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

Feasibility of microwave remediation of simulative crude oil-contaminated soil assisted by bluecoke-based modifiers

Microwave (MW) remediation of organics-contaminated soil technology offers the advantages of high efficiency and minimal damage, representing a new approach of soil thermal remediation. However, soil, being a weak MW-absorbing medium, struggles to convert MW energy into thermal energy, thus failing to attain the necessary temperature for thermal remediation. This paper prepared two new bluecoke (BC)-based modifiers (KHCO3@BC and KHCO3/MnO2@BC) to address temperature problem of MW remediation, as well as enhance soil quality. Their composition, structure and electromagnetic properties were analyzed to investigate their role in assisting with the MW remediation of an artificially crude oil-contaminated soil were investigated. Additionally, the industrial feasibility of MW remediation was addressed for the first time. The results showed that the KHCO3 and MnO2 particles in the two modifiers were covered on the BC surface and exhibited local agglomeration. Their carbon crystalline grain size increased, and the electromagnetic properties were weaker than those of the BC. Following 10 min of MW remediation assisted by KBC or KMnBC, the remediation temperatures exceeded 300 °C, with the removal rates of PHs reaching 76.16% and 88.31%, respectively. The organic matter content, soil potassium and mechanical fraction of the remediated soil were improved, but soil acidification still needed to be further addressed. The industrial application analysis indicated that the technical process and techno-economics of MW remediation of crude oil-contaminated soil were feasible, suggesting significant potential for the large-scale industrial application.

Efficient degradation of chlorpyrifos and intermediate in soil by a novel microwave induced advanced oxidation process: A two-stage reaction

The application of microwave/peroxymonosulfate (MW/PMS) in soil remediation has been limited by some shortages including low utilization efficiency of oxidants, low MW absorption capacity of soil particles and incomplete degradation of intermediate. In this study, heating pad waste (HPW) was added in the MW/PMS system to increase the ability of absorbing MW and degradation efficiency of toxic intermediate. A two-stage method for degradation of chlorpyrifos (CPF) and its intermediate 3,5,6-trichloro-2-pyridinol (TCP) by MW/PMS assisted with HPW was proposed. In the first stage, more than 90% of CPF was degraded within 15 min before the addition of HPW, and most of the CPF was converted into TCP through direct or indirect pathways under the action of 1O2. In the second stage, more than 70% of the generated TCP was rapidly degraded through SO4•- oxidation and electron transfer. The TCP was further degraded with the assistance of HPW through methylation, hydroxylation and dechlorination etc., and the toxicity of degradation products was decreased significantly. pH and soil organic matter had little influences on CPF and TCP degradation. Therefore, a new strategy for remediation of CPF contaminated-soil was provided based on MW/PMS technology and the concept of "treating waste with waste".

Magnetic Fe-doped silicon carbide induced microwave activated persulfate for decabromodiphenyl ether removal: Mechanism and unique degradation pathway

In this work, the magnetic nanocomposite Fe@SiC was prepared by a hydrothermal method and determined by SEM, XRD, XPS, FTIR and VNA. Fe3O4 particles were loaded onto SiC with great success, and the synthesized composites had favorable microwave absorption properties. Fe@SiC was used to activate persulfate in a microwave field for the degradation of BDE209 in soil. Specifically, the synergistic interaction between microwaves and Fe@SiC showed excellent catalytic performance in activating PS to degrade BDE209 (90.1% BDE209 degradation in 15 min). The presence of •OH, O2•- and 1O2 was demonstrated based on quench trapping and EPR experiments. LC‒MS was applied to determine the intermediates and propose the possible degradation pathway for BDE209 in the MW/Fe@SiC/PS system, and it was found that BDE209 produced almost no lower brominated diphenyl ethers. Therefore, the toxicity of BDE209 was found to be reduced using toxicity assessment software. Overall, this work provides an effective approach for the degradation of BDE209 in environmental remediation.

Removal of total petroleum hydrocarbons from oil-based drilling cuttings by a heat activation persulfate-based process

Oil-based drilling cuttings (OBDC) are typical hazardous wastes generated during shale gas extraction. In this study, two persulfate-based advanced oxidation processes (AOPs), heat/PMS and heat/PDS, have been used to treat OBDC. The results showed that for the heat/PMS process, within a certain range, the oxidant dosage, temperature, and reaction time were significantly positively correlated with the degree of total petroleum hydrocarbon (TPH) removal. When these parameters were increased from their initial values to 3.57 mmol/g, 70°C, and 80 min, respectively, TPH removal rates increased significantly, by 20.95%, 18.68%, and 16.41%, respectively. However, further increases in these parameters had little effect on the TPH removal rate. Similar observations were made for the heat/PDS process. There are other differences between the two processes, including that the heat/PDS process required less oxidant to reach an effective activation state than the heat/PMS process, but required a higher temperature and a longer reaction time. Fourier-transform infrared spectrometry and gas chromatography-mass spectrometry have shown that both processes could effectively remove the light components of linear paraffins contained in OBDC. The heat/PMS process performed significantly better than the heat/PDS process in removing aromatic hydrocarbons and long-chain alkanes. Scanning electron microscopy, energy-dispersive spectrometry, and X-ray diffraction analysis implied that the elemental and mineral compositions of OBDC were not significantly modified by reaction in the heat/PMS and heat/PDS processes. This study may provide theoretical support for the technological development of heat activation and persulfate-based AOPs to remove TPH from OBDC.

