Removal of sorbed polycyclic aromatic hydrocarbons from soil, sludge and sediment samples using the Fenton's reagent process

Enhanced in-situ sediment remediation by calcium peroxide coupled with zero-valent iron: Simultaneous nitrogen removal and phosphorus stabilization

As the potential causes of eutrophication, nitrogen (N) and phosphorus (P) in sediments have received wide attention. However, few of the in-situ sediment remediation methods can achieve simultaneous N removal and P stabilization in sediments. In this study, different impacts on N, P and organic matter (OM) properties of sediments and overlying water with different proportions of calcium peroxide (CaO2) coupling with zero-valent iron (ZVI) were explored through incubation experiments. Compared with CaO2 or ZVI alone, the total nitrogen (TN) removal ratios in the whole system at 0.6 g/kg CaO2 coupled with 40 g/kg ZVI increased by 167.91% and 152.04%, respectively. Due to the enhancement of oxidation, the removal efficiency of OM from sediments increased by 118.51%. Meanwhile, the genera related to denitrification (e.g., Anaerobacillus, Haloplasma, and Clostridium_sensu_stricto_8) were also enriched in this coupling group, which was due to the enhanced decomposition of OM and the electron donation of ZVI. In addition, CaO2 coupled with ZVI stabilized P through chemical precipitation, which converted organic phosphorus (Org-P) into more stable calcium bounded P (Ca-P) in sediments. Hence the coupling effectively increased total P (TP) content in sediments and reduced P concentration in water.

Potassium peroxoborate: A sustained-released reactive oxygen carrier with enhanced PAHs contaminated soil remediation performance

Seeking for a safe, efficient, inexpensive, and eco-friendly oxidizer is always a big challenge for in-situ chemical oxidation (ISCO) technology. This study adopted the potassium peroxoborate (PPB), a novel peroxide, for soil remediation for the first time. PPB based chemical oxidation system (PPB-CO) could efficiently degrade polycyclic aromatic hydrocarbons (PAHs) without other reagents added, reaching 72.1 %, 64.2 %, and 50.0 % removal rates for naphthalene, phenanthrene, and pyrene after 24 h reaction, respectively. The superior total PAHs removal efficiency (60.6 %) was 3.6-4.7 times higher than that of other commercial peroxides (2Na2CO3•3H2O, CaO2, and H2O2). Mechanism analysis revealed that varieties of reactive oxygen species (ROS) can be generated by PPB through Fenton-like or non-Fenton routines, including H2O2, perborates species, O2•-, •OH, and 1O2. The sustainable generation of H2O2 reduced the disproportionation effect of H2O2 by 86 %, significantly improving the utilization rate. Moreover, sandbox experiments and actual contaminated soil remediation experiments verified the feasibility of PPB-CO in a real polluted site. This work provides a novel strategy for effectively soil remediation, highlighting the selection and application of new oxidants.

A novel mycelial pellet applied to remove polycyclic aromatic hydrocarbons: High adsorption performance & its mechanisms

Mycelial pellets formed by Penicillium thomii ZJJ were applied as efficient biosorbents for the removal of polycyclic aromatic hydrocarbons (PAHs), which are a type of ubiquitous harmful hydrophobic pollutants. The live mycelial pellets were able to remove 93.48 % of pyrene at a concentration of 100 mg/L within 48 h, demonstrating a maximum adsorption capacity of 285.63 mg/g. Meanwhile, the heat-killed one also achieved a removal rate of 65.01 %. Among the six typical PAHs (pyrene, phenanthrene, fluorene, anthracene, fluoranthene, benzo[a]pyrene), the mycelial pellets preferentially adsorbed the high molecular weight PAHs, which also have higher toxicity, resulting in higher removal efficiency. The experimental results showed that the biosorption of mycelial pellets was mainly a spontaneous physical adsorption process that occurred as a monolayer on a homogeneous surface, with mass transfer being the key rate-limiting step. The main adsorption sites on the surface of mycelia were carboxyl and N-containing groups. Extracellular polymeric substances (EPS) produced by mycelial pellets could enhance adsorption, and its coupling with dead mycelia could achieve basically the same removal effect to that of living one. It can be concluded that biosorption by mycelial pellets occurred due to the influence of electrostatic and hydrophobic interactions, consisting of five steps. Furthermore, the potential applicability of mycelial pellets has been investigated considering diverse factors. The mycelia showed high environmental tolerance, which could effectively remove pyrene across a wide range of pH and salt concentration. And pellets diameters and humic acid concentration had a significant effect on microbial adsorption effect. Based on a cost-effectiveness analysis, mycelium pellets were found to be a low-cost adsorbent. The research outcomes facilitate a thorough comprehension of the adsorption process of pyrene by mycelial pellets and their relevant applications, proposing a cost-effective method without potential environmental issues (heat-killed mycelial pellets plus EPS) to removal PAHs.

Occurrence, spatiotemporal trends, fate, and treatment technologies for microplastics and organic contaminants in biosolids: A review

This review provides a comprehensive overview of the occurrence, fate, treatment and multi-criteria analysis of microplastics (MPs) and organic contaminants (OCs) in biosolids. A meta-analysis was complementarily analysed through the literature to map out the occurrence and fate of MPs and 10 different groups of OCs. The data demonstrate that MPs (54.7% occurrence rate) and linear alkylbenzene sulfonate surfactants (44.2% occurrence rate) account for the highest prevalence of contaminants in biosolids. In turn, dioxin, polychlorinated biphenyls (PCBs) and phosphorus flame retardants (PFRs) have the lowest rates (<0.01%). The occurrence of several OCs (e.g., dioxin, per- and polyfluoroalkyl substances, polycyclic aromatic hydrocarbons, pharmaceutical and personal care products, ultraviolet filters, phosphate flame retardants) in Europe appear at higher rates than in Asia and the Americas. However, MP concentrations in biosolids from Australia are reported to be 10 times higher than in America and Europe, which required more measurement data for in-depth analysis. Amongst the OC groups, brominated flame retardants exhibited exceptional sorption to biosolids with partitioning coefficients (log Kd) higher than 4. To remove these contaminants from biosolids, a wide range of technologies have been developed. Our multicriteria analysis shows that anaerobic digestion is the most mature and practical. Thermal treatment is a viable option; however, it still requires additional improvements in infrastructure, legislation, and public acceptance.

Formation of organic chloride in the treatment of textile dyeing sludge by Fenton system

In the oxidation treatment of textile dyeing sludge, the quantitative and transformation laws of organic chlorine are not clear enough. Thus, this study mainly evaluated the treatment of textile dyeing sludge by Fenton and Fenton-like system from the aspects of the influence of Cl^-, the removal of polycyclic aromatic hydrocarbons (PAHs) and organic carbon, and the removal and formation mechanism of organic chlorine. The results showed that the organic halogen in sludge was mainly hydrophobic organic chlorine, and the content of adsorbable organic chlorine (AOCl) was 0.30 mg/g (dry sludge). In the Fenton system with pH=3, 500 mg/L Cl^-, 30 mmol/L Fe²⁺ and 30 mmol/L H₂O₂, the removal of phenanthrene was promoted by chlorine radicals (•Cl), and the AOCl in sludge solid phase increased to 0.55 mg/g (dry sludge) at 30 min. According to spectral analysis, it was found that •Cl could chlorinate aromatic and aliphatic compounds (excluding PAHs) in solid phase at the same time, and eventually led to the accumulation of aromatic chlorides in solid phase. Strengthening the oxidation ability of Fenton system increased the formation of organic chlorines in liquid and solid phases. In weak acidity, the oxidation and desorption of superoxide anion promoted the removal and migration of PAHs and organic carbon in solid phase, and reduced the formation of total organic chlorine. The Fenton-like system dominated by non-hydroxyl radical could realize the mineralization of PAHs, organic carbon and organic chlorines instead of migration. This paper builds a basis for the selection of sludge conditioning methods.

