Influence of pyrene combination state in soils on its treatment efficiency by Fenton oxidation

Efficient chlorinated alkanes degradation in soil by combining alkali hydrolysis with thermally activated persulfate

Alkali activation is the most commonly used activation method for persulfate (PS) in in-situ remediation. However, the role of alkali in pollutant degradation is still elusive, limiting the optimization of relevant remediation strategies. In this study, we found that chlorinated alkanes (e.g., tetrachloroethane (TeCA)) could be efficiently degraded by thermal-alkali activation of PS. The main role of alkali was not activating PS but hydrolyzing the chlorinated alkanes, which was evidenced by the immediate conversion of TeCA into trichloroethylene (TCE) with NaOH and PS or with sole NaOH solution. Electron paramagnetic resonance analysis also showed that with a high NaOH/PS molar ratio (4:1) the intensity of oxidative radicals decreased, implying that high levels of alkali did not favor the formation of free radicals. Interestingly, better degradation of TeCA and its product TCE was observed by the combination of alkaline hydrolysis and thermal activation of PS (where alkali was added 6 h before PS rather than simultaneously) in comparison to thermal-alkali activation of PS. This study provides new insights into the remediation of chlorinated alkane-contaminated soils by in-situ chemical oxidation.

Biochar-assisted Fenton-like oxidation of benzo[a]pyrene-contaminated soil

In the present study, the biochar derived from sunflower husks was used as a mediator in the heterogeneous Fenton process. The physical and chemical characteristics were studied in terms of specific surface area, elemental contents, surface morphology, surface functional groups, thermal stability, and X-ray crystallography. The main aim was to evaluate the effectiveness of biochar in a heterogeneous Fenton process catalyzed by hematite toward the degradation of benzo[a]pyrene (BaP) in Haplic Chernozem. The Fenton-like reaction was performed at a pH of 7.8 without pH adjustment in chernozem soil. The effects of operating parameters, such as hematite dosage and H₂O₂ concentrations, were investigated with respect to the removal efficiency of BaP. The overall degradation of 65% was observed at the optimized conditions where 2 mg g^-1 hematite and 1.25 M H₂O₂ corresponded to the H₂O₂ to Fe ratio of 22:1. Moreover, the biochar amendment showed an increment in the removal efficiency and promotion in the growth of spring barley (Hordeum sativum distichum). The BaP removal was reached 75 and 95% after 2.5 and 5% w/w addition of biochar, respectively. The results suggested that the Fenton-like reaction's effectiveness would be greatly enhanced by the ability of biochar for activation of H₂O₂ and ejection of the electron to reduce Fe(III) to Fe(II). Finally, the presence of biochar could enhance the soil physicochemical properties, as evidenced by the better growth of Hordeum sativum distichum compared to the soil without biochar. These promising results open up new opportunities toward the application of a modified Fenton reaction with biochar for remediating BaP-polluted soils.

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.

A new foam-based method for the (bio)degradation of hydrocarbons in contaminated vadose zone

An innovative foam-based method for Fenton reagents (FR) and bacteria delivery was assessed for the in situ remediation of a petroleum hydrocarbon-contaminated unsaturated zone. The surfactant foam was first injected, then reagent solutions were delivered and propagated through the network of foam lamellae with a piston-like effect. Bench-scale experiments demonstrated the feasibility of the various treatments with hydrocarbon (HC) removal efficiencies as high as 96 %. Compared to the direct injection of FR solutions, the foam-based method led to larger radii of influence and more isotropic reagents delivery, whereas it did not show any detrimental effect regarding HC oxidation. Despite 25 % of HCs were expelled from the treated zone because of high foam viscosity, average degradation rates were increased by 20 %. At field-scale, foam and reagent solutions injections in soil were tracked both using visual observation and differential electric resistivity tomography. The latter demonstrated the controlled delivery of the reactive solutions using the foam-based method. Even if the foam-based method duration is about 5-times longer than the direct injection of amendment solutions, it provides important benefits, such as the confinement of harmful volatile hydrocarbons during Fenton treatments, the enhanced reagents delivery and the 30 % lower consumption of the latter.

