Removal of Bound PAH Residues in Contaminated Soils by Fenton Oxidation

Migration of fluoranthene, phenanthrene, and pyrene in soil environment during the growth of Brassica rapa subsp. chinensis

The escalating concern surrounding fluoranthene (FLN), phenanthrene (Phe), and pyrene (Pyr), underscores the urgency to investigate their dynamics in the context of agricultural ecosystems. Brassica rapa subsp. chinensis (Bok choy), a globally consumed vegetable, holds particular significance in this scenario. This study explores the migration and transformation of FLN, Phe, and Pyr from soil to Brassica rapa subsp. chinensis during its growth. The germination rates of seeds in these treatments varied, with soil+Bok choy and soil+FLN+Bok choy treatments showing higher rates (77.8 %), while soil+mix+Bok choy exhibited the lowest rate (11.1 %) after 3 days. Analyzing the distribution of FLN, Phe, and Pyr in Brassica rapa subsp. chinensis parts after 30 days revealed a sequence of accumulation in stem> root> leaf. This study provides information on practical implications for regulating the soil-plant migration and transformation of FLN, Phe, and Pyr, offering valuable insights for migration of PAHs pollution in agricultural settings.

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.

Neutralization of Industrial Alkali-Contaminated Soil by Different Agents: Effects and Environmental Impact

Industrial soil is susceptible to acid or alkali pollution, but studies focused on the remediation of such soil are still limited. This manuscript investigated the neutralization effect of five agents (hydrochloric acid, citric acid, ferrous sulfate, calcium superphosphate and raw gypsum) to alkali polluted soil. The results showed that regarding the initial pH after the neutralizing agent addition, it was better to set it lower than the target, as the pH would rebound. None of the five agents caused an obvious increase in the heavy metal contents of the leachates, but they all caused an increase in electrical conductivity, which indicated an increase in soil salinity. The leachates showed a luminous gain to Vibrio fischeri. However, remediation with hydrochloric acid would cause significant inhibition of germination and root elongation of pakchoi. In addition, the addition of neutralizing agents reshaped the soil microbial community structure in different patterns. Soils treated with hydrochloric acid and ferrous sulfate seemed to improve the microbial richness. The neutralization might be favorable for the biodegradation of polycyclic aromatic hydrocarbons (PAHs), which usually coexist in industrial contaminated soil. In general, the neutralization of alkaline industrial soils using ferrous sulfate, superphosphate and gypsum brought minimal environmental risk, among which ferrous sulfate was the first recommendation in industrial soil after a comprehensive comparison.

Insights into the effects of Fenton oxidation on PAH removal and indigenous bacteria in aged subsurface soil

Combined chemical oxidation and bioremediation is a promising method of treating polycyclic aromatic hydrocarbon (PAH) contaminated soil, wherein indigenous soil bacteria play a critical role in the subsequent biodegradation of PAHs after the depletion of the oxidant. In this study, different Fenton conditions were applied by varying either the oxidation mode (conventional Fenton (CF), Fenton-like (LF), modified Fenton (MF), and graded modified Fenton (GMF)) or the H₂O₂ dosage (0%, 3%, 6%, and 10% (v/v)) to treat PAH contaminated soil. The results revealed that when equal dosages of H₂O₂ are applied, PAHs are significantly removed following oxidation treatment, and the removal percentages obeyed the following sequence: CF > GMF > MF > LF. In addition, higher dosages of H₂O₂ improved the PAH removal from soil treated with the same oxidation mode. The ranges of total PAHs removal efficiencies in the soil added 3%, 6%, and 10% of H₂O₂ (v/v) were 18.04%∼59.48%, 31.88%∼71.83%, and 47.56%∼78.16%, respectively. The PAH removal efficiency decreased with increasing ring numbers for the same oxidation treatment. However, the negative influences on soil bacterial abundance, community composition, and function were observed after Fenton treatment. After Fenton oxidation, the bacterial abundance in the soil received 3%, 6%, and 10% of H₂O₂ (v/v) decreased 1.96-2.69, 2.44-3.22, and 3.09-3.42 orders of magnitude compared to the untreated soil. The soil bacterial abundance tended to be impacted by the oxidation mode and H₂O₂ dosage simultaneously. While the main factor influencing the soil bacterial community composition was the H₂O₂ dosages. The results of this study showed that different oxidation mode and H₂O₂ dosage exhibited different effects on PAHs removal and soil bacteria (including abundance, community composition, and function), and there was a trade-off between the removal of PAHs and the adverse impact on soil bacteria.