Degradation of pyrene in contaminated soil by the dielectric barrier discharge combined with the MnFe2O4 catalyst

In this work, a spinel oxide of MnFe2O4 was used as the dielectric barrier discharge (DBD) catalyst for the remediation of pyrene-contaminated soil. The performances were investigated through tuning voltage, frequency, catalyst dosage, and soil moisture. Under the optimal conditions, such as the voltage of 10.0 kV, the discharge frequency of 1.0 kHz, MnFe2O4 dosage of 0.3 g, air flow rate of 2.0 L min-1, soil humidity of 5.3%, and degradation efficiency of DBD/MnFe2O4 for pyrene could reach 79.26% after 10 min treatment, which was much higher than that of DBD for pyrene of 42.56%. The DBD/MnFe2O4 system also showed the high degradation efficiency of other pollutants including phenanthrene, p-nitrophenol, and p-nitrophenol in contaminated soil. The enhancing mechanism of the DBD/MnFe2O4 system was discussed.

Decrypting the synergistic action of the Fenton process and biochar addition for sustainable remediation of real technogenic soil from PAHs and heavy metals

The objective of this study was to demonstrate the feasibility and the relevance of combining biochar with the Fenton process for the simultaneous improvement of polycyclic aromatic hydrocarbons (PAHs) degradation and immobilization of heavy metals (HMs) in real soil remediation processes at circumneutral pH. The evaluation of PAHs degradation results was performed through multivariate statistical tools, including principal component analysis (PCA) and partial least squares (PLS). PCA showed that the level of biochar amendment decisively affected the degree of degradation of total PAHs, highlighting the role of biochar in catalyzing the Fenton reaction. Moreover, the PLS model was used to interpret the important features of each PAH's physico-chemical properties and its correlation to degradation efficiency. The electron affinity of PAHs correlated positively with the degradation efficiency only if the level of biochar amendment sat at 5%, explained by the ability of biochar to transfer the electrons to PAHs, improving the Fenton-like degradation. Moreover, the addition of biochar reduced the mobilization of HMs by their fixation on their surface, reducing the Fenton-induced metal leaching from the destruction of metal-organic complexes. In overall, these results on the high immobilization rate of HMs accompanied with additional moderate PAHs degradation highlighted the advantages of using a biochar-assisted Fenton-like reaction for sustainable remediation of technogenic soil.

Petroleum-contaminated soil: environmental occurrence and remediation strategies

Soil is an environmental matrix that carries life for all living things. With the rise of human activities and the acceleration of population, the soil has been exposed in part to pollution by the discharge of various xenobiotics and persistent pollutants into it. The disposal of toxic substances such as polycyclic aromatic hydrocarbons (PAHs) alters soil properties, affects microbial biodiversity, and damages objects. Considering the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and clean-up of PAH-polluted sites represents an important technological and environmental challenge for sustainable growth and development. Though several treatment methods to remediate PAH-polluted soils exist, interesting bacteria, fungi, and their enzymes receive considerable attention. The aim of the present review is to discuss PAHs' impact on soil properties. Also, this review illustrates physicochemical and biological remediation strategies for treating PAH-contaminated soil. The degradation pathways and contributing factors of microbial PAH-degradation are elucidated. This review also assesses the use of conventional microbial remediation compared to the application of genetically engineered microorganisms (GEM) that can provide a cost-effective and eco-friendly PAH-bioremediation strategy.

Removal of organotin compounds and metals from Swedish marine sediment using Fenton's reagent and electrochemical treatment

Metal and tributyltin (TBT) contaminated sediments are problematic for sediment managers and the environment. This study is the first to compare Fenton's reagent and electrochemical treatment as remediation methods for the removal of TBT and metals using laboratory-scale experiments on contaminated dredged sediment. The costs and the applicability of the developed methods were also compared and discussed. Both methods removed > 98% TBT from TBT-spiked sediment samples, while Fenton's reagent removed 64% of the TBT and electrolysis 58% of the TBT from non-spiked samples. TBT in water phase was effectively degraded in both experiments on spiked water and in leachates during the treatment of the sediment. Positive correlations were observed between TBT removal and the added amount of hydrogen peroxide and current density. Both methods removed metals from the sediment, but Fenton's reagent was identified as the most potent option for effective removal of both metals and TBT, especially from highly metal-contaminated sediment. However, due to risks associated with the required chemicals and low pH level in the sediment residue following the Fenton treatment, electrochemical treatment could be a more sustainable option for treating larger quantities of contaminated sediment.

Chemical remediation and advanced oxidation process of polychlorinated biphenyls in contaminated soils: a review

Polychlorinated biphenyls (PCBs) are synthetic organic compounds ubiquitously distributed worldwide due to their persistence, long-range atmospheric transport, and bioaccumulation. Owing to teratogenic properties, PCBs are a global environmental problem. Different physical, biological, and chemical techniques are utilized for the remediation of PCBs. This review paper discusses the recent development in photocatalytic and chemical techniques for the remediation of PCBs in contaminated soils. In particular, the photocatalytic degradation of PCBs combined with soil washing, Fe-based reductive dichlorination, and advanced oxidation process (Fenton advance oxidation and persulfate oxidation) is discussed and reviewed in detail. The review suggested that advanced oxidation is an efficient remediation technique with 77-99% of removal efficiency of PCBs. Persulfate oxidation is the most suitable technique which could work at normal environmental conditions (such as pH, temperature, soil organic matter (SOM), etc.). Different environmental factors such as pH, temperature, and SOM affect the Fe-based reductive dechlorination and Fenton advance oxidation techniques. The surfactants and organic solvents used in soil washing combined with photocatalytic degradation affect the degradation capability of these techniques. This review will contribute to PCBs degradation by the detailed discussion of development in chemical technique future perspective and research needs.

Enhanced PAHs-contaminated site soils remediation by mixed persulfate and calcium peroxide

Polycyclic aromatic hydrocarbons (PAHs) remain in the site soils after relocated coking plants and oil refineries pose huge constraints to the subsequent land utilization. However, single persulfate (PS) or calcium peroxide (CP) remediation strategies can only inefficiently oxidize some PAHs in soil. This work sought to optimize PS/CP oxidation remediation strategy and verify its practical application effect in soil samples spiked with PAHs. The results showed that the mixed PS/CP oxidation remediation was better than the single oxidants strategies; it had high remediation performance in different particles and pollution loads of PAHs-contaminated soils. Simultaneously, reactive radicals (SO₄·^- and ·OH) were detected, and one side-product (CaSO₄) was characterized. This work optimized the mixed PS/CP system (0.3 mol/L PS, and 8 g/kg CP, together with 0.18 mol/L Fe²⁺ and 0.11 mol/L C₂O₄^2-), and the corresponding Total-PAHs removal rate was 85.41%. Compared to the cost based on benzopyrene (BaP) removal, the study provided a cost-effective mixed PS/CP oxidation remediation technique (1.22 $/ton), widely applicable in soils polluted with various organic contaminants represented such as PAHs.

