Activation of persulfate and removal of ethyl-parathion from soil: Effect of microwave irradiation

Pesticides luminescent sensing by a Tb3+-doped Zn metal-organic framework with selectivity towards parathion

Organophosphorus pesticides (OPPs) such as parathion have extensive uses in agriculture and household applications. Chronic exposure to these pesticides can cause severe health and environmental issues. Therefore, a current ecological concern is associated with accumulating these noxious OPPs in food and water sources. In this work, a new Tb3+-doped Zn-LMOF (Zn-LMOF= (3D) {[Zn3(1,4 benzenedicarboxylate)3(EtOH)2]·(EtOH)0.6}∞) was synthesized by a solvent-free reaction between the Zn-LMOF and the salt TbCl3·6H2O using a high-speed ball milling. The Tb@Zn-LMOF was thoroughly characterized by multiple spectroscopic tools, including Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy, and studied in-depth as a luminescent sensor for a series of pesticides (parathion, malathion, methalaxil, carbofuran, iprodione, captan and glyphosate) in aqueous methanol. The Tb@Zn-LMOF is a long-lived green-emitting compound with luminescence originated by an efficient antenna effect from the excited energy levels of Zn-LMOF toward the 5D state of Tb3+ ions, as it is displayed by its strong emission bands at 488, 545, 585, and 620 nm and a lifetime of 1.01 ms upon excitation at 290 nm. Additions of pesticides to a neutral methanolic dispersion of Tb@Zn-LMOF modified its green emission intensity with a pronounced selectivity toward parathion within the micromolar concentration range. The detection limit for parathion was calculated to be 3.04 ± 0.2 μM for Tb@Zn-LMOF. Based on 31P NMR and mass spectrometry studies, it is attributed to the release of lanthanide ions from Tb@Zn-LMOF with the simultaneous formation of a Tb3+-parathion complex.

Activation of persulfate for the degradation of ethyl-parathion in soil: Combined effects of microwave with biochar

Sulfate radical (SO4•-), formed by persulfate (PS) activation during advanced oxidation process (AOPs), can be used for the remediation of organic contaminated soil. However, the role of biochar and microwave (MW) in the activation of PS is not fully understood, especially the corresponding mechanism. Herein, biochar combined with MW was used to activate PS for the remediation of ethyl-parathion (PTH)-polluted soil. The dynamic evolutions of PTH under different conditions, such as biochar content, particle size, reaction temperature, and the degradation mechanisms of PTH were also systematically investigated. Significant enhancement performance on PTH removal was observed after adding biochar, which was 88.78% within 80 min. Meanwhile, activating temperature exhibited remarkable abilities to activate PS for PTH removal. The higher content of adsorption sites in nano-biochar facilitated the removal of PTH. Furthermore, chemical probe tests coupled with quenching experiments confirmed that the decomposition of PS into active species, such as SO4•-, •OH, O2•- and 1O2, contributed to the removal of PTH in biochar combined with MW system, which could oxidize PTH into oxidative products, including paraoxon, 4-ethylphenol, and hydroquinone. The results of this study provide valuable insights into the synergistic effects of biochar and MW in the PS activation, which is helpful for the potential application of biochar materials combined with MW-activated PS in the remediation of pesticide-polluted soils.

Microbe combined with Fe2+-heat activated persulfate to decompose phenanthrene in red soil: comparison of acid-resistant degrading microflora and indigenous bacteria

This work is designed to counteract the deficiency of targeted research on the PAHs polluted specific soil, especially when the chemicals extremely denatured it. Phenanthrene-contaminated red soil was treated through two-stage process: persulfate oxidation (on dosages of 3.48%, 5.21%, and 6.94%, combined with Fe2+ and β-cyclodextrin, then heated) followed by biodegradation (indigenous bacteria vs. acid-resistant PAHs-degrading microflora (named ADM)) for 90 days. The dosage of oxidant greatly affected the removal efficiencies, which ranged from 46.78 to 85.34% under different treatment. After undergoing oxidation, the soil pH dropped below 3.0 synchronously and retained relatively strong oxidation state. The indigenous bacteria in red soil showed considerable degradation potential that will not vanish upon the sudden change of soil properties, whose average combined removal reached 95.43%, even higher than subgroups of bioaugmentation, but the population structure showed extremely simplex (Proteobacteria as superior occupied proportion of 91.77% after 90-day rehabilitation). The ADM screened from the coking wastewater was dominated by Klebsiella (75.4%) and Pseudomonas (23.6%), whose cooperation with 6.94% persulfate made the residual PHE reduced to less than 50 mg·kg-1 in about 28 days. High-throughput sequencing analysis showed that the microbial community composition of the ADM applied-group was more abundant in the later stage of remediation. ADM inoculation has the advantages of shortening the restoration period and having a positive impact on the soil micro-ecology.