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.

Removal of Bound PAH Residues in Contaminated Soils by Fenton Oxidation

The availability of bound residues of polycyclic aromatic hydrocarbons (PAHs), in reference to their parent compounds, can be enhanced by microbial activity and chemical reactions, which pose severe risks for the ecosystems encompassing contaminated soils. Considerable attention has been raised on how to remove these bound residues from PAH-contaminated soils. This paper provides a novel application of Fenton oxidation in the removal of bound residues of model PAHs, such as naphthalene (NAP), acenaphthene (ACP), fluorene (FLU) and anthracene (ANT), from naturally contaminated soils. The citric acid-enhanced Fenton treatment resulted in the degradation of bound PAH residues that followed pseudo-first-order kinetics, with rate constants within 4.22 × 10−2, 1.25 × 10−1 and 2.72 × 10−1 h−1 for NAP, FLU, and ANT, respectively. The reactivity of bound PAH residues showed a correlation with their ionization potential (IP) values. Moreover, the degradation rate of bound PAH residues was significantly correlated with H2O2-Fe2+ ratio (m/m) and H2O2 concentrations. The highest removal efficiencies of bound PAH residues was up to 89.5% with the treatment of chelating agent oxalic acid, which was demonstrated to be superior to other acids, such as citric acid and hydrochloric acid. This study provides valuable insight into the feasibility of citric acid-Fenton and oxalic acid-Fenton treatments in rehabilitating bound PAH residues in contaminated soils.

Fenton oxidation to remediate PAHs in contaminated soils: A critical review of major limitations and counter-strategies

Fenton oxidation constitutes a viable remediation strategy to remove polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. This review is intended to illustrate major limitations associated with this process like acidification, PAH unavailability, and deterioration of soil quality along with associated factors, followed by a critical description of various developments to overcome these constraints. Considering the limitation that its optimal pH is around 3, traditional Fenton treatment could be costly, impractical in soil due to the high buffering capacity of soils and associated hazardous effects. Use of various chelating agents (organic or inorganic) allowed oxidation at circumneutral pH but factors like higher oxidant demand, cost and toxicity should be considered. Another alternative is the use of iron minerals that can catalyze Fenton-like oxidation over a wide range of pH, but mobility of these particles in soils (i.e. saturated and unsaturated zones) should be investigated prior to in-situ applications. The PAH-unavailability is the crucial limitation hindering their effective degradation. Research data is compiled describing various strategies to address this issue like the use of availability enhancement agents, extraction or thermal pretreatment. Last section of this review is devoted to describe the effects of various developments in Fenton treatment onto soil quality and native microbiota. Finally, research gaps are discussed to suggest future directions in context of applying Fenton oxidation to remediate contaminated soils.

Selection of oxidant doses for in situ chemical oxidation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs): A review

In situ chemical oxidation (ISCO) is a promising alternative to thermal desorption for the remediation of soils contaminated with organic compounds such as polycyclic aromatic hydrocarbons (PAHs). For field application, one major issue is the selection of the optimal doses of the oxidizing solution, i.e. the oxidant and appropriate catalysts and/or additives. Despite an extensive scientific literature on ISCO, this choice is very difficult because many parameters differ from one study to another. The present review identifies the critical factors that must be taken into account to enable comparison of these various contributions. For example, spiked soils and aged, polluted soils cannot be compared; PAHs freshly spiked into a soil are fully available for degradation unlike a complex mixture of pollutants trapped in a soil for many years. Another notable example is the high diversity of oxidation conditions employed during batch experiments, although these affect the representativeness of the system. Finally, in this review a methodology is also proposed based on a combination of the stoichiometric oxidant demand of the organic pollutants and the design of experiments (DOE) in order to allow a better comparison of the various studies so far reported.

Degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge with ultrasound and Fenton processes: Effect of system parameters and synergistic effect study

To establish an efficient oxidation process for the degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge, the effects of various operating parameters were optimized during the ultrasound process, Fenton process and the combined ultrasound-Fenton process. The results showed that the ultrasonic density of 1.80w/cm(3), both H2O2 and Fe(2+) dosages of 140mmol/L and pH 3 were favorable conditions for the degradation of PAHs. The degradation efficiency of high molecular weight PAHs was close to or even higher than that of light molecular weight PAHs. The highest degradation efficiencies of Σ16 PAHs were obtained within 30min in the order of: Fenton (83.5%) >ultrasound-Fenton (75.5%) >ultrasound (45.5%), then the efficiencies were decreased in the other of: ultrasound-Fenton (73.0%) >Fenton (70.3%) >ultrasound (41.4%) in 60min. The extra PAHs were released from the intracellular substances and the cavities of sludge due to the disruption of sludge during the oxidation process. Also, the degradation of PAHs could be inhibited by the other organic matter in the sludge. The combined ultrasound-Fenton process showed more efficient than both ultrasound process and Fenton process not only in the surface of sludge but also in the sludge interior.

Sorption and degradation of carbaryl in soils amended with biochars: influence of biochar type and content

Biochars that were produced from three different biomass materials were amended to a soil to elucidate their influence on the fate of carbaryl. Sorption and degradation of carbaryl in soils amended with the biochars were investigated. The results showed that the amendment of biochars to soil enhanced the sorption of carbaryl. The nonlinearity of sorption isotherm and sorption affinity of carbaryl increased with the content and pyrolytic temperature of the biochars. Both chemical and biological degradation of carbaryl were influenced by biochars. The biochars enhanced the chemical hydrolysis of carbaryl in soil, with biochars produced at 700 °C (BC700) exhibiting greater impact, due to their strong liming effect. In contrast, BC350 (produced at 350 °C) promoted the biodegradation of carbaryl in soil by different extents, while BC700 obviously reduced the biodegradation of carbaryl. The enhanced activities of natural microorganisms in the soil and the lowered bioavailability of carbaryl acted together to determine the biodegradation.

Feasibility of treating aged polycyclic aromatic hydrocarbons (PAHs)-contaminated soils using ethyl lactate-based Fenton treatment via parametric and kinetic studies

This study focuses on the feasibility of treating aged polycyclic aromatic hydrocarbons (PAHs)-contaminated soils using ethyl lactate (EL)-based Fenton treatment via a combination of parametric and kinetic studies. An optimised operating condition was observed at 66.7 M H2O2 with H2O2/Fe(2+) of 40:1 for low soil organic carbon (SOC) content and mildly acidic soil (pH 6.2), and 10:1 for high SOC and very acidic soil (pH 4.4) with no soil pH adjustment. The desorption kinetic was only mildly shifted from single equilibrium to dual equilibrium of the first-order kinetic model upon ageing. Pretreatment with EL fc = 0.60 greatly reduced the mass transfer coefficient especially for the slow desorbed fraction (kslow) of high molecular weight (HMW) PAHs, largely contributed by the concentration gradient created by EL-enhanced solubility. As the major desorption obstacle was almost fully overcome by the pretreatment, the pseudo-first-order kinetic reaction rate constant of PAHs degradation of aged soils was statistically discernible from that of freshly contaminated soils but slightly reduced in high SOC and high acidity soil. Stabilisation of H2O2 by EL addition in combination with reduced Fe(2+) catalyst were able to slow the decomposition rate of H2O2 even at higher soil pH.