Typical groundwater contamination in the vicinity of industrial brownfields and basic methods of their treatment

The article deals with simple methods of decontamination of groundwater from the vicinity of brownfields contaminated with organic and inorganic substances. In the literature, thousands of articles on this issue at various sophisticated levels of knowledge can be found. The articles are mostly suitable as an extension of scientific knowledge; however, regarding potential costs and respectively scale-up problems, the applications are limited. It turns out that the vast majority of contaminated water can be effectively decontaminated by simple methods, in a coagulation-sedimentation sequence → simple oxidation and reduction methods for separated water (Fenton reaction, photocatalysis, ozonation, reductive dehalogenation with zero metals) → adsorption of remaining pollutants on simple sorbents, eg on biochar → (possibly bioremediation or advanced physical methods such as membrane filtration) → final purification on activated carbon. Due to the usually limited volume loads of soils with pollutants in the vicinity of brownfields, it is not economically advantageous to build demanding decontamination units for water purification. Usually, the simplest solution is the system to pump-and-treat around the source of contamination, with the main emphasis on highly effective removal of pollutants from water that returns underground. Groundwater was taken from boreholes leading to the saturated zone in the vicinity of several selected industrial brownfields. The solutions are shown on individual typical cases.

Production, characterisation, utilisation, and beneficial soil application of steel slag: A review

Slags are a co-product produced by the steel manufacturing industry and have mainly been utilised for aggregates in concreting and road construction. The increased utilisation of slag can increase economic growth and sustainability for future generations by creating a closed-loop system, circular economy within the metallurgical industries. Slags can be used as a soil amendment, and slag characteristics may reduce leachate potential of heavy metals, reduce greenhouse gas emissions, as well as contain essential nutrients required for agricultural use and environmental remediation. This review aims to examine various slag generation processes in steel plants, their physicochemical characteristics in relation to beneficial utilisation as a soil amendment, and environmental implications and risk assessment of their utilisation in agricultural soils. In relation to enhancing recycling of these resources, current and emerging techniques to separate iron and phosphorus slag compositions are also outlined in this review. Although there are no known immediate direct threats posed by slag on human health, the associated risks include potential heavy metal contamination, leachate contamination, and bioaccumulation of heavy metals in plants, thereby reaching the food chain. Further research in this area is required to assess the long-term effects of slag in agricultural soils on animal and human health.

The extent of sludge solubilization allows to estimate the efficacy of ozonation for removal of polycyclic aromatic hydrocarbons (PAHs) in municipal sewage sludge

Ozone treatment has been proven as an effective technology for removing PAHs in municipal sewage sludge. However, given the complex interaction of PAHs with sludge extracellular polymeric substances (EPS), effective sludge disintegration is required to make PAHs more accessible to oxidants, which also affects PAHs partitioning. Here, we investigated two treatment systems, namely ozonation (ozone) and sequential hydrodynamic cavitation and ozonation (HC+ozone), under varied conditions, to determine whether the extent of sludge disintegration can estimate a measurable removal of PAHs. The results showed that both the PAHs removal efficiency and kinetics highly depended on pH and ozone dose. Although no significant removal of PAHs occurred during HC treatment, the observed rate constants for Σ₁₆ PAHs removal in HC+ozone system were 1.2-1.4-fold higher than those obtained in ozone system under the same condition. The accelerated PAHs removal could be attributed to the reduced flocs size (80% smaller) and increased soluble EPS concentration (5-fold higher) with HC pretreatment. Lastly, a positive correlation was noted between the PAHs removal efficiency and soluble EPS concentration (R² = 0.85), indicating the important role of dissolved and colloidal matter (DCM) for PAHs partitioning between aqueous and particulate phases.

The Use of an Ultrasonic Field in Support of Classical Methods of Oxidising Component Leached from Microplastics in Bottom Sediments

The work detailed here examined the impact of selected unit methods and ultrasonic removal of the widespread plastic additive di(2-ethylhexyl) phthalate (DEHP) from the bottom sediments of a body of water. To this end, hydrogen peroxide and a classic or modified Fenton process were used, supplemented by an ultrasonic field. The latter had a vibration frequency of 20 kHz and an acoustic wave intensity of 3.97 W/cm². The impact of process parameters such as reaction environment, reaction time, initial impurity content, aging of the impurity, influence of processes on the content of organic matter and dissolved organic carbon, and elution of selected components from the matrix were all analysed. It emerged that the most effective process by which to remove DEHP from a solid matrix involved a modified Fenton process assisted by an ultrasonic field. The highest average degradation efficiency achieved in this way was 70.74%, for C₀ = 10 mg/kg d.w. and t = 60 min.

Treatment of simulated textile sludge using the Fenton/Cl- system: The roles of chlorine radicals and superoxide anions on PAHs removal

The main content of this work is to investigate the removal of polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, and fluoranthene) from simulated sludge solid phase employing an Fenton/Cl^- system under various Cl^- contents and pH values. The steady-state concentrations of the hydroxyl, chlorine, and dichloride anion radicals ([·OH]_ss, [·Cl]_ss, and [Cl₂^·-]_ss) in heterogeneous system were first measured using tert-butanol, nitrobenzene, and benzoic acid. The outcomes exhibited that increasing the Cl^- content from 50 to 2000 mg/L (pH = 3.0) or raising the pH from 3.0 to 5.0 (1000 mg/L Cl^-) caused [·OH]_ss to continuously decrease and [Cl₂^·-]_ss and the concentration of superoxide anions (HO₂·/O₂^·-) to continuously increase. When the pH was 3.0 and the Cl^- concentration was 1000 mg/L, [·Cl]_ss had a maximum value of 9.27 × 10^-14 M. Combining the results of PAH removal, radical quenching, and product analysis, it was found that ·Cl in the Fenton/Cl^- system promoted the oxidative degradation of phenanthrene without forming chlorination byproducts. Furthermore, HO₂·/O₂^·- was helpful in removing anthracene and fluoranthene. Under the environment of high Cl^- content (≥1000 mg/L), PAHs could be removed more effectively by using HO₂·/O₂^·-. This investigation underpins further study on the regulation of reactive species and the efficient degradation of target organic matter in Fenton/Cl^- system, and provides a basis for studying the formation of chlorinated or toxic byproducts in the process of treating textile dyeing sludge by Fenton.

Porous cage-like hollow magnetic carbon-doped CoO nanocomposite as an advanced sorbent for magnetic solid-phase extraction of nine polycyclic aromatic hydrocarbons

In this study, porous cage-like hollow magnetic carbon-doped CoO nanocomposite (CoO@C) was successfully synthesized using a metal-organic frameworks (MOFs) as precursor by one-step calcination method in this work. The obtained nanoporous composite showed excellent magnetic response by taking advantage of the magnetism of CoO even without the Fe₃O₄, making it an advanced sorbent for magnetic solid-phase extraction (MSPE). The Co-MOF and CoO@C were characterized by XRD, TGA, SEM, TEM, vibrating sample magnetometry, and FT-IR spectroscopy. Based on this, a method using CoO@C for MSPE coupled with HPLC was established for the analysis of nine polycyclic aromatic hydrocarbons (PAHs) from various real water samples. The amount of sorbent, extraction times, extraction temperature, desorption times, oscillation rate, and elution volume were optimized. Under the optimal conditions, the method had good relative standard deviations (RSDs) of 1.1%-6.5% and a satisfying linearity range of 0.5-1000 μg L^-1. The low LOD and LOQ for nine PAHs were found to be 0.06-1.30 μg L^-1 and 0.19-4.30 μg L^-1, respectively. The experimental results indicated that the prepared nanocomposite showed excellent adsorption capacity compared to other commercial sorbents and has potential applications for the removal of hazardous pollutants from environmental samples.