Enhanced persulfate activation by ethylene glycol-mediated bimetallic sulfide for imidacloprid degradation

CuFeS2 is regarded as a promising catalyst for heterogeneous activation to remove organic contaminants in wastewater. However, effects of solvents in regulating material synthesis and catalytic activity are still not clear. Herein, we reported the role of water, ethanol, ethylene glycol (EG), glycerol, and polyethylene glycol 200 on the synthesis of CuFeS2 micro-flowers and their performance in activating persulfate (PS) to remove imidacloprid (IMI) pesticide. The results showed that the solvent had an effect on the morphology, crystallinity, yields, specific surface areas and unpaired electrons of CuFeS2 micro-flowers. The degradation experiments revealed the efficient catalytic activity of EG-mediated CuFeS2 for heterogeneous PS activation. SO4•- and •OH were identified in EG-CuFeS2/PS system and •OH (90.4%) was the dominant reactive species. Meanwhile, stable 20% of η[PMSO2] (the molar ratio of PMSO2 generation to PMSO consumption) was achieved and demonstrated that Fe(IV) was also involved in the degradation process. Moreover, S2- promoted the cycling of Fe3+/Fe2+ and Cu2+/Cu+, enhancing the synergistic activation and reusability of the catalyst. Density functional theory (DFT) calculations verified that PS was adsorbed by Fe atom and electron transfer occurred on the catalyst surface. Three possible degradation pathways of IMI were proposed by analysis of the degradation intermediates and their toxicities were evaluated by ECOSAR. This study not only provides a theoretical foundation for catalyst design, but also promotes the industrial application of bimetallic sulfide Fenton-like catalysts for water management.

Multistage utilization of soybean straw-derived P-doped biochar for aquatic pollutant removal and biofuel usage

Biochar is of great importance to realizing solid biowastes reduction and environmental remediation. Modifying biochar for better performance is also of great concern to achieve property improvement. P-doped biochar from soybean straw is prepared for multistage utilization to realize water pollutant removal and biofuel usage. The results suggest that the prepared biochar is adequate for sulfadiazine adsorption and has stable performance under coexisting ions and aquatic pH. Furthermore, the higher heating value of the biochar is close to coal and thus can be an alternative to fossil fuel. The maximum sulfadiazine adsorption amount of P-doped biochar is 252.24 mg·g-1, and the P-doped biochar HHV is 24 MJ·kg-1 which can be an alternative to coal. The greenhouse gas and pollutant emission potential are also considered to explore the environmental impact of P-doped biochar production and usage. Overall, the optimal ratio of soybean straw: K3PO4 is 3:1.

Contaminant containment for sustainable remediation of persistent contaminants in soil and groundwater

Contaminant containment measures are often necessary to prevent or minimize offsite movement of contaminated materials for disposal or other purposes when they can be buried or left in place due to extensive subsurface contamination. These measures can include physical, chemical, and biological technologies such as impermeable and permeable barriers, stabilization and solidification, and phytostabilization. Contaminant containment is advantageous because it can stop contaminant plumes from migrating further and allow for pollutant reduction at sites where the source is inaccessible or cannot be removed. Moreover, unlike other options, contaminant containment measures do not require the excavation of contaminated substrates. However, contaminant containment measures require regular inspections to monitor for contaminant mobilization and migration. This review critically evaluates the sources of persistent contaminants, the different approaches to contaminant remediation, and the various physical-chemical-biological processes of contaminant containment. Additionally, the review provides case studies of contaminant containment operations under real or simulated field conditions. In summary, contaminant containment measures are essential for preventing further contamination and reducing risks to public health and the environment. While periodic monitoring is necessary, the benefits of contaminant containment make it a valuable remediation option when other methods are not feasible.

Effects of persulfate-assisted hydrothermal treatment of municipal sludge on aqueous phase characteristics and phytotoxicity

Hydrothermal technology (HT) has received much attention in recent years as a process to convert wet organic waste into hydrochar. The aqueous phase (HTAP) produced by this process is still a burden and has become a bottleneck issue for HT process development. In this study, we provide the first investigation of the HTAP characteristics, phytotoxicity, and their correlation with persulfate (PS) (PS, 2.0 mmol/g TS)-assisted municipal sludge HT. The results showed that PS accelerated the hydrolysis of protein substances and increased the concentration of NH₄⁺ by 13.4% to 190.5% and that of PO₄^3- by 24.2% to 1103.7% in HTAP at hydrothermal temperatures of 120 to 240 °C. PS can reduce the phytotoxicity of HTAP by reducing aldehydes, ketones, N heterocyclic compounds, and particle size and by increasing its humification index. The maximum values of the root length and biomass of pakchoi (Brassica chinensis L.) seedlings occurred when electrical conductivity was 0.2 mS/cm of HTAP. This work provided a new strategy for the selection and design of HTAP management strategies.

Insight into enhanced degradation of tetracycline over peroxymonosulfate activated via biochar-based nanocomposite: performance and mechanism

Rice husk biochars (BCs) doped with ferric chloride were prepared by one-pot method, characterized by SEM, EDS, BET, XRD, and FTIR, and utilized to catalyze peroxymonosulfate (PMS) for tetracycline (TC) degradation. Various influencing factors in the BC/PMS/TC system were investigated, as well as the recycling performance of the optimal BC. The mechanism of BC activation of PMS and degradation of TC were analyzed based on the free radicals quenching experiment and the pathways of TC degradation. The results demonstrated that bBC3 was an excellent catalyst with large specific surface area; the amounts of oxidant and catalyst were important factors affecting the catalytic performance of PMS, while pH had less effect on TC degradation; 10 mM of chloride ions inhibited the TC degradation, while 20 mM promoted the TC degradation; other ions and humic acid inhibited the TC degradation at the set concentrations; activation of PMS by bBC3 yielded species with strong oxidative activity, which were primarily responsible for TC degradation. The bBC3 obtained stable performance for removing TC. This study provided a pathway for the deep utilization of waste rice husks besides an effective method for degrading TC.