Evaluation of in situ catalysed hydrogen peroxide propagation (CHP) for phenanthrene and fluoranthene removals from soil and its associated impacts on soil functionality

Extensive contamination of soils by highly recalcitrant contaminants such as polycyclic aromatic hydrocarbons (PAHs) is an environmental problem arising from rapid industrialisation. This work focusses on the remediation of soil contaminated with 3- and 4-aromatic ring PAHs (phenanthrene (PHE) and fluoranthene (FLUT)) through catalysed hydrogen peroxide propagation (CHP). In the present work, the operating parameters of the CHP treatment in packed soil column was optimised with central composite design (H2O2/soil 0.081, Fe(3+)/soil 0.024, sodium pyrophosphate (SP)/soil 0.024, pH of SP solution 7.73). The effect of contaminant aging on PAH removals was also investigated. Remarkable oxidative PAH removals were observed for the short aging and extended aging period (up to 86.73 and 70.61 % for PHE and FLUT, respectively). The impacts of CHP on soil biological, chemical and physical properties were studied for both spiked and aged soils. Overall, the soil functionality analyses after the proposed operating condition demonstrated that the values for soil respiration, electrical conductivity, pH and iron precipitation fell within acceptable limits, indicating the compatibility of the CHP process with land restoration.

Pyrene removal from contaminated soils by modified Fenton oxidation using iron nano particles

BACKGROUND

The problems related to conventional Fenton oxidation, including low pH required and production of considerable amounts of sludge have led researchers to investigate chelating agents which might improve the operating range of pH and the use of nano iron particle to reduce the excess sludge. The pyrene removal from contaminated soils by modified Fenton oxidation at neutral pH was defined as the main objective of the current study.

METHODS

Varying concentrations of H2O2 (0-500 mM) and iron nano oxide (0-60 mM), reaction times of 0.5-24 hours and variety of chelating agents including sodium pyrophosphate, sodium citrate, ethylene diamine tetraacetic, fulvic and humic acid were all investigated at pyrene concentration levels of 100 - 500 mg/kg.

RESULTS

By applying the following conditions (H2O2 concentration of 300 mM, iron nano oxide of 30 mM, sodium pyrophosphate as chelating agent, pH 3 and reaction time of 6 hours) the pyrene removal efficiency at an initial concentration of 100 mg/kg was found to be 99%. As a result, the pyrene concentration was reduced from 100 to 93 mg/kg once the above optimum conditions are met.

CONCLUSIONS

In this research, the modified Fenton oxidation using iron nano oxide at optimum conditions is introduced as an efficient alternative method in lab scale for chemical remediation or pre-treatment of soils contaminated by pyrene at neutral pH.

Adsorption and catalytic hydrolysis of carbaryl and atrazine on pig manure-derived biochars: impact of structural properties of biochars

Biochars were produced from pig manure to elucidate the influence of biochars with high ash contents on the fate of pesticides. Adsorption and catalytic hydrolysis of carbaryl and atrazine on original biochars and deashed biochars were investigated. The two pesticides were substantially adsorbed by the biochars, with organic carbon normalized sorption coefficient (K(oc)) values of 10(2.65)-10(3.66) L/kg for carbaryl and 10(1.90)-10(3.57) L/kg for atrazine at C(e) of 0.5 mg/L. Hydrophobic effect alone could not explain the sorption, and several other processes including pore-filling and π-π electron donor-acceptor interactions were involved in pesticide adsorption. Adsorption increased greatly on the deashed biochar, indicating that some organic sorption sites in the original biochars were blocked or difficult to access due to their interactions with inorganic moiety. The pesticides were found to hydrolyze faster in the presence of biochars, and in the presence of biochar pyrolyzed at 700 °C, carbaryl and atrazine were decomposed by 71.8% and 27.9% in 12 h, respectively. The elevated solution pH was the main reason for the enhanced hydrolysis; however both the mineral surface and dissolved metal ions released from the biochars were confirmed to catalyze the hydrolysis.

Modified Fenton oxidation of polycyclic aromatic hydrocarbon (PAH)-contaminated soils and the potential of bioremediation as post-treatment

This work focuses on the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil using modified Fenton (MF) treatment coupled with a novel chelating agent (CA), a more effective technique among currently available technologies. The performance of MF treatment to promote PAH oxidation in artificially contaminated soil was investigated in a packed column with a hydrogen peroxide (H(2)O(2)) delivery system simulating in-situ soil flushing which is more representative of field conditions. The effectiveness of process parameters H(2)O(2)/soil, Fe(3+)/soil, CA/soil weight ratios and reaction time were studied using a 2(4) three level factorial design experiments. An optimised operating condition of the MF treatment was observed at H(2)O(2)/soil 0.05, Fe(3+)/soil 0.025, CA/soil 0.04 and 3h reaction time with 79.42% and 68.08% PAH removals attainable for the upper and lower parts of the soil column respectively. The effects of natural attenuation and biostimulation process as post-treatment in the remediation of the PAH-contaminated soil were also studied. In all cases, 3-aromatic ring PAH (phenanthrene) was more readily degraded than 4-aromatic ring PAH (fluoranthene) regardless of the bioremediation approach. The results revealed that both natural attenuation and biostimulation could offer remarkable enhancement of up to 6.34% and 9.38% in PAH removals respectively after 8 weeks of incubation period. Overall, the results demonstrated that combined inorganic CA-enhanced MF treatment and bioremediation serves as a suitable strategy to enhance soil quality particularly to remediate soils heavily contaminated with mixtures of PAHs.

Oxidation of a PAH polluted soil using modified Fenton reaction in unsaturated condition affects biological and physico-chemical properties

A batch experiment was conducted to assess the impact of chemical oxidation using modified Fenton reaction on PAH content and on physico-chemical and biological parameters of an industrial PAH contaminated soil in unsaturated condition. Two levels of oxidant (H(2)O(2), 6 and 65 g kg(-1)) and FeSO(4) were applied. Agronomic parameters, bacterial and fungal density, microbial activity, seed germination and ryegrass growth were assessed. Partial removal of PAHs (14% and 22%) was obtained with the addition of oxidant. The impact of chemical oxidation on PAH removal and soil physico-chemical and biological parameters differed depending on the level of reagent. The treatment with the highest concentration of oxidant decreased soil pH, cation exchange capacity and extractable phosphorus content. Bacterial, fungal, and PAH degrading bacteria densities were also lower in oxidized soil. However a rebound of microbial populations and an increased microbial activity in oxidized soil were measured after 5 weeks of incubation. Plant growth on soil treated by the highest level of oxidant was negatively affected.

Fractionation of polycyclic aromatic hydrocarbon residues in soils

Understanding the forms and availabilities of polycylic aromatic hydrocarbons (PAHs) would have considerable benefits for their risk assessment, and is of crucial importance for food security and remediation strategies in contaminated sites. In this work, the forms of six PAHs (fluorene, phenanthrene, fluoranthene, pyrene, benzo[a]anthracene, and benzo[a]pyrene) in soils were separated into three fractions including a desorbing fraction, a non-desorbing fraction, and a bound residual fraction using a sequential extraction mass balance approach. The desorbing and non-desorbing fractions were extracted with hydroxypropyl-beta-cyclodextrin (HPCD) and dichloromethane:acetone (1:1, vol/vol), respectively. The desorbing and non-desorbing fractions always dominated the total PAH content in soils. The proportion of bound PAH residue in nonsterilized soils was small (<16%), and even smaller (4.5%) in sterilized soils. The concentrations of the desorbing fraction of PAHs as well as the percentage of this fraction to the total PAH content in soils clearly decreased in 0-16 weeks, which may be due to microbial biodegradation and its transfer to other fractions in soils. The concentrations of the non-desorbing PAH fractions increased in sterilized soils, while remaining nearly constant or decreasing to some extent in nonsterilized soils after 16 weeks. The proportion of non-desorbing PAH fractions significantly increased in 16 week-incubation, and this proportion was positively correlated with the molecular weights of the PAHs tested, indicating that larger PAHs are more likely to be present in non-desorbing fractions. The bound PAH residue tended to increase at first and decrease thereafter over the 0-16-week period, and microbes played an important role in the formation of bound residue.