L FA-BC, 200 mg/L PS, pH 7, and 20 °C with 107 CFU/mL E. coli in DI water). The FA-BC/PS effectively eliminated various initial concentrations of E. coli (105–108 CFU/mL). The E. coli inactivation rate decreased from 0.1426 min−1 to 0.0883, 0.1268 min−1, and 0.1093 min−1 with the presence of 10 mg/L humic acid, 100 mg/L Cl−, and 100 mg/L HCO3−, respectively. In addition, after three cycles of disinfection tests using FA-BC/PS, the E. coli inactivation rate only slightly decreased from 0.1426 to 0.1288 min−1. The FA-BC/PS also effectively removed the E. coli in real stormwater with a 99.2 % inactivation efficiency within 180 min. The FA-BC/PS in fixed-bed column tests revealed the continuous and high inactivation of E. coli in water. Increasing the FA-BC amount (1.5 %–5 %) and PS concentration (50–200 mg/L) and decreasing the flow rate (2–4 mL/min) caused the lower E. coli concentration in effluent. Therefore, the FA-BC/PS can be considered as a promising and efficient technique for water disinfection.

Nitrogen-containing carbon hollow nanocube-confined cobalt nanoparticle as a magnetic and efficient catalyst for activating monopersulfate to degrade a UV filter in water

While bis(4-hydroxyphenyl) ketone (BHK) represents one of the most typical UV filters, which, however, exhibits xenohormone toxicities, very few studies exist for investigating elimination of BHK from water. As sulfate radical-based oxidation processes are validated for degrading emerging contaminants, this current work attempts developing advantageous sulfate radical-based processes through activating monopersulfate (MPS) for eliminating BHK in water. Since cobalt (Co)-containing catalysts are effective catalysts for MPS activation, this study proposes to develop a Co NP-containing catalyst, in which Co NPs are confined in hollow N-containing carbon nanocube (HCoNC) derived from a cobaltic metal-organic framework (Co-MOF). The cubic Co-MOF would be firstly afforded through a surfactant-assisted method. The resultant cubic Co-MOF would be then modified with tannic acid (TAA) to etch its interior for affording the cubic Co-MOF with the hollow structure, which is subsequently converted into Co NP-containing hollow N- containing carbon nanocube (HCoNC) through carbonization. HCoNC can exhibit significantly superior catalytic activities than the non-hollow CoNC and Co3O4 nanoparticles for MPS activation to BHK degradation. The activation energy (Ea) for degrading BHK by MPS is 45.3 kJ/mol, which is much lower than reported values. HCoNC could be reusable over 5 consecutive BHK degradation cycles without decreasing catalytic activities. The MPS activation and plausible BHK degradation route by HCoNC+MPS is elucidated by experimental investigations as well as density functional theory (DFT) calculation to provide insightful mechanism of BHK degradation process.

Regulating activation pathway of Cu/persulfate through the incorporation of unreducible metal oxides: Pivotal role of surface oxygen vacancies

In this paper, we surprisingly found that the incorporation of unreducible metal oxides MxOy (M = Mg, Zn, Ca, Ba, Al) onto CuO hybrid magnetic nano ferric oxide (Cu@Fe3O4) may alter the reaction pathway in persulfate activation, and increase the reaction rate constant. The activation of peroxymonosulfate (PMS) by Cu@Fe3O4 led to a classic sulfate radical based oxidation process (SR-AOP) with an acetaminophen (ACE) degradation rate constant of 0.004 min−1, while 1O2-dominated nonradical oxidation process was disclosed in CuM@Fe3O4 with wildly fluctuated reaction rate constants from 0.003 to 0.242 min−1. Mechanism studies indicated that singlet oxygen (1O2) derived from the direct oxidation of superoxide anions radicals (O2−) or the recombination of O2− was the main reactive oxygen species (ROS) in CuM@Fe3O4/PMS system. A series of characterization experiments (pHpzc tests, XPS, H2-TPR, et al.) and DFT calculation disclosed that the addition of an unreducible metal M yielded many positive effects: (1) the formation of surface oxygen vacancies (OV) raised the zero point charge (pHpzc) of CuM@Fe3O4, thus enhanced the adsorption and activation of PMS; (2) promoting the generation of a new Cu species (Cu3+) on the surface of CuM@Fe3O4, which then participated in the generation of 1O2. The different reducibility of Cu3+ led to differences in the catalytic properties of CuM@Fe3O4. In addition, the effects of various water matrix species and the results of reusability experiment, mineralization experiment, and ecotoxicity test exhibited that CuM@Fe3O4/PMS system possessed excellent practical application value.