Insight into the roles of endogenous minerals in the activation of persulfate by graphitized biochar for tetracycline removal

Owing to its environmental-friendliness, low-cost, and outstanding characteristics, biochar has been widely used for the catalytic degradation of various organic pollutants. In this study, a pre- and post-deashing graphitized biochar (DBC800 and PBC800-A) was prepared and compared with the pristine biochar (PBC800) to activate persulfate (PS) for tetracycline (TC) degradation. The influence of the natural endogenous mineral on the catalytic ability of biochar was investigated. Characterization results show that the inherent endogenous mineral in biochar not only acted as a natural pore-forming agent to promote the formation of the porous structure, but also facilitated the formation of edge defective structures, and altered the surface functional groups, as well as increased the carbonization and graphitization degree of biochar. The PBC800-A exhibited a much higher catalytic efficiency on PS activation and TC oxidative degradation with the reaction rate of 0.06055 min^-1, 7.14 times as that of DBC800 (0.00861 min^-1) and 4.63 times as that of PBC800 (0.00158 min^-1). The endogenous minerals were conducive to the generation of free radicals and promoted the oxidative degradation of TC, which was mainly attributed to the improved carbon configuration. The post-deashing treatment was also found to significantly improve the electron transport efficiency of biochar by removing the residual ash, thereby promoting the generation of singlet oxygen. This study demonstrated that the natural minerals in biochar was beneficial for the degradation of TC, and more alternative natural minerals can be applied to co-pyrolysis with biochar for the remediation of refractory organic pollutants.

Impact of humic acid on degradation of benzo(a)pyrene polluted Haplic Chernozem triggered by modified Fenton-like process

In this study, the applicability of a modified Fenton reaction for remediation of polycyclic aromatic hydrocarbons (PAHs) was demonstrated in chernozem soil. The main aim was to investigate the impact of variation of humic acid (HA) on the modified Fenton capabilities to degrade of benzo(a)pyrene (BaP). Experimental was designed with two independent variables, including hydrogen peroxide (H₂O₂) and hematite (α-Fe₂O₃), to determine the most effective BaP treatment conditions with exploring natural and an extra added amount of HA. For modified Fenton reaction at Haplic Chernozem, the best BaP degradation conditions resulted in an overall degradation of 68% with the following conditions: 0.95 M H₂O₂; 17.54 mg/g hematite; pH 7.8 without adjustment; 24 h; unsaturated (soil: water ratio 1:0.5). In the soil supplemented with 1% HA, Fenton-like reaction was found to perform better and resulted in 76% BaP degradation with less amount of hematite dosage (16.71 mg). The fact that HA, a significant class of naturally occurring compounds in soil, supports the Fenton reaction has strong relevance in the field of enhancing PAHs degradation field to obtain a more economical route.

Enhanced oxidative degradation of decabromodiphenyl ether in soil by coupling Fenton-persulfate processes: Insights into degradation products and reaction mechanisms

Decabromodiphenyl ether (BDE-209) has extreme hydrophobicity, which results in its significant accumulation in soil, sediments and other solid materials. In this work, an oxidation method coupling Fenton with persulfate (PS) was proposed for the effective degradation of BDE-209 adsorbed on solid surfaces. After adding 0.1 M PS to the Fenton system at 1.0 h, the removal rate of BDE-209 was significantly increased from 62.2% to 94.0%. The degradation of BDE-209 in various soil samples was also investigated by the coupling Fenton-PS method. Removal efficiency of 73.4-95.8% was obtained, suggesting that this coupling method was feasible in real application. According to the radical scavenging experiments, •OH dominated the overall reaction of BDE-209 in the coupling system. Meanwhile, the enhanced removal was attributed to the generation of SO₄^•- from the catalytic decomposition of PS. The calculated energy barriers for SO₄^•- attacking on the carbons were smaller than •OH initiated reactions, which further confirmed that SO₄^•- plays a role in the accelerated removal of BDE-209. The initial attack of BDE-209 by SO₄^•- generated the SO₄^•- adducts, which may undergo debromination or CO bond cleavage reaction together with subsequent hydroxyl substitution to form the primary product OH-Nona-BDEs and pentabromophenol. Under the successive attack of radicals, these primary products were further transformed into lower-brominated hydroxylation products and bromophenols via direct debromination and hydroxyl substitution reaction. This work provides an economical and effective method for treating BDE-209 contaminated soils and samples.

Validation of Sample Preparation Methods for Microplastic Analysis in Wastewater Matrices—Reproducibility and Standardization

There is a growing interest in monitoring microplastics in the environment, corresponding to increased public concerns regarding their potential adverse effects on ecosystems. Monitoring microplastics in the environment is difficult due to the complex matrices that can prevent reliable analysis if samples are not properly prepared first. Unfortunately, sample preparation methods are not yet standardized, and the various efforts to validate them overlook key aspects. The goal of this study was to develop a sample preparation method for wastewater samples, which removes natural organic matter without altering the properties of microplastics. Three protocols, based on KOH, H2O2, and Fenton reactions, were chosen out of ten protocols after a literature review and pre-experiments. In order to investigate the effects of these reagents on seven polymers (PS, PE, PET, PP, PA, PVC, and PLA), this study employed µFTIR, laser diffraction-based particle size analysis, as well as TD-Pyr-GC/MS. Furthermore, the study discussed issues and inconsistencies with the Fenton reactions reported in the literature in previous validation efforts. The findings of this study suggest that both H2O2 and Fenton reactions are most effective in terms of organic matter removal from microplastic samples while not affecting the tested polymers, whereas KOH dissolved most PLA and PET particles.

Natural aeolian dust particles have no substantial effect on atmospheric polycyclic aromatic hydrocarbons (PAHs): A laboratory study based on naphthalene

Natural aeolian dust (AD) particles are potential carriers of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. The heterogeneous interaction between them may lead to worsened air quality and enhanced cytotoxicity and carcinogenicity of ambient particulates in downwind areas, and this topic requires in-depth exploration. In this study, AD samples were collected from four Asian dust sources, and their physical properties and compositions were determined, showing great regional differences. The physical and chemical interactions of different AD particles with naphthalene (Nap; model PAH) were observed in aqueous systems. The results showed that AD particles from the Loess Plateau had weak adsorption to Nap, which was fitted by the Langmuir isotherm. There was no obvious adsorption to Nap found for the other three AD samples. This difference seemed to depend mainly on the specific surface area and/or the total pore volume. In addition, the Nap in the aqueous solution did not undergo chemical reactions under dark conditions and longwave ultraviolet (UV) radiation but degraded under shortwave UV radiation, and 2-formylcinnamaldehyde and 1,4-naphthoquinone were the first-generated products. The degradation of Nap in the aqueous solution was probably initiated by photoionization, and the reaction rate constant (between 1.44 × 10^-4 min^-1 and 8.55 × 10^-4 min^-1) was much lower than that of Nap with hydroxyl radicals. Instead of inducing or promoting the chemical change in Nap, the AD particles slowed photodegradation due to the extinction of radiation. Therefore, it is inferred that natural AD particles have no substantial effect on the transportation and transformation of PAHs in the atmosphere.

