Microwave-activated Persulfate Research Articles

High-efficiency degradation of Fe-CNs in SPL through microwave-activated persulfate

Cyanide in spent potlining (SPL) is primarily present as sodium cyanide (NaCN) and iron (II, III) cyanide complexes (Fe-CNs). NaCN is easy to degrade, while Fe-CNs is extremely difficult to degrade. In this work, a novel microwave-activated persulfate technology (MW-PS) was firstly proposed to degrade Fe-CNs promptly and efficiently. The removal rate of 99.88 % was achieved within 180 s under optimal conditions of pH = 10.15, [oxidant]:[Fe-CNs] molar ratio of 5:1, and microwave power of 300 W. The remaining total cyanide content was less than 0.04 mg·L−1. The degradation mechanism of ferrocyanide (II) and ferricyanide (III) in the MW-PS degradation system was systematically analyzed through electron paramagnetic resonance (EPR) and element identification techniques. The ROS (SO4−, HO, O2−, and 1O2) generated under microwave activation and first attacked the C-Fe complex bond in Fe-CNs, causing the bond to dissociate and release the free CN−, and then CN− was thoroughly oxidized. This work develops a simple and high-efficiency decyanation technology for complex cyanide contained industrial waste disposal.

Aerobic and anaerobic regulation induced different degradation behaviors of parachloronitrobenzene in soil by microwave activated persulfate oxidation

Persulfate (PS) oxidation is a promising soil remediation technology. Information regarding pollutant degradation in soil by PS-based technique under different oxidizing atmospheres is still lacking. In this study, p-chloronitrobenzene (p-CNB) degradation in soil in a microwave (MW) activated persulfate (MW/PS) system was evaluated under aerobic and anaerobic conditions. The experimental results demonstrated that anaerobic condition was more conducive to p-CNB degradation. Only 46% of p-CNB was degarded within 60 min treatment under aerobic conditions, but it increased to more than 80% under anaerobic conditions. The increase of PS dosage and MW temperature both promoted p-CNB degradation. SO4•− and •OH played important roles in p-CNB degradation under aerobic conditions, and p-CNB was mainly converted to hydroxylated byproducts including 4-nitrophenol and hydroquinone. The reductive radical S2O8•- was responsible for p-CNB degradation under anaerobic conditions, and aminated byproducts were generated. The residual toxicities of these byproducts were predicted to be decreased, compared with those of p-CNB. Furthermore, by regulating the aerobic and/or anaerobic conditions, other pollutants including pyrene and ethion were also effectively removed in the MW/PS system. Overall, this study highlighted new insights into degradation behaviors of pollutants by MW/PS treatment via aerobic and anaerobic regulation.

Enhancement of Removal of VOCs and Odors from Wood by Microwave-Activated Persulfate.

Since traditional methods for removing volatile organic compounds (VOCs) from wood consume large amounts of energy and generate environmental pollution, it is desired to develop a convenient and green treatment method. Oxidation by microwave-activated persulfate (MW-PS) is a promising alternative method that has been used to eliminate VOCs from wood. The penetration of microwave energy can destroy the wood pit membranes and increase VOC emissions. The VOCs are further degraded by ·OH and SO4•–, which are generated via the activation of microwaves. This phenomenon can be detected by the electron paramagnetic resonance spectrometry. The 35 types of main VOCs of natural wood were determined, including alkanes/terpenes, alcohols/ethers, esters, aldehydes/ketones, and others. In the MW-PS system, 23 compounds were removed with an efficiency of 100%. Specifically, as one of the major compounds, the content of alkanes/terpenes was sharply decreased, and no alcohols/ethers and esters were detected. It was found that the optimal conditions of the MW-PS system for the minimum release of VOCs from wood were the microwave power of 462 W, irradiation time of 30 min, and PS dosage of 0.5 mmol/L.

Crystallographic manganese oxides enhanced pyrene contaminated soil remediation in microwave activated persulfate system

• Mn x O y enhanced MW/PS oxidation is used to remedy pyrene polluted site. • Enhancement effect on pyrene removal by Mn x O y is explored. • Radical and non-radical processes both contribute to pyrene removal. • Conversion of Mn(IV) to Mn(III) promotes ROS formation and pyrene removal. • Pyrene degradation pathways involve ring-opening and hydroxylation. Polycyclic aromatic hydrocarbons (PAHs) contaminated sites have attracted worldwide concern due to their carcinogenic, mutagenic, and teratogenic natures. Crystallographic manganese oxides (Mn x O y ) are ubiquitous in soils. In this study, Mn x O y enhanced PAHs contaminated soil remediation in a microwave activated persulfate (MW/PS) system was conducted, and pyrene was selected as a target pollutant. Significant enhancement performance on pyrene removal was observed after adding Mn x O y , which ranked as β -MnO 2 > α -MnO 2 > γ -MnO 2 > Mn 2 O 3 . Pyrene removal efficiency was enhanced from 65.7% to 85.6% within 15 min of treatment when β -MnO 2 dosage increased from 0 to 0.1 g. Mn x O y in the MW/PS system improved the production of active substances and converted radical process into non-radical process via conversion of Mn(IV) to Mn(III) and Mn-O-Mn to Mn-O-X. 1 O 2 played significant roles in pyrene degradation, whereas the presence of β -MnO 2 alleviated the shielding effects of SO 4 − and OH scavengers. Pyrene molecular structures were destroyed, and some ring-opening and/or lower ring byproducts were generated. Residual toxicity of pyrene and its degradation byproducts was predicted. This work provided a potential pathway to promote PAHs contaminated soil remediation via Mn x O y enhanced MW/PS oxidation, and highlighted new insights into the mechanism of PS activation by metal oxides.

Remediation of organophosphorus pesticide polluted soil using persulfate oxidation activated by microwave

Contaminated sites from pesticide industry have attracted global concern due to the characteristics of organic pollution with high concentrations and complete loss of habitat conditions. Remediation of organophosphorus pesticide polluted soil using microwave-activated persulfate (MW/PS) oxidation was investigated in this study, with parathion as the representative pesticide. Approximately 90 % of parathion was degraded after 90 min of MW/PS oxidation treatment, which was superior to those by single PS or MW treatment. Relatively greater performances for parathion degradation were obtained in a relatively larger PS dosage, higher microwave temperature, and lower organic matter content. Appropriate soil moisture favored parathion degradation in soil. SO4−, OH, O2−, and 1O2 generated in the MW/PS system all contributed to parathion degradation. Multiple spectroscopy analyses indicated that PO and PS bonds in parathion were destroyed after MW/PS oxidation, accompanied by generation of hydroxylated and carbonylated byproducts. The soil safety after parathion degradation was assessed via model prediction. Furthermore, MW/PS oxidation also exhibited great performance for degradation of other organophosphorus pesticides, including ethion, phorate, and terbufos.

An investigation of refractory organics in membrane bioreactor effluent following the treatment of landfill leachate by the O3/H2O2 and MW/PS processes

In this study, refractory organics in a membrane bioreactor (MBR) effluent were investigated following the treatment of landfill leachate by the ozone combined hydrogen peroxide (O3/H2O2) and microwave-activated persulfate (MW/PS) processes. The treatment efficiency and the transformation characteristics of refractory organics and reactive oxygen species were determined. It was found that an acidic environment and an increase in the O3 dosage improved the organic removal efficiency in the O3/H2O2 process, and the use of H2O2 improved the treatment efficiency, while excessive H2O2 inhibited it. In the MW/PS process, an increase in the PS dosage and MW power greatly improved the treatment efficiency, while an alkaline environment inhibited it. Under the optimized reaction parameters, the O3/H2O2 and MW/PS processes effectively degraded refractory organics (i.e., humic acid and fulvic acid) into components with a smaller molecular weight and simpler structure. The humification, aromaticity, and conjugation of organics in wastewater were greatly reduced. Compared to the O3/H2O2 process, the MW/PS process had a better treatment effect on refractory organics, and there were more low molecular weight organics (<1 kDa) in the treated wastewater. Because O3 is the main selective oxidant in the O3/H2O2 process, a large amount of organic acids were accumulated. A large amount of hydroxyl radicals and sulfate radicals with strong oxidation ability were produced in the MW/PS process, and therefore the combined action of hydroxyl and sulfate radicals can efficiently decompose humus and intermediate organics. Overall, the MW/PS process was more effective in treating the MBR effluent than the O3/H2O2 process. The results of this study provide a reference for the selection of an advanced oxidation process to eliminate refractory organics in landfill leachate.

Oxidative removal of recalcitrant organics in shale gas flowback fluid by the microwave-activated persulfate process.

Shale gas flowback fluid (SGF) is generated during shale gas extraction and typically contains a variety of toxic and refractory organic compounds. In this work, a microwave-activated persulfate process (MW-PS process) was developed to pretreat SGF. The major factors influencing the treatment efficiency of the MW-PS process (PS dose, initial pH, MW power, and reaction time) were optimized, and the synergetic effect (SE), degradation of recalcitrant matter, and energy consumption were systematically investigated. Results showed that the SE of the process reached a high index (i.e., 9.85), suggesting a significant synergetic effect of MW and PS. In addition, under the optimal MW-PS condition (PS dose of 2.5g/L, MW power of 900W, and initial pH of 2), chemical oxygen demand removal reached 66.40% in a short reaction time of 10min. Other analyses demonstrated that benzene series compounds, organic acids, lipid substances, alkanes, antioxidants, and fluorescent dissolved organic matter in SGF were decomposed to smaller-molecule organic matter, suggesting that refractory and toxic organic matter was removed by the MW-PS treatment process. Overall, the results of this study showed that MW-PS technology is an effective and promising method to treat SGF once the operation parameters are optimized.

Efficient oxidation of high levels of soil-sorbed phenanthrene by microwave-activated persulfate: implication for in situ subsurface remediation engineering

Purpose In situ chemical oxidation using activated persulfate is increasingly applied for source destruction of hydrophobic organic contaminants (HOCs), e.g., PAHs, the target group contaminants of this study. However, the low aqueous solubility and strong sequestration of HOCs by soil aggregates are major hurdles for the oxidation of HOCs in the subsurface. This study aimed to investigate the potential of using microwave-activated persulfate to tackle the above issues and accelerate the remediation of HOC-contaminated sites.

Degradation and dechlorination of pentachlorophenol by microwave-activated persulfate.

The degradation performance of pentachlorophenol (PCP) by the microwave-activated persulfate (MW/PS) process was investigated in this study. The results indicated that degradation efficiency of PCP in the MW/PS process followed pseudo-first-order kinetics, and compared with conventional heating, microwave heating has a special effect of increasing the reaction rate and reducing the process time. A higher persulfate concentration and reaction temperature accelerated the PCP degradation rate. Meanwhile, increasing the pH value and ionic strength of the phosphate buffer slowed down the degradation rate. The addition of ethanol and tert-butyl alcohol as hydroxyl radical and sulfate radical scavengers proved that the sulfate radicals were the dominant active species in the MW/PS process. Gas chromatography-mass spectrometry (GC-MS) was employed to identify the intermediate products, and then a plausible degradation pathway involving dechlorination, hydrolysis, and mineralization was proposed. The acute toxicity of PCP, as tested with Photobacterium phosphoreum, Vibrio fischeri, and Vibrio qinghaiensis, was negated quickly during the MW/PS process, which was in agreement with the nearly complete mineralization of PCP. These results showed that the MW/PS process could achieve a high mineralization level in a short time, which provided an efficient way for PCP elimination from wastewater.

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.

Decomposition of perfluorooctanoic acid by microwaveactivated persulfate: Effects of temperature, pH, and chloride ions

Microwave-hydrothermal treatment of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S2O82−) has been found effective. However, applications of this process to effectively remediate PFOA pollution require a better understanding on free-radical scavenging reactions that also take place. The objectives of this study were to investigate the effects of pH (pH = 2.5, 6.6, 8.8, and 10.5), chloride concentrations (0.01–0.15 mol·L−1), and temperature (60°C, 90°C, and 130°C) on persulfate oxidation of PFOA under microwave irradiation. Maximum PFOA degradation occurred at pH 2.5, while little or no degradation at pH 10.5. Lowering system pH resulted in an increase in PFOA degradation rate. Both high pH and chloride concentrations would result in more scavenging of sulfate free radicals and slow down PFOA degradation. When chloride concentrations were less than 0.04 mol·L−1 at 90°C and 0.06 mol·L−1 at 60°C, presence of chloride ions had insignificant impacts on PFOA degradation. However, beyond these concentration levels, PFOA degradation rates reduced significantly with an increase in chloride concentrations, especially under the higher temperature.

A novel advanced oxidation process to degrade organic pollutants in wastewater: Microwave-activated persulfate oxidation

This article, for the first time, provides a novel advanced oxidation process based on sulfate radical (SO4*-) to degrade organic pollutants in wastewater: microwave (MW)-activated persulfate oxidation (APO) with or without active carbon (AC). Azo dye acid Orange 7 (AO7) is used as a model compound to investigate the high reactivity of MW-APO. It is found that AO7 (up to 1000 mg/L) is completely decolorized within 5-7 min under an 800 W MW furnace assisted-APO. In the presence of chloride ion (up to 0.50 mol/L), the decolorization is still 100% completed, though delayed for about 1-2 min. Experiments are made to examine the enhancement by AC. It is exciting to find that the 100% decolorization of AO7 (500 mg/L) is achieved within 3 min by MW-APO using 1.0 g/L AC as catalyst, while the degradation efficiency maintains at 50% by MW energy without persulfate after about 5 min. Besides the destruction of visible light chromophore band of AO7 (484 nm), during MW-APO, two bands in the ultraviolet region (228 nm and 310 nm) are rapidly broken down. The removal of COD is about 83%-95% for 500 mg/L AO7. SO4*- is identified with quenching studies using specific alcohols. Both SO4*- and *OH could degrade AO7, but SO4*- plays the dominant role. In a word, MW-APO AC is a new catalytic combustion technology for destruction of organic contamination even for high concentration.