A heterogeneous photocatalytic sulfate radical-based oxidation process for efficient degradation of 4-chlorophenol using TiO2 anchored on Fe oxides@carbon

A photocatalytic sulfate radical-based advanced oxidation process was studied to degrade 4-chlorophenol (4-CP) using persulfate (PS) catalyzing UV light and heterogeneous catalyst. In this regards, ferroferric oxide nanoparticles anchored on activated carbon (FOC) was applied as a supporter of TiO2 nanoparticles for fabricating of a recoverable photocatalyst (FOCT). Some analysis techniques including PL, UV–vis DRS, XRD, FESEM-EDS, BET, TEM and VSM were utilized to determine the optical, structural, textural and physicochemical characteristics of FOCT. The reaction mechanisms of PS activation and the generation of free radicals were described in details. Moreover, degradation intermediate products were identified and reaction pathway were proposed. It was found that photocatalytic activity and oxidation performance of pure TiO2 were improved after decoration on FOC. An excellent elimination efficiency was achieved in coupling of FOCT and UV irradiation with PS. Over 99 % of 4-CP (60 mg/L) and 49 % of TOC were removed by FOCT/UV/PS at optimum operational conditions. Furthermore, high PCP decontamination rate (> 86 %) was obtained, even at high concentrations (100 mg/L). During consecutive five runs of catalyst use, the degradation rate was decreased slightly to 88 % with a negligible decline in Fe and Ti leaching, demonstrating the excellent reusability and durability of FOCT in oxidation process. SO4– and HO radicals were detected as main reactive species that involved in the degradation of 4-CP over FOCT/UV/PS system. Thanks to good performance and easy recovery of catalyst, FOCT/UV/PS hybrid system has a great potential for environmental remediation perspectives.

Degradation of methylene blue utilizing cobalt-impregnated zeolite beta via sulfate radical-based advanced oxidation process

Sulfate radical-based oxidation process (SRAOP) is an efficient way to completely degrade toxic dyes from wastewater. The purpose of this study is to utilize zeolite beta to support cobalt ions as a catalyst for such application. Zeolite beta was synthesized hydrothermally with SiO2/Al2O3 ratio of 30. Cobalt was impregnated into zeolite beta via wet impregnation method, with cobalt loading of 2wt% and 5wt% Co2+/zeolite beta. Catalyst characterization was done by XRD, ICP, SEM-EDS, FT-IR, BET, and TPD. Methylene blue was used as model dye to investigate the catalytic capability of the catalyst. The set up for the batch reaction was a 500 mL beaker containing 200 mL of 100 ppm dye mechanically stirred at 300 rpm. Oxone concentration was 2mM and the catalyst loading was varied with concentrations of 0.1, 0.5 and 1 g/L. UV-vis was employed to determine the concentration of dye remaining in the solution. Catalyst particle size ranged from 150 to 300 nm with BET surface area of 576.2 m2/g. The dye exhibited adsorption activity to the zeolite, where 92.4% of the dye were adsorbed after 2 hours. Degradation capability of the catalyst was satisfactory, reaching 100% removal after 45 minutes. The study showed that utilization of zeolite beta as a support for cobalt shows promising results for SRAOP application.

Enhanced degradation of tetracycline hydrochloride using photocatalysis and sulfate radical-based oxidation processes by Co/BiVO4 composites

The Co/BiVO4 composites were prepared by wet impregnation method and used to combine photocatalysis and sulfate radical-based oxidation processes for degradation of tetracycline hydrochloride. The effect factors including the mass percentage of cobalt and peroxymonosulfate (PMS) concentration were investigated in detail. The tetracycline hydrochloride solution with an initial concentration of 40 mg/L could be completely degraded within only 25 min in Co/BiVO4+Vis + PMS system. By cyclic degradation experiment, as-prepared Co/BiVO4 composites had good reusability and stability. Free radicals quenching experiment indicated that SO4− and OH played an important role for degradation of tetracycline hydrochloride. We confirmed the redox cycle of Co2+/Co3+ during the PMS activation process by X-ray photoelectron spectroscopy. Based on the above results, a possible enhanced reaction mechanism was proposed.

Peroxymonosulfate activation by iron(III)-tetraamidomacrocyclic ligand for degradation of organic pollutants via high-valent iron-oxo complex

Herein, we proposed a new catalytic oxidation system, i.e., iron(III)-tetraamidomacrocyclic ligand (FeIII-TAML) mediated activation of peroxymonosulfate (PMS), for highly efficient organic degradation using p-chlorophenol (4-CP) as a model one. PMS/FeIII-TAML is capable of degrading 4-CP completely in 9 min at the initial 4-CP of 50 μM and pH = 7, whereas the recently explored system, H2O2/FeIII-TAML, could only result in ∼22% 4-CP removal in 20 min under otherwise identical conditions. More attractively, inorganic anions (i.e., Cl−, SO42−, NO3−, and HCO3−) exhibited insignificant effect on 4-CP degradation, and the negative effect of natural organic matters (NOM) on the degradation of 4-CP in PMS/FeIII-TAML is much weaker than the sulfate radical-based oxidation process (PMS/Co2+). Combined with in-situ XANES spectra, UV-visible spectra, electron paramagnetic resonance (EPR) spectra, and radical quenching experiments, high-valent iron-oxo complex (FeIV(O)TAML) instead of singlet oxygen (1O2), superoxide radical (O2•−), sulfate radicals (SO4•−) and hydroxyl radicals (HO•) was the key active species responsible for 4-CP degradation. The formation rate (kI) and consumption rate (kII) of the FeIV(O)TAML in PMS/FeIII-TAML were pH-dependent in the range of 6.0–11.5. As expected, increasing the FeIII-TAML and PMS dosage resulted in a higher steady-state concentration of FeIV(O)TAML and enhanced the 4-CP degradation accordingly. In addition, the oxidation capacity of PMS was almost totally utilized in PMS/FeIII-TAML for 4-CP oxidation due to the two-electron abstraction from 4-CP by one PMS. We believe this study will shed new light on effective PMS activation by Fe-ligand complexes to efficiently degrade organic contaminants via nonradical pathway.