Electrokinetic-Fenton for the remediation low hydraulic conductivity soil contaminated with petroleum

The use of electrokinetic Fenton (EK Fenton) process, as promising soil remediation approach, was investigated by using an iron electrode with different supporting electrolytes (tap water, H₂O₂, and citric acid) to depollute soil spiked with petroleum where kaolin was selected as low hydraulic conductivity. The results clearly confirm that, the combination of electrokinetic remediation (EK) and Fenton technologies, is an efficient oxidizing approach for removing hydrocarbons from this kind of soil. In fact, the electrokinetic Fenton reactions and the control of the soil pH conditions by adding citric acid enhanced the oxidation process because the addition of the H₂O₂ with iron electrode resulted in higher removal efficiencies (89%) for total petroleum hydrocarbons (TPHs). These figures allowed to confirm that EK Fenton process with pH control contributed for the transport of H₂O₂ and Fe²⁺ ions in the soil by electromigration and eletro-osmotic phenomena. Conversely, no control of pH conditions when only EK was applied, achieved lower hydrocarbons removal (27%) after 15 d of treatment due to the precipitation of iron ions. Finally, the efficiency of the EK Fenton remediation prevented the generation of secondary effluent with higher organic content, avoiding its treatment by other advanced oxidation process.

Effects of the structures and micropores of sedimentary organic matter on the oxidative degradation of benzo(a)pyrene by Na2S2O8

In this study, we investigated how the desorption and degradation processes of radiolabeled benzo[a]pyrene (BaP) that was aged in various marine sediments were influenced by sedimentary organic matter properties. The stable OC fraction (STOC) and the demineralized fraction (DM) were isolated and characterized via advanced solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR) and a CO₂ gas adsorption technique, respectively. Sodium persulfate preferentially removed the unstable OC fractions (USOC) and the aromatic C groups, and the residual STOC fractions were enriched with aliphatic C groups. The aliphatic C showed stronger resistance to degradation by persulfate than that of the aromatic C. A first-order kinetic model described the degradation process by sodium persulfate solutions very well (R² > 0.997). The desorption percentages, degradation percentages and rates k (h^-1) of BaP gradually decreased from the estuarine sediments to the offshore marine sediments and were highly significantly and negatively correlated with STOC-bulk, F_aliph-bulk, and V_o-bulk (R²>0.903, p < 0.01). It was demonstrated that sodium persulfate degraded not only desorbed BaP but also a portion of the bound BaP fraction that was difficult to desorb. The BaP fractions that sorbed on USOC were degraded initially; then, the fractions of BaP that were released from STOC were degraded. This study demonstrated the important roles of STOC, aliphatic moieties, and micropores in the degradation process of BaP during the Na₂S₂O₈ treatment of the sediments.

Marine sediment toxicity: A focus on micro- and mesocosms towards remediation

Micro- and/or mesocosms are experimental tools bringing ecologically relevant components of the natural environment under controlled conditions closest to the real world, without losing the advantage of reliable reference conditions and replications, providing a link between laboratory studies and filed studies in natural environments. Here, for the first time, a formal comparison of different types of mesocosm applied to the study of marine contaminants is offered, considering that pollution of coastal areas represented a major concern in the last decades because of the abundance of discharged toxic substances. In particular, the structural characteristics of micro- and mesocosms (m-cosms) used to study marine contaminated sediments were reviewed, focusing on their advantages/disadvantages. Their potentiality to investigate sediment remediation have been discussed, offering new perspective on how the use of m-cosms can be useful for the development of practical application in the development of solutions for contaminated sediment management in the contaminated marine environment.

Petroleum hydrocarbons degradation in contaminated soil using the plants of the Aster family

Oil extraction is one of the causes of soil contamination with the total petroleum hydrocarbons. The objective of this study was to clarify the effect of Asteraceae plants on the degradation of petroleum hydrocarbon in contaminated soil. Initial soils with 40 and 90 g kg^-1 of total petroleum hydrocarbon (TPH) were prepared. There were three treatments: (1) no addition, (2) addition of FeCl₃ and nitrilotriacetic acid (NTA) solution, and (3) addition of FeCl₃ + NTA and the cultivation of nine Asteraceae plants. The concentration of TPH was measured using infrared spectrophotometer, 2 and 3 months after transplanting (MAT). Shoot and root dry weights were measured 3 MAT. The concentration of TPH in soil cultivated with Cosmos caudatus was lower than that of the initial soil (40 g kg^-1 TPH), 2 MAT. The concentrations of TPH in soils cultivated with Calendula officinalis, Callistephus chinensis, C. caudatus, and Tagetes sp. were also lower than that in the initial soil, 3 MAT. The concentrations of TPH in soils cultivated with Achillea filipendulina, Anthemis tinctoria, Tagetes erecta, Chrysanthemum coronarium, C. officinalis, C. chinensis, and C. caudatus were lower than that in the initial soil (90 g kg^-1 TPH), 2 MAT. The concentrations of TPH in soils cultivated with T. erecta, A. tinctoria, Zinnia elegans, C. chinensis, C. caudatus, and Tagetes sp. were lower than that in the initial soil, 3 MAT. A. filipendulina and C. coronarium died at both 40 and 90 kg^-1 TPH soils. These results suggest that the roots of Asteraceae plants degrade petroleum hydrocarbon in contaminated soil and C. chinensis and Z. elegans are more suitable for using TPH remediation. Plant survival and extensive root system are important factors for the remediation of TPH in contaminated soil.

Impact of a Modified Fenton Process on the Degradation of a Component Leached from Microplastics in Bottom Sediments

This paper describes work to assess the possibility of a modified Fenton process being used to remove the hard-to-degrade plasticizer di(2-ethylhexyl) phthalate (DEHP) from the bottom sediments of a reservoir. The modifications in question entail iron(II) ions being replaced by iron(III), as well as facilitation of the process using a chelating agent. Analysis further revolved around the impact of such factors as amounts of reagents, reaction of the environment, initial contents of the contaminant, and the presence of other “competing” contaminants also of a hard-to-decompose nature. As the maximum efficiency of DEHP removal obtained did not exceed 30%, the low susceptibility to degradation is made clear, as is the need for earlier desorption of the contaminant from the matrix. The effect of the modified Fenton process on the content of organic matter and dissolved organic carbon was also considered, as was the tendency to cause selected metals and plant nutrients to leach from bottom sediments.

Comment on "thermal remediation alters soil properties - A review"

This comment is intended to highlight the role of thermal treatment to improve the availability of organic pollutants in contaminated soils for subsequent remediation by other techniques.

Treatment of petroleum hydrocarbons contaminated soil by Fenton like oxidation

Experimental tests were carried out in solid phase reactors on a microcosm scale, to removal old petroleum pollution by Fenton like oxidation process. In order to optimize the process, parametric study and statistically designed experiment have been undertaken by considering the amount influence of hydrogen peroxide (H₂O₂), endogenous and zero-valent iron (Fe) and ethylene diamine tetraacetic acid (EDTA) as chelating agent. The measurement of residual total petroleum hydrocarbons for different H₂O₂/Fe molar ratios and pH in the vicinity of neutrality highlighted oxidation rates ranging between 29.0 and 39.3%. The Fenton like (FL) oxidation was optimal for H₂O₂/Fe molar ratio of 15/4. The use EDTA led to result up 72.2% for H₂O₂/total Fe/EDTA molar ratio of 15/4/4 after 48 h of treatment. The statistical analysis of data by factorial design, has allowed the modeling of Fenton like process performances in the operating domain. It showed that hydrogen peroxide amount, interaction effects of oxidant-catalyst, catalyst-chelating agent, and oxidant-catalyst-chelating agent, were the influential parameters. Moreover, these results suggest that endogenous iron could be used as a source of iron in the presence of the chelating agent to activate FL oxidation. A better accuracy (80.0%) was obtained by statistical analysis for H₂O₂/endogenous Fe/EDTA molar ratio of 20/1/1.

