Treatability assessment of polycyclic aromatic hydrocarbons contaminated marine sediments using permanganate, persulfate and Fenton oxidation processes

Oil and gas platforms degrade benthic invertebrate diversity and food web structure

Oil and gas exploitation introduces toxic contaminants such as hydrocarbons and heavy metals to the surrounding sediment, resulting in deleterious impacts on marine benthic communities. This study combines benthic monitoring data over a 30-year period in the North Sea with dietary information on >1400 taxa to quantify the effects of active oil and gas platforms on benthic food webs using a multiple before-after control-impact experiment. Contamination from oil and gas platforms caused declines in benthic food web complexity, community abundance, and biodiversity. Fewer trophic interactions and increased connectance indicated that the community became dominated by generalists adapting to alternative resources, leading to simpler but more connected food webs in contaminated environments. Decreased mean body mass, shorter food chains, and the dominance of small detritivores such as Capitella capitata near to structures suggested a disproportionate loss of larger organisms from higher trophic levels. These patterns were associated with concentrations of hydrocarbons and heavy metals that exceed OSPAR's guideline thresholds of sediment toxicity. This study provides new evidence to better quantify and manage the environmental consequences of oil and gas exploitation at sea.

Roles of oxidant, activator, and surfactant on enhanced electrokinetic remediation of PAHs historically contaminated soil

Electrokinetic (EK) remediation technology can enhance the migration of reagents to soil and is especially suitable for in situ remediation of low permeability contaminated soil. Due to the long aging time and strong hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) from historically polluted soil, some enhanced reagents (oxidant, activator, and surfactant) were used to increase the mobility of PAHs, and remove and degrade PAHs in soil. However, under the electrical field, there are few reports on the roles and combined effect of oxidant, activator, and surfactant for remediation of PAHs historically contaminated soil. In the present study, sodium persulfate (PS, oxidant, 100 g L^-1) or/and Tween 80 (TW80, surfactant, 50 g L^-1) were added to the anolyte, and citric acid chelated iron(II) (CA-Fe(II), activator, 0.10 mol L^-1) was added to catholyte to explore the roles and contribution of enhanced reagents and combined effect on PAHs removal in soil. A constant voltage of 20 V was applied and the total experiment duration was 10 days. The results showed that the removal rate of PAHs in each treatment was PS + CA-Fe(II) (21.3%) > PS + TW80 + CA-Fe(II) (19.9%) > PS (17.4%) > PS + TW80 (11.4%) > TW80 (8.1%) > CK (7.5%). The combination of PS and CA-Fe(II) had the highest removal efficiency of PAHs, and CA-Fe(II) in the catholyte could be transported toward anode via electromigration. The addition of TW80 reduced the electroosmotic flow and inhibited the transport of PS from anolyte to the soil, which decreased the removal of PAHs (from 17.4 to 11.4% with PS, from 21.3 to 19.9% with PS+CA-Fe(II)). The calculation of contribution rates showed that PS was the strongest enhancer (3.3~9.9%), followed by CA-Fe(II) (3.9~8.5%) (with PS), and the contribution of TW80 was small and even negative (-1.4~0.6%). The above results indicated that the combined application of oxidant and activator was conducive to the removal of PAHs, while the addition of surfactant reduced the EOF and the migration of oxidant and further reduced the PAHs removal efficiency. The present study will help to further understand the role of enhanced reagents (especially surfactant) during enhanced EK remediation of PAHs historically contaminated soil.

Accelerated PAH Transformation in the Presence of Dye Industry Landfill Leachate Combined with Fungal Membrane Lipid Changes

The ascomycete fungus Nectriella pironii, previously isolated from soil continuously contaminated by dye industry waste, was used for the biodegradation of phenanthrene (PHE), benz[a]anthracene (B[a]A), and benz[a]pyrene (B[a]P). The degradation of polycyclic aromatic hydrocarbons (PAHs) by N. pironii was accelerated in the presence of landfill leachate (LL) collected from the area of fungus isolation. The rate of cometabolic elimination of PHE and B[a]P in the presence of LL was, respectively, 75% and 94% higher than in its absence. LC-MS/MS analysis revealed that PAHs were converted to less-toxic derivatives. The parallel lipidomic study showed changes in membrane lipids, including a significant increase in the content of phosphatidylcholine (PC) (almost double) and saturated phospholipid fatty acids (PLFAs) and a simultaneous reduction (twofold) in the content of phosphatidylethanolamine (PE) and unsaturated PLFAs, which may have promoted the fungus to PHE + LL adaptation. In the presence of PHE, an intense lipid peroxidation (fivefold) was observed, confirming the stabilization of the cell membrane and its extended integrity. Determining the course of elimination and adaptation to harmful pollutants is essential for the design of efficient bioremediation systems in the future.

Study on the migration mechanisms of water-soluble agents in high-pressure rotary jetting remediation

High-pressure rotary jetting (HPRJ) remediation is a recent-applied technology for in situ remediation of contaminated soils. The effectiveness of remediation depends upon the migration and distribution of the injected agents in the soil. However, the corresponding migration mechanisms have received little attention. In this study, laboratory HPRJ tests and numerical simulations were performed using chlorine (Cl^-) as a tracer to investigate the transport during HPRJ and the subsequent advection and diffusion. The test results showed that the HPRJ transported Cl^- into the mixing zone by eroding the sand, and the radius of the mixing zone could be reasonably predicted by the erosion model. The Cl^- concentration decreased linearly along the radial direction in the mixing zone. In addition, the Cl^- transport distance increased with the increase in nozzle diameter, jetting times, especially injection pressure, and decreased with an increasing rotation speed. The Cl^- concentration and radial uniformity were correlated positively with rotation speed, particularly nozzle diameter and jetting times. Numerical simulation showed that part of Cl^- migrated from the mixing zone to diffusion zone by advection-diffusion after rotary jetting, which contributed positively to the agent distribution distance and uniformity. The Cl^- migration was dominated by advection in the initial stage (30 days), while diffusion became more important thereafter.

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.

A novel electrokinetic remediation with in-situ generation of H2O2 for soil PAHs removal

Electrokinetic-Fenton (EK-Fenton) technology requires a high dose of H₂O₂ to produce •OH radicals, which adds a high cost to the remediation process and raises safety concerns during transportation and storage of H₂O₂. Moreover, the remediation efficiency of the conventional EK-Fenton process is low due to the meaningless consumption of H₂O₂ on the electrodes and the alkaline environment near the cathode. In this work, a modified CMK3-gas diffusion electrode (CMK3-GDE) is fabricated. This cathode can continuously generate H₂O₂, and the cumulative H₂O₂ concentration can reach 0.23 M during 10 days of the test. The utilization of cation exchange membranes (CEMs) efficiently restricts the decomposition of H₂O₂ on the electrodes and prevents the alkalization of the soil near the cathode, resulting in a 13.7-43.2% increase of the removal efficiency of polycyclic aromatic hydrocarbons (PAHs). In this new treatment process, PAHs are mainly oxidized into quinones, ketones, alcohols, and small molecule acids, and all these products have lower toxicities than PAHs. The EK-Fenton/CMK3-GDE-CEM system exhibits excellent remediation efficiency for treating PAHs polluted soil, which could be a sustainable, eco-friendly, and low-cost strategy for soil remediation.

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.

A novel chitosan-urea encapsulated material for persulfate slow-release to degrade organic pollutants

A novel eco-friendly material (CS-U@PS) for persulfate slow-release to effectively degrade organic pollutants (methyl orange and pyrene) was synthesized using chitosan and urea as the encapsulated framework materials via an emulsion cross-linking method for the first time. The obtained CS-U@PS exhibits spherical shapes with a uniform size of approximately 2-3 µm according to the particle-size distribution and SEM image results. The slow-release mechanism was proposed through a kinetics model study and the Ritger-Peppas model fit well (r² = 0.9699) to indicate that the slow-release process is non-Fickian diffusion. The influences of urea and PS dosages and oxidative conditions on methyl orange degradation were studied, and all the results suggested that urea played an important role in PS slow-release and can also catalyze the activation of PS by iron to further produce radicals and improve the removal efficiency of pollutants. A pyrene removal rate of 90.53% was achieved in aqueous solutions and an above 80% removal rate was obtained in weakly acidic or neutral soil environments by CS-U@PS activated by Fe²⁺ with citric acid as the chelating agent. Therefore, the fabricated slow-release oxidation materials exhibit application potential for the remediation of organic polluted groundwater and soil.

Optimization of PAHs oxidation from contaminated soil using modified nanoscale zero-valent iron combined with potassium permanganate

A novel synergistic oxidation technology based on modified nanoscale zero-valent iron (nZVI) and potassium permanganate (KMnO₄) was developed for polycyclic aromatic hydrocarbons (PAHs) remediation in actual contaminated soil. In this study, three surfactants were used as dispersants to modify nZVI, including poly acrylic (PAA), sorbitan monolaurate (SPAN-20) and sugar esters (SE). The following parameters were studied to optimize the coupling oxidation process: dispersants/nZVI ratio, dosage of oxidant based on soil oxidation demand (SOD), amount of modified nanomaterials added in the coupling system. By using zeta potential, XRD, SEM, BET characterization methods, the results show that nZVI successfully coated with 5% PAA, 20% SE and 10% SPAN-20 have the best stability and mobility to effectively reduce the agglomeration effect. The conditions for treating PAH contaminated soil with the three best modified nanocomposites combined with KMnO₄ were studied. The optimal conditions were defined as [SE-nZVI] = 10% and [KMnO₄] = 40% SOD_max for 24 h at 25 °C. The synergistic oxidation process under these optimal conditions and the two unoptimized processes of KMnO₄ and nZVI-KMnO₄ degraded 85%, 58.9% and 62% of PAHs, respectively. This showed that the treatment effect of the optimized oxidation process was improved by 1.3-1.5 times. Further, by using gas chromatography-mass spectrometry (GC-MS), adsorption and electrophilic substitution reaction were speculated as the oxidation mechanism of PAHs treated by the coupling system of SE-nZVI-KMnO₄. PAHs could finally be decomposed into 9-methylene-9H-fluorene, fluoranthene and 1,5-diphenyl-1,4-pentadiyn-3-one and reached a safer status in the soil.

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

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

Assessment of seasonal relationship between polycyclic aromatic hydrocarbon accumulation and expression patterns of oxidative stress-related genes in muscle tissues of red mullet (M. barbatus) from the Northern Adriatic Sea

In this study, we examined the seasonal association between Polycyclic Aromatic Hydrocarbon (PAH) concentrations and mRNA expression profiles of some antioxidant genes (i.e. CAT, GST and SOD), as well as lipid peroxidation (LPO), in muscle of sexually inactive females of red mullet (Mullus barbatus). Fish were captured in a fishery area of the Northern Adriatic Sea during both winter and summer. We found significantly (p < 0.05) higher ∑HMW-PAHs concentrations in muscle of specimens caught during winter than summer. On the basis of sampling season, red mullets exhibited different gene expression profiles of antioxidant enzymes showing lower levels of both CAT and GST in winter than in summer. Accordingly, CAT was found to be negatively associated with ∑PAH concentrations, especially ∑LMW-PAH, in individuals collected during winter. Seasonal-related downregulation of some oxidative stress biomarker expression is suggestive of greater susceptibility of red mullets to PAHs during winter.

Remediation of polycyclic aromatic hydrocarbons by sulfate radical advanced oxidation: Evaluation of efficiency and ecological impact

Remediation of polycyclic aromatic hydrocarbon (PAH) contamination in soil remains expensive and difficult. Sulfate radical advanced oxidation processes (SR-AOPs) can be used for in situ PAH oxidation but their efficiency and ecological impacts require evaluation. Here, we tested the remediation efficiency and ecological impacts of an SR-AOP combining sodium persulfate and ferrous sulfate (FS), the FS SR-AOP with the chelating agent citric acid (FS+CA), and the FS SR-AOP with chelating agent and the surfactant IGEPALCA-720 (FS+CA+IG) compared with natural attenuation (control, CK). We measured PAH, soil physicochemical properties (pH, soil organic matter [SOM]), and soil biological properties (polyphenol oxidase [PPO] activity, peroxidase [POD] activity, soil microbes) in contaminated soil samples after incubation with FS, FS+CA, FA+CA+IG, or CK for 1, 15, and 30 d. Compared with CK, all SR-AOPs significantly decreased PAH after 1 d, with FS+CA+IG showing the highest efficiency (80.8%) and PAH removal peaking at 15 d. FS+CA+IG treatment reduced SOM the least and soil pH the most; after 30 d, SOM recovered to ~80% of the level observed in CK, but soil pH decreased further. PPO and POD activities were highest after 15 and 30 d of FS+CA+IG treatment. Real-time quantitative PCR demonstrated that SR-AOPs significantly decreased quantities of PAH-degrading bacteria, soil bacteria, fungi, and actinobacteria at 1 d, but after 30 d, the microbes recovered to levels similar to those observed in CK, with no significant differences among SR-AOPs. SR-AOPs reduced bacterial diversity and changed the dominant phylum from Acidobacteria to Firmicutes. In summary, SR-AOP treatment with both the chelating agent and the surfactant produced the best PAH removal and least SOM destruction but the largest pH decrease, although some factors recovered with longer incubation. This study provides key information for improving PAH remediation and evaluating its ecological impact.

Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review

Persistent organic contaminants affecting soil and groundwater pose a significant threat to ecosystems and human health. Fenton oxidation is an efficient treatment for removing these pollutants in the aqueous phase at acidic pH. However, the in-situ application of this technology for soil remediation (where pHs around neutrality are required) presents important limitations, such as catalyst (iron) availability and oxidant (H2O2) stability. The addition of chelating agents (CAs), forming complexes with Fe and enabling Fenton reactions under these conditions, so-called chelate-modified Fenton process (MF), tries to overcome the challenges identified in conventional Fenton. Despite the growing interest in this technology, there is not yet a critical review compiling the information needed for its real application. The advantages and drawbacks of MF must be clarified, and the recent achievements should be shared with the scientific community. This review provides a general overview of the application of CAs to enhance the Fenton process for the remediation of soils polluted with the most common organic contaminants, especially for a deep understanding of the activation mechanisms and influential factors. The existing shortcomings and research needs have been highlighted. Finally, future research perspectives on the use of CAs in MF and recommendations have been provided.

Promoted oxidation of polycyclic aromatic hydrocarbons in soils by dual persulfate/calcium peroxide system

In situ chemical oxidations (ISCO) have been demonstrated as effective ways for remediating soils contaminated with organic pollutants by complete mineralization. This work aims to develop a technology for the oxidation remediation of soils contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) using a dual calcium peroxide (CP)/persulfate (PS) oxidant system activated by oxalic acid (OA)-chelating Fe²⁺. The dual peroxide system was set up, and the effects of 5 single factors (i.e., CP dosage, PS dosage, Fe²⁺ dosage, OA concentration, and soil/water ratio) on PAHs degradation were studied using the single-factor experiment. The response surface method was then introduced to obtain the optimized experimental conditions (CP dosage, PS dosage, OA concentration) of the dual peroxide system. The result shows that the dual peroxide system significantly increased the PAHs degradation and the maximum PAHs degradation efficiency (70.8%) was achieved by the dual peroxide system under optimal conditions (PS dosage, CP concentration, Fe²⁺/PS ratio, and Fe²⁺/OA ratio was 8.89 g/kg, 0.18 mol/L, 1/4 and 0.62) at neutral soil condition. This study is an illustration of the promising efficiency of the dual peroxide system for PAH oxidation in the neutral soil and has great potential for remediation of PAHs contaminated farmland soils.

Remediation of contaminated soil and groundwater using chemical reduction and solidification/stabilization method: a case study

This study presents a systematic on-site remediation case involving both heavy metal and organic contaminants in soil and groundwater in a historically industrial-used site in Shanghai, China. Lab-scale experiments and field tests were conducted to determine the optimum parameters for the removal of contaminants in soil and groundwater. It has been found that the remediation goal of hexavalent chromium in soil could be achieved with the mass content of added sodium hydrosulfite and ferrous sulfate reaching 3% + 6%. The total chromium in the groundwater was effectively removed, when the mass ratio of sodium metabisulfite was not less than 3 g/L, and the added quick lime made pH value not less than 9. The concentrations of arsenic and 1,2-dichloropropane in the groundwater decreased evidently after extraction and mixing of groundwater. The pH and calcium chloride dosage added should be larger than 9.5 and 5 g/L, respectively, to remove phosphate in groundwater. The removal efficiency of those contaminants was examined and evaluated after the on-site remediation. The results demonstrated that it was feasible to use the chemical reduction and solidification/stabilization methods for the on-site ex situ remediation of this site, which could be referenced for the realistic remediation of similar sites.

Electrokinetical enhanced delivery of acidic potassium permanganate and removal of copper-pyrene compound pollution in a red soil

Soil contaminated by combinations of heavy metals and organic pollutants has become an increasingly prominent environmental issue. Developing efficient technologies to synchronously decontaminate such co-contaminated sites is challenging and imperative. In our previous study for the treatment of Copper (Cu) and pyrene contaminated soil, electrokinetics (EK) coupled acidic permanganate (PM) performed best for degradation of pyrene near the injection spot, but it unfortunately prevented the migration of Cu. In order to further enhance the removal efficiency of these contaminants, in this study, batch experiments were conducted to investigate the feasibility of delivering PM by EK under regular refreshment of acidoxidant along with amplification of voltage gradient. The results showed that PM can be transported from cathode to anode to S2 section (near the anode) with a slow mass transfer rate via electromigration and reversed electroosmotic flow, and further delivery was achieved when Cu and pyrene were coexisted. The reaction of pyrene with PM produced a lower soil pH condition, which was conductive to the transport of Cu, and the existence of Cu promoted the migration of PM. The coexistence of Cu and pyrene favored the removal efficiency of the pollutants, and 92.8% of Cu and 70.7% of pyrene were removed after 15 d EK treatment. Thus, EK + acidic PM with regularly supplement of oxidant is appropriate to achieve complete mass depletion of heavy metals and PAHs, especially in low buffered soils.

Nonionic and anionic surfactant-washing of polycyclic aromatic hydrocarbons in estuarine sediments around an industrial harbor in southern Taiwan

Various surfactants, such as nonionic Triton X-100 and Simple Green™ (SG), and anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were utilized to remove polycyclic aromatic hydrocarbons (PAHs) from heavily contaminated harbor sediments dredged from Kaohsiung Harbor in Taiwan. Desorption/re-sorption equilibrium, kinetics, and washability of PAHs using the selected surfactant were evaluated under different critical micelle concentrations (CMC). Experimental results revealed that the desorption rate of high molecular weight PAHs was greater than those of low molecular weight PAHs, and the anionic SDS was relatively effective in the removal of total PAHs (>50%) compared to the other surfactants. The correlation between the effectiveness of the surfactant washing processes and the physicochemical properties of individual PAH was statistically analyzed. The resulting data suggested that hydrophobic factors (K_ow, K_oc and S_w) affected PAH treatability more than the reactivity of PAH (electron affinity and ionization potential). Since the adsorption of anionic surfactant altered the hydrophobicity of organic matter in the sediment, PAHs preferred transferring from the sediment to the hydrophobic core of micelles in aqueous solution. Nevertheless, the nonionic surfactant enhanced the PAH partition in the aqueous phase, thus increasing the micellar solubilization of PAH.

Modeling and optimization of imidacloprid degradation by catalytic percarbonate oxidation using artificial neural network and Box-Behnken experimental design

Due to its toxicity and persistence, pesticide pollution poses a serious threat to human health and the environment. Imidacloprid or IMD is an archetypal neonicotinoid insecticide commonly used to protect a variety of crops worldwide. The present study examines the applicability of two numerical tools -- artificial neural network (ANN) and response surface methodology - Box Behnken design (RSM-BBD) -- to model and optimize oxidative IMD degradation by sodium percarbonate (SPC). The influences of SPC dose, Fe²⁺ catalyst dosage, and solution pH on IMD removal were evaluated. An ANN composed of an input layer with three neurons, a hidden layer with eight optimum neurons, and an output layer with one neuron was developed to map the complex non-linear process at different levels. Seventeen designed runs of different experimental conditions were derived from RSM-BBD. These experimental conditions and their response values showed to be best fitted in a reduced cubic model equation. Sensitivity analyses revealed the relative importance of the various components: Fe²⁺ (40.4%) > pH (31.1%) > SPC dose (28.5%). The two model were highly predictive with overall coefficients of determination and root-mean-square errors of 0.9983 and 0.31 for ANN, while 0.9996 and 0.20 for RSM-BBD. Overall, the present study established ANN and RSM-BBD as valuable and effective tools for catalytic SPC oxidation of IMD contaminants. SPC is a cleaner alternative to other oxidants for pesticide degradation as it is non-toxic, safe to handle, and produces by-products that inherently exist in the natural water matrix.

Oxidation of nine petroleum hydrocarbon compounds by combined hydrogen peroxide/sodium persulfate catalyzed by siderite

A system consisting of hydrogen peroxide/persulfate (H₂O₂/S₂O₈^2-) catalyzed by siderite was attempted to oxidize nine representative petroleum hydrocarbon compounds [benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, 1,2,4-trimethylbenzene, methyl-tert-butyl ether, and naphthalene] that tend to persist in the environment. Oxidation under different siderite dosages, H₂O₂:S₂O₈^2- ratios, and pH conditions were investigated. Results indicated that oxidation rates increased from 1.21-4.62 to 1.77-8.94 d^-1 as siderite increased from 0.16 to 0.48 g/40 mL (H₂O₂:Na₂S₂O₈ = 5:1, initial pH = 3.0), except for naphthalene (decreased from 0.58 to 0.45 d^-1 with increased siderite dosage). When the H₂O₂:S₂O₈^2- ratio was increased from 1:1 to 5:1 (siderite = 0.16 g, initial pH = 3.0), the oxidation rates increased from 0.02-0.73 to 0.33-2.19 d^-1. However, as pH increased to > 5.5 (siderite = 0.16 g, H₂O₂:Na₂S₂O₈ = 2.5:1), the oxidation rates of petroleum hydrocarbons decreased to 0.003-0.09 d^-1, which was approximately 90% less than that at pH = 3.0. The partial correlations and principal component analysis of the experimental data were conducted. Overall, both siderite dosage and H₂O₂:S₂O₈^2- ratio correlated positively with oxidation efficiency. The oxidation potential by H₂O₂/S₂O₈^2- mixtures towards the target petroleum hydrocarbon compounds seemed to be more sensitive to pH conditions than to siderite dosages or H₂O₂:S₂O₈^2- ratios.

The efficient degradation of organic pollutants in an aqueous environment under visible light irradiation by persulfate catalytically activated with kaolin-Fe2O3

Characterizations and properties of catalysts.

Activation of persulfate by CoO nanoparticles loaded on 3D mesoporous carbon nitride (CoO@meso-CN) for the degradation of methylene blue (MB)

A simple and facile synthesis method is developed for the fabrication of CoO loaded ordered mesoporous carbon nitride (CoO@meso-CN) composites, at various CoO loadings, and used, for the first time, to activate persulfate (PS) for methylene blue (MB) degradation. The interfacial interaction between the ultrafine CoO nanoparticles, immobilized by high surface area, regular mesopores, and graphitic nature of the meso-CN support can further enhance the catalytic activation of PS for methylene blue (MB) degradation. Among all catalysts studied, the 5-wt% CoO@meso-CN exhibits the best catalytic performance with a k_obs of 0.264 min^-1. High initial pH, especially at pH-11, is more beneficial for PS activation. Furthermore, the CoO@meso-CN nanocatalyst is highly stable with a consistently high degree of MB degradation and negligible cobalt leaching for at least 5 consecutive catalytic cycles. Both SO₄^- and OH are the major reactive species based on results of EPR and quenching experiments. The degradation intermediates of MB are also identified by HPLC/MS/MS and the possible degradation pathway is proposed. Results clearly demonstrate that CoO@meso-CN is a promising green catalyst with enormous potential for the remediation of hazardous chemicals using PS.

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.

Strategies for oxidation of PAHs in aged contaminated soil by batch reactors

Polycyclic aromatic hydrocarbons (PAH) are neutral, nonpolar and hydrophobic molecules that tend to sorb onto soil organic matter. Chemical oxidation is a good choice to avoid the limitations of bioremediation. To evaluate the efficiency of different types of oxidation (permanganate, hydrogen peroxide, and persulfate) and activation (heat, alkaline, and iron), batch reactors were prepared. The soil was contaminated with phenanthrene and pyrene (1200 ± 200 and 2800 ± 100mg per kg of dry soil, respectively) and aged for fifteen months. Treatments were prepared with 10g of contaminated dry soil and 20ml of water and incubated at room temperature for 7 days. Analyses of phenanthrene and pyrene concentrations, soil pH and electric conductivity were performed. Counts of heterotrophic cultivable bacteria on R2A medium and PAH-degraders were carried out after 7 days of treatment. The persulfate treatment at room temperature, without the addition of activators, achieved better results than treatments with the same doses of permanganate or hydrogen peroxide. All the strategies to improve persulfate treatments yielded higher degradation of pyrene than the biological control, as expected from the structural description of this compound by Clar's model. The thermal activation of persulfate (65°C for 6h) led to the degradation of more than 90% of both PAHs after 7 days of treatment.

In situ remediation of contaminated marinesediment: an overview

Sediment tends to accumulate inorganic and persistent hydrophobic organic contaminants representing one of the main sinks and sources of pollution. Generally, contaminated sediment poses medium- and long-term risks to humans and ecosystem health; dredging activities or natural resuspension phenomena (i.e., strongly adverse weather conditions) can remobilize pollution releasing it into the water column. Thus, ex situ traditional remediation activities (i.e., dredging) can be hazardous compared to in situ techniques that try to keep to a minimum sediment mobilization, unless dredging is compulsory to reach a desired bathymetric level. We reviewed in situ physico-chemical (i.e., active mixing and thin capping, solidification/stabilization, chemical oxidation, dechlorination, electrokinetic separation, and sediment flushing) and bio-assisted treatments, including hybrid solutions (i.e., nanocomposite reactive capping, bioreactive capping, microbial electrochemical technologies). We found that significant gaps still remain into the knowledge about the application of in situ contaminated sediment remediation techniques from the technical and the practical viewpoint. Only activated carbon-based technologies are well developed and currently applied with several available case studies. The environmental implication of in situ remediation technologies was only shortly investigated on a long-term basis after its application, so it is not clear how they can really perform.