Enhanced degradation of polycyclic aromatic hydrocarbons by biodegradation combined with a modified Fenton reaction

Bibliometric analysis and research progress on hydrogen peroxide and persulfate oxidation processes in the remediation of actual oil-contaminated soil

Oil pollution poses significant harm to both the ecological environment and human health. The primary sources of oil pollutants in soil are leaks that occur during the extraction, transportation, and production phases. In the face of the severe situation of global soil pollution, chemical oxidation technology has shown potential in the remediation of oil-contaminated soil. However, most current research on chemical oxidation technology remains in the laboratory stage, with limited discussion on its characteristics and application conditions in the actual treatment of oil-contaminated sites. To address this gap, this paper applies bibliometric methods to analyze the development trends of chemical oxidation technology and provides a comprehensive review from the perspective of its real-world applications in remediating oil-contaminated soil. It explores commonly used activators, enhancement measures, and key influencing factors of advanced oxidation processes, focusing particularly on those based on hydrogen peroxide and persulfate. The study highlights significant advantages, such as improving remediation efficiency, reducing treatment time, and compatibility with other remediation methods. Nevertheless, challenges remain, including soil acidification, limited pollutant targeting, and high operational costs. To address these issues, this paper proposes innovative directions such as the development of green and efficient activators, optimization of oxidant application strategies, and integration of chemical oxidation with other remediation technologies. These findings aim to establish a robust theoretical foundation and provide strong technical support for future chemical oxidation treatments of such soils. Through this research, we aspire to develop more scientific and effective strategies and methods for the remediation of oil-contaminated soil.

Remediation of carcinogenic PAHs from landfill leachate by Electro-Fenton process - Optimization and modeling

PAHs is the group of emerging micro-pollutants present in most environmental matrices that has the tendency to bioaccumulate and cause carcinogenic effects to human health. The present research involved the quantification and treatment of leachate produced from secured landfill, to eliminate the PAHS. Electro-Fenton process, a class of advanced oxidation process, is adopted to degrade the PAHs using titanium electrodes as both anode and cathode. Artificial intelligence based statistical tool "Central Composite Design" a module of JMP -19 software was used to design the experiments and optimize the critical parameters involved in the research. It was observed that the value of P is significant (P < 0.05) for all the independent variables evidencing the significant correlation between experimental values and predicted values of the software. The value of R2 obtained was 0.96 and 0.97 for COD and PAHs respectively. The maximum removal efficiency of COD and PAH was found to be 84.24% and 90.78% respectively. The optimized conditions obtained from the central composite design were: pH = 5; Fe2+ = 0.1 g/L; H2O2 = 2 g/L; reaction time = 60 min; and electric intensity = 0.2 A. Additionally, optimized experimental conditions were used to study the removal efficiencies of individual 16 PAHs and are also reported. From the close proximity of experimental and predicted results of the software it can be proved that central composite design is efficient enough to be used as a statistical tool in design and analysis for treatment of landfill leachate.

Degradation of crude oil-associated polycyclic aromatic hydrocarbons by marine-derived fungi

One of the major environmental concerns today is hydrocarbon contamination resulting from the activities related to the petrochemical industry. Crude oil is a complex mixture of hydrocarbons like alkanes, naphthene and polycyclic aromatic hydrocarbons (PAHs). PAHs are known to be highly toxic to humans and animals due to their carcinogenic and mutagenic effects. PAHs are environmentally recalcitrant due to their hydrophobicity which makes them difficult to degrade, thus making them persistent environmental contaminants. The mechanical and chemical methods in practice currently to remove hydrocarbon contaminants have limited effectiveness and are expensive. Bioremediation is a cost-effective technology for treating hydrocarbon-contaminated sites as it results in the complete mineralisation of the pollutant. This study demonstrates the degradation of crude oil and associated PAHs using ten fungal cultures isolated from the aquatic environment. The current study reported a 98.6% and 92.9% reduction in total PAHs in crude oil by Fusarium species, i.e. isolate NIOSN-T4 and NIOSN-T5, respectively. The fungal isolate, NIOSN-T4, identified as Fusarium equiseti, showed maximum PAH degradation efficiency of LMW PAHs 97.8%. NIOSN-M126, identified as Penicillium citrinum, exhibited a 100% removal of HMW PAHs. Microorganisms possess an untapped potential for various applications in biotechnology, and the current study demonstrated the potential of marine fungi for use in the bioremediation of xenobiotic hydrocarbons in the environment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03753-2.

An Ultrasound-Fenton Process for the Degradation of 2,4,6-Trinitrotoluene

2,4,6-Trinitrotoluene (TNT), one of the main compounds in ammunition wastewater, is harmful to the environment. In this study, the treatment efficiency of 2,4,6-TNT by different treatment processes, including ferrous ion (Fe2+), hydrogen peroxide (H2O2), Fenton, ultrasound (US) irradiation, US + Fe2+, US + H2O2 and US-Fenton process, was compared. The results showed that US-Fenton was the most effective among all methods studied. The effects of initial pH, reaction time and H2O2 to Fe2+ molar ratio were investigated. The results showed that the removal of TNT, TOC and COD was maximum at an initial pH of 3.0 and H2O2 to Fe2+ molar ratio of 10:1. TNT, TOC and COD removal was fast in the first 30 min, reaching 83%, 57% and 50%, then increased gradually to 99%, 67% and 87% until 300 min, respectively. Semi-batch mode operation increased the removal of TNT and TOC by approximately 5% and 10% at 60 min, respectively. The average carbon oxidation number (ACON) was increased from -1.7 at 30 min to a steady-state value of 0.4, indicating the mineralization of TNT. Based on GC-MS analysis, 1,3,5-trinitrobenzene, 2,4,6-trinitrobenzene acid, 3,5-dinitrobenznamine and 3,5-dinitro-p-toluidine were the major byproducts from the US-Fenton process. The TNT degradation pathway was proposed, which involved methyl group oxidation, decarboxylation, aromatic ring cleavage and hydrolysis.

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.

Recent advances in Ponceau dyes monitoring as food colorant substances by electrochemical sensors and developed procedures for their removal from real samples

Ponceau dyes are one of the food coloring materials that are added to various pharmaceutical, health and food products and give them an appearance. These dyes contain contaminants such as Benzidine, 4-Aminobiphenyl, and 4-Aminoazobenzene that are safe in small amounts, but they are not approved by the US Food and Drug Administration (US-FDA) for human consumption. This study comprehensively was reviewed the properties, applications, chemistry, and toxicity of Ponceau dyes as food colorant substances. Electroanalysis of Ponceau dyes was discussed in detail, and the various electrochemical sensors used to detect and monitor these dyes as food colorant were examined. The applied methods of removing and degradation of these dyes in municipal and industrial wastes were also discussed. Conclusions and future perspectives to motivate future research were also explored.

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.

Remediation of phenanthrene contaminated soil by ferrous oxalate and its phytotoxicity evaluation

Phenanthrene contaminated soil was remediated by the photochemical process of ferrous oxalate. Without using H₂O₂ and adjusting soil pH, phenanthrene in contaminated soil was degraded effectively by the ferrous oxalate under visible light irradiation. Ferrous oxalate possesses excellent visible light absorption ability which benefits the degradation of phenanthrene in soil under visible light irradiation. Via the Fe(II)/Fe(III) catalytic cycle of ferrous oxalate, H₂O₂ and Fe(II) could be produced continuously and H₂O₂ was further catalyzed by Fe(II) and released hydroxyl radicals (•OH) to degrade the phenanthrene in soil. The dosage of ferrous oxalate, moisture content of soil, and soil thickness were most important factors for degradation of phenanthrene in soil. In addition, a good mixing of ferrous oxalate and soil was vital for enhancing the degradation ratio of phenanthrene. After phenanthrene contaminated soil was treated by ferrous oxalate, the toxicity of treated soil was evaluated via the lettuce cultivation experiments. It was demonstrated the toxicity of phenanthrene contaminated soil was significantly reduced by ferrous oxalate according to the growth indexes of lettuces, including root length, leaf length, and fresh weight. This environment-friendly soil remediation method based on ferrous oxalate has huge potential in the remediation of organic pollutant contaminated soil.

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.

The addition of biochar as a sustainable strategy for the remediation of PAH-contaminated sediments

The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH-contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi-PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m² g^-1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low-temperature biochar-amended sediments. Finally, biochar is effective in co-application with Fe²⁺ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.

Improving the treatment of waste activated sludge using calcium peroxide

The treatment and disposal of waste activated sludge (WAS) has become one of the major challenges for the wastewater treatment plants (WWTPs) due to large output, high treatment costs and enriched substantial emerging contaminants (ECs). Therefore, reducing sludge volume, recovering energy and resource from WAS, and removing ECs and decreasing environmental risk have gained increasing attentions. Calcium peroxide (CaO₂), a versatile and safe peroxide, has been widely applied in terms of WAS treatment including sludge dewatering, anaerobic sludge digestion and anaerobic sludge fermentation due to its specific properties such as generating free radicals and alkali, etc., providing supports for sludge reduction, recycling, and risk mitigation. This review outlines comprehensively the recent progresses and breakthroughs of CaO₂ in the fields of sludge treatment. In particular, the relevant mechanisms of CaO₂ enhancing WAS dewaterability, methane production from anaerobic digestion, short-chain fatty acids (SCFA) and hydrogen production from anaerobic fermentation, and the removal of ECs in WAS and role of experiment parameters are systematically elucidated and discussed, respectively. Finally, the knowledge gaps and opportunities in CaO₂-based sludge treatment technologies that need to be focused in the future are prospected. The review presented can supply a theoretical basis and technical reference for the application of CaO₂ for improving the treatment of WAS.

Recent Advances in the Study of the Remediation of Polycyclic Aromatic Compound (PAC)-Contaminated Soils: Transformation Products, Toxicity, and Bioavailability Analyses

Polycyclic aromatic compounds (PACs) encompass a diverse group of compounds, often found in historically contaminated sites. Different experimental techniques have been used to remediate PACs-contaminated soils. This brief review surveyed over 270 studies concerning remediation of PACs-contaminated soils and found that, while these studies often measured the concentration of 16 parent polycyclic aromatic hydrocarbons (PAHs) pre- and post-remediation, only a fraction of the studies included the measurement of PAC-transformation products (PAC-TPs) and other PACs (n = 33). Only a few studies also incorporated genotoxicity/toxicity/mutagenicity analysis pre- and post-remediation (n = 5). Another aspect that these studies often neglected to include was bioavailability, as none of the studies that included measurement of PAH-TPs and PACs included bioavailability investigation. Based on the literature analysis, future remediation studies need to consider chemical analysis of PAH-TPs and PACs, genotoxicity/toxicity/mutagenicity, and bioavailability analyses pre- and post-remediation. These assessments will help address numerous concerns including, among others, the presence, properties, and toxicity of PACs and PAH-TPs, risk assessment of soil post-remediation, and the bioavailability of PAH-TPs. Other supplementary techniques that help assist these analyses and recommendations for future analyses are also discussed.

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.

Biodegradation and post-oxidation of fuel-weathered field soil

Owing to the less volatile and less biodegradable nature of weathered fuel-contaminated soil, it cannot be easily remediated using conventional bioremediation approaches. Therefore, this study was aimed to enhance the landfarming bioremediation process by introducing post-oxidation for the degradation of the residual total petroleum hydrocarbons (TPH) in fuel-contaminated field soil. A laboratory-scale landfarming bioaugmentation process was performed by using oil-degrading microbes, nutrients, and surfactants, followed by chemical oxidation as a post treatment. The results demonstrated that the addition of microbes and nutrients gradually decreased the TPH concentration of the soil (initial TPH = 5932 ± 267 mg/kg) with a removal efficiency of 70-72% (TPH > 800 mg/kg; Korean limit for non-residential sites). However, the use of post-oxidation treatments with 5% KMnO₄ decreased the TPH to approximately 401-453 mg/kg (TPH below 500 mg/kg; residential site limit) with an overall efficiency of 92-93% compared to the corresponding value of 13% for the control (water treatment). Performing landfarming through biodegradation followed by chemical oxidation as a post treatment could successfully remove the weathered TPH in soil below the regulatory limits. Furthermore, the post-oxidation treatment may oxidize the less biodegradable portions only after biodegradation, thereby minimizing the oxidant demand and enhancing the soil properties such as the pH, amount of natural substrates and microbial population.

Organic Matter Characterization and Phytotoxic Potential Assessment of a Solid Anaerobic Digestate Following Chemical Stabilization by an Iron-Based Fenton Reaction

Digestates, a byproduct of the anaerobic bioconversion of organic wastes for the production of biogas, are highly variable in chemical and biological properties, thus limiting their potential use in agriculture as soil amendment. Using a lab-scale glass reactor, we aimed to assess the feasibility to chemically stabilize the solid fraction of an anaerobic digestate by applying a Fenton reaction under constant pH (3.0), temperature (70 °C), reaction time (8 h), and various combinations of H₂O₂ and Fe²⁺. In Fenton-treated samples, the phytotoxic potential (determined on a test plant), total phenols, and the bad smell odor index markedly declined, whereas total C and N remained unaltered. Thermogravimetric (TG) analysis and Fourier transform infrared (FT-IR) spectroscopy revealed contrasting changes in extracted humic and fulvic fractions being increased or depleted, respectively, in aromatic substances. Process feasibility and optimum conditions for an effective biomass stabilization were achieved with a H₂O₂/Fe²⁺ ratio between 0.02 and 0.03.

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.

Bacteria involved in biodegradation of creosote PAH - A case study of long-term contaminated industrial area

Polycyclic aromatic hydrocarbons (PAH) contained in creosote oil are particularly difficult to remove from the soil environment. Their hydrophobic character and low bioavailability to soil microorganisms affects their rate of biodegradation. This study was performed on samples of soil that were (for over forty years) subjected to contamination with creosote oil, and their metagenome and physicochemical properties were characterized. Moreover, the study was undertaken to evaluate the biodegradation of PAHs by autochthonous consortia as well as by selected bacteria strains isolated from long-term contaminated industrial soil. From among the isolated microorganisms, the most effective in biodegrading the contaminants were the strains Pseudomonas mendocina and Brevundimonas olei. They were able to degrade more than 60% of the total content of PAHs during a 28-day test. The biodegradation of these compounds using AT7 dispersant was enhanced only by Serratia marcescens strain. Moreover, the addition of AT7 improved the effectiveness of fluorene and acenaphthene biodegradation by Serratia marcescens 6-fold. Our results indicated that long-term contact with aromatic compounds induced the bacterial strains to use the PAHs as a source of carbon and energy. We observed that supplementation with surfactants does not increase the efficiency of hydrocarbon biodegradation.

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.

Synthesis of functionalized mesoporous material from rice husk ash and its application in the removal of the polycyclic aromatic hydrocarbons

The rice husk ash (RHA) was used as an alternative source of silica for the synthesis of the functionalized mesoporous material, which was used in the removal of the PAHs naphthalene (Nap), benzo[b]fluoranthene (B[b]F), benzo[k]fluoranthene (B[k]F), and benzo[a]pyrene (B[a]P) from aqueous media. The PABA-MCM-41 (RHA) was characterized using FTIR, TGA, SAXS, and N₂ adsorption-desorption analyses. Removal experiments were performed to determine the initial concentrations, individual adsorption in comparison with the mixture of the PAHs, PABA-MCM-41 (RHA) amount, pH, time, and temperature, and the results obtained were statistically analyzed. The PABA-MCM-41 (RHA) presented the S_BET, V_T, and D_BJH values of 438 m² g^-1, 0.41 cm³ g^-1, and 3.59 nm, respectively, and good thermal stability. The q_e values found in the kinetic equilibrium for the PAHs mixture followed increasing order: Nap < B[a] P < B[k]F < B[b]F, with removal percentages of 89.08 ± 0.00, 93.85 ± 0.28, 94.54 ± 0.10, and 97.80 ± 0.05%, respectively. Graphical abstract.

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.

Stable-Isotope Probing-Enabled Cultivation of the Indigenous Bacterium Ralstonia sp. Strain M1, Capable of Degrading Phenanthrene and Biphenyl in Industrial Wastewater

To identify and obtain the indigenous degraders metabolizing phenanthrene (PHE) and biphenyl (BP) from the complex microbial community within industrial wastewater, DNA-based stable-isotope probing (DNA-SIP) and cultivation-based methods were applied in the present study. DNA-SIP results showed that two bacterial taxa (Vogesella and Alicyclobacillus) were considered the key biodegraders responsible for PHE biodegradation only, whereas Bacillus and Cupriavidus were involved in BP degradation. Vogesella and Alicyclobacillus have not been linked with PHE degradation previously. Additionally, DNA-SIP helped reveal the taxonomic identity of Ralstonia-like degraders involved in both PHE and BP degradation. To target the separation of functional Ralstonia-like degraders from the wastewater, we modified the traditional cultivation medium and culture conditions. Finally, an indigenous PHE- and BP-degrading strain, Ralstonia pickettii M1, was isolated via a cultivation-dependent method, and its role in PHE and BP degradation was confirmed by enrichment of the 16S rRNA gene and distinctive dioxygenase genes in the DNA-SIP experiment. Our study has successfully established a program for the application of DNA-SIP in the isolation of the active functional degraders from an environment. It also deepens our insight into the diversity of indigenous PHE- and BP-degrading communities.IMPORTANCE The comprehensive treatment of wastewater in industrial parks suffers from the presence of multiple persistent organic pollutants (POPs), such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), which reduce the activity of activated sludge and are difficult to eliminate. Characterizing and applying active bacterial degraders metabolizing multiple POPs therefore helps to reveal the mechanisms of synergistic metabolism and to improve wastewater treatment efficiency in industrial parks. To date, SIP studies have successfully investigated the biodegradation of PAHs or PCBs in real-world habitats. DNA-SIP facilitates the isolation of target microorganisms that pose environmental concerns. Here, an indigenous phenanthrene (PHE)- and biphenyl (BP)-degrading strain in wastewater, Ralstonia pickettii M1, was isolated via a cultivation-dependent method, and its role in PHE and BP degradation was confirmed by DNA-SIP. Our study provides a routine protocol for the application of DNA-SIP in the isolation of the active functional degraders from an 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.

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.

Highly efficient treatment of real benzene dye intermediate wastewater by simple limestone and lime neutralization-coagulation with improved Fenton oxidation

Multistage Fenton oxidation is a favored method for the treatment of benzene dye intermediate (BDI) wastewater, but the pH adjustments required after each stage of the Fenton process with a simple way is still a challenge. Limestone pretreatment and lime neutralization-coagulation were used to solve the problem in multistage Fenton process. First, we determined the optimal conditions of Fenton oxidation using the Box-Behnken response surface method. Limestone pretreatment before the multistage Fenton process allowed for simultaneous pH adjustment and 14.15% COD removal. Most notably, the lime cream neutralization-coagulation process effectively adjusted the pH after each stage of the Fenton process. The optimum CaO particle size, lime mass fraction, mixing time, and stirring speed were determined by orthogonal tests. COD removal (89.23%) was obtained when lime cream neutralization-coagulation was applied to the three-staged Fenton process, while only 58.57% COD removal was obtained by the unadjusted single-staged Fenton process. The COD and wastewater color were reduced from 10,600 mg/L and 12,200 multiples to 495 mg/L and 20 multiples, respectively, using the adjusted process. This improved method provides a promising cost-effective way to efficiently treat real BDI wastewater.

Active iron bound to SOM catalyzes the oxidization of alkanes in soil by H2O2

To explore the oxidation effects and mechanisms for the oxidation of alkanes by H2O2 in a Fenton system catalyzed by two types of iron bound to soil organic matter (Fe-SOM) in crude oil-contaminated soil, an oxidation experiment was performed in active Fe-SOM and Fe-SOM systems. The results showed that the TPH removal ability of active Fe-SOM (average 0.36 g TPH/g Fe-SOM) was 2.25-fold higher than the corresponding value of Fe-SOM. Active Fe-SOM contained both -NH2 and -OH functional groups, and had a higher content of iron with high binding energy, while Fe-SOM only contained -NH2 groups. Thus, a large yield of hydroxyl radicals (·OH) was generated (8.92 a.u.) by active Fe-SOM catalyzing the decomposition of H2O2, while the corresponding yield of ·OH in the Fe-SOM system was only 4.81 a.u. In addition, the removal efficiency of C17-C23 (70%) was comparable to that of C24-C30 (69%), not restricted by the hydrophobicity of different alkanes. The alkane removal by active Fe-SOM was higher than that by Fe-SOM, although the content of Fe-SOM was double that of active Fe-SOM. In summary, the active Fe-SOM formed in the soil sample containing humic acid-like and hydrophobic acid derivates could catalyze H2O2 decomposition to improve the removal efficiency of crude oil in contaminated soil.

Generation of hydroxyl radicals by Fe-polyphenol-activated CaO2 as a potential treatment for soil-borne diseases

An Fe-polyphenol catalyst was recently developed using anhydrous iron (III) chloride and coffee grounds as raw materials. The present study aims to test the application of this Fe-polyphenol catalyst with two hydrogen peroxide (H2O2) sources in soil as a new method for controlling the soil-borne disease caused by Ralstonia solanacearum and to test the hypothesis that hydroxyl radicals are involved in the catalytic process. Tomato cv. Momotaro was used as the test species. The results showed that powdered CaO2 (16% W/W) is a more effective H2O2 source for controlling bacterial wilt disease than liquid H2O2 (35% W/W) when applied with an Fe-polyphenol catalyst. An electron paramagnetic resonance spin trapping method using a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) assay and Fe-caffeic acid and Fe-chlorogenic acid complexes as models showed that these organometallic complexes react with the H2O2 released by CaO2, producing hydroxyl radicals in a manner that is consistent with the proposed catalytic process. The application of Fe-polyphenol with powdered CaO2 to soil could be a new environmentally friendly method for controlling soil-borne diseases.

Feasibility of oxidation-biodegradation serial foam spraying for total petroleum hydrocarbon removal without soil disturbance

This study evaluated surface foam spraying technology, which avoids disturbing the soil, to deliver chemical oxidant and oil-degrading microbes to unsaturated soil for 30 days. Hydrogen peroxide foam was sprayed once onto diesel contaminated soil for oxidation of soil total petroleum hydrocarbon (TPH). Periodic bioaugmentation foam was sprayed every three days for biodegradation of soil TPH. Foam spraying employing oxidation-bioaugmentation serial application significantly reduced soil TPH concentrations to 550 mg·kg^-1 from an initial 7470 mg·kg^-1. This study selected an optimal hydrogen peroxide concentration of 5%, which is capable of treating diesel oil contaminated soil following biodegradation without supplementary iron. Application of hydrogen peroxide by foam spraying increased the infiltration of hydrogen peroxide into the unsaturated soil. Surface foam spraying provided the aqueous phase of remediation agents evenly to the unsaturated soil and resulted in relatively similar soil water content throughout the soil. The easy and even infiltration of remediation reagents increased their contact with contaminants, resulting in enhanced oxidation and biodegradation. Fractional analysis of TPH showed C18-C22 present in diesel as biodegradation recalcitrant hydrocarbons. Recalcitrant hydrocarbons were reduced by 92% using oxidation-biodegradation serial foam, while biodegradation alone only reduced the recalcitrant fraction by 25%.

Treatment of PAH-contaminated soil using cement-activated persulfate

In this study, a novel method for the treatment of polycyclic aromatic hydrocarbon -contaminated soil using cement-activated persulfate was developed. The removal of PAHs in soil rose with increasing initial persulfate concentration, initial Portland cement (PC) concentration, and oxidation reaction time. At an initial persulfate and PC concentration of 19.20 mmol/kg and 10% of soil weight and a reaction time of 2 h, the removal rate of PAHs reached 57.3%. Residual PAHs were mainly adsorbed within the soil granules and thus became less available. The mechanism of PC facilitating the oxidation reaction was that PC addition can increase the pH and temperature of the system. When the soil was stabilized/solidified by 10% of PC, the leaching concentration of PAHs and TOC was significantly higher than that leached from untreated soil. Persulfate oxidation decreased the leaching concentration of PAHs but increased the leaching concentration of TOC in solidification/stabilization products. The addition of activated carbon can decrease the leaching concentrations of both PAHs and TOC. Freeze-thaw durability tests revealed that the leachability of PAHs was not affected by freeze-thaw cycles. The unconfined compressive strength (UCS) of treated soil samples after 12 freeze-thaw cycles was only 49.0% of that curing for 52 days, but the UCS was still > 1 MPa. The treated soil samples can resist disintegration during the process of freeze-thaw cycles.

Degradation of folic acid wastewater by electro-Fenton with three-dimensional electrode and its kinetic study

The three-dimensional electro-Fenton method was used in the folic acid wastewater pretreatment process. In this study, we researched the degradation of folic acid and the effects of different parameters such as the air sparging rate, current density, pH and reaction time on chemical oxygen demand (COD) removal in folic acid wastewater. A four-level and four-factor orthogonal test was designed and optimal reaction conditions to pretreat folic acid wastewater by three-dimensional electrode were determined: air sparge rate 0.75 l min^-1, current density 10.26 mA cm^-2, pH 5 and reaction time 90 min. Under these conditions, the removal of COD reached 94.87%. LC-MS results showed that the electro-Fenton method led to an initial folic acid decomposition into p-aminobenzoyl-glutamic acid (PGA) and xanthopterin (XA); then part of the XA was oxidized to pterine-6-carboxylic acid (PCA) and the remaining part of XA was converted to pterin and carbon dioxide. The kinetics analysis of the folic acid degradation process during pretreatment was carried out by using simulated folic acid wastewater, and it could be proved that the degradation of folic acid by using the three-dimensional electro-Fenton method was a second-order reaction process. This study provided a reference for industrial folic acid treatment.

Comprehensive review on toxicity of persistent organic pollutants from petroleum refinery waste and their degradation by microorganisms

Control and prevention of environmental pollution has become a worldwide issue of concern. Aromatic hydrocarbons including benzene, toluene, ethyl benzene, xylene (BTEX) and polyaromatic hydrocarbons (PAHs) are persistent organic pollutants (POPs), released into the environment mainly by exploration activities of petroleum industry. These pollutants are mutagenic, carcinogenic, immunotoxic and teratogenic to lower and higher forms of life i.e. microorganisms to humans. According to the International Agency for Research on Cancer (IARC) and United States Environmental Protection Agency (U.S. EPA), Benzo[a]pyrene (BaP) is carcinogenic in laboratory animals and humans. Aromatic hydrocarbons are highly lipid soluble and thus readily absorbed from environment in gastrointestinal tract of mammals. Treatment and remediation of petroleum refinery waste have been shown either to reduce or to eliminate genotoxicity of these pollutants. Bioremediation by using microorganisms to treat this waste is showing a promising technology as it is safe and cost-effective option among various technologies tested. The main aim of this review is to provide contemporary information on variety of aromatic hydrocarbons present in crude oil (with special focus to mono- and poly-aromatic hydrocarbons), exposure routes and their adverse effects on humans. This review also provides a synthesis of scientific literature on remediation technologies available for aromatic hydrocarbons, knowledge gaps and future research developments in this field.

Optimization of hydrogen peroxide-to-hemoglobin ratio for biocatalytic mineralization of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils

This study investigates the efficiency of hemoglobin (Hb)-catalyzed biocatalytic reactions for removal of polycyclic aromatic hydrocarbons (PAHs) in a historically PAHs-contaminated soil and of benzo(a)pyrene (BaP) in an artificially BaP-contaminated soil. PAHs removal tests at various H₂O₂-to-Hb mass ratios (0-3.7) showed that the PAHs removal was greater at H₂O₂-to-Hb mass ratio of ≥3. This was attributed to the greater removal of high molecular weight PAHs at higher H₂O₂-to-Hb mass ratios. The BaP removal increased from 36% to 85% with increasing H₂O₂-to-Hb mass ratio from 1 to 3, and further increase in H₂O₂-to-Hb mass ratio decreased the BaP removal. Thus, the optimal H₂O₂-to-Hb mass ratio for BaP removal was determined to be 3 in the artificially BaP-contaminated soil. The BaP removal in the presence of only Hb can be attributed to the capture of BaP by Hb. The increased BaP removal in the presence of H₂O₂ is likely due to BaP mineralization as the BaP removal and the CO₂ generated showed a strong positive correlation (R² = 0.999). Overall, this study shows that the Hb-catalyzed biocatalytic reactions can effectively remove PAHs in soil.

Remediation of water contaminated with diesel oil using a coupled process: Biological degradation followed by heterogeneous Fenton-like oxidation

The treatment of a synthetically prepared wastewater containing diesel oil has been investigated using combined treatment schemes based on the biological treatment followed by an advanced oxidation process. 78% of diesel oil was degraded by Acinetobacter venetianus in 96 h, while the removal efficiency of chemical oxygen demand (COD) in the aqueous phase was only 56.8%, indicating that degraded metabolites existed in solution. To solve this problem, a Fenton-like system consisting of nanoscale zero-valent iron (nZVI) and hydrogen peroxide was used for further oxidation of the metabolites after biodegradation. Results showed that the total COD removal increased from 56.8% to 89% under the optimal condition. In addition, effects of initial pH (2.0-9.0), ZVI dosage (0-2.0 g L-1), hydrogen peroxide (H₂O₂) dosage concentration (0-15 mmol L-1) and temperature (298-308 K) on the treatment efficiency of the combined process were studied. Scanning electron microscopy (SEM) demonstrated that changes to the surface of nZVI occurred. GC-MS revealed that the degraded metabolites were mineralized practically by nZVI/H₂O₂ system. The results points towards the potential of Fenton-like oxidation as a short post-treatment after a biological process for the treatment of organic pollutants in wastewater.

Effect of Fenton pre-oxidation on mobilization of nutrients and efficient subsequent bioremediation of crude oil-contaminated soil

Fenton pre-oxidation and a subsequent bioremediation phase of 80 days were used to investigate the importance of matching concentration of residual indigenous bacteria and nutrient levels on subsequent bioremediation of crude oil. Experiments were performed using either high (>10^7.7 ± 0.2 CFU/g soil) or low (<10^5.9 ± 0.1 CFU/g soil) concentrations of bacteria and three different nutrient levels: enough (C/N > 9.8), moderate (C/N:5-9.8), and lacking nutrient level (C/N < 5) conditions. Weak Fenton pre-oxidation (225 mM H₂O₂ and 2.9 mM Fe²⁺) resulted in highly matching between nutrient level and the population of residual indigenous bacteria. Up to 53% of total petroleum hydrocarbon (TPH) and 58% of main hydrocarbon (C₁₅C₂₅, during the first 10 days) were removed from the soil. Under matching conditions, the activity of indigenous bacteria and nutrient mobilization were enhanced, promoting the bioremediation of crude oil. In addition, the biodegradation of long chain molecules (C₂₆C₃₀) required a high level of NH₄⁺-N.

Remediation approaches for polycyclic aromatic hydrocarbons (PAHs) contaminated soils: Technological constraints, emerging trends and future directions

For more than a decade, the primary focus of environmental experts has been to adopt risk-based management approaches to cleanup PAH polluted sites that pose potentially destructive ecological consequences. This focus had led to the development of several physical, chemical, thermal and biological technologies that are widely implementable. Established remedial options available for treating PAH contaminated soils are incineration, thermal conduction, solvent extraction/soil washing, chemical oxidation, bioaugmentation, biostimulation, phytoremediation, composting/biopiles and bioreactors. Integrating physico-chemical and biological technologies is also widely practiced for better cleanup of PAH contaminated soils. Electrokinetic remediation, vermiremediation and biocatalyst assisted remediation are still at the development stage. Though several treatment methods to remediate PAH polluted soils currently exist, a comprehensive overview of all the available remediation technologies to date is necessary so that the right technology for field-level success is chosen. The objective of this review is to provide a critical overview in this respect, focusing only on the treatment options available for field soils and ignoring the spiked ones. The authors also propose the development of novel multifunctional green and sustainable systems like mixed cell culture system, biosurfactant flushing, transgenic approaches and nanoremediation in order to overcome the existing soil- contaminant- and microbial-associated technological limitations in tackling high molecular weight PAHs. The ultimate objective is to ensure the successful remediation of long-term PAH contaminated soils.

A Modified Approach for in Situ Chemical Oxidation Coupled to Biodegradation Enhances Light Nonaqueous Phase Liquid Source-Zone Remediation

Field and batch experiments were conducted to assess whether a modified approach for in situ chemical oxidation (ISCO) (with MgO₂ and Fe₂O₃ particles recovered from acid mine drainage treatment) can enhance LNAPL (light nonaqueous phase liquid) dissolution and produce bioavailable soluble compounds. This modified ISCO approach was coupled to biodegradation to further remove residual compounds by microbially mediated processes. Pure palm biodiesel (B100) was chosen to represent a poorly water-soluble compound that behaves like LNAPLs, and 100 L was released to a 2 m² area excavated down to the water table. A past adjacent B100-field experiment under natural attenuation was conducted as a baseline control. Results demonstrated the enhancement of organic compound dissolution and production of soluble compounds due to the modified in situ chemical oxidation. The slow release of H₂O₂ by MgO₂ decomposition (termed partial chemical oxidation) and production of soluble compounds allowed the stimulation of microbial growth and promoted a beneficial response in microbial communities involved in oxidized biodiesel compound biodegradation. This is the first field experiment to demonstrate that this modified ISCO approach coupled to biodegradation could be a feasible strategy for the removal of poorly water-soluble compounds (e.g., biodiesel) and prevent the long-term effects generally posed in source zones.

Electrochemical oxidation of the polycyclic aromatic hydrocarbons in polluted concrete of the residential buildings

Polycyclic aromatic hydrocarbons (PAH) have been listed by the United States Environmental Protection Agency (US EPA) and by the European Community as priority environmental pollutants. The removal of PAHs from soils, sediments and waste water has attracted attention of scientists and engineers for several decades. Electrochemical oxidation of PAH compounds in water, is receiving increasing attention, due to its convenience and simplicity. In this study we performed electrochemical oxidation of 16 EPA PAHs mixture in 10% NaCl aqueous solution in potentiostatic conditions, at voltage 1 V. Decrease of concentration of some individual PAHs, up to 70% referred to their starting concentration, after 60 min of electrolysis, was confirmed by UPLC/PDA analysis. In further work investigation was extrapolated to in situ removal of PAHs from concrete, as the medium where, to our knowledge, such way of PAH removal has not been investigated before. High concentrations of PAH contamination occurred in the concrete structure of the residential buildings in Belgrade in 2014. Application of DC voltage of 50 V between nickel and stainless steel electrodes packed in the concrete wall, moisturized with the 10% NaCl solution, led to considerable removal of the pollutants by oxidation process throughout the concrete.

Combination of Fenton processes and biotreatment for wastewater treatment and soil remediation

There is a continuously increasing worldwide concern for the development of wastewater and contaminated soil treatment technologies. Fenton processes and biological treatments have long been used as common technologies for treating wastewater and polluted soil but they still need to be modified because of some defects (high costs of Fenton process and long remediation time of biotreatments). This work first briefly introduced the Fenton technology and biotreatment, and then discussed the main considerations in the construction of a combined system. This review shows a critical overview of recent researches combining Fenton processes (as pre-treatment or post-treatment) with bioremediation for treatment of wastewater or polluted soil. We concluded that the combined treatment can be regarded as a novel and competitive technology. Furthermore, the outlook for potential applications of this combination in different polluted soil and wastewater, as well as the mechanism of combination was also discussed.

Physical-chemical evaluation of hydraulic fracturing chemicals in the context of produced water treatment

Produced water is a significant waste stream that can be treated and reused; however, the removal of production chemicals-such as those added in hydraulic fracturing-must be addressed. One motivation for treating and reusing produced water is that current disposal methods-typically consisting of deep well injection and percolation in infiltration pits-are being limited. Furthermore, oil and gas production often occurs in arid regions where there is demand for new water sources. In this paper, hydraulic fracturing chemical additive data from California are used as a case study where physical-chemical and biodegradation data are summarized and used to screen for appropriate produced water treatment technologies. The data indicate that hydraulic fracturing chemicals are largely treatable; however, data are missing for 24 of the 193 chemical additives identified. More than one-third of organic chemicals have data indicating biodegradability, suggesting biological treatment would be effective. Adsorption-based methods and partitioning of chemicals into oil for subsequent separation is expected to be effective for approximately one-third of chemicals. Volatilization-based treatment methods (e.g. air stripping) will only be effective for approximately 10% of chemicals. Reverse osmosis is a good catch-all with over 70% of organic chemicals expected to be removed efficiently. Other technologies such as electrocoagulation and advanced oxidation are promising but lack demonstration. Chemicals of most concern due to prevalence, toxicity, and lack of data include propargyl alcohol, 2-mercaptoethyl alcohol, tetrakis hydroxymethyl-phosphonium sulfate, thioglycolic acid, 2-bromo-3-nitrilopropionamide, formaldehyde polymers, polymers of acrylic acid, quaternary ammonium compounds, and surfactants (e.g. ethoxylated alcohols). Future studies should examine the fate of hydraulic fracturing chemicals in produced water treatment trains to demonstrate removal and clarify interactions between upstream and downstream processes.

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.

Novel insights into enhanced dewatering of waste activated sludge based on the durable and efficacious radical generating

This study aims to develop a high-efficiency radical oxidation process for enhancing the dewaterability of waste activated sludge (WAS). Radical scavenging studies combined with electron paramagnetic resonance (EPR) were carried out for the direct radical identification and effectiveness evaluation of radical oxidation. The results indicated that Fe(II)-activated CaO₂ can pose a superior effect on dewatering WAS due to its distinctive capacity of stable •OH production and the high reaction efficiency of regulated-released •OH with water-holding organics. The mechanism for the enhanced dewatering performance was also explored. The rupture of sludge colloidal flocs and the reduction of hydrophilic functional groups in loosely bound extracellular polymeric substances (LB-EPS) were found to be mainly responsible for the release of interstitial water and improved dewaterability, respectively. In addition, an inference about the relationship between interfacial water and zeta potential of different EPS fractions was established by the simultaneous measurement of the binding affinities of Ca²⁺ and Fe²⁺/Fe³⁺ for EPS and bound water content. All these results provide the direct evidence that Fe(II)-activated CaO₂ is a promising pretreatment reagent for sludge disposal.

IMPLICATIONS

Fe(II)-activated CaO₂ was first proposed to be highly effective in enhancing the dewaterability of waste activated sludge. Electron paramagnetic resonance (EPR) spectroscopy provided the direct evidence for the specific advantages of CaO₂, especially the capacity of durable and efficacious •OH production leading to the excellent conditioning performance.

Improved treatment approach for the removal of aromatic compounds using polymeric beads in Fenton pretreatment and biological oxidation

An improved approach based on the use of iron-doped polymeric beads (IPB) as Fenton catalyst in the pretreatment and biomass-doped polymeric bead (BPB) in the biological oxidation has been reported for the removal of different aromatic mixtures present as pollutants in the aqueous solutions. Degradation has been investigated at fixed loading of IPB as 2.5 % weight basis and varying loading of hydrogen peroxide so as to understand the effect of oxidant loading on the extent of degradation. It has been observed that the maximum removal efficiency as 75.5, 81.4, and 59.1 % was obtained for the benzene-toluene-naphthalene-xylene (BTNX), benzene-toluene-ethylbenzene-xylene (BTEX), and benzene-toluene-naphthalene-p-nitrophenol (BTNp-NP) mixtures, respectively, at a 40-min pretreatment and optimum pH of 3.5. The biodegradability index was also observed in the favorable range of 0.4 to 0.5 after the pretreatment at optimum H₂O₂ loading of 1.5 g L^-1. Maximum COD removal efficiency of 99.2, 99.3, and 99.6 % was obtained using the biological oxidation treatment for 40 h for the case of BTNX, BTEX, and BTNp-NP mixtures, respectively. Analysis of kinetic models revealed that degradation followed three distinct stages based on fitting of the three-stage model and BPB was found to be more efficient as compared to the primary activated sludge (PAS) and modified activated sludge (MAS). Reusability studies confirmed that both IPB and BPB were effective over many cycles giving stable performance during degradation without leaching of Fe³⁺ ions into the solution.

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.

Oxidation of disinfectants with Cl-substituted structure by a Fenton-like system Cu(2+)/H2O2 and analysis on their structure-reactivity relationship

As widely used chemicals intended to protect human being from infection of microorganisms, disinfectants are ubiquitous in the environment. Among them chlorine-substituted phenol is a basic structure in many disinfectant molecules. Removal of these pollutants from wastewater is of great concern. The oxidative degradation of antimicrobial agents such as triclosan, chlorofene, and dichlorofene by a Fenton-like system Cu(2+)/H2O2 was examined. Reaction conditions such as temperature, initial concentrations of H2O2 and Cu(2+), and pH were optimized using triclosan as a representative. The degradation kinetics of the above disinfectants followed pseudo-first-order kinetics under the investigated conditions. Fourteen chlorophenols (CPs) with different chlorine substitution were also studied to evaluate the influence of molecular structure on the degradation process in the Cu(2+)/H2O2 system. Fourteen structure-related parameters were calculated using Gaussian 09 program. A quantitative structure-activity relationship (QSAR) model was established using SPSS software with measured rate constant (k) as dependent variable and calculated molecular descriptors as independent variables. A three-parameter model including energy of HOMO (E homo), molar heat capacity at constant volume (Cv(θ)), and the most positive net charge of hydrogen atoms (qH(+)) was selected for k prediction, with correlation coefficient R(2) = 0.878. Analyses of the model demonstrated that the Cv(θ) was the most significant factor affecting the k of chlorophenols. Variance analysis and standard t-value test were used to validate the model.

Coupling chemical oxidation and biostimulation: Effects on the natural attenuation capacity and resilience of the native microbial community in alkylbenzene-polluted soil

Coupling chemical oxidation with bioremediation could be a cost-effective system to cope with soil and groundwater pollution. However, the effects of chemical oxidation on autochthonous microbial communities are scarcely known. A detailed analysis that considers both the efficiency of the two technologies and the response of the microbial communities was performed on a linear alkylbenzene-polluted soil and groundwater samples. The impacts of a modified Fenton's reaction (MFR) at various dosages and of permanganate on the microbiota over 4 weeks were assessed. The permanganate and MFR negatively affected microbial abundance and activity. However, the resilience of certain microbial populations was observed, with a final increase in potential hydrocarbon-degrading populations as determined by both the alkB gene abundance and the predominance of well-known hydrocarbon-degrading phylotypes such as Rhodococcus, Ochrobactrum, Acinetobacter and Cupriavidus genera as determined by 16S rRNA-based DGGE fingerprinting. The assessment of the chemical oxidant impact on autochthonous microbiota should be considered for the optimization of coupled field remediation technologies.

Distribution, partition and removal of polycyclic aromatic hydrocarbons (PAHs) during coking wastewater treatment processes

In this study, we report the performance of a full-scale conventional activated sludge (A-O1-O2) treatment in eliminating polycyclic aromatic hydrocarbons (PAHs). Both aqueous and solid phases along with the coking wastewater treatment processes were analyzed for the presence of 18 PAHs. It was found that the target compounds occurred widely in raw coking wastewater, treated effluent and sludge samples. In the coking wastewater treatment system, 4-5 ring PAHs were the dominant compounds, while 4 rings PAHs predominated in the sludge samples. Over 98% of the PAH removal was achieved in the coking wastewater treatment plant (WWTP), with the total concentration of PAHs being 21.3 ± 1.9 μg L(-1) in the final effluent. During the coking wastewater treatment processes, the association of the lower molecular weight PAH with suspended solids was generally less than 60%, while the association of higher molecular weight PAHs was greater than 90%. High distribution efficiencies (Kdp and Kds) were found, suggesting that adsorption was the potential removal pathway of PAHs. Finally, the mass balances of PAHs in various stages of the coking WWTP were obtained, and the results indicated that adsorption to sludge was the main removal pathway for PAHs in the coking wastewater treatment processes.