Effects of compositions, chemical structures, and microporosity of sedimentary organic matter on degradation of benzo(a)pyrene by hydrogen peroxide

We investigated how the degradation of 7-¹⁴C-BaP aged in sediments by H₂O₂ treatment was influenced by the chemical structures, compositions, and microporosity of sedimentary organic carbon (SOC). Unstable OC (USOC), stable OC (STOC), mineral-protected OC (MOC), and chemically resistant OC (ROC) fractions were fractionated. The chemical structures and microporosity of the ROC fractions were characterized by ¹³C solid-state nuclear magnetic resonance (NMR) and CO₂ adsorption technique, respectively. A first-order, two-compartment kinetics model described the degradation process very well (R² > 0.980). The BaP degradation ratios increased with the increasing USOC contents and decreased with the increasing ROC contents. The BaP parent compound in the aqueous solution was almost completely degraded. The considerable portions of oxidized intermediates were detected in different SOC fractions, which represented either oxidized intermediates or parent compounds. The very good multivariate regressions among the degradation kinetics parameters, SOC structures and micropore volumes demonstrated that ROC-bulk, aliphatic moieties, and microporosity played crucial roles in protecting sorbed BaP from being degraded by H₂O₂. The results showed that ROC, aliphatic moieties, and microporosity played vital roles in Bap degradation process in sediments during H₂O₂ treatment, which is reported for the first time in this study.

Fenton-like and potassium permanganate oxidations of PAH-contaminated soils: Impact of oxidant doses on PAH and polar PAC (polycyclic aromatic compound) behavior

Potassium permanganate and Fenton-like oxidations were applied on two PAH-contaminated soils collected on former coking plant and gas plant sites. The impact of oxidant dose on the polycyclic aromatic compound (PAC) evolution, including 16 US-EPA PAHs, 11 oxygenated- and 4 nitrogen heterocyclic-PACs (O- and N-PACs) was studied for both treatments. The content of extractable organic matter and PACs was determined prior and after oxidation. Overall, permanganate treatment was more efficient than Fenton-like to decrease the PAH content, this latter being limited by the contamination availability. However, permanganate treatment resulted in incomplete PAH degradation, leading to the formation of O-PACs, that was limited with the application of higher dose. It underlines the importance of the dose and the oxidant type in the selection of oxidation parameters for remediation purpose, as improper use of oxidant can lead to the accumulation of oxidation by-products that could be as toxic as the parent compounds.

Wastewater Treatment by Catalytic Wet Peroxidation Using Nano Gold-Based Catalysts: A Review

Nowadays, there is an increasing interest in the development of promising, efficient, and environmentally friendly wastewater treatment technologies. Among them are the advanced oxidation processes (AOPs), in particular, catalytic wet peroxidation (CWPO), assisted or not by radiation. One of the challenges for the industrial application of this process is the development of stable and efficient catalysts, without leaching of the metal to the aqueous phase during the treatment. Gold catalysts, in particular, have attracted much attention from researchers because they show these characteristics. Recently, numerous studies have been reported in the literature regarding the preparation of gold catalysts supported on various supports and testing their catalytic performance in the treatment of real wastewaters or model pollutants by CWPO. This review summarizes this research; the properties of such catalysts and their expected effects on the overall efficiency of the CWPO process, together with a description of the effect of operational variables (such as pH, temperature, oxidant concentration, catalyst, and gold content). In addition, an overview is given of the main technical issues of this process aiming at its industrial application, namely the possibility of using the catalyst in continuous flow reactors. Such considerations will provide useful information for a faster and more effective analysis and optimization of the CWPO process.

Enhanced Fenton-like oxidation of hydroxypropyl guar gum catalyzed by EDTA-metal complexes in a wide pH range

A series of EDTA-metal complexes was prepared for the Fenton oxidation catalysts and Fe(II)L exhibits high catalytic performance for degradation of hydroxypropyl guar gum in a wide pH range 7.0-13.0. The viscosity of hydroxypropyl guar gum can be reduced with the 10.0% H₂O₂ and 5.0% Fe(II)L. The viscosity average molecular weight of hydroxypropyl guar gum was decreased from almost 2 million to 3,199. Most important of all, the chemical oxygen demand (COD) value can be decreased to 104 mg/L from 8,080 mg/L with enough H₂O₂, and Fe(II)L also shows great catalytic ability in the degradation of various polymers by H₂O₂. The proposed mechanism of the activation of H₂O₂ by the complex was studied.

State of the art and future challenges for polycyclic aromatic hydrocarbons is sediments: sources, fate, bioavailability and remediation techniques

Polycyclic aromatic hydrocarbons (PAHs) are amongst the most abundant contaminants found in the aquatic environment. Due to their toxicity and carcinogenicity, their sources, fate, behaviour, and cleanup techniques have been widely investigated in the last several decades. When entering the sediment-water system, PAH fate is determined by particular PAH and sediment physico-chemical properties. Most of the PAHs will be associated with fine-grained, organic-rich, sediment material. This makes sediment an ultimate sink for these pollutants. This association results in sediment contamination, and in this manner, sediments represent a permanent source of water pollution from which benthic organisms may accumulate toxic compounds, predominantly in lipid-rich tissues. A tendency for biomagnification can result in critical body burdens in higher trophic species. In recent years, researchers have developed numerous methods for measuring bioavailable fractions (chemical methods, non-exhaustive extraction, and biomimetic methods), as valuable tools in a risk-based approach for remediation or management of contaminated sites. Contaminated sediments pose challenging cleanup and management problems, as conventional environmental dredging techniques are invasive, expensive, and sometimes ineffective or hard to apply to large and diverse sediment sites. Recent studies have shown that a combination of strategies including in situ approaches is likely to provide the most effective long-term solution for dealing with contaminated sediments. Such in situ approaches include, but are not limited to: bioaugmentation, biostimulation, phytoremediation, electrokinetic remediation, surfactant addition and application of different sorbent amendments (carbon-rich such as activated carbon and biochar) that can reduce exposure and limit the redistribution of contaminants in the environment.

Removal of phenanthrene and pyrene from contaminated sandy soil using hydrogen peroxide oxidation catalyzed by basic oxygen furnace slag

Soil contamination with polycyclic aromatic hydrocarbons (PAHs) is a serious problem in Northeast China, especially in the steel industrial area. The objective of this study was to evaluate the feasibility of using basic oxygen furnace (BOF) slag to activate the Fenton-like remediation of PAH-contaminated soil to achieve the objectives of "waste control by waste" and "resource recycling" in Chinese steel industry. The effects of BOF slag dosages, H₂O₂ concentrations, and exothermicity-driven evaporation were evaluated with respect to the removal efficiencies of phenanthrene (Phe) and pyrene (Pyr). Results indicated that PAH oxidation was proportional to the BOF slag dosages and was increased exponentially with H₂O₂ concentrations. Evaporation due to increasing temperature caused by exothermic reaction played an important role in total soil PAH losses. The sequential Fenton-like oxidation with a 3-times application of 15% H₂O₂ and the same BOF slag repeatedly used were able to remove 65.87% of Phe and 58.33% of Pyr, respectively. Soluble iron oxides containing in BOF slag were reduced, while amorphous iron oxide concentration remained stable during the repeated Fenton-like process. Column study mimics real field applications showing high removal efficiencies of Phe (36.05-83.20%) and Pyr (21.79-68.06%) in 30-cm depth of soil profile. The tests on soluble heavy metal concentrations after the reactions with high slag dosage or high H₂O₂ concentration confirmed that BOF slag would not cause heavy metal contamination. Consequently, BOF slag may provide an efficient way for enhancing the Fenton-like based remediation of heavily PAH-polluted soil with little risk on collateral heavy metal contamination. However, an external gas collection and purification equipment would be essential to eliminate the evaporated PAHs.

Remediation of PAH-Contaminated Soil by Combining Surfactant Enhanced Soil Washing and Iron-Activated Persulfate Oxidation Process

There is increasing concern regarding soils contaminated with polycyclic aromatic hydrocarbons (PAHs). In the present study, the remediation of soil spiked with PAHs was explored by the combination of soil washing with sodium dodecyl sulfate (SDS) and subsequent oxidation through persulfate (PS) activated by Fe²⁺, nanoscale zero-valent iron (nZVI), and SiO₂-coated nZVI (SiO₂/nZVI). Results demonstrated that the removal of phenanthrene (PHE), fluoranthene (FLU), and pyrene (PYR) by SDS is an efficient means for soil decontamination. At SDS concentration of 20 g/L, the removal efficiencies of PHE, PYR, and FLU were 37%, 40%, and 44%, respectively. For the degradation of PAHs and SDS in the soil washing effluents, the efficiencies of PS activated with SiO₂/nZVI were not significantly different from those of PS activated with nZVI and Fe²⁺ (p > 0.05). In practice, SiO₂/nZVI is more preferable due to the improved antioxidation and dispersibility. At the dosage of 2 g/L (in the amount of iron) of SiO₂/nZVI, the removal efficiencies of PHE, FLU, PYR, and SDS within 30 min of treatment were 75%, 85%, 87%, and 34%, respectively. The degradation of SDS was much lower than those of PAHs, which facilitated the recycle of SDS. Our findings suggest that PS activated with SiO₂/nZVI is a promising method for the treatment of soil washing effluents containing SDS and PAHs.

Multiple lines of evidence of sediment quality in an urban Marine Protected Area (Xixová-Japuí State Park, SP, Brazil)

Marine Protected Areas (MPAs) aim to protect habitats, biodiversity, and ecological processes as a conservation tool. These areas have been affected by contamination, which threats the biodiversity and ecological functioning. In this study, we evaluated the sediment quality of Xixová-Japuí State Park (XJSP), an MPA located in an urbanized Bay (Santos, Southeast Brazil) by integrating multiple lines-of-evidence. Six sites were selected within the XJSP and analyzed for sediment chemistry, toxicity, and benthic community descriptors using Sediment Quality Triad approach (SQT). Whole-sediment Toxicity Identification Evaluation (TIE) was employed as a complementary line of evidence to confirm the presence of domestic effluent discharges as a potential stressor. The SQT showed that sediments collected within XJSP are impacted by contaminants, exhibiting chronic toxicity and changes in benthic community. TIE results indicated that trace metals, organic contaminants, and ammonia contributed to the observed effects. Our results also indicate a lack of effectiveness of MPA in protecting the biodiversity due to the contamination sources, which requires efforts to pollution control in order to ensure the environmental conservation and management plan goals.

Mechanisms for light-driven evolution of environmentally persistent free radicals and photolytic degradation of PAHs on Fe(III)-montmorillonite surface

Environmentally persistent free radicals (EPFRs) have been widely detected in superfund sites and atmospheric particles contaminated with organic contaminants, but the impacts of environmental factors such as light irradiation on the formation and evolution of EPFRs remain unclear. In the present study, in-situ irradiated Fourier transform infrared spectrometer and electron paramagnetic resonance were applied to probe the formation mechanisms of EPFRs during photo-transformation of polycyclic aromatic hydrocarbons (PAHs) on montmorillonite surface. EPFRs were only detected on Fe(III)-montmorillonite containing PAHs with relatively high electron-donating ability, such as anthracene (ANT), but not in the systems of Fe(III)-montmorillonite spiked with phenanthrene or Na(I)-montmorillonite. The 1/e lifetime of the EPFRs was much shorter under light irradiation (5.49 h) than in dark (30.3 h), suggesting that light irradiation facilitated the transformation of EPFRs. On the one hand, light irradiation promoted direct electron transfer from ANT to the mineral surface, accelerating the formation of PAHs-type radical cations. On the other hand, light irradiation induced the generation of reactive oxygen species, which facilitated the transformation from radical cations to oxygenic EPFRs, which finally led to ANT degradation. This work clarified the underlying mechanisms for EPFRs generation and evolution on clay minerals.

The combined effects of surfactant solubilization and chemical oxidation on the removal of polycyclic aromatic hydrocarbon from soil

A method for the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soils was proposed involving a combination of surfactant-aided soil washing and chemical oxidation by activated persulfate (SP). In this study, Triton X-100 (TX-100) and SP was applied to the soil, either concurrently or sequentially. Results indicated that surfactant followed by amendment with a solution of SP, TX-100 + SP(l), was most effective in decreasing PAHs concentrations in a sandy loam soil (SS) and a silty clay soil (NS) from 1220 mg/kg and 2730 mg·kg^-1 to 414 mg·kg^-1 and 180 mg·kg^-1, respectively. Compared with extraction alone and oxidation alone, TX-100 + SP(l) increased the removal of PAHs by 10-20%. TX-100 improved the degradation of 3-4 ring PAHs (M-PAHs) and 5-6 ring PAHs (H-PAHs) in SS, by approximately 8%-11%. The oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) including furans and xanthene exhibited greater reductions in soil when amended with the TX-100 and SP, than under TX-100 extraction or SP oxidation alone. Overall, increased removal of PAHs in contaminated soil can occur through simultaneous application of TX-100 and SP, relative to the sole use of TX-100 or SP. The sequential combination of surfactant and oxidant was most effective for the elimination of PAHs, especially for M-PAHs and H-PAHs in sandy loam contaminated soil.

In Situ Nanoscale Investigation of Step Retreat on Fluoranthene Crystal Surfaces

Fluoranthene, a polycyclic aromatic hydrocarbon, has been detected on Earth as well as in asteroids and meteorites and may have played a role in the formation of life. Increasing the ionic strength of aqueous solutions has been observed to lower the fluoranthene solubility, but it is unclear how solution composition controls the release rate of fluoranthene to an aqueous solution. To elucidate this, we performed in situ atomic force microscopy experiments in which we characterized the sublimation and dissolution behavior of fluoranthene crystal surfaces. From this, we quantify the step retreat rate upon exposure to air, deionized water, and a 0.4 M NaCl or 0.1 M MgSO₄ solution. Surface roughness is the main factor that determines the dissolution or sublimation rate. The results imply that during fluoranthene remediation or breakdown in meteorites and asteroids, ionic strength will be more important than chemical composition for controlling fluoranthene release into solution.

Combined ultrasound with Fenton treatment for the degradation of carcinogenic polycyclic aromatic hydrocarbons in textile dying sludge

To develop an effective method to remove the toxic and carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from textile dyeing sludge, five CPAHs were selected to investigate the degradation efficiencies using ultrasound combined with Fenton process (US/Fenton). The results showed that the synergistic effect of the US/Fenton process on the degradation of CPAHs in textile dyeing sludge was significant with the synergy degree of 30.4. During the US/Fenton process, low ultrasonic density showed significant advantage in degrading the CPAHs in textile dyeing sludge. Key reaction parameters on CPAHs degradation were optimized by the central composite design as followed: H₂O₂ concentration of 152 mmol/L, ultrasonic density of 408 W/L, pH value of 3.7, the molar ratio of H₂O₂ to Fe²⁺ of 1.3 and reaction time of 43 min. Under the optimal conditions of the US/Fenton process, the degradation efficiencies of five CPAHs were obtained as 81.23% (benzo[a]pyrene) to 84.98% (benz[a]anthracene), and the benzo[a]pyrene equivalent (BaP_eq) concentrations of five CPAHs declined by 81.22-85.19%, which indicated the high potency of US/Fenton process for removing toxic CPAHs from textile dyeing sludge.

Remediation of oil-contaminated harbor sediments by chemical oxidation

Oil hydrocarbons are widespread pollutants in sub-surface sediments with serious threats to terrestrial and aquatic environment. However, very limited data is available about remediation of historically contaminated sediments. This study reports the use of magnetite-catalyzed chemical oxidation (H₂O₂ and Na₂S₂O₈) to degrade oil hydrocarbons in aged contaminated sediments. For this purpose, oil contaminated sediments were sampled from three different locations in France including two harbors and one petroleum industrial channel. These sediments were characterized by different hydrocarbon index (HI) values (3.7-9.0gkg^-1), total organic carbon contents (1.9%-8.4%) and textures (sand, slit loam and silt). Chemical oxidation was performed in batch system for one week at circumneutral pH by: H₂O₂ alone, H₂O₂/Fe(II), H₂O₂/magnetite, Na₂S₂O₈ alone, Na₂S₂O₈/Fe(II), and Na₂S₂O₈/magnetite. Results obtained by GC-FID indicated substantial hydrocarbon degradation (40-70%) by H₂O₂/magnetite and Na₂S₂O₈/magnetite. However, oxidants alone or with soluble Fe(II) caused small degradation (<5%). In the presence of H₂O₂/magnetite, degradation of extractable organic matter and that of HI were highly correlated. However, no such correlation was observed for Na₂S₂O₈/magnetite which resulted in higher removal of HI indicating its selective oxidation behavior. Treatment efficiency was negatively influenced by organic carbon and carbonate contents. For being the first study to report chemical oxidation of oil hydrocarbons in real contaminated sediments, it may have practical implications to design a remediation strategy for target contaminants.

Evaluation of the Fenton process effectiveness in the remediation of soils contaminated by gasoline: Effect of soil physicochemical properties

The remediation of four different soils contaminated by gasoline was performed using Fenton processes. Herein, the effect of the main physicochemical characteristics of the soils in the Fenton performance is emphasized. Fenton processes were applied in a column system, with and without addition of soluble iron (II), using undisturbed soil samples collected in four regions of the Paraná State (Brazil). Two groups of contaminants were monitored during the remediation process: BTEX (benzene, toluene, ethylbenzene and xylenes) and TRHs (total recoverable hydrocarbons). Superior degradation efficiencies were observed in the soils with elevated mineral iron content (Red Argisol, Red-Yellow Argisol and Red Latosol), while the soils with low iron content (Spodosol) presented comparable degradation efficiencies only in the presence of soluble Fe²⁺. Although the presence of mineral iron enabled the Fenton processes, a good correlation between the iron content and the degradation efficiency was not observed, suggesting a dependence on the chemical nature of the native iron. BTEX leaching was observed in all systems, suggesting that the process should be applied with caution, especially in soils with high drainage.

Validation of a Method for Extracting Microplastics from Complex, Organic-Rich, Environmental Matrices

Complex and organic-rich solid substrates such as sludge and soil have been shown to be contaminated by microplastics; however, methods for extracting plastic particles have not yet been systemically tested or standardized. This study investigated four main protocols for the removal of organic material during analysis of microplastics from complex solid matrices: oxidation using H₂O₂, Fenton's reagent, and alkaline digestion with NaOH and KOH. Eight common polymer types were used to assess the influence of reagent exposure on particle integrity. Organic matter removal efficiencies were established for test sludge and soil samples. Fenton's reagent was identified as the optimum protocol. All other methods showed signs of particle degradation or resulted in an insufficient reduction in organic matter content. A further validation procedure revealed high microplastic extraction efficiencies for particles with different morphologies. This confirmed the suitability of Fenton's reagent for use in conjunction with density separation for extracting microplastics. This approach affords greater comparability with existing studies that utilize a density-based technique. Recommendations for further method optimization were also identified to improve the recovery of microplastic from complex, organic-rich environmental samples.

Regeneration performance of clay-based adsorbents for the removal of industrial dyes: a review

The present review covers the regeneration capacity and adsorption efficiency of different adsorbents for the treatment of industrial dyes to control water pollution. Various techniques and materials have been employed to remove organic pollutants from water; however, adsorption techniques using cost-effective, ecofriendly, clay-supported adsorbents are widely used owing to their simplicity and good efficiency. Among all the natural adsorbents, activated carbon has been found to be the most effective for dye adsorption; however, its use is restricted due to its high regeneration cost. Clays and modified clay-based adsorbents are the most efficient clarifying agents for organic pollutants as compared to activated carbon, organic/inorganic, and composite materials. Regeneration is an important aspect to stimulate the adsorption efficiency of the exhausted/spent adsorbent for water treatment. A number of techniques, including chemical treatment, supercritical extraction, thermal, and photocatalytic and biological degradation, have been developed to regenerate spent or dye-adsorbed clays. This review discusses how these techniques enhance the adsorption and retention potential of spent low-cost adsorbents and reflects on the future perspectives for their use in wastewater treatment.

Degradation of di (2-ethylhexyl) phthalate in sediment by a surfactant-enhanced Fenton-like process

This is the premier study reporting the remediation of di (2-ethylhexyl) phthalate (DEHP) contaminated sediment by a surfactant-enhanced Fenton-like system. Three widely used non-ionic surfactants were tested, and the order for desorption and solubilization of DEHP was determined as Tween 80 > Triton X-100 > Brij 35. The degradation of DEHP was studied at a near natural pH of 6.0 by two Fenton treatments: (i) Fe³⁺/H₂O₂ and (ii) Fe³⁺/PCA/H₂O₂. Results show that the addition of PCA can significantly enhance DEHP removal from 48.9% to 92.5%. This is consistent with observation that PCA maintained at a relative high level of iron ions, which can catalyze H₂O₂ to generate the reactive hydroxyl radicals (OH). Most of the added Tween 80 and a portion of OM were co-oxidized together with DEHP due to the non-selective nature of OH, which leaded to an increase in DOC content and decreases in sediment pH and total N content. The results provide an efficient and eco-friendly technique for the remediation of DEHP contaminated sediment, and also give insight to its environmental implications.