Ecotoxicity of parathion during its dissipation mirrored by soil enzyme activity, microbial biomass and basal respiration

The application of parathion (PTH) in agriculture can result in its entry into the soil and threaten the soil environment. Monitoring the PTH residues and assessing toxicity on soil health are of paramount importance to the public. Herein, the dissipation of PTH and concomitant influence on microbial activities [FDA hydrolase (FDA‒H), microbial biomass carbon (MBC) and basal respiration (BR)] in coastal solonchaks were investigated. Results showed that the dissipation of PTH in tested soil declined linearly, and the half-lives varied from 5.6 to 56.8 days, depending on pollutant concentrations. The FDA‒H activity and MBC were negatively affected by PTH pollution and exhibited a significantly positive correlation. Two‒way ANOVA analysis demonstrated that microbial activities were affected not only by PTH dose and incubation time but also by their interactions. The integrated biomarker response (IBR/n) index values on day 120 were between 1.02 and 2.89, larger than those on day 1 during PTH dissipation. This implied that the soil quality did not recover though there was no PTH residue in the soil at the end of the experiment. These findings suggested that microbial activities integrated with IBR/n index could elucidate the hazardous impacts of PTH dissipation on biochemical cycling and microorganisms in soil.

Efficient activation of persulfate by Nickel-supported cherry core biochar composite for removal of bisphenol A

In this study, low-cost and easily obtained biochar was chosen to prepare nickel-modified biochar materials (Ni/BC) through a one-step activation pyrolysis method. Characterization with X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy proved the existence of Ni⁰ and NiO nanocrystals in Ni/BC catalyst. The optimal Ni_0.5/BC exhibited excellent peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation efficiency toward bisphenol A (BPA) degradation. The Ni_0.5/BC (0.03 g) reacted with 1.0 g L^-1 PMS or PDS could completely remove 20 mg L^-1 BPA in 10 min with the first-order kinetic constants (k₁) of 0.322 min^-1 (PMS) and 0.336 min^-1 (PDS). More importantly, the composite has better structural and functional attributes for the BPA degradation with universal applicability at wide pH and temperature range, proving as a better degradation mediator with high adaptation for numerous organic pollutants. Catalytic activity decreased slightly even after 4 cycles. Based on the quenching experiment and electron paramagnetic resonance, it was found that SO₄^•-, •OH and ¹O₂ were the dominant active species in BPA degradation process. Therefore, this work not only supplies a promising catalyst for the removal of organic contaminants, but also is beneficial for the further development of alternative catalysts for sulfate radical based advanced oxidation processes.

Mechanism of the improved Fe(III)/persulfate reaction by gallic acid for ibuprofen degradation

Gallic acid (GA), a natural plant polyphenol, was applied as amendment of Fe(III)/persulfate (PS) system for ibuprofen (IBP) degradation in this study. The impacts of all agentia (GA, Fe(III), PS) concentration and initial pH values on IBP removal efficiency were investigated, and their corresponding observed pseudo-first-order rate constants (k_obs) were calculated. The addition of GA has significantly improved elimination efficiency of IBP due to the enhanced Fe(III)/Fe(II) cycle. Electron paramagnetic resonance (EPR) results confirmed that SO₄^•-, HO^• and O₂^•- were involved in GA/Fe(III)/PS system. However, quenching experiments further affirmed the impact of SO₄^•- and HO^• towards IBP decomposition instead of O₂^•-, with contribution ratio to IBP removal was 69.12% and 30.88%, respectively. SO₄^•- was the main radicals formed by directly activation of PS with Fe(II), while HO^• was the transformation product of SO₄^•-. Based on instrumental analysis (stopped-flow UV-vis spectrum and MS) and theoretical calculation, the potential reaction mechanism between GA and Fe(III) in the presence of PS was further proposed. GA complexed with Fe(III) firstly and the Fe(III)-GA complex was then converted into quinone substance, accompanied by the generation of Fe(II). Furthermore, the application of GA extended the optimal pH range to neutral as well, which made it a promising treatment in practical application.