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.

Co-Mn-Fe spinel-carbon composite catalysts enhanced persulfate activation for degradation of neonicotinoid insecticides: (Non) radical path identification, degradation pathway and toxicity analysis

The extensive utilization of neonicotinoid insecticides (NNIs) in agricultural practices ultimately poses a significant threat to both the environment and human health. This work focuses on the efficient degradation and detoxification of the representative NNI, thiamethoxam (THX), and explores the underlying mechanism using a Co-Fe-Mn mixed spinel doped carbon composite catalyst activated persulfate. The findings demonstrate that the composite effectively degrades THX, achieving a degradation rate of 95% in 30 mins, while requiring only a fraction (one-sixteenth) of the oxidant dosage compared to pure carbon. The study aimed to examine the negative impact of reactive halogens on reactive oxygen species within a saline environment. The degradation byproducts were linked to the presence of two common electron-withdrawing groups, namely halogens and nitro in the THX molecule. It was hypothesized that the degradation process was primarily influenced by C-N bond breaking and hydroxylation occurring between the diazine oxide and 2-chlorothiazole rings. Consequently, dehalogenation and carbonylation processes facilitated the elimination of halogenated components and pharmacophores from the THX, leading to detoxification. In addition to the identified free radical pathway including SO4•-, •OH and O2•- contributed to THX degradation, the participation of non-radical pathways (1O2 and electron transfer) were also confirmed. The efficacy of detoxification was further validated through toxicity assessment, employing quantitative conformation relationship prediction and microbial culture utilizing Bacillus subtilis.

Real-time emission characteristics, health risks, and olfactory effects of VOCs released from soil disturbance during the remediation of an abandoned chemical pesticide industrial site

Volatile organic compounds (VOCs) released along with soil disturbance during the remediation of abandoned industrial sites have attracted great attention due to their possible toxicity and odour. However, the real-time emission characteristics of these VOCs and their subsequent effects on health and olfaction are less understood. In this study, the gaseous VOCs released from soil disturbance by excavators and drilling rigs at an abandoned chemical pesticide plant were monitored online with a laboratory-built single photoionization time-of-flight mass spectrometer (SPI-TOFMS). Twelve main VOCs with total mean concentrations ranging from 2350 to 3410 μg m-3 were observed, with dichloromethane (DCM) having a significant contribution. The total concentrations of the remaining 11 VOCs increased substantially during soil disturbance, with the total mean concentrations increasing from 18.65-39.05 to 37.95-297.94 μg m-3 and those of peak concentrations increasing from 28.46-58.97 to 88.38-839.13 μg m-3. This increase in VOC concentrations during soil disturbance leads to an enhanced heath risk for on-site workers. The distinctive difference between the mean and peak concentrations of VOCs indicates the importance of using mean and peak concentrations, respectively, for risk and olfactory evaluation due to the rapid response of the human nose to odours. As a result, the cumulative noncarcinogenic risk at the relatively high pollutant plot was higher than the occupational safety limit, while the total carcinogenic risks at all monitored scenarios exceeded the acceptable limit. Among the VOCs investigated, DCM and trichloroethylene (TCE) were determined to be crucial pollutants for both noncarcinogenic and carcinogenic risks of VOCs. With regard to olfactory effects, organic sulphides, including dimethyl disulphide (DMDS), dimethyl sulphide (DMS), and dimethyl trisulphide (DMTS) were identified as dominant odour contributors (78.28-92.11%) during soil disturbance.

