Elimination Of Polycyclic Aromatic Hydrocarbons Research Articles

Efficiency of Hydrogen Peroxide and Fenton Reagent for Polycyclic Aromatic Hydrocarbon Degradation in Contaminated Soil: Insights from Experimental and Predictive Modeling

This study investigates the degradation kinetics of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil using hydrogen peroxide (H2O2) and the Fenton process (H2O2/Fe2+). The effect of oxidant concentration and the Fenton molar ratio on PAH decomposition efficiency is examined. Results reveal that increasing H2O2 concentration above 25 mmol/samples leads to a slight increase in the rate constants for both first- and second-order reactions. The Fenton process demonstrates higher efficiency in PAH degradation compared to H2O2 alone, achieving decomposition yields ranging from 84.7% to 99.9%. pH evolution during the oxidation process influences PAH degradation, with alkaline conditions favoring lower elimination rates. Fourier-transform infrared (FTIR) spectroscopy analysis indicates significant elimination of PAHs after treatment, with both oxidants showing comparable efficacy in complete hydrocarbon degradation. The mechanisms of PAH degradation by H2O2 and the Fenton process involve hydroxyl radical formation, with the latter exhibiting greater efficiency due to Fe2+ catalysis. Gaussian process regression (GPR) modeling accurately predicts reduced concentration, with optimized ARD-Exponential kernel function demonstrating superior performance. The Improved Grey Wolf Optimizer algorithm facilitates optimization of reaction conditions, yielding a high degree of agreement between experimental and predicted values. A MATLAB 2022b interface is developed for efficient optimization and prediction of C/C0, a critical parameter in PAH degradation studies. This integrated approach offers insights into optimizing the efficiency of oxidant-based PAH remediation techniques, with potential applications in contaminated soil remediation.

Greenery planning for urban air pollution control based on biomonitoring potential: Explicit emphasis on foliar accumulation of particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs)

In this study, efficiencies of eight indigenous plants of Baishnabghata Patuli Township (BPT), southeast Kolkata, India, were explored as green barrier species and potentials of plant leaves were exploited for biomonitoring of particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs). The present work focused on studying PM capturing abilities (539.32−2766.27 μg cm−2) of plants (T. divaricata, N. oleander and B. acuminata being the most efficient species in retaining PM) along with the estimation of foliar contents of PM adhered to leaf surfaces (total sPM (large + coarse): 526.59−2731.76 μg cm−2) and embedded within waxes (total wPM (large + coarse): 8.73−34.51 μg cm−2). SEM imaging used to analyse leaf surfaces affirmed the presence of innate corrugated microstructures as main drivers for particle capture. Accumulation capacities of PAHs of vehicular origin (total index, TI > 4) were compared among the species based on measured concentrations (159.92−393.01 μg g−1) which indicated T. divaricata, P. alba and N. cadamba as highest PAHs accumulators. Specific leaf area (SLA) of plants (71.01−376.79 cm2 g−1), a measure of canopy−atmosphere interface, had great relevance in PAHs diffusion. Relative contribution (>90%) of 4–6 ring PAHs to total carcinogenic equivalent and potential as well as 5−6 ring PAHs to total mutagenic equivalent and potential had also been viewed with respect to benzo[a]pyrene. In−depth analysis of foliar traits and adoption of plant−based ranking strategies (air pollution tolerance index (APTI) and anticipated performance index (API)) provided a rationale for green belting. Each of the naturally selected plant species showed evidences of adaptations during abiotic stress to maximize survival and filtering effects for reductive elimination of ambient PM and PAHs, allowing holistic management of green spaces.

Mycoremediation Approach to Green Air: Phenanthrene and Anthracene Degrading Ability by Fusarium solani Isolate P11M-46

There are many health issues associated with air pollution that are rapidly increasing with time across the globe. Among many air pollutants, polycyclic aromatic hydrocarbons (PAHs) are of particular concern because of their carcinogenicity, genotoxicity, and long persistence in the environment. The majority of these PAHs release into the air through anthropogenic activities and natural sources. After releasing into the air, PAHs usually return to the ground due to their high molecular weight. These hydrocarbon depositions can be categorized as wet or dry depositions. One of the most prominent deposition surfaces of these pollutants is the phyllosphere. Microorganisms such as fungi perform a key role in PAHs elimination through bioremediation processes. Epiphytic fungi such as Fusarium solani isolate P11M-46 utilizes the deposited phenanthrene and anthracene on the phyllosphere and convert those PAHs in to non-toxic levels. The aim of this study was to evaluate the ability of F. solani isolate P11M-46 to degrade phenanthrene and anthracene, through a mycoremediation approach. Leaf samples were collected from Panchikawatta, Orugodawatta, Pettah, Maradana, Colombo Fort, and Sapugaskanda urban areas in Sri Lanka. Furthermore, PAH degradation ability of isolated F. solani isolate P11M-46 was confirmed through High Performance Liquid Chromatography (HPLC). The effects of by-products produced from the biodegradation process on living beings were evaluated using Artemia salina and the by-products were identified using Gas Chromatography and Mass Spectrometry (GCMS). According to HPLC results, F. solani isolate P11M-46 showed 68% of degradation percentage in phenanthrene while exhibiting 76% degradation in anthracene within 6 days. The GCMS analysis confirmed that the by-products were Phenol, 2-(phenylmethyl) from phenanthrene and 9, 10-anthracenedione from anthracene. Toxicity assay with A. salina confirmed that these byproducts were not toxic to the phyllosphere. The findings of the present study revealed the potential use of phyllosphere F. solani isolate P11M-46 in the remediation of environmental pollutants phenanthrene and anthracene. And also the by-products produced during their degradation mechanism were also confirmed as nontoxic compounds. Therefore, F. solani isolate P11M-46 could be effectively used in the bioremediation of phenanthrene and anthracene in polluted environments as a bioremediator. 
 Keywords: Polycyclic aromatic hydrocarbons, Bioremediation, HPLC, GCMS, Toxicity

Effects of Exposure Timing on cyp1a Expression, PAH Elimination, and Lipid Utilization in Lumpfish Embryos Exposed to Produced Water.

Intentional discharges of produced water from oil production platforms to the marine environment contain a complex mixture of toxicants, including polycyclic aromatic hydrocarbons (PAHs). Early life stages of fish are highly sensitive to petrogenic exposure, and short-term exposure during critical periods of embryonic development may have detrimental effects on larvae health and survival. However, why different periods are more sensitive to exposure than others are not fully understood. Three identical exposure experiments (48 h, approx. 30 μg/L tPAH, sum 42 PAHs) on lumpfish (Cyclopterus lumpus) embryos were conducted where only exposure timing was varied: 0-48 h post fertilization (hpf, starting before chorion hardening), 36-84 hpf (starting after chorion hardening), and 240-288 hpf (during organogenesis). Total PAH (tPAH) uptake at the end of exposure was 5× higher when exposed during fertilization than when exposed late (during organogenesis). The first evidence of cyp1a induction in lumpfish during embryogenesis was observed after 84 hpf. Early exposure affected lipid droplet coagulation, indicating altered lipid utilization during embryogenesis. Although no significant impacts of exposure were observed on hatching success, hatching was delayed when exposed at the latest time point. This study shows that chorion properties, lipid content, biotransformation potential, and timing of produced water exposure during lumpfish embryogenesis affected PAH uptake and elimination.

Isolation and characterization of bacteria with potential naphthalene-degradation form “La Escondida” lagoon, Reynosa, Mexico

Bioremediation, is currently one of the most studied techniques for the elimination of polycyclic aromatic hydrocarbons in soils. However, in order to have a more efficient degradation process, the use of autochthonous bacteria from the contaminated region is recommended because these bacteria are adapted to the climatic and environmental conditions of the site to be remedied. The aim of this work was to isolate and characterize bacteria strains from the city of Reynosa, Mexico, with the potential to degrade naphthalene. Strain isolation was carried out whit soil samples from the shore of“La Escondida” lagoon, a former landfill of pollutants of the petrochemical industry. The isolates were subjected to the emulsion index test as a selective factor to later evaluate their effect in the drop collapse, drop displacement and naphthalene tolerance tests. Finally, sixty-two strains were identified by amplification of the 16S rRNA gene. Ten strains showed the best values in the drop collapse, oil displacement and naphthalene tolerance tests. Four strains had the best naphthalene degradation potential; Pseudomonas aeruginosa (1P2 and 5P2), Bacillus cereus (5S1) and Bacillus subtillis (P52). A degradation of naphthalene was observed in the IR spectrum and UPLC chromatogram after 12 days by 1P2 strain.

Fate of organic pollutants in sewage sludge during thermal treatments: Elimination of PCBs, PAHs, and PPCPs

The use of biochar and hydrochar, the solid by-product from thermal treatments of biomass, as organic soil fertilizers is becoming increasingly popular. However, few studies have examined the fate of organic pollutants in these organic amendments such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals and personal care products (PPCPs). In this study, we investigated pyrolysis process and hydrothermal carbonization (HTC) as promising methods to treat organic pollutants in two raw sludges (stabilized sewage sludge and sludge cake). Biochars (pyrolysis temperatures of 450 °C and 600 °C) and hydrochars (HTC temperature of 180 °C) produced from two raw sludges, and resulting chars were analyzed for the presence of three organic pollutants groups including PCBs, PAHs, PPCPs. During the HTC process, the reduction in concentration of pharmaceuticals was higher than the other groups. Most of these compounds were removed during the pyrolysis process at 450 °C, however; at 600 °C (≥99.9%) all organic pollutants were removed from the produced biochars. These results confirm the usefulness of a pyrolysis process at above 600 °C for the elimination of organic pollutants from biochars to produce chars with little or no organic pollutants as a safe amendment to improve degraded soils.

Microbial communication during bioremediation of polyaromatic hydrocarbons

Human activity pollution has been shown to harm the environment, ecology, and health impacts. The polycyclic aromatic hydrocarbons (PAHs) produced by the industries such as tannery, distillery, pulp paper, and oil refineries are a major source of contaminant. PAHs are found all across the world, owing to long-term human pollution sources. PAHs' physico-chemical features, such as hydrophobicity and electrochemical stability, contribute to their environmental persistence and contribute to their carcinogenic and health effects. Numerous analytical and biological techniques for the qualitative and quantitative assessment of PAHs have been proposed. Bioaccumulation, adsorption, chemical oxidation, photolysis, volatilization, and microbiological degradation are the principal breakdown pathways of PAHs in the environment. Microbial populations, such as bacteria, fungi, and algae, play a crucial role in the biological elimination of PAHs. Oxidase, manganese peroxidases, lipases, and laccases are the enzymes involved in PAHs breakdown. The synthesis of surfactants by bacteria increases PAHs bioavailability and improves the elimination process of PAHs. Temperature, pH, aeration, moisture content, nutrition availability, absence of hazardous chemicals, and the kind and number of degrading microbial populations are all factors that influence PAHs decomposition. Microbial degradation mechanisms result in intermediate metabolites and carbon dioxide mineralization. The elimination of PAHs is improved by molecular approaches such as gene engineering and protein engineering. This review discussed the benefits of bioremediation strategies that were investigated for precise evaluation and were trusted at both the regulatory and scientific studies levels.

A comprehensive study on simultaneous enhancement of sludge dewaterability and elimination of polycyclic aromatic hydrocarbons by Fe2+ catalyzing O3 process

Simultaneous removal of polycyclic aromatic hydrocarbons (PAHs) in the process of enhancement of sludge dewaterability via oxidation of hydroxyl radicals (•OH) and flocculation of Fe3+ by Fe2+-catalyzing O3 were investigated as a novel research focus. The results showed that capillary suction time (CST) and water content of dewatered sludge cake (Wc) were reduced from 57.9 s and 85.1% to 13.6 s and 69.65% under the optimum usage of 60 mg/g dry solids (DS) O3 and 80 mg/g DS FeSO4, respectively. The relevant dewatering mechanism of Fe2+-catalyzing O3 treatment was elucidated. It was found that extracellular polymeric substances-bound (EPS-bound) and intracellular water was dramatically released through destroying sludge cells and EPS gel-like structure by produced •OH. In addition, the results of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and 13C NMR spectroscopy revealed that •OH oxidized and mineralized hydrophilic organic matters intensifying hydrophobicity of sludge surface. Moreover, Fe3+ generated by oxidation of Fe2+ agglomerated fragmented fine particles into large aggregates and decreased exposure of hydrophilic sites by neutralizing negative charge, which promoted water-solids separation. Meanwhile, sludge surface roughness was decreased which was determined by material type upright confocal laser microscope (CLM). As a consequence, •OH and Fe3+ were mainly responsible for enhancement of sludge dewaterability. Moreover, more than 40% of removal rate of PAHs was accomplished by Fe2+-catalyzed O3 treatment mitigating the environmental risks of PAHs spread.

Influence of sludge organic matter on elimination of polycyclic aromatic hydrocarbons (PAHs) from waste activated sludge by ozonation: Controversy over aromatic compounds

Ozonation has been widely used as a viable advanced oxidation process (AOP) for elimination of PAHs in waste activated sludge through effective sludge disintegration and abatement of organic pollutants. However, sludge organic matter (SOM) influences PAHs degradation during ozone treatment is still rarely understood. In this study, we investigated such an influence with the aid of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and the corresponding two-dimensional correlation analysis (2D-COS) strategy. The results showed that the degradation of SOM macromolecules in the order of aromatic substances > aliphatic carbon > α carbon > amides groups > O-alkyl upon ozone treatment. Moreover, the PAHs removal efficiency was positively correlated with the aromaticity of sludge (R2 = 0.84–0.98), while negative associated with its aliphaticity (R2 = 0.81–0.95). Lastly, humic acid (HA) was used as a proxy of aromatic SOM to further explore their interaction with PAHs in sludge matrix. The results revealed that freely dissolved (HA-D) and suspended particulates (HA-S) imposed distinctively different influence on ozone-based PAHs degradation. The HA-S facilitated the elimination of PAHs by 7.95 ± 0.11%, while those HA-D reduced the removal efficiency by 16.70 ± 0.13%.

Improvement of the Rhizoremediation efficiency of PAHs contaminated soil under cysteine treatment along with modeling

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of pollutants with mutagenic and carcinogenic properties. This study aimed to assess the effects of cysteine on the growth and resistance of the Festuca plant against PAHs-induced stress. The experiment was designed in six different groups and included control, contaminated soil with pyrene (Py) and phenanthrene (Phe) (200, 300, and 400 mg kg−1), and supplementation with cysteine (100, 200 mg L-1), all with or without the cultivation of Festuca grass. During the two 45- and 90-day periods, changes in the population of bacteria, the activity of soil enzymes: dehydrogenase (DHA) and peroxidase (POD), and the level of pyrene and phenanthrene removal were investigated. Furthermore, the Response Surface Methodology (RSM) model was also applied to determine the relationships between input and response parameters. Then, using the sensitivity analysis by Monte Carlo simulation, the effect of the examined parameters on the response parameters was determined. The results demonstrated that cysteine supplementation, along with Festuca cultivation, increased the number of bacteria, improved the activity of enzymes, and elevated the elimination of PAHs (p-value < 0.05).

Utilization of activated carbon derived from waste plastic for decontamination of polycyclic aromatic hydrocarbons laden wastewater.

Serious environmental deterioration caused by synthetic waste plastics, and the pollution of freshwater resources are the most alarming and marked challenges of the 21st century. Therefore, immense scientific efforts are being made towards the management of waste plastics and treatment of polluted water. The current study reports on the utilization of waste polyethylene terephthalate (wPET) and waste polystyrene (wPS) for fabrication of activated carbon (AC) and its application for the removal of hazardous polycyclic aromatic hydrocarbons (PAHs) pollutants from water. AC was prepared from wPET and wPS by carbonization under a N2 atmosphere followed by chemical activation with 1 M KOH and 1 M HCl. The AC was characterized by scanning electron microscopy, surface area analysis, and Fourier transform infrared spectroscopy. Adsorption of PAHs from aqueous solutions through AC was examined by batch adsorption tests. The optimum parameters for maximum adsorption of PAHs were found to be: initial PAHs concentration 40 ppm, 2 h contact time, pH 3, 5, and 7, 50 °C temperature and adsorbent dose of 0.8 g. Kinetic and isotherm models were applied to evaluate the adsorbent capacity for PAHs adsorption. The kinetic study shows that the adsorption of these PAHs onto AC follows pseudo-second-order kinetics. The experimental results demonstrated that the Langmuir isotherm model best fitted the data. The thermodynamic factors calculated such as entropy change (ΔS°), enthalpy change (ΔS°) and free energy change (ΔG°) show that the adsorption process is non-spontaneous and endothermic in nature. Results were also compared with the efficiencies of some commercial adsorbents used in practice. This examination revealed that the novel plastic-derived AC possesses a great potential for elimination and recovery of PAH elimination from industrial wastewater.

Enhancement and analysis of Anthracene degradation by Tween 80 in LMS-HOBt

This study examines the specific effect of Tween 80 on the conversion of anthracene (ANT) in laccase medium system regarding surfactant chemical changes and mechanism. The conversion rate and degradation products of ANT were investigated in different concentrations of Tween 80 solution. Between Tween 80 concentration 0–40 critical micelle concentrations (CMC), the kinetic parameter-k (h−1) and corresponding half-life T1/2 decreased with increasing concentration. When Tween 80 was above 20 CMC the laccase-medium system converted > 95% of ANT to anthraquinone within 12 h. During the entire enzymatic reaction, the laccase activity in the system increased with increasing Tween 80 concentration. Combined with GC/MS analysis of the product, it was speculated that hydrogens belonging to the ether-oxygen bond and carbon–carbon double bond α-CH of Tween 80, were removed by the laccase-media system, promoting its degradation. Additionally, enhanced activity caused by oxygen free radicals (ROS) such as RO• and ROO•, continuously oxidized Tween 80, which in turn produced free radicals while converting ANT. This study provides new theoretical support toward the application of surfactants in the elimination of polycyclic aromatic hydrocarbons.

Microbial community structure and co-occurrence are essential for methanogenesis and its contribution to phenanthrene degradation in paddy soil

Although polycyclic aromatic hydrocarbons (PAHs) degradation under methanogenesis is an ideal approach to remediating PAH-polluted soil, the contribution of methanogenesis to soil PAH elimination and the relationships between microbial ecological characteristics and PAH degradation during this process remain unclear. Here, we conducted a short-term (60 days) incubation using a paddy soil amended with phenanthrene and examined the effects of a specific methanogenic inhibitor (2-bromoethanesulfonate, BES) on this process. As treatment assessments, the methane production activity (MPA), phenanthrene degradation rate (PDR), and microbial ecological characteristics were determined. The results indicated that BES significantly inhibited both soil MPA and PDR, and we detected a positive relationship between MPA and PDR. Furthermore, BES significantly altered the soil microbial community structure, and it was the microbial community structure but not α-diversity was significantly correlated with soil MPA and PDR. BES decentralized the co-occurrence of bacterial genera but intensified the co-occurrence of methanogens. Moreover, certain bacterial taxa, including Bacteroidetes-vadinHA17, Gemmatimonas, and Sporomusaceae, were responsible for the MPA and PDR in this paddy soil. Collectively, these findings confirm the role of methanogenesis in PAH elimination from paddy soil, and reveal the importance of microbial co-occurrence characteristics in the determination of soil MPA and pollutant metabolism.

Toxicity evaluation of the metabolites derived from the degradation of phenanthrene by one of a soil ubiquitous PAHs-degrading strain Rhodococcus qingshengii FF

Rhodococcus qingshengii strain FF is a soil ubiquitous strain that has a high polycyclic aromatic hydrocarbons (PAHs) biodegradation capability. In this work, phenanthrene was used as a PAH model compound. The accumulated pattern of the metabolites of phenanthrene by strain FF was investigated, and their toxicity to Vibrio fischeri, effect on microbiota diversity of farmland soil and influence on seed of wheat were evaluated. Total of 29 main intermediates were observed for the phenanthrene degradation process. Pyrogallol was the predominant accumulated metabolite, and 59% of the accumulated metabolites were oxygen-containing PAHs that have only one benzene ring. The acute toxicity assessment showed the accumulated metabolites in later phase were more toxic to Vibrio fischeri. Microbe and wheat seed response to the different stages of phenanthrene metabolites indicated pollution significantly decreased microbial richness and evenness of farmland soil and lower germinal length, root length or root number of wheat seed. These results indicated that not only the elimination of PAHs, but also the easily accumulated metabolites produced during the PAHs degradation process should be paid enough attention. The comprehensive evaluation of toxicity during the degradation process would provide useful information for the use of microbe-orientated strategies in PAHs bioremediation.

Effects of organic matter addition on chronically hydrocarbon-contaminated soil.

Soil is the recipient of organic pollutants as a consequence of anthropogenic activities. Hydrocarbons are contaminants that pose a risk to human and environmental health. Bioremediation of aging contaminated soils is a challenge due to the low biodegradability of contaminants as a result of their interaction with the soil matrix. The aim of this work was to evaluate the effect of both composting and the addition of mature compost on a soil chronically contaminated with hydrocarbons, focusing mainly on the recovery of soil functions and transformations of the soil matrix as well as microbial community shifts. The initial pollution level was 214ppm of polycyclic aromatic hydrocarbons (PAHs) and 2500ppm of aliphatic hydrocarbons (AHs). Composting and compost addition produced changes on soil matrix that promoted the release of PAHs (5.7 and 15 % respectively) but not the net PAH elimination. Interestingly, composting stimulated AHs elimination (about 24 %). The lack of PAHs elimination could be attributed to the insufficient PAHs content to stimulate the microbial degrading capacity, and the preferential consumption of easily absorbed C sources by the bacterial community. Despite the low PAH catabolic potential of the aging soil, metabolic shift was driven by the addition of organic matter, which could be monitored by the ratio of Proteobacteria to Actinobacteria combined with E4/E6 ratio. Regarding the quality of the soil, the nutrients provided by the exogenous organic matter contributed to the recovery of the global functions and species diversity of the soil along with the reduction of phytotoxicity.

Towards efficient elimination of polycyclic aromatic hydrocarbons (PAHs) from waste activated sludge by ozonation

Sewage sludge is one of the sinks for PAHs accumulation and concerns are growing regarding the environmental risk of the discharge of PAHs in waste activated sludge (WAS) as a major byproduct of sewage treatment. Here, we evaluated the effectiveness of ozone treatment to eliminate the 16 priority PAHs in WAS. The PAHs removal efficiency increased with ozone dosage and was strongly pH dependent. Even at ozone dosage of 40 mg O3·g−1, the PAHs removal efficiency at pH 9.0 (44.5%) was significantly higher than that observed at pH 5.0 and 200 mg O3·g−1 (41.7%). The pH-dependent elimination behavior of PAHs was attributed to the varying yield of hydroxyl radicals (OH) and degree of sludge disintegration (R2 = 0.88–0.92). Over 96% of the PAHs were in the particulate flocs (PF) phase, while the fraction bound to the freely dissolved (FS) and dissolved and colloidal (DC) matters was negligible, indicating the need of WAS disintegration during ozonation to make PAHs more accessible to O3 molecules and OH to initiate oxidation reactions. Failure of the three-compartment model to describe the PAHs sorption behavior in sludge matrix during ozonation implied that oxidation reaction occurred simultaneously with the partitioning of PAHs from PS to DC/FS fraction. Lastly, the results of the intermittent ozonation experiment demonstrated the interference of soluble organic compounds during PAHs degradation, particularly proteins and humic substances, as O3 and OH scavengers. At ozone dosage of 120 mg O3·g−1 (pH 9.0), the PAHs removal efficiency was improved by 19.5% by intermittent ozonation, as compared to continuous ozonation under the same conditions.

Backward modeling of urinary test reliability for assessing PAH health risks: An approximation solution for naphthalene.

Urine sample tests are one of the most common methods of estimating human exposure to polycyclic aromatic hydrocarbons (PAHs) and assessing population health risks. To evaluate the reliability of the urine test and the impact of other PAH elimination routes on the health risk estimated by this test, we proposed a backward modeling framework integrating other common elimination routes of PAH metabolites to calculate the overall intake rate of the parent PAH based on the levels of corresponding main metabolites in urine. Due to limited biotransformation data, we selected naphthalene as an example to evaluate model performance and collected urine samples from 234 random adults in Shenzhen. The overall intake rates of naphthalene were then simulated and compared to current literature data. The simulated intake rates of naphthalene ranged from 3.70×10-3mgd-1 to 1.95mgd-1 and followed a lognormal distribution with a median value of 6.51×10-2mgd-1. The results indicated that, if naphthalene exposure occurred only via food for the population of Shenzhen, the literature data fell within the most frequent interval [3.70×10-3, 4.45×10-2] but were lower than the simulated median value. However, if other exposure routes were considered, the allocation factor-adjusted literature data were close to the simulated median values. In addition, under normal physiological conditions, the simulated results were more sensitive to 1-hydroxynaphthalene (1-OHN) and 2-hydroxynaphthalene (2-OHN) levels in urine than other biometric variables, which is due to the limited load of 1-OHN and 2-OHN in human elimination routes. Furthermore, the suggested safety levels of 1-OHN and 2-OHN in urine to protect 99% of the general population of Shenzhen were 6.40×10-6 and 3.75×10-5mgL-1, which could be used as regulatory indicators based on the high reliability of the model.

Enhanced degradation of polycyclic aromatic hydrocarbons in aged subsurface soil using integrated persulfate oxidation and anoxic biodegradation

Coupling chemical oxidation and biodegradation to remediate polycyclic aromatic hydrocarbons (PAHs) contaminated soil has gained great attention in recent decades. However, there remains a knowledge gap concerning the integration of persulfate oxidation and anoxic biodegradation of PAHs in subsurface soil. In this study, the potential of integrated persulfate oxidation and anoxic biodegradation of PAHs in aged subsurface soil are investigated. Dynamic changes in the soil bacterial abundance and community composition are also examined. The soil bacterial abundance and community composition were negatively influenced following the application of different dosages of persulfate (e.g., 1% and 3% (wt/wt)), but these were found to be gradually restored after the depletion of persulfate. The bacteria that were capable of degrading PAHs under anoxic conditions were predominated by the phyla Proteobacteria and Firmicutes. The results also indicated an increasing trend in Firmicutes and a decreasing trend in Proteobacteria with increasing dosages of persulfate applied to the soil. The observations also suggested that the elimination of PAHs was primarily attributed to persulfate oxidation in the soil that received 3% (wt/wt) persulfate. However, persulfate oxidation and anoxic biodegradation were both responsible for the abatement of PAHs in the soil when 1% (wt/wt) of persulfate was applied. In addition, in the successful treatment (1% (wt/wt) persulfate), the integrated treatment was more effective in PAH removal than either one alone. The results of this study imply that integrated persulfate and anoxic biodegradation may be a promising alternative for the remediation of PAH contaminated subsurface soil.

Co-treatment of an oily sludge and aged contaminated soil: permanganate oxidation followed by bioremediation

The bioremediation of an oily sludge (321 ± 30 mg of polycyclic aromatic hydrocarbons/kgDRY SLUDGE and 13420 ± 1300 mg of aliphatic hydrocarbons/kgDRY SLUDGE) by mixture with contaminated soil (23 ± 2 mg of polycyclic aromatic hydrocarbons/kgDRY SOIL and 98 ± 10 mg of aliphatic hydrocarbons/kgDRY SOIL) was studied. Furthermore, the effect of oxidative pretreatments (persulfate and permanganate) on the performance of the global process was examined.The treatments reached contamination levels lower than the original residues, indicating the presence of synergic processes between a highly contaminated sludge and soil with a selected hydrocarbon-degrading community.Pretreatment with permanganate significantly improved biodegradation, possibly due to the increase in bioavailability and biodegradability of petroleum hydrocarbons. Two months of incubation was enough to reach the complete elimination of polycyclic aromatic hydrocarbons and 92% elimination of aliphatic hydrocarbons. Monitoring using five parameters (concentration of total petroleum hydrocarbons, total cultivable heterotrophic bacteria count, lipase and dehydrogenase activities, and polycyclic aromatic hydrocarbon-degrading bacteria count) as an approach for a preliminary scanning of the effectiveness of a treatment is proposed based on principal components analysis.

Exploring the effect of composting technologies on the recovery of hydrocarbon contaminated soil post chemical oxidative treatment

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants that contaminate large areas. They are mainly released to environment by anthropogenic activities principally due to the petrochemical industry. The low biodegradation rate characteristic of PAHs in aged contaminated soils could be overcome trough the chemical oxidation. In this study, composting with the soil and stimulation with mature compost were the strategies applied in soil microcosms after chemical oxidation with ammonium persulfate in a PAHs chronically contaminated soil.A 29% of PAHs elimination and an increase of their bioavailability were found after chemical oxidation with ammonium persulfate. Due to the oxidative treatment the total bacterial and the gram-positive population PAH dioxygenase genes were significantly reduced and no gram-negative PAHs degraders were detected.The following application of organic amendments produced a higher increase in total bacteria and recovery of the degrading population of GP PAH after one year of treatment, in comparison with the pre-oxidized soil bioremediation, only promoted by irrigation and aeration. Also a significant increase in the content of bioavailable PAHs was observed. However, from both composting strategies only the stimulation with mature compost led to a net PAHs removal. Taking into account the residual dissolved total carbon and humification degree (E4/E6 ratio), it was attributed to the preferential consumption of more easily degradable compounds than hydrocarbons the low removal efficiency observed after one year of treatment.Due to the high bioavailable content of PAH and the residual sulfate, long-term treatments will require careful monitoring to reduce environmental risks.