Activation of persulfate by homogeneous and heterogeneous iron catalyst to degrade chlortetracycline in aqueous solution

This study investigates the removal of chlortetracycline (CTC) antibiotic using sulfate radical-based oxidation process. Sodium persulfate (PS) was used as a source to generate sulfate radicals by homogeneous (Fe2+) and heterogeneous (zero valent iron, ZVI) iron as a catalyst. Increased EDTA concentration was used to break the CTC-Fe metal complexes during CTC estimation. The influence of various parameters, such as PS concentration, iron (Fe2+ and ZVI) concentration, PS/iron molar ratio, and pH were studied and optimum conditions were reported. CTC removal was increased with increasing concentration of PS and iron at an equal molar ratio of PS/Fe2+ and PS/ZVI processes. PS/Fe2+ and PS/ZVI oxidation processes at 1:2 (500 μM PS and 1000 μM) molar ratio showed 76% and 94% of 1 μM CTC removal in 2 h. Further increased molar ratio 1:2 onwards, PS/Fe2+ process showed a slight increase in CTC degradation whereas in PS/ZVI process showed similar degradation to 1:2 (PS/Fe) ratio at constant PS 500 μM concentration. Slower activation of persulfate which indirectly indicates the slower generation of sulfate radicals in PS/ZVI process showed higher degradation efficiency of CTC. The detected transformation products and their estrogenicity results stated that sulfate radicals seem to be efficient in forming stable and non-toxic end products.

Erythromycin oxidation and ERY-resistant Escherichia coli inactivation in urban wastewater by sulfate radical-based oxidation process under UV-C irradiation

This study evaluates the feasibility of UV-C-driven advanced oxidation process induced by sulfate radicals (SO4−) in degrading erythromycin (ERY) in secondary treated wastewater. The results revealed that 10 mg L−1 of sodium persulfate (SPS) can result in rapid and complete antibiotic degradation within 90 min of irradiation, while ERY decay exhibited a pseudo-first-order kinetics pattern under the different experimental conditions applied. ERY degradation rate was strongly affected by the chemical composition of the aqueous matrix and it decreased in the order of: ultrapure water (kapp = 0.55 min−1) > bottled water (kapp = 0.26 min−1) > humic acid solution (kapp = 0.05 min−1) > wastewater effluents (kapp = 0.03 min−1). Inherent pH conditions (i.e. pH 8) yielded an increased ERY degradation rate, compared to that observed at pH 3 and 5. The contribution of hydroxyl and sulfate radicals (HO and SO4−) on ERY degradation was found to be ca. 37% and 63%, respectively. Seven transformation products (TPs) were tentatively elucidated during ERY oxidation, with the 14-membered lactone ring of the ERY molecule being intact in all cases. The observed phytotoxicity against the tested plant species can potentially be attributed to the dissolved effluent organic matter (dEfOM) present in wastewater effluents and its associated-oxidation products and not to the TPs generated from the oxidation of ERY. This study evidences the potential use of the UV-C/SPS process in producing a final treated effluent with lower phytotoxicity (<10%) compared to the untreated wastewater. Finally, under the optimum experimental conditions, the UV-C/SPS process resulted in total inactivation of ERY-resistant Escherichia coli within 90 min.

Formation of brominated disinfection byproducts from natural organic matter isolates and model compounds in a sulfate radical-based oxidation process.

A sulfate radical-based advanced oxidation process (SR-AOP) has received increasing application interest for the removal of water/wastewater contaminants. However, limited knowledge is available on its side effects. This study investigated the side effects in terms of the production of total organic bromine (TOBr) and brominated disinfection byproducts (Br-DBPs) in the presence of bromide ion and organic matter in water. Sulfate radical was generated by heterogeneous catalytic activation of peroxymonosulfate. Isolated natural organic matter (NOM) fractions as well as low molecular weight (LMW) compounds were used as model organic matter. Considerable amounts of TOBr were produced by SR-AOP, where bromoform (TBM) and dibromoacetic acid (DBAA) were identified as dominant Br-DBPs. In general, SR-AOP favored the formation of DBAA, which is quite distinct from bromination with HOBr/OBr(-) (more TBM production). SR-AOP experimental results indicate that bromine incorporation is distributed among both hydrophobic and hydrophilic NOM fractions. Studies on model precursors reveal that LMW acids are reactive TBM precursors (citric acid > succinic acid > pyruvic acid > maleic acid). High DBAA formation from citric acid, aspartic acid, and asparagine was observed; meanwhile aspartic acid and asparagine were the major precursors of dibromoacetonitrile and dibromoacetamide, respectively.