Review on the contamination and remediation of polycyclic aromatic hydrocarbons (PAHs) in coastal soil and sediments

The rapid economic and population growth in coastal areas is causing increasingly serious polycyclic aromatic hydrocarbons (PAHs) pollution in these regions. This review compared the PAHs pollution characteristics of different coastal areas, including industrial zones, commercial ports, touristic cities, aquacultural & agricultural areas, oil & gas exploitation areas and megacities. Currently there are various treatment methods to remediate soils and sediments contaminated with PAHs. However, it is necessary to provide a comprehensive overview of all the available remediation technologies up to date, so appropriate technologies can be selected to remediate PAHs pollution. In view of that, we analyzed the characteristics of the remediation mechanism, summarized the remediation methods for soil or sediments in coastal areas, which were physical repair, chemical oxidation, bioremediation and integrated approaches. Besides, this review also reported the development of new multi-functional green and sustainable systems, namely, micro-nano bubble (MNB), biochar, reversible surfactants and peracetic acid. While physical repair, expensive but efficient, was regarded as a suitable method for the PAHs remediation in coastal areas because of land shortage, integrated approaches would produce better results. The ultimate aim of the review was to ensure the successful restructuring of PAHs contaminated soil and sediments in coastal areas. Due to the environment heterogeneity, PAHs pollution in coastal areas remains as a daunting challenge. Therefore, new and suitable technologies are still needed to address the environmental issue.

Fenton oxidation for soil remediation: A critical review of observations in historically contaminated soils

Fenton-based treatments have received tremendous attention in recent decades as viable strategies for soil decontamination. Historically contaminated soils are characterized by particular contamination types, pollution composition patterns, soil constituents, and complex soil-pollutant interactions arising due to long-term pollutant aging. These major pitfalls dictate the remediation efficiency in a significantly different way in soils with a history of contamination than that in a spiked soil. It becomes, therefore, highly challenging to treat historically contaminated soils. Despite the immense amount of collected research data in these soils, to our knowledge, no comprehensive review of this topic has been published. This article is intended to provide a critical review of the applications, limitations, and implications of various Fenton-based processes exclusively in these soils. These processes are differentiated on the basis of experimental conditions, reaction chemistry, efficiency, and impacts on soil biota. These processes are critically evaluated to illustrate the promising techniques with a brief description of related challenges and their potential solutions. Moreover, coupling Fenton oxidation with other remediation techniques such as bioremediation, chemical reduction, and soil washing has also been discussed. The last part of this review describes the effects of these processes onto soil quality and native biota, and how they can be addressed. It is also highly demanding to identify the processes which are not likely to evolve in practice either due to their poor efficiency, treatment cost, or environmental impacts. Future critical research directions have been identified to promote research for the upscaling of this technique for real field application.

Comparison of naphthalene removal performance using H2O2, sodium percarbonate and calcium peroxide oxidants activated by ferrous ions and degradation mechanism

The presence of polycyclic aromatic hydrocarbons (PAHs) in groundwater is making a great threat to human health in the world which has received an increasing environmental concern. Among various Fenton oxidation processes, 97.6%, 92.1% and 89.4% naphthalene (NaP) removals were observed using hydrogen peroxide (H₂O₂), sodium percarbonate (SPC) and calcium peroxide (CP) as oxidants activated by Fe(II) in ultrapure water tests, respectively. While, the inhibitory effect on NaP degradation caused by the weak alkaline solution pH and the presence of HCO₃^- in actual groundwater could be compensated by doubling dosages of oxidants and Fe(II) to different extent. 98.0%, 49.8% and 11.5% of NaP were degraded by using H₂O₂, SPC and CP, respectively, strongly suggesting the best H₂O₂ performance among them. It was observed that 83.3% and 9.6% inhibition on NaP degradation in H₂O₂/Fe(II)/NaP system occurred in the presence of isopropyl alcohol and chloroform, confirming that both hydroxyl radical (HO) and superoxide anion radical () contributed to NaP degradation in Fenton process and HO was the prominent radical. The presence of HO was further demonstrated by electro-spin resonance spectrometer analysis. The identification of transformation products of NaP revealed that hydroxylation and ring rupture were the main NaP degradation pathways.

Remediation of soils and sediments polluted with polycyclic aromatic hydrocarbons: To immobilize, mobilize, or degrade?