Microwave-induced steam distillation (MISD) remediation in petroleum hydrocarbon-contaminated sites: From process improvement to pilot application

The process improvement, a pilot remediation test and the decontamination mechanism of microwave-induced steam distillation (MISD) for petroleum hydrocarbons (PHs) removal were conducted. Processes of multistage steam distillation and carbon reinforcement were compared to determine the best remediation process. Pilot project was then carried out to explore the applicability of MISD in site-scale remediation. The remediation efficiency, procedures and influencing factors of site-scale MISD project were studied by monitoring variations of soil moisture, temperature and PHs concentrations. Furthermore, the decontamination mechanisms of PHs were clarified based on kinetic analysis. The results showed that the multistage steam distillation could improve 10%∼15% remediation efficiency, and the carbon reinforcement could shorten remediation duration of each steam distillation stage by 50%. Pilot MISD project adopted multistage steam distillation process and went through four (initial, rapid heating-up, gentle heating-up and quasi-equilibrium) remediation stages (overall temperature ≤100 °C). The final PHs removal rate was about 60%, which would get better with greater proportion of low boiling points components and stronger vapor extraction. Kinetic studies showed that PHs was removed by steam stripping and limited by intraparticle diffusion in the "steam distillation zone", while local high temperature (＞100 °C) greatly improved PHs volatilization and provided activation energy for PHs desorbed and degraded in the "selective heating zone".

Peroxymonosulfate activation through ferromagnetic bimetallic spinel sulfide composite (Fe3O4/NiCo2S4) for organic pollutant degradation

Spinel sulfides are a good candidate as heterogeneous catalysts for wastewater treatment through peroxymonosulfate (PMS) activation. In this paper, magnetic Fe₃O₄/NiCo₂S₄ composite was successfully synthesized by hydrothermal method. Catalyst screening displayed that the composite catalyst with a Fe₃O₄:NiCo₂S₄ molar ratio of 1:3 (i.e.,0.33-Fe₃O₄/NiCo₂S₄) is the most optimal. The results showed that 0.33-Fe₃O₄/NiCo₂S₄ composite catalyst had superior catalytic activity, achieving 99.8%,65.1% and 40.7% of RhB, COD and TOC removals within 30 min with 180 m g/L PMS and 75 mg/L catalyst. We proposed a potential catalytic mechanism of PMS activation by Fe₃O₄/NiCo₂S₄ in two aspects. On the one hand, sulfur species such as S^2- and S₂^2- enhance the Co³⁺/Co²⁺, Ni³⁺/Ni²⁺ and Fe³⁺/Fe²⁺ cycles on Fe₃O₄/NiCo₂S₄ surface. On the other hand, there is the synergistic effect of Co³⁺/Co²⁺, Ni³⁺/Ni²⁺ and Fe³⁺/Fe²⁺ cycles in activating PMS. Overall, owing to its excellent catalytic activity, reusability, and easy recovery, Fe₃O₄/NiCo₂S₄ is a potentially useful catalyst for remediation of contaminated water.

Catalytic Degradation of Organic Contaminants by Microwave-Assisted Persulfate Activation System: Performance and Mechanism

In this study, a nickel ferrite (NiFe2O4) system was constructed to purify a phenol solution in water. During the process, the influences of several critical operating parameters including the NiFe2O4 amount, PS dosage, MW power, initial pH value, and different natural water anions were systematically studied. The results indicated that the constructed system performed excellently regarding the removal efficiency (97.74%) of phenol within 30 min. Meanwhile, the influence of co-existing anions such as Cl−, NO3−, H2PO4−, and HCO3− was also studied, which displayed an inhibiting action on phenol degradation, while HA facilitated it. To explore the reaction mechanism of this system, major free radical quenching experiments were conducted, and it was confirmed that both SO4•− and HO• were primary radicals. Moreover, stability experiments confirmed the apt stability of the NiFe2O4 system. Besides, the mineralization and toxicity analysis performed during phenol degradation also confirmed the superiority of the as-constructed system. Furthermore, the possible degradation mechanism of phenol was proposed. Hence, this system could be applied in advanced wastewater treatment.

Removal of Arsenic from Wastewater by Using Nano Fe3O4/Zinc Organic Frameworks

Efficient removal of arsenic in wastewater is of fundamental importance due to the increasingly severe arsenic pollution. In this study, a new composite adsorbent (Fe₃O₄@ZIF-8) for As(V) removal from wastewater was synthesized by encapsulating magnetic Fe₃O₄ nanoparticles into metal organic frameworks. In order to evaluate the feasibility of Fe₃O₄@ZIF-8 as an adsorbent for As(V) removal, the adsorption properties of Fe₃O₄@ZIF-8 were systematically explored by studying the effects of dosage, pH, adsorption isotherm, kinetics, and thermodynamics. Additionally, the characterization of Fe₃O₄@ZIF-8 before and after adsorption was analyzed thoroughly using various tests including SEM-EDS, XPS, BET, XRD, TG, FTIR, and the properties and arsenic removal mechanism of the Fe₃O₄@ZIF-8 were further studied. The results showed that the Fe₃O₄@ZIF-8 has a specific surface area of 316 m²/g and has excellent adsorption performance. At 25 °C, the initial concentration of arsenic was 46.916 mg/L, and pH 3 was the optimum condition for the Fe₃O₄@ZIF-8 to adsorb arsenic. When the dosage of the Fe₃O₄@ZIF-8 was 0.60 g/L, the adsorption of arsenic by the Fe₃O₄@ZIF-8 can reach 76 mg/g, and the removal rate can reach 97.20%. The adsorption process of arsenic to the Fe₃O₄@ZIF-8 can be well described by the Langmuir isotherm model and the second-order kinetic equation. At pH 3 and temperature 298 K, the maximum adsorption capacity of arsenic by the Fe₃O₄@ZIF-8 was 116.114 mg/g. Through the analysis of thermodynamic parameters, it is proved that the adsorption process of arsenic by the Fe₃O₄@ZIF-8 is a spontaneous endothermic reaction. The Fe₃O₄@ZIF-8 has broad prospects for removing As(V) pollution in wastewater, because of its strong adsorption capacity, good water stability, and easy preparation.

A multi-aspect application of microwave radiation on rehabilitating and improving the geotechnical properties of polluted-sand-clay mixture

Crude oil products are among the most common pollutants of soils which can drastically affect the engineering properties of soils. In the current study, a series of laboratory tests were conducted to investigate the interaction between crude oil and sandy soil with clay and the effect of crude oil, crude oil residence time, absorbent additives type and content, microwave power, specimen weight, maximum grain size and fine grain fraction on the removal efficiency of pollution through microwave radiation to extract optimum values for potential and high efficiency in hydrocarbon removal. The present study also investigated geotechnical properties, including cohesion, internal friction angle, shear strength in three conditions before and during pollution and after cleanup utilizing direct shear and static triaxial tests. The results showed that the presence of clay particles, oil content and saturation effect in the soil could significantly control the engineering soil behavior. In the presence of 4% crude oil in direct shear tests, the whole oil content is accumulated on clay particles due to the high specific area of clay particles, reducing the cohesion and the internal friction angle. By contrast, beyond the 4% of crude oil, sand particle in the soil was the controlling factor of the whole behavior of the mixture. In triaxial tests, the trend of soil parameters is almost similar to direct shear tests by increasing crude oil, except that, with an increase of 4% of oil, the friction angle of the soil increases due to the presence of a large number of flocculated clay particles.

Efficient degradation of anthracene in soil by carbon-coated nZVI activated persulfate

The easy passivation defect of nano zero-valent iron (nZVI) greatly limits its application in site pollution remediation. Carbon coating can effectively inhibit the passivation of nZVI, but its effectiveness in the soil is still unknown. This study investigated the feasibility of carbon-coated nZVI (Fe⁰@C) as a persulfate (PS) activator to degrade anthracene (ANT) in soil. The results show that the Fe⁰@C/PS system can remove 51.6% of ANT in the soil after 0.5 h of reaction, and reach 76.4% after 12 h of reaction. Not only that, the Fe⁰@C/PS system shows a good removal effect on ANT within the initial pH range of 3-9. Free radical scavenging experiments show that superoxide radicals (O₂^•-) and singlet oxygen (¹O₂) are mainly responsible for the removal of ANT, while O₂^•- may be mainly used as a precursor for the generation of ¹O₂. The activation of PS by Fe⁰@C can generate a large number of free radicals, and soil components (such as β-MnO₂) can promote the conversion of O₂^•- to ¹O₂. Furthermore, the possible degradation pathway of ANT was also proposed. The findings are of great significance to fill up the knowledge gaps in the application of nZVI in soil remediation.

Remediation of phenol contaminated soil using persulfate activated by ball-milled colloidal activated carbon

The degradation of phenolic compounds through persulfate (PS) activation is a valuable approach for soil/groundwater remediation. Several reports have been made related to PS activation and contaminant degradation using carbo-catalysts; however, there is no detailed study on soil remediation by colloidal activated carbon. This study demonstrates the phenol (PhOH) degradation efficiency in spiked and field-contaminated soils by a novel and low-cost ball-milled colloidal activated carbon (CAC_BM) catalyst. The CAC_BM/PS system exhibited outstanding degradation performance for PhOH in both spiked and field-contaminated soils. Optimum condition for degradation of 5.63 mmol PhOH kg soil^-1 was achieved at 2.5 mg CAC_BM g soil^-1, 5 mM PS, and a solid-liquid ratio of 1:5 at 25 °C in the wide pH range of 3-11. Radical scavenger experiments and electron spin resonance (ESR) spectroscopy revealed that both radical (^•OH and SO₄^•-) and non-radical (¹O₂) species were involved in the CAC_BM/PS system. PhOH degradation in soil phase followed several degradation pathways, resulting in various intermediate byproducts such as acetic acid, maleic acid, p-benzoquinone, fumaric acid, and ferulic acid as analyzed by ultra-high-performance liquid chromatography with mass spectroscopy (UPLC-MS). The CAC_BM/PS system showed a promising potential in the remediation of organic-contaminated soil.

Application of sulfate radicals-based advanced oxidation technology in degradation of trace organic contaminants (TrOCs): Recent advances and prospects

The large amount of trace organic contaminants (TrOCs) in wastewater has caused serious impacts on human health. In the past few years, Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are widely recognized for their high removal rates of recalcitrant TrOCs from water. Peroxymonosulfate (PMS) and persulfate (PS) are stable and non-toxic strong oxidizing oxidants and can act as excellent SO₄^•- precursors. Compared with hydroxyl radicals(·OH)-based methods, SR-AOPs have a series of advantages, such as long half-life and wide pH range, the oxidation capacity of SO₄^•- approaches or even exceeds that of ·OH under suitable conditions. In this review, we present the progress of activating PS/PMS to remove TrOCs by different methods. These methods include activation by transition metal, ultrasound, UV, etc. Possible activation mechanisms and influencing factors such as pH during the activation are discussed. Finally, future activation studies of PS/PMS are summarized and prospected. This review summarizes previous experiences and presents the current status of SR-AOPs application for TrOCs removal. Misconceptions in research are avoided and a research basis for the removal of TrOCs is provided.

Tailored design of three-dimensional rGOA-nZVI catalyst as an activator of persulfate for degradation of organophosphorus pesticides

In this study, three-dimensional reduced graphene oxide aerogel (rGOA)-supported nanozero-valent iron (rGOA-nZVI) was successfully synthesized via tailored design and applied to activate persulfate (PS) to degrade three organophosphorus pesticides (OPPs; phorate, terbufos and parathion) in water and a historically contaminated soil. The results showed that loading nZVI nanoparticles on rGOA could prevent the aggregation of nZVI. rGOA-nZVI presented a better catalytic performance for PS activation to degrade the three OPPs than bare nZVI and rGOA, with degradation efficiencies of greater than 99.5% within 5 min. pH had negligible effects on the PS activated by rGOA-nZVI (rGOA-nZVI/PS). EPR measurements and radical quenching experiments showed that ·SO₄^- and ·OH were the main radicals responsible for OPP removal in the rGOA-nZVI/PS system. Furthermore, nine intermediates were identified, and the oxidation and scission of C-S-C, P-S/O and PS were the dominant degradation pathways of the three OPPs in aqueous solutions treated with rGOA-nZVI/PS. Additionally, rGOA-nZVI/PS achieved degradation efficiencies of 95.1% for phorate, 79.9% for terbufos and 89.1% for parathion in the contaminated soil, and the detected intermediates could be further degraded except triethylphosphate. Overall, this study provides practical knowledge for OPP removal by rGOA-nZVI/PS in wastewater and actual contaminated soil.

The aging behavior of polyvinyl chloride microplastics promoted by UV-activated persulfate process

Microplastics (MPs) experienced different aging processes in environment. Literatures about effect of artificially-accelerated aging on MPs behavior are still insufficient. The accelerated process induced by ultraviolet(UV)-activated persulfate (PS) is a promising technology for obtaining different aged MPs to understand long-term aging behavior. In the work, the aging behavior of polyvinyl chloride (PVC) accelerated by UV/PS system were investigated. It exhibited a dechlorination with 58.495 ± 6.090 mg/L Cl^- release after 35 h UV-activated PS (0.01 M) process. The treatment led to significant alternations on surface morphology and chemical feature of PVC. The crystallinity was increased, and average size was reduced from 154.11 µm to 119.28 µm with aging time. Subsequently, many smaller size particles were produced. Furthermore, the process induced the breaking of backbone. Simultaneously, more oxygen-containing functional groups were identified. The oxidation reaction accelerated by sulfate radical (SO₄^•-) and reactive oxygen species (ROS) was predominant, which immensely promoted aging process. Sustained high levels of free radical contributed to production of alcohols and carboxylic acids short chain organics. The study explored aging behavior of PVC accelerated by UV/PS system, which could be helpful for understanding environmental behavior and providing further information to assess potential risks of MPs.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Pyrene contaminated soil remediation using microwave/magnetite activated persulfate oxidation

Polycyclic aromatic hydrocarbons (PAHs) are important mutagen prevalent in the contaminated sites, bringing potential risks to human health. Iron oxides are important natural components in soils. Pyrene removal in soil using persulfate (PS) oxidation activated by microwave (MW) and magnetite (Fe₃O₄) was investigated. Fe₃O₄ significantly promoted pyrene removal in the soil; 91.7 % of pyrene was degraded within 45 min treatment. Pyrene removal rate in the Fe₃O₄/MW/PS system was 5.18 and 3.00 times higher than that in the Fe₃O₄/PS and MW/PS systems. Increasing in Fe₃O₄ dosage, PS concentration, MW temperature, and soil moisture content in the selected range were conducive for pyrene degradation. SO₄^•-, ^•OH, O₂^•-, and ¹O₂ were responsible for pyrene degradation, and the conversion of Fe (Ⅱ) in the Fe₃O₄ to Fe (Ⅲ) contributed to the formation of O₂^•- and ¹O₂. Characteristic bands of pyrene were more obviously destroyed by the Fe₃O₄/MW/PS oxidation, in comparison with MW/PS oxidation. Ring hydroxylation and ring-opening reactions were the main degradation pathways of pyrene. The toxicities of the formed byproducts were significantly reduced after treatment. This study provided a promising option for pyrene contaminated soil remediation.

Degradation of TBBPA by nZVI activated persulfate in soil systems

Tetrabromobisphenol A (TBBPA) greatly impacts on ecosystems and human health due to its high environmental toxicity and persistence. Persulfate (PS) advanced oxidation technology to remove organic pollutants in soils has received intense attention. In this study, nanoscale zero-valent iron (nZVI) was synthesized through the borohydride reduction method to explore its activating potential towards PS to accelerate the degradation of TBBPA in soils. The degradation behaviors of TBBPA in soils were investigated by batch experiments. The degradation efficiency of TBBPA (5 mg kg^-1) was 78.32% within 12 h under the following reaction conditions: 3 g kg^-1 nZVI, 25 mM PS, and pH 5.5 at 25 °C. Notably, PS can be used effectively, and the pH changed slightly in the reaction system. Oxidative degradation of TBBPA is favored at higher temperatures and lower pH values, while it is inhibited when the amount of catalyst increases significantly. The coexisting heavy metal ions such as Zn(II) and Ni(II) inhibit TBBPA degradation, while Cu(II) accelerates the degradation. Radical scavenging and electron spin resonance (ESR) tests further confirmed the generation of SO₄^·-, ·OH, and O₂^·- in nZVI activated PS. The intermediates identified by gas chromatograph-mass spectrometry analysis indicated that TBBPA via debromination and the cleavage between the isopropyl group and one of the benzene rings complete degradation. These findings provide new insight into the mechanism of nZVI activation of PS and will promote its application in the degradation of refractory organic compounds.

Enhancing the activation of persulfate using nitrogen-doped carbon materials in the electric field for the effective removal of p-nitrophenol

Degradation of nonbiodegradable organic compounds into harmless substances is one of the main challenges in environmental protection. Electrically-activated persulfate process has served as an efficient advanced oxidation process (AOP) to degrade organic compounds. In this study, we synthesized three nitrogen-doped carbon materials, namely, nitrogen-doped activated carbon plus graphene (NC), and nitrogen-doped activated carbon (NAC), nitrogen-doped graphene (NGE), and three nitrogen-doped carbon material-graphite felt (GF) cathodes. The three nitrogen-doped carbon materials (NC, NGE, NAC) were characterized using X-ray diffraction, Raman spectroscopy, X-ray electron spectroscopy, and nitrogen desorption-adsorption. The electron spin resonance technique was used to identify the presence of hydroxyl radicals (˙OH), sulfate radicals (SO₄˙^-) and singlet oxygen (¹O₂) species. The results showed that NC was more conducive for the production of free radicals. In addition, we applied NC-GF to an electro-activated persulfate system with the degradation of p-nitrophenol and investigated its performance for contaminant degradation under different conditions. In general, the nitrogen-doped carbon electrode electro-activated persulfate process is a promising way to treat organic pollutants in wastewater.

Insight into the roles of electrolysis-activated persulfate oxidation in the waste activated sludge dewaterability: Effects and mechanism

Sludge dewatering, as one of the most important steps of sludge treatment, can facilitate transportation and improve disposal efficiency by reducing the volume of sludge. This study investigated the effects of electrolysis-activated persulfate oxidation on improving sludge dewaterability. The results indicated that the sludge capillary suction time (CST) and water content of dewatered sludge cake (Wc) reduced from 93.7 s and 87.8% to 9.7 s and 68.3% respectively at the optimized process parameters: electrolysis voltage of 40 V, electrolysis time of 20 min, and 1.2 mmol/g TS S₂O₈^2-. Correlation analysis revealed that the enhancement of sludge dewaterability was closely associated with the increased floc size and zeta potential, decreased protein content in three-layers extracellular polymeric substances (EPS) and viscosity (R = -0.868, p = 0.002; R = -0.703, p = 0.035; R ≥ 0.961, p < 0.001; R = 0.949, p < 0.001). Four protein fluorescence regions in EPS were analyzed by three-dimensional excitation-emission matrix parallel factor (3D-EEM-PARAFAC). The protein secondary structure was changed after the treatment, and the reduction of α-helix/(β-sheet + random coil) indicated that more hydrophobic sites were exposed. Analysis by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and rheological test demonstrated that the hydrophilic functional groups of the sludge were decreased and the sludge mobility was significantly enhanced after the treatment with electrolysis-activated persulfate oxidation. Moreover, bound water was converted to free water during SO₄·^- and ·OH generated by electrolysis-activated persulfate degraded EPS and attacked sludge cells. Meanwhile, scanning electron microscopy (SEM) images revealed that the treated sludge formed porous channel structures, which promoted the flowability of the water. These findings provide a new insight based on electrolysis-activated persulfate oxidation in sludge treatment for enhancing sludge dewaterability.

A Critical Review on Removal of Gaseous Pollutants Using Sulfate Radical-based Advanced Oxidation Technologies

Excessive emissions of gaseous pollutants such as SO₂, NO_x, heavy metals (Hg, As, etc.), H₂S, VOCs, etc. have triggered a series of environmental pollution incidents. Sulfate radical (SO₄•^-)-based advanced oxidation technologies (AOTs) are one of the most promising gaseous pollutants removal technologies because they can not only produce active free radicals with strong oxidation ability to simultaneously degrade most of gaseous pollutants, but also their reaction processes are environmentally friendly. However, so far, the special review focusing on gaseous pollutants removal using SO₄•^--based AOTs is not reported. This review reports the latest advances in removal of gaseous pollutants (e.g., SO₂, NO_x, Hg, As, H₂S, and VOCs) using SO₄•^--based AOTs. The performance, mechanism, active species identification and advantages/disadvantages of these removal technologies using SO₄•^--based AOTs are reviewed. The existing challenges and further research suggestions are also commented. Results show that SO₄•^--based AOTs possess good development potential in gaseous pollutant control field due to simple reagent transportation and storage, low product post-treatment requirements and strong degradation ability of refractory pollutants. Each SO₄•^--based AOT possesses its own advantages and disadvantages in terms of removal performance, cost, reliability, and product post-treatment. Low free radical yield, poor removal capacity, unclear removal mechanism/contribution of active species, unreliable technology and high cost are still the main problems in this field. The combined use of multiactivation technologies is one of the promising strategies to overcome these defects since it may make up for the shortcomings of independent technology. In order to improve free radical yield and pollutant removal capacity, enhancement of mass transfer and optimization design of reactor are critical issues. Comprehensive consideration of catalytic materials, removal chemistry, mass transfer and reactor is the promising route to solve these problems. In order to clarify removal mechanism, it is essential to select suitable free radical sacrificial agents, probes and spin trapping agents, which possess high selectivity for target specie, high solubility in water, and little effect on activity of catalyst itself and mass transfer/diffusion parameters. In order to further reduce investment and operating costs, it is necessary to carry out the related studies on simultaneous removal of more gaseous pollutants.

Cysteine enhanced degradation of monochlorobenzene in groundwater by ferrous iron/persulfate process: Impacts of matrix species and toxicity evaluation in ISCO

Monochlorobenzene (MCB), a solvent and synthetic intermediate, has been widely detected in groundwater at industrial contaminated sites. Cysteine (Cys) enhanced Fe²⁺/persulfate (Fe²⁺/Cys/PS) process with high degradation efficiency of organic pollutants has the potential for in-situ chemical oxidation of MCB. In this study, we systematically explored the impacts of common anions (CO₃^2-, HCO₃^-, SO₄^2-, NO₃^-, NO₂^-, PO₄^3-, HPO₄^2-, H₂PO₄^-, Cl^-, Br^-), cations (NH₄⁺, Mg²⁺, Al³⁺, Mn²⁺, Cu²⁺) and natural organic matter (NOM) on the degradation kinetics of MCB by the novel Fe²⁺/Cys/PS process and evaluated the ecotoxicity. The results showed that the removal of MCB in absence of matrices was enhanced by Cys due to its reduction and complexation ability. All of the anions inhibited the MCB degradation through the scavenging of SO₄^•- and HO^•, though the inhibition degree of SO₄^2-and NO₃^- was slight. Cations such as NH₄⁺, Mg²⁺ and Al³⁺ hardly interfered with the reaction. Low concentrations of Cu²⁺ and NOM promoted the MCB oxidation, but the promotion strength weakened and turned into inhibition with the increased concentration of Cu²⁺ and NOM. The toxicity assessment of the transformation products (TPs) in the presence of Cl^- and Br^- based on the quantitative structure-activity relationships model showed the potentially higher toxicity of some TPs than their parent MCB. These results indicate that groundwater matrices may interfere with the MCB oxidation process. To accurately evaluate the effects of groundwater matrices on Fe²⁺/Cys/PS process for MCB oxidation and its potential toxicity, the field tests should be carried out in the future.

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.

Improving dewaterability of waste activated sludge by thermally-activated persulfate oxidation at mild temperature

The mass production of waste activated sludge in wastewater treatment plants may lead to environmental pollution and sludge dewatering is an essential process during its treatment. The oxidation of extracellular polymeric substances (EPS) was the core step to achieve deep sludge dewatering. In this study, thermally-activated sodium persulfate (SPS) process was managed to improve the dewaterability of waste activated sludge (WAS) and its internal mechanism was systematically elaborated. Experimental results showed that with 2.0 mmol/g VSS SPS at 80 °C, capillary suction time (CST) was roughly 59.74% of that in raw sludge. Under this condition, 14.66 ± 0.10 × 10¹¹ kg/m of specific resistance to filtration (SRF) and 61.8% ± 0.1% of water content (W_C) was determined, respectively. A solubilization/oxidation process was proposed to unravel the mechanism of the enhanced dewaterability of WAS in thermally-activated SPS process. Mild temperature efficiently disrupted the sludge flocs and broke cell walls, releasing large amounts of EPS into bulk phase. Meanwhile, mild temperature accelerated the decomposition of SPS to generate sulfate radicals (SO₄^-) and hydroxyl radicals (OH) for oxidizing EPS, facilitating the conversion of bound hydrated water into free water and achieving solid-water separation. The higher reaction temperature favored sludge dewatering, whereas overdosing SPS posed no significant impact. Further analysis illustrated that tyrosine protein-like, tryptophan protein-like, fulvic acid-like and humic acid-like substances in various EPS fractions together exerted the influence on sludge dewatering. Furthermore, the synergy process could alter the secondary structure of protein, which caused a loose structure of EPS and the exposure of hydrophobic sites, facilitating the dehydration of sludge flocs. The details of how thermally-activated SPS process enhanced sludge dewaterability provided the theoretical and technical basis for the application of the process under a real-world situation.