Selective degradation of antibiotic in a novel Cu7S4/peroxydisulfate system via heterogeneous Cu(III) formation: Performance, mechanism and toxicity evaluation

Efficient degradation of antibiotic by peroxydisulfate (PDS)-based advanced oxidation processes in complex water environment is challenging due to the interference of impurities and the low activation efficiency of PDS caused by its symmetric structure. Herein, a novel Cu₇S₄/PDS system was developed, which can selectively remove tetracycline hydrochloride (TC) without interference of inorganic ions (e.g., Cl^- and HCO₃^-) and natural organic matter (e.g., humic acid). The results of quenching and probe experiments demonstrated that surface high-valent copper species (Cu(III)), rather than radicals and ¹O₂, are main active species for TC degradation. Cu(III) can be generated via Cu(I)/O₂ and Cu(II)/Cu(I)/PDS systems and the S species on the surface of Cu₇S₄ promotes the cycle of Cu(II)/Cu(I) and Cu(III)/Cu(II), resulting in continuous generation of Cu(III). In addition, the degradation pathways of TC were proposed based on product analysis and DFT theory calculations. The acute toxicity, developmental toxicity and mutagenicity of treated TC were significantly reduced according to the results of toxicity estimation software tool. This study shows a promising Cu₇S₄/PDS system for the degradation and detoxication of antibiotic in complex water environment, while also providing a comprehensive understanding of PDS activation by Cu₇S₄ to generate active Cu(III) species.

Thoughtful design of a covalent organic framework with tailor-made polarity and pore size for the enrichment of bisphenols and their derivatives: Extraction performance, adsorption mechanism and toxicity evaluation

A stable, reusable and cost-effective covalent organic framework (COF) with medium polarity was successfully decorated on Fe₃O₄. The Fe₃O₄@COF contained tailor-made polarity and pore size that fitted well with bisphenols and their derivatives (BPs). When coupling magnetic solid-phase extraction (MSPE) with high-performance liquid chromatography (HPLC) detection, the Fe₃O₄@COF featured efficient recognition and enrichment for BPs due to π-π stacking, C-H⋯π interactions, pore-filling effect, dispersion force and hydrophobic interactions. Under optimized conditions, calibration plots exhibited good linearity (5-1000 ng mL^-1), and limits of detection (LOD) ranged from 0.15 to 0.39 ng mL^-1. The method was successfully employed in quantifying BPs in authentic lake and river water samples with satisfactory recoveries ranging from 81.4% to 120%. Molecular dynamics simulation revealed extraction mechanisms, and a microscopic behavior related to the clustering property of the emerging brominated compounds was first discovered. Ecotoxicological assessments of target pollutants were conducted from multiple aspects, highlighting the harmfulness of the chemicals and the significance of the analytical method. The proposed methodology offered sensitive detection and quantification, which was beneficial for the timely tracking of the concentration, transportation and distribution of BPs to better explore their environmental behavior and tackle contamination problems in complex environmental matrices.

Efficient degradation of clothianidin and thiamethoxam in contaminated soil by peroxymonosulfate process

The widespread use of neonicotinoids has led to their frequent detection in the environment and potential environmental risk in recent years. Clothianidin (CLO) and thiamethoxam (TMX), as the second generation of neonicotinoid insecticides, are usually used as seed agents with a high risk of residue in the soil. Efficient degradation of CLO and TMX in soil using peroxymonosulfate (PMS) process was investigated in the present study. The degradation efficiencies of CLO and TMX reached 91.4% and 98.6% in 60 min with the addition of 20 mM PMS at pH 5.5 and 25℃. High degradation efficiencies of CLO were achieved with a high PMS dosage and temperature or a low CLO concentration and initial pH. The degradation of CLO was reduced in the presence of high concentration of inorganic anions (Cl^-, HCO₃^-). Soil organic matter might be one critical factor in the degradation of CLO and TMX. Radical scavenger experiments confirmed SO₄^•- and ¹O₂ were the dominant reactive species on the CLO and TMX degradation. Based on the detected degradation intermediates, the degradation pathways of CLO and TMX include dichlorination, hydroxylation, cleavage of C-N or C-C bond and further oxidation in the PMS-based soil. Overall, the PMS process is one effective and economical method for the remediation of the neonicotinoid contaminated soil.

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.

Activation of peroxymonosulfate by palygorskite-mediated cobalt-copper-ferrite nanoparticles for bisphenol S degradation: Influencing factors, pathways and toxicity evaluation

Peroxymonosulfate (PMS)-based advanced oxidation process is considered a potential technology for water treatment. Here, palygorskite (PAL)-mediated cobalt-copper-ferrite nanoparticles (16%-CoCu_0.4Fe_1·6O₄@PAL, donated as 16%-CCFO@PAL) were employed for PMS activation to remove bisphenol S (BPS). BPS degradation was greater than 99% under the optimal conditions within 25 min, on which the effects of various influencing factors were explored. The adsorption dissociation energy of PMS over 16%-CCFO@PAL was -6.27 eV, which was lower than that of the Cu-free catalyst (-6.15 eV), demonstrating the excellent catalytic ability of 16%-CCFO@PAL. The efficient catalytic ability of 16%-CCFO@PAL was also verified in real water samples. The oxidation intermediates were identified and their generations were systematically analyzed by DFT calculations. The possible degradation pathways of BPS were proposed and the toxicity of products was predicted. BPS affected the normal development of zebrafish embryos and the levels of sex hormone in adult male zebrafish, and was harmful to the tissues, such as testis, liver, and intestine of zebrafish. The 16%-CCFO@PAL/PMS process can effectively reduce the toxicity of BPS-polluted water. This study paves the way for the real application of 16%-CCFO@PAL/PMS oxidation process and provides a new perspective for the evaluation of water toxicity.

Continuous Fe(II)-dosing scheme for persulfate activation: Performance enhancement mechanisms in a slurry phase reactor

Mechanisms involved in the superior performance of the continuous Fe²⁺ dosing scheme over the single Fe²⁺ dosing scheme was thoroughly investigated. The kinetics and stoichiometry of the phenol removal/persulfate consumption strongly depended on the volumetric or molar Fe²⁺ feeding rate, Fe²⁺ concentration in the feed solution, and Fe²⁺ feeding mode (continuous or single dose). The process performance was determined by the molar Fe²⁺ feeding rate rather than the volumetric Fe²⁺ feeding rate or the Fe²⁺ concentration in the feed solution. The phenol degradation rate increased as the molar Fe²⁺ feeding rate increased to 2.77 mmol/min but decreased as the Fe²⁺ feeding rate increased further. The sulfate radical was predominant radical species formed in continuous Fe²⁺ dosing mode. The hydroxyl and sulfate radicals were both important in single Fe²⁺ dose mode. The presence of hydroxyl radicals in single Fe²⁺ dosing mode decreased the amount of phenol oxidation that occurred, probably because the hydroxyl radicals were readily scavenged by soil organic matter. Continuous Fe²⁺ dosing facilitated phenol mineralization, which was indicated by total organic carbon measurements and toxicity tests performed using Hyalella azteca.

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

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.

Enhanced thermal activation of persulfate by coupling hydrogen peroxide for efficient degradation of pyrene

In this study, H₂O₂ was introduced into thermally activated persulfate oxidation system (T-HPS), and the oxidation of pyrene (PYR) was investigated by the combined T-HPS technology. The results showed that H₂O₂ could significantly improve the reactivity of the thermally activated persulfate system (T-PS), with 240-min PYR degradation ratio increasing from 79.3% to 97.2% at 70 °C. In the T-HPS system, as persulfate initial concentration increased from 5 to 100 μM, the kinetic rate constant (k_obs) of PYR degradation increased from 4.70 × 10^-3 to 3.01 × 10^-2 min^-1, but the k_obs did not show a positive association with H₂O₂ concentration with the same range, and the highest k_obs was obtained at the H₂O₂ initial concentration of 20 μM. The optimal ratio of PS and H₂O₂ was set at 1:1 with the initial concentrations of the two oxidants both being 20 μM. Furthermore, PYR could be removed efficiently in a wide range of pH, and the best PYR degradation performance was obtained under neutral pH. Scavenging experiments demonstrated that OH played a more important role in PYR degradation in the T-HPS system than in the T-PS system. As suggested by the Arrhenius equation, the activation energy decreased from 124.5 to 107.4 kJ mol^-1 after adding H₂O₂ to the T-PS system. This study provides a new oxidation approach that could prompt the T-PS activity by adding a suitable dosage of H₂O₂.

Selective Degradation of Electron-Rich Organic Pollutants Induced by CuO@Biochar: The Key Role of Outer-Sphere Interaction and Singlet Oxygen

Efficient degradation of organic pollutants by oxidative radicals is challenging in the complex soil environment because of the invalid consumption of radicals by nontarget background substances and the generation of secondary halogenated organic pollutants. Nonradical-based oxidation is a promising pollutant removal method due to its high selectivity and environmental adaptability. Herein, a biochar-supported sheetlike CuO (e-CuO@BC) was developed, which exhibited efficient activation of peroxydisulfate (PDS) via nonradical pathways. The activation mechanisms were identified as (i) formation of surface-bonding active complexes via an outer-sphere interaction between e-CuO@BC and PDS and (ii) the continuous generation of ¹O₂ by the cycling of the Cu(I)/Cu(II) redox couple. In addition, the activation of PDS primarily occurred at the crystal facet (001) of e-CuO occupied by Cu atoms and was well facilitated by the Cu-O-C bond, which induced electron-rich centers around CuO. Two oxidative species from PDS activation, including surface-bonding active complexes and ¹O₂, showed a highly selective degradation toward electron-rich pollutants. Moreover, a highly efficient mineralization of organic pollutants and an effective inhibition on the generation of toxic byproducts (i.e., halogenated organics) was indicated by the intermediate and final degradation products. This study provides a comprehensive understanding of the heterogeneous activation process of PS by the e-CuO@BC catalyst for electron-rich organic pollutant removal.

Comparison of sunlight-AOPs for levofloxacin removal: kinetics, transformation products, and toxicity assay on Escherichia coli and Micrococcus flavus

Levofloxacin (LFX) is a widely used antibiotic medication. Persistent traces of LFX in water and wastewater may induce bacterial resistance. Photon-driven advanced oxidation processes (AOPs) can assist in attaining complete abatement of LFX for environmental protection. This work benchmarks different solar AOPs based on hydroxyl radical (OH^•) and sulphate radical (SO₄^•-) chemistry. Other oxidant precursors, as radical sources, were used to selectively control the generation of either hydroxyl radical (i.e., H₂O₂), sulphate radical (i.e., peroxydisulphate (PDS)), or a controlled mixture ratio of both OH^•/SO₄^•- (i.e., peroxymonosulphate (PMS)). The influence of pH on degradation performance was evaluated using unbuffered and buffered solutions. Simulated irradiation/PMS process exhibited a strong pH-dependence attaining partial degradation of ca. 56% at pH 5 up to complete degradation at pH 7. Despite the similitudes on the abatement of target pollutant LFX in pristine solutions, only simulated irradiation/PDS treatment achieved effective abatement of LFX in wastewater samples given the higher selectivity of SO₄^•-. Toxicity tests were conducted with Escherichia coli (LMG2092) and Micrococcus flavus (DSM1790), demonstrating successful inhibition of the antibiotic character of polluted waters, which would contribute to preventing the development of resistant bacterial strains. Finally, a degradative pathway was suggested from the by-products and intermediates identified by LC-MS. Results demonstrate that the degradation of specific functional groups (i.e., piperazine ring) is associated with the loss of antibacterial character of the molecule.

Combining Soil Vapor Extraction and Electrokinetics for the Removal of Hexachlorocyclohexanes from Soil

This paper focuses on the evaluation of the mobility of four hexachlorocyclohexane (HCH) isomers by soil vapor extraction (SVE) coupled with direct electrokinetic (EK) treatment without adding flushing fluids. SVE was found to be very efficient and remove nearly 70 % of the four HCH in the 15-days of the tests. The application of electrokinetics produced the transport of HCH to the cathode by different electrochemical processes, which were satisfactorily modelled with a 1-D transport equation. The increase in the electric field led to an increase in the transport of pollutants, although 15 days was found to be a very short time for an efficient transportation of the pollutants to the nearness of the cathode. Loss of water content in the vicinity of the cathode warns about the necessity of using electrokinetic flushing technologies instead of simple direct electrokinetics. Thus, results point out that direct electrokinetic treatment without adding flushing fluids produced low current intensities and ohmic heating that contributes negatively to the performance of the SVE process. No relevant differences were found among the removal of the four isomers, neither in SVE nor in EK processes.

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.

Novel combination of bioleaching and persulfate for the removal of heavy metals from metallurgical industry sludge

The objective of this study was to remove heavy metals from metallurgical industry sludge by bioleaching alone and bioleaching combined with persulfate (PDS). The results showed that the removal of Cu, Zn, Pb, and Mn reached 70%, 83.8%, 25.2%, and 76.9% by bioleaching alone after 18 days, respectively. The experiment of bioleaching combined with PDS was carried out in which the optimal additive dosage of K₂S₂O₈, 8 g/L, was added to bioleaching after 6 d. After 1 h, the removal of four heavy metals reached 75.1, 84.3, 36.7, and 81.6%, respectively. Compared with bioleaching alone, although the increase in removal efficiency was only slightly increased, the treatment cycle was distinctly shortened from 18 to 6 days + 1 h. The scanning electron microscopy (SEM) results showed that the surface morphology of the sludge was changed significantly by the combined treatment. The content of heavy metals was significantly reduced after bioleaching combined with PDS by energy dispersive X-ray spectroscopy (EDX). Through electron paramagnetic resonance (EPR) and free radical quenching experiments, it was indicated that sulfate radicals [Formula: see text] plays a leading role in the combined treatment. The treated sludge mainly existed in a stable form, and the bioavailability was reduced with European Community Bureau of Reference (BCR) morphology analysis. This study proved that the combination of bioleaching and PDS could not only shorten the treatment cycle but also further improve the efficiency of heavy metal leaching. It provides a novel treatment method for the removal of heavy metals from metallurgical industry sludge.

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.

Enhanced degradation of 2,4-dichlorophenoxyacetic acid by electro-fenton in flow-through system using B, Co-TNT anode

A flow-through system was constructed for 2,4-dichlorophenoxyacetic acid (2,4-D) degradation for the first time using efficient boron and cobalt co-doped TiO₂ nanotubes (B, Co-TNT) as the anode and carbon black doped carbon felt (CB-CF) that had a high H₂O₂ yield as the cathode. Compared with dimensionally stable anode (DSA), whether in anodic oxidation (AO) or AO-electro-Fenton (EF) system, 2,4-D degradation in B, Co-TNT anode system was more efficient accompanying with a lower energy consumption (Ec). Different operating parameters including applied current density, initial pH and flow rate were explored, supporting that the optimal Fe²⁺ dosage was 0.5 mM while decreasing the initial pH and increasing the current intensity and flow rate were beneficial to 2,4-D removal. In this AO-EF system, the involved mechanisms for 2,4-D degradation were anodization and Fenton oxidation, possessing the comprehensive effect of ^•OH and SO₄^•- with their contribution of 92.7% and 4.8%, respectively. This flow-through AO-EF system performed a stable performance, and an efficient degradation performance with low Ec (5.8-29.5 kWh (kg TOC)^-1) was obtained for different kinds of contaminants (methylene blue, phenol, p-nitrophenol and sulfamethazine). Therefore, B, Co-TNT anode coupled with CB-CF cathode in flow-through system was effective for contaminants degradation.

Performance and mechanisms of microwave-assisted zerovalent iron/pyrite for advance remediation of strongly alkaline high Cr(VI) contaminated soil

Strongly alkaline high Cr(VI) contaminated (SAHCR) soil poses a high risk to the environment and public health, yet lacks rapid and efficient remediation technology. In this study, a novel approach combining microwave irradiation with zerovalent iron/pyrite (FeS₂/ZVI) was developed for the remediation of SAHCR soil. The results indicated that fast and efficient remediation of the SAHCR soil was achieved by microwave irradiation-assisted FeS₂/ZVI, with 99.9% of removal rate of Cr(VI) within 10 min, and Cr(VI) concentration from 3900.8 plummeted to 2.38 mg kg^-1. The data of Cr(VI) reduction kinetics at different temperatures indicated that the activation energies (E_a) for microwave-FeS₂/ZVI system was 27.4 kJ mol^-1, 28.5% lower than that without microwave irradiation, suggesting that in addition to the heating effect of microwave, the accelerated Cr(VI) reduction also comes from the catalytic effect of "hot spots" on FeS₂/ZVI under microwave irradiation. Furthermore, it was demonstrated that microwave irradiation promoted the transformation of reduced Cr(III) into the stable FeCr₂O₄ mineral and the excellent long-term stability of the remediated SAHCR soil. These findings can provide a perspective for advanced remediation of the difficult-to-treat SAHCR soil by the synergism of microwave irradiation with the iron-sulfur based reducing materials.

Effectiveness and mechanism of cyanide remediation from contaminated soils using thermally activated persulfate

Persulfate (PS)-based advanced oxidation processes have been frequently employed for contaminant remediation, but the effectiveness of PS oxidation for the elimination of cyanide-bearing contaminants from soil, and the underlying mechanisms, have rarely been explored. This study investigated the degradation of two iron-cyanide (Fe-CN) complexes (ferricyanide and ferrocyanide) with thermally activated PS via two remediation strategies, namely one-step oxidation (direct PS oxidation) and two-step oxidation (alkaline extraction followed by PS oxidation). The two-step oxidation process was more effective for the elimination of cyanide pollutants from soil, reaching >94% remediation efficiency for both Fe-CN complexes studied. The presence of dissolved soil components, especially soil organic matter, increased consumption of PS during the remediation process. A combined analysis based on electron paramagnetic resonance (EPR), free radical scavenging, and degradation product identification revealed that SO₄^- and HO were the principal reactive radicals responsible for Fe-CN degradation. Based on the determination of radical species and identification of decomposition products, a transformation pathway for Fe-CN complexes during thermally activated PS oxidation is proposed. Overall, this study demonstrates the effectiveness of the thermally activated PS oxidation technique for cyanide elimination from polluted soil. Further study is required to verify the feasibility of this method for field applications.

Carbon materials in persulfate-based advanced oxidation processes: The roles and construction of active sites

Many researchers have paid more attention to the progress of carbon materials owing to their advantages, such as high activity, low cost, large surface area, high conductivity and high stability. Carbon materials have been widely used in persulfate-based advanced oxidation processes (PS-AOPs), especially for graphene (G), carbon nanotubes (CNTs) and biochar (BC). Various strategies are applied to promote their activity, however, up to now, the relationship between the structures of carbon materials and their activities in PS-AOPs has not been specifically reviewed. The methods to switch reaction pathway (radical and nonradical pathways) in carbon-persulfate-based AOPs have not been systematically explored. Hereon, this review illustrated the active sites of G, CNTs, BC and other carbon materials, and generalized the modification methods to promote the activity of carbon materials and to switch reaction pathway in PS-AOPs. The roles of carbon materials in PS-AOPs were discussed around reactive oxygen species (ROS) and the structures. ROS are frequently complex in AOPs, but main ROS generation is related to the active sites on carbon materials. The structures of carbon materials (e.g., metal-carbon bonds, the electron-deficient C atoms, unbalanced electron distribution and graphitized structures) play a decisive role in the nonradical pathway. Finally, future breakthroughs of carbon materials were proposed for practical engineering and multi-field application.

Pesticides Xenobiotics in Soil Ecosystem and Their Remediation Approaches

Globally, the rapid rise in the human population has increased the crop production, resulting in increased pesticide xenobiotics. Despite the fact that pesticide xenobiotics toxify the soil environment and ecosystem, synthetic pesticides have increased agricultural yields and reduced disease vectors. Pesticide use has increased, resulting in an increase in environmental pollution. Various methods of controlling and eliminating these contaminants have been proposed to address this issue. Pesticide impurity in the climate presents a genuine danger to individuals and other oceanic and earthly life. If not controlled, the pollution can prompt difficult issues for the climate. Some viable and cost-effective alternative approaches are needed to maintain this emission level at a low level. Phytoremediation and microbial remediation are effective methods for removing acaricide scrapings from the atmosphere using plants and organisms. This review gives an overview of different types of xenobiotics, how they get into the environment, and how the remediation of pesticides has progressed. It focuses on simple procedures that can be used in many countries. In addition, we have talked about the benefits and drawbacks of natural remediation methods.

Green remediation potential of immobilized oxidoreductases to treat halo-organic pollutants persist in wastewater and soil matrices - A way forward

The alarming presence of hazardous halo-organic pollutants in wastewater and soils generated by industrial growth, pharmaceutical and agricultural activities is a major environmental concern that has drawn the attention of scientists. Unfortunately, the application of conventional technologies within hazardous materials remediation processes has radically failed due to their high cost and ineffectiveness. Consequently, the design of innovative and sustainable techniques to remove halo-organic contaminants from wastewater and soils is crucial. Altogether, these aspects have led to the search for safe and efficient alternatives for the treatment of contaminated matrices. In fact, over the last decades, the efficacy of immobilized oxidoreductases has been explored to achieve the removal of halo-organic pollutants from diverse tainted media. Several reports have indicated that these enzymatic constructs possess unique properties, such as high removal rates, improved stability, and excellent reusability, making them promising candidates for green remediation processes. Hence, in this current review, we present an insight of green remediation approaches based on the use of immobilized constructs of phenoloxidases (e.g., laccase and tyrosinase) and peroxidases (e.g., horseradish peroxidase, chloroperoxidase, and manganese peroxidase) for sustainable decontamination of wastewater and soil matrices from halo-organic pollutants, including 2,4-dichlorophenol, 4-chlorophenol, diclofenac, 2-chlorophenol, 2,4,6-trichlorophenol, among others.

Theoretical and experimental insights into the mechanisms of C6/C6 PFPiA degradation by dielectric barrier discharge plasma

As an emerging alternative legacy perfluoroalkyl substance, C6/C6 PFPiA (perfluoroalkyl phosphinic acids) has been detected in aquatic environments and causes potential risks to human health. The degradation mechanisms of C6/C6 PFPiA in a dielectric barrier discharge (DBD) plasma system were explored using validated experimental data and density functional theory (DFT) calculations. Approximately 94.5% of C6/C6 PFPiA was degraded by plasma treatment within 15 min at 18 kV. A relatively higher discharge voltage and alkaline conditions favored its degradation. C6/C6 PFPiA degradation was attributed to attacks of •OH, •O₂^-, and ¹O₂. Besides PFHxPA and C2 -C6 shorter-chain perfluorocarboxylic acids, several other major intermediates including C4/C6 PFPiA, C4/C4 PFPiA, and C3/C3 PFPiA were identified. According to DFT calculations, the potential energy surface was proposed for possible reactions during C6/C6 PFPiA degradation in the discharge plasma system. Integrating the identified intermediates and DFT results, C6/C6 PFPiA degradation was deduced to occur by stepwise losing CF₂, free radical polymerization, and C-C bond cleavage. Furthermore, the DBD plasma treatment process decreased the toxicity of C6/C6 PFPiA to some extent. This study provides a comprehensive understanding of C6/C6 PFPiA degradation by plasma advanced oxidation.

Bisphenol S degradation via persulfate activation under UV-LED using mixed catalysts: Synergistic effect of Cu-TiO2 and Zn-TiO2 for catalysis

A photocatalyst composed of Zn-TiO₂ and Cu-TiO₂ through simple physical mixing was used to activate persulfate(PS) for Bisphenol S (BPS) degradation. Zn-TiO₂ and Cu-TiO₂ were prepared with a sol gel method and were characterized by X-ray diffraction (XRD), Raman, Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The two catalysts have shown an obvious synergistic effect in the photocatalytic degradation process. When 5 mM persulfate and 0.3 g/L catalyst were used, the removal rate of mixed catalyst (0.2 g/L Zn-TiO₂ and 0.1 g/L Cu-TiO₂) is 100 % in 18 min, which is significantly better than that of 0.3 g/L Zn-TiO₂(58 %) and 0.3 g/L Cu-TiO₂(90 %). Typically, the effects of various operation parameters, including the ratio of Cu-TiO₂/Zn-TiO₂, catalyst dosage, persulfate dosage, initial concentration of BPS, and initial solution pH, were examined. Reactive oxygen species (ROS) in the UV/mixed catalyst/PS process was identified by scavenger and electron paramagnetic resonance (EPR) tests. The superoxide radicals generated by both Zn-TiO₂ and the hydrolysis of persulfate in the system could accelerate the Cu (II)/Cu(I) redox cycles and results in the synergistic effect. This study proposed a new and effective way to improve the reaction by simply combining two catalysts, and unraveled the mechanism behind the synergistic effect, which could provide new ideas to use the catalyst more effectively for wastewater treatment or other areas.

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.

The radical and non-radical oxidation mechanism of electrochemically activated persulfate process on different cathodes in divided and undivided cell

Electrochemically activated persulfate (PS) employing stainless steel (SS), carbon felt (CF) and carbon black modified CF (CB-CF) as the cathode, in the divided and undivided cell, respectively, for degradation of atrazine (ATZ) was first investigated using novel B, Co-doped TiO₂ nanotubes (B, Co-TNT) anode. In undivided cell, ATZ degradation was followed the order of CF<CB-CF<SS. The main radical for ATZ removal in SS and CF system was ^•OH, while on CB-CF cathode, it was the comprehensive contribution of ^•OH and SO₄^•-. ^•OH in SS system was more inclined to free ^•OH, while in CF and CB-CF systems it was more likely to be surface ^•OH. In divided anode cell, ^•OH was responsible for ATZ degradation in all three cathodes system. However, in divided cathode cell, ^•OH played a major role for ATZ degradation in SS cathode system. In CF and CB-CF cathode systems, the ATZ degradation was the comprehensive effect of ^•OH and SO₄^•- with the contribution of ^•OH and SO₄^•- was 91.7%, 8.3%, and 96.3%, 3.6%, respectively. The quenching studies showed that non-radical oxidation occurred in anode chamber in the presence of PS. Besides, the intermediates in divided and undivided cell were detected by LC-MS, and the possible degradation pathway was proposed.

Kinetics and catalytic efficiency of soil fluorescein diacetate hydrolase under the pesticide parathion stress

Fluorescein diacetate hydrolase (FDA-H) is an accurate biochemical method measuring the total microbial activity in soil, which indicates soil quality under ambient environmental changes such as pesticide parathion (PTH). However, the influence of PTH on the kinetics of FDA-H is still unknown. In this study, fifteen farmland soils were exposed to acute PTH pollution to investigate how the kinetic characteristics of FDA-H change with PTH concentration. Results showed that PTH strongly inhibited the FDA-H activities. The values of maximum reaction velocity (V_max) ranged from 0.29 to 2.18 × 10^-2 mM g^-1 soil h^-1 and declined by 42.30%-71.01% under PTH stress. The Michaelis constant (K_m) values ranged between 2.90 and 14.17 × 10^-2 mM and exhibited three forms including unchanged, increased (38.16-242.65%) and decreased (13.41-39.23%) when exposed to PTH. Based on the changes in two kinetic parameters, the inhibition of PTH on FDA-H was classified as three types, i.e., noncompetitive, linear mixed and uncompetitive inhibition. The competitive inhibition constant (K_ic) and noncompetitive constant (K_iu) ranged from 0.064 to 0.447 mM and 0.209 to 0.723 mM, respectively, which were larger than the K_m in values. The catalytic efficiency (V_max/K_m) of FDA-H is a sensitive integrated parameter to evaluate the PTH toxicity due to the higher inhibition ratio than the V_max. The PTH toxicity to FDA-H decreased with increase of soil organic matter and total nitrogen contents. This implied that the PTH toxicity could be alleviated by an increasing content of soil organic matter due to its buffering capacity to PTH. Besides, soils with a higher content of total nitrogen could provide stable environment for FDA-H to maintain its functionality under PTH pollution. Thus, the results of this study have great implications to the risk assessment of parathion in soils.