Polycyclic aromatic hydrocarbons (PAHs) are generated due to incomplete burning of organic substances. Use of fossil fuels is the primary anthropogenic cause of PAHs emission in natural settings. Although several PAH compounds exist in the natural environmental setting, only 16 of these compounds are considered priority pollutants. PAHs imposes several health impacts on humans and other living organisms due to their carcinogenic, mutagenic, or teratogenic properties. The specific characteristics of PAHs, such as their high hydrophobicity and low water solubility, influence their active adsorption onto soils and sediments, affecting their bioavailability and subsequent degradation. Therefore, this review first discusses various sources of PAHs, including source identification techniques, bioavailability, and interactions of PAHs with soils and sediments. Then this review addresses the remediation technologies adopted so far of PAHs in soils and sediments using immobilization techniques (capping, stabilization, dredging, and excavation), mobilization techniques (thermal desorption, washing, electrokinetics, and surfactant assisted), and biological degradation techniques. The pros and cons of each technology are discussed. A detailed systematic compilation of eco-friendly approaches used to degrade PAHs, such as phytoremediation, microbial remediation, and emerging hybrid or integrated technologies are reviewed along with case studies and provided prospects for future research.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters β^m and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (K_m) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.

Physical-Chemical Study of Anthracene Selective Oxidation by a Fe(III)-Phenylporhyrin Derivative

In this work, we studied the anthracene oxidation by hydroxyl radicals. Hydroxyl radical was generated by reaction of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Fe (III) (TPPFe) with hydrogen peroxide under visible radiation at a nitrogen atmosphere. The TPPFe was synthesized by Adler Method followed by metal complexation with Fe (III) chloride hexahydrate. Hydroxyl radical was detected by fluorescence emission spectroscopy and we studied kinetic of anthracene selective oxidation by hydroxyl radicals through the differential method. The TPPFe was characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) measurements. The results indicated that TPPFE was compound by micro-particles with a size distribution of around 2500 nm. Kinetic results showed that the apparent rate constant for the oxidation of anthracene increased exponentially on as temperature increases, furthermore, the activation energy for the Anthracene oxidation by hydroxyl radicals under visible irradiation was 51.3 kJ/mol. Finally, anthraquinone was the main byproduct generated after oxidation of anthracene by TPP-Fe under visible irradiation.

Biochar-Supported FeS/Fe3O4 Composite for Catalyzed Fenton-Type Degradation of Ciprofloxacin

The Fenton-type oxidation catalyzed by iron minerals is a cost-efficient and environment-friendly technology for the degradation of organic pollutants in water, but their catalytic activity needs to be enhanced. In this work, a novel biochar-supported composite containing both iron sulfide and iron oxide was prepared, and used for catalytic degradation of the antibiotic ciprofloxacin through Fenton-type reactions. Dispersion of FeS/Fe3O4 nanoparticles was observed with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). Formation of ferrous sulfide (FeS) and magnetite (Fe3O4) in the composite was validated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ciprofloxacin (initial concentration = 20 mg/L) was completely degraded within 45 min in the system catalyzed by this biochar-supported magnetic composite at a dosage of 1.0 g/L. Hydroxyl radicals (·OH) were proved to be the major reactive species contributing to the degradation reaction. The biochar increased the production of ·OH, but decreased the consumption of H2O2, and helped transform Fe3+ into Fe2+, according to the comparison studies using the unsupported FeS/Fe3O4 as the catalyst. All the three biochars prepared by pyrolysis at different temperatures (400, 500 and 600 °C) were capable for enhancing the reactivity of the iron compound catalyst.

Fuzzy Coordination Control Strategy and Thermohydraulic Dynamics Modeling of a Natural Gas Heating System for in Situ Soil Thermal Remediation

Soil contamination remains a global problem. Among the different kinds of remediation technologies, in situ soil thermal remediation has attracted great attention in the environmental field, representing a potential remedial alternative for contaminated soils. Soils need to be heated to a high temperature in thermal remediation, which requires a large amount of energy. For the natural gas heating system in thermal remediation, a fuzzy coordination control strategy and thermohydraulic dynamics model have been proposed in this paper. In order to demonstrate the superiority of the strategy, the other three traditional control strategies are introduced. Analysis of the temperature rise and energy consumption of soils under different control strategies were conducted. The results showed that the energy consumption of fuzzy coordination control strategy is reduced by 33.9% compared to that of the traditional control strategy I, constant natural gas flow and excess air ratio. Further, compared to the traditional control strategy II, constant excess air ratio and desired outlet temperature of wells, the strategy proposed can reduce energy consumption by 48.7%. The results illustrate the superiority of the fuzzy coordination control strategy, and the strategy can greatly reduce energy consumption, thereby reducing the cost of in situ soil thermal remediation.