Desorption Of Polycyclic Aromatic Hydrocarbons Research Articles

Large-scale soil application of hydrochar: Reducing its polycyclic aromatic hydrocarbon content and toxicity by heating

The beneficial roles of hydrochar in carbon sequestration and soil improvement are widely accepted. Despite few available reports regarding polycyclic aromatic hydrocarbons (PAHs) generated during preparation, their potential negative impacts on ecosystems remain a concern. A heating treatment method was employed in this study for rapidly removing PAHs and reducing the toxicity of corn stover-based hydrochar (CHC). The result showed total PAHs content (∑PAH) decreased and then sharply increased within the temperature range from 150 °C to 400 °C. The ∑PAH and related toxicity in CHC decreased by more than 80% under 200 °C heating temperature, compared with those in the untreated sample, representing the lowest microbial toxicity. Benzo(a)pyrene produced a significant influence on the ecological toxicity of the hydrochar among the 16 types of PAHs. The impact of thermal treatment on the composition, content, and toxicity of PAHs was significantly influenced by the adsorption, migration, and desorption of PAHs within hydrochar pores, as well as the disintegration and aggregation of large molecular polymers. The combination of hydrochar with carbonized waste heat and exhaust gas collection could be a promising method to efficiently and affordably reduce hydrochar ecological toxicity.

Heat and mass transfer induced by alternating current during desorption of PAHs from soil using electrical resistance heating.

The transfer of heat and contaminants by alternating current (AC) and the removal mechanism of polycyclic aromatic hydrocarbons (PAHs) in electrical resistance heating (ERH) need further study. The main factors affecting heat transfer and water evaporation in the ERH experiment were studied, and the desorption efficiency, temporal and spatial distribution and kinetic behavior under various conditions were analyzed. The results suggested that moisture content was a necessary condition to ensure effective heating of soil, and soil moisture content above 30% was recommended. Higher voltage intensity and/or ion concentration meant stronger input power, resulting in the rapider heating process and the shorter the boiling time. At a low desorption temperature (about 100°C), the Phe desorption mainly depended on the volatilization of surface Phe and the co-boiling of Phe-water. In ERH, the participation of AC would accelerate the diffusion of pollutants from the internal pores of soil particles and their redistribution with water phase, thus improving the Phe removed by co-boiling. It was noteworthy that AC just greatly promoted solid-liquid mass transfer, but it hardly promoted desorption directly, and the removal still depended on Phe-water co-boiling. The Phe desorption efficiency could be significantly improved from 14.0~18.4% to 59.6~70.8% under the combined action of current strengthening Phe diffusion and co-boiling. Thermogravimetric and product analysis confirmed that no new organic matter was generated, but only Phe entered the gas phase through phase change.

A novel and thorough research into desorption behavior of PAHs from sediments to seawater: Aging process, thermodynamics, kinetics, influencing factors

Understanding the desorption process of polycyclic aromatic hydrocarbons (PAHs) from sediments is crucial for evaluating pollutant transport and transformation rule. However, there have been limited studies on the desorption behavior of PAHs from sediments, particularly in relation to the aging process. Herein, batch desorption experiments were conducted to investigate the effects of the aging process, desorption mechanism, and influencing factors on the desorption behavior of PAHs from sediments. The results showed that the aging process significantly inhibited the desorption of PAHs. Specifically, the desorption rates of phenanthrene (Phe), pyrene (Pyr), and benzo(a)pyrene (BaP) were reduced by 38.60%, 23.27%, and 17.64%, respectively. The aging processes of sediments involved molecular penetration, bond breaking, and cross-linking, which resulted in tighter agglomeration of the sediment particles. A thermodynamic analysis of the desorption process revealed that it was a spontaneous and feasible heat-absorbing reaction. The desorption process could be divided into three stages: fast desorption, slow desorption and smooth desorption. Kinetic analyses revealed that the limiting factor for PAHs desorption was the chemisorption via hydrogen bonding, ligand bonding, and chemical bonding, between the sediment and the PAHs. Strongly acidic or basic conditions inhibited PAHs desorption, while low salt and dissolved oxygen concentrations promoted desorption. Additionally, smaller sediment particle sizes with larger specific surface areas resulted in higher adsorption capacities, decreasing the likelihood of PAHs desorption. The findings of this study provide important insights into the desorption mechanism and influencing factors of PAHs.

Surfactant-enhanced anoxic degradation of polycyclic aromatic hydrocarbons (PAHs) in aged subsurface soil at high temperature (60 °C)

Thermally enhanced anoxic biodegradation is emerging as a promising method for removing PAHs from subsurface soil. However, some PAHs still remain in soil following remediation with thermally enhanced anoxic degradation due to low bioavailability of these residual PAHs. The effects of five surfactants (Tween 80, TX 100, Brij 30, SDS, and SDBS) on the desorption of PAHs, anoxic degradation of PAHs, and native bacteria in soil at high temperature (60 °C) were evaluated in this study. The desorption of PAHs in soil increased as surfactant concentration increased. Low doses of surfactants (0.08%, w/w) enhanced the growth of potential PAHs degrading bacteria and promoted the anoxic degradation of PAHs, whereas high doses of surfactants (0.3%–0.8%, w/w) displayed the opposite effect, and the degree of inhibition increased with increasing surfactant concentration. The results also indicated that the inhibitory effect of anionic surfactants (SDS and SDBS) on microbial growth and PAHs degradation is stronger than that of nonionic surfactants (Tween 80, TX 100 and Brij 30) at the same concentration. These results suggest a feasible way of enhancing the anoxic degradation of PAHs in soil where heat cannot be effectively utilized when in situ thermal desorption (ISTD) technology is used.

The adsorption of PAHs on microplastics and desorption in the simulated human digestive system

Plastic debris is widely distributed in the aquatic environment and interacts with other pollutants. Microplastics (MPs) have a stronger binding ability with pollutants and could unconsciously ingested by humans, thus becoming the carrier of pollutants into the human body and affecting human health. In this study, polycyclic aromatic hydrocarbons (PAHs) were selected as model pollutants, polyethylene (PE) and polymethyl methacrylate (PMMA) were selected as research objects. The adsorption of PAHs on different kinds of MPs and desorption behavior in a simulated human digestