Thermal Activation Of Persulfate Research Articles

Toxicity and biodegradability evaluation of HCHs-polluted soils after persulfate remediation treatments

Soils contaminated with lindane (γ-hexachlorocyclohexane, γ–HCH) wastes are widespread due to its massive production and high persistence. A noticeable case is in the Sardas and Bailín landfills (Spain), where INQUINOSA discharged tons of lindane wastes. The current work evaluates the remediation of polluted surface soil (HCHs = 409 mg kg−1) from these emplacements by two persulfate (PS)-activated on-site treatments: thermal (PS/T) and alkaline activation, the last one also intensified by temperature (PS/NaOH/T). The possible adverse effects of the chemical treatments on acute toxicity (associated with reagents, pH, by-product generation, etc.) of all phases involved (soils, soil organic extracts, reaction supernatants, and soil elutriates) towards Vibrio fischeri and Artemia salina were evaluated. Biodegradability assays were also performed. Both treatments presented high efficiency in pollutant degradation (XHCHs ≥ 90 % and dechlorination degree ≈ 80 %). After PS/T treatment, the soil and organic extract acute toxicity (Vibrio fischeri and Artemia salina) was reduced to the minimum level, and neither the reaction supernatant nor the soil leachate exhibited acute toxicity. Vibrio fischeri-soil acute toxicity remained unaltered after PS/NaOH/T treatment, which was attributed to the high NaOH concentration used. The toxicity of this soil elutriate was low, although that of aqueous reaction supernatant presented non-negligible values. In the case of Artemia salina bioassay, the alkaline treatment leads to a more significant decrease in toxicity than the thermal activation of PS. Finally, the biodegradability of treated soils increased, highlighting the suitability of PS-activated treatments for the remediation of HCHs-polluted soils.

Enhanced degradation of HCH in soil by synergetic alkaline hydrolysis and thermal activation of persulfate

Enhanced degradation of HCH in soil by synergetic alkaline hydrolysis and thermal activation of persulfate

Ofloxacin Degradation over Nanosized Fe3O4 Catalyst viaThermal Activation of Persulfate Ions

In this work, an Fe3O4 catalyst was synthetized in a single step via electrochemical synthesis. The Fe3O4 catalyst was used to evaluate the degradation of Ofloxacin (OFX) using a heterogeneous advanced oxidation process with sodium persulfate (PS). PS activation was successfully achieved via thermal conventional heating directly and subsequently applied for the degradation of OFX. The degradation kinetics were studied under different conditions, such as catalyst and oxidant concentration and temperature. The results show that a higher reaction temperature, catalyst and initial PS dose strongly influence the degradation efficiency. Thermal activation of persulfate was tested at 20, 40 and 60 °C. At 60 °C, the half-time of OFX was 23 times greater than at 20 °C, confirming the activation of persulfate. Mineralization studies also showed that under optimized conditions (20 mM of persulfate, 1 g/L catalyst and 100 mg/L OFX), a 66% reduction in organic matter was observed, in contrast to that obtained at 40 °C and 20 °C, which was null. The reusability, as tested through the fourth reuse cycle, resulted in a 38% reduced degradation efficiency when comparing the first and last cycle. Furthermore, the electrosynthesized catalyst presented similar degradation efficiencies in both real water and MilliQ, mainly because of the Cl2− generation at high Cl− concentrations that takes place in Cl− contaminated water.

Insights into atrazine degradation by thermally activated persulfate: Evidence from dual C–H isotope analysis and DFT simulations

SO4– -assisted oxidation was of great concern and the accurate interpretation of reaction pathway was crucial. Innovatively, this study introduced compound-specific isotope fractionation analysis (CSIA) into atrazine (ATZ) degradation by heat-activated persulfate (PS), in order to provide “in-situ” and “fingerprinted” analysis of reaction contribution and bond cleavage process based on isotope fractionation. As results, radical oxidants including SO4- and OH were generated through thermal activation of PS, and proved to play dominate roles in ATZ degradation. Inconceivably, the isotope fractionation by single SO4-dominated reaction showed weak and positive C isotope fractionation, with εC of 1.58 ‰ at pH 4 and 0.65 ‰ at pH 7, respectively. Reactions by single SO4- and OH can be distinguished resulting from their significantly different ε and ɅC/H values. Changes of δ13C and δ2H values during ATZ degradation by heat-activated PS followed Rayleigh equation well, with the εC, εH and ɅC/H values of −1.5 ‰, −21.1 ‰, 6.60 at pH 4 and −2.7 ‰, −36.6 ‰, 10.02 at pH 7 respectively. The relative contribution of SO4- radical to ATZ degradation was ca.100 % at pH 4 and 83.9 % at pH 7. The isotope fractionation study and DFT calculations suggested that single electron transfer with the cleavage of C-Cl bond was dominated and displayed inverse C isotope fractionation for SO4- oxidation, which was different from that of OH oxidation and more selective to dehalogenate reaction. This research emphasized the promising technology of CSIA, which can achieve accurate identification of reaction contribution and pathways in advanced oxidation process.

Efficient chlorinated alkanes degradation in soil by combining alkali hydrolysis with thermally activated persulfate

Alkali activation is the most commonly used activation method for persulfate (PS) in in-situ remediation. However, the role of alkali in pollutant degradation is still elusive, limiting the optimization of relevant remediation strategies. In this study, we found that chlorinated alkanes (e.g., tetrachloroethane (TeCA)) could be efficiently degraded by thermal-alkali activation of PS. The main role of alkali was not activating PS but hydrolyzing the chlorinated alkanes, which was evidenced by the immediate conversion of TeCA into trichloroethylene (TCE) with NaOH and PS or with sole NaOH solution. Electron paramagnetic resonance analysis also showed that with a high NaOH/PS molar ratio (4:1) the intensity of oxidative radicals decreased, implying that high levels of alkali did not favor the formation of free radicals. Interestingly, better degradation of TeCA and its product TCE was observed by the combination of alkaline hydrolysis and thermal activation of PS (where alkali was added 6 h before PS rather than simultaneously) in comparison to thermal-alkali activation of PS. This study provides new insights into the remediation of chlorinated alkane-contaminated soils by in-situ chemical oxidation.

Degradation of HCHs by thermally activated persulfate in soil system: Effect of temperature and oxidant concentration

Soils contaminated with hexachlorocyclohexanes (HCHs) are a legacy of the heavy use of lindane during the 20th century. This pesticide production generated large amounts of residues of other HCH isomers, which were habitually mismanaged. The sediments treated in this work (coming from an old lindane landfill) are an example of this environmental problem of global dimensions. The efficient remediation of these sediments, mainly contaminated with β-HCH (99 mg kg−1) and α-HCH (254 mg kg−1) isomers, is still a challenge. The thermal activation of persulfate (PS) required excessive reaction times, which could be reduced by optimizing the variables of the process. This study aims to explore the effect of using higher reaction temperatures (35, 45, and 55 ºC) and initial oxidant concentrations (10, 20, 40, 60, and 80 g L−1). Batch experiments (liquid/soil = 2/1, 100 rpm) were performed to evaluate the influence of these two variables in HCHs abatement, dechlorination degree, generation of intermediate compounds, and oxidant consumption. An increase in the reaction temperature accelerates the pollutant oxidation and dechlorination rate and decreases the concentration of chlorinated byproducts. The initial PS concentration also plays a crucial role in HCHs degradation. At selected operating conditions (55 ºC, PS = 80 g L−1), a conversion of HCHs around 83% was achieved, without chlorinated byproducts (chlorine balance ≈ 100%) at only 9 days of treatment. A plausible pathway for the degradation of HCHs-polluted soils by thermally activated PS has been proposed from the identified species, involving a scheme of series-parallel reactions.

The overlooked oxidative dissolution of silver sulfide nanoparticles by thermal activation of persulfate: Processes, mechanisms, and influencing factors

The widely occurring silver sulfide nanoparticles (Ag2S-NPs) are regarded as stable Ag species in subsurface environments, where are often disturbed by human activities, such as the application of advanced oxidation technologies (e.g. persulfate based in situ chemical oxidation (PS-ISCO)) in the remediation of contaminated soil and groundwater. However, stability of Ag2S-NPs was rarely investigated referring to these processes. Here, we systematically investigated the dissolution process of Ag2S-NPs in thermal activation of PS system. Results showed that dissolution of Ag2S-NPs fitted the pseudo-first-order kinetics and the kobs increased from 0.017 h−1 to 0.249 h−1 with increasing PS concentration from 2 mM to 10 mM (36 h, 40 °C). Quenching experiments and EPR results showed that sulfate radical (SO4•–) and hydroxyl radical (•OH) were the dominant oxidants in inducing the oxidative dissolution of Ag2S-NPs. XPS analysis showed that surface-bound S2− in Ag2S-NPs was oxidized and transformed into aqueous sulfur species. The released Ag+ may also act as effective catalysts to activate PS and therefore promote the oxidation process. These findings suggest that stability of Ag2S-NPs should be reevaluated to better understand its risk to the ecological system in the subsurface environment where ISCO was widely applied.

Reductive Hexachloroethane Degradation by S2O8•- with Thermal Activation of Persulfate under Anaerobic Conditions.

Despite that persulfate radical (S2O8•-) is an important radical species formed from the persulfate (PS) activation process, its reactivity toward contaminant degradation has rarely been explored. In this study, we found that S2O8•- efficiently degrades the contaminant hexachloroethane (HCA) under anaerobic conditions, whereas HCA degradation is negligible in the presence of oxygen. We observed dechlorination products such as pentachloroethane, tetrachloroethylene, and Cl- during HCA degradation, which suggest that HCA degradation is mainly a reductive process under anaerobic conditions. Using free radical quenching and electron paramagnetic resonance (EPR) experiments, we confirmed that S2O8•- forms from the reaction between sulfate radical (SO4•-) and S2O82-, which are the dominant reactive species in HCA degradation. Density functional theory (DFT) calculations were used to elucidate the pathways of HCA degradation and S2O8•- radical decomposition. Further investigation showed that S2O8•- can efficiently degrade HCA and DDTs in soil via reduction during the thermal activation of PS under anaerobic conditions. The finding of this study provide a novel strategy for the reductive degradation of contaminant when PS-based in situ chemical oxidation used in the remediation of soil and groundwater, particularly those contaminated with highly halogenated compounds.

Strategies for oxidation of PAHs in aged contaminated soil by batch reactors

Polycyclic aromatic hydrocarbons (PAH) are neutral, nonpolar and hydrophobic molecules that tend to sorb onto soil organic matter. Chemical oxidation is a good choice to avoid the limitations of bioremediation.To evaluate the efficiency of different types of oxidation (permanganate, hydrogen peroxide, and persulfate) and activation (heat, alkaline, and iron), batch reactors were prepared. The soil was contaminated with phenanthrene and pyrene (1200 ± 200 and 2800 ± 100mg per kg of dry soil, respectively) and aged for fifteen months. Treatments were prepared with 10g of contaminated dry soil and 20ml of water and incubated at room temperature for 7 days. Analyses of phenanthrene and pyrene concentrations, soil pH and electric conductivity were performed. Counts of heterotrophic cultivable bacteria on R2A medium and PAH-degraders were carried out after 7 days of treatment. The persulfate treatment at room temperature, without the addition of activators, achieved better results than treatments with the same doses of permanganate or hydrogen peroxide. All the strategies to improve persulfate treatments yielded higher degradation of pyrene than the biological control, as expected from the structural description of this compound by Clar's model. The thermal activation of persulfate (65°C for 6h) led to the degradation of more than 90% of both PAHs after 7 days of treatment.

Mechanistic investigations in sono-hybrid (ultrasound/Fe2+/UVC) techniques of persulfate activation for degradation of Azorubine

Persulfate-based oxidation of recalcitrant pollutants has been investigated as an alternative to OH radical based advanced oxidation processes due to distinct merits such as greater stability and non-selective persistent reactivity of SO4- oxidant species. The present study has attempted to highlight mechanistic features of persulfate-based decolorization of textile dye (Azorubine) using sono-hybrid techniques of activation. Three activation techniques, viz. sonolysis, Fe2+ ions and UVC light and combinations thereof, have been examined. UVC is revealed to be the most efficient decolorization technique. The mechanism of sonolysis (i.e. thermal activation of persulfate in the bubble-bulk interfacial region) is revealed to be almost independent of the mechanism of UVC. Fe2+ activation is revealed to have an adverse interaction with UVC due to scavenging of sulfate radicals by Fe2+ ions. The best hybrid activation technique for persulfate-based degradation and mineralization of Azorubine is UVC+ultrasound. Due to independent mechanisms, degradation and mineralization of the dye obtained with simultaneous application of UVC and ultrasound is nearly equal to the sum of degradation and mineralization obtained using individual techniques.

Kinetics and transformation pathways on oxidation of fluoroquinolones with thermally activated persulfate

Three typical fluoroquinolones (FQs), ciprofloxacin, norfloxacin and enrofloxacin were degraded using the thermal activation of persulfate (PS). The degradation rates of FQs generally increased with the rise of PS/fluoroquinolone ratio (20:1–80:1) and temperature but decreased with the increase of initial pH values. The major degradation mechanisms of fluoroquinolones by thermally activated PS were proposed. Abundant intermediates identified by liquid chromatography–tandem mass spectrometry (LC–MS/MS) indicated that the oxidation would occur mainly on the C–F bonds (for ciprofloxacin and enrofloxacin) or the C–H (for norfloxacin) bonds on the quinolone groups, causing hydroxyl substitution as well as hydrogen abstraction, and on the piperazine groups following a series of substitutions, additions and eliminations resulting in the final open-loop reactions.

Degradation of carbon tetrachloride in aqueous solution in the thermally activated persulfate system

Thermal activation of persulfate (PS) has been identified to be effective in the destruction of organic pollutants. The feasibility of carbon tetrachloride (CT) degradation in the thermally activated PS system was evaluated. The experimental results showed that CT could be readily degraded at 50°C with a PS concentration of 0.5M, and CT degradation and PS consumption followed the pseudo-first order kinetic model. Superoxide radical anion (O2−) was the predominant radical species responsible for CT degradation and the split of CCl was proposed as the possible reaction pathways for CT degradation. The process of CT degradation was accelerated by higher PS dose and lower initial CT concentration. No obvious effect of the initial pH on the degradation of CT was observed in the thermally activated PS system. Cl−, HCO3−, and humic acid (HA) had negative effects on CT degradation. In addition, the degradation of CT in the thermally activated PS system could be significantly promoted by the solvents addition to the solution. In conclusion, the thermally activated PS process is a promising option in in-situ chemical oxidation/reduction remediation for degrading highly oxidized organic contaminants such as CT that is widely detected in contaminated sites.

Degradation of sulfamethoxazole by microwave-activated persulfate: Kinetics, mechanism and acute toxicity

Thermal activation of persulfate was confirmed to be effective in the destruction of organic pollutants. Microwave heating has different inherent mechanism from that of conventional heating, and the application of microwave heating to chemical reactions has attracted great interest. The objective of this study was to evaluate the degradation of sulfamethoxazole (SMX) in a microwave-activated persulfate (MW/PS) system. The results indicated that MW/PS degradation of SMX followed pseudo-first-order kinetics, and compared with conventional heating, microwave heating has a special effect on SMX degradation with higher reaction rate and shorter process time. The process of SMX degradation was accelerated by higher reaction temperature, persulfate dose or pH in the MW/PS system, while higher initial SMX concentration and the presence of phosphates slowed down the degradation rates. High level of chloride showed some inhibition on the SMX degradation, while low chloride level and carbonate enhanced the SMX degradation. 3-Amino-5-methylisoxazole, sulfanilic acid, hydroxyl-SMX and nitroso-SMX derivatives were identified as the major degradation intermediate products by HPLC/MS. The possible reaction pathways including hydroxylation of the benzene ring, oxidation of the amine group at the benzene ring and the S–N cleavage were proposed. The acute toxicity tests with Photobacterium phosphoreum, Vibrio fischeri and Vibrio qinghaiensis indicated that the inhibitory effect of the 10-time diluted unheated SMX mixture solution being 22.6–48.0%, increased to >99.9% after 4 min and decreased to <−10% after 60 min MW/PS treatment that could be attributed to the rapid formation and subsequent disappearance of oxidation products.

Persulfate oxidation of MTBE- and chloroform-spent granular activated carbon

Activated persulfate (Na 2S 2O 8) regeneration of methyl tert-butyl ether (MTBE) and chloroform-spent GAC was evaluated in this study. Thermal-activation of persulfate was effective and resulted in greater MTBE removal than either alkaline-activation or H 2O 2–persulfate binary mixtures. H 2O 2 may serve multiple roles in oxidation mechanisms including Fenton-driven oxidation, and indirect activation of persulfate through thermal or ferrous iron activation mechanisms. More frequent, lower volume applications of persulfate solution (i.e., the persulfate loading rate), higher solid/solution ratio (g GAC mL −1 solution), and higher persulfate concentration (mass loading) resulted in greater MTBE oxidation and removal. Chloroform oxidation was more effective in URV GAC compared to F400 GAC. This study provides baseline conditions that can be used to optimize pilot-scale persulfate-driven regeneration of contaminant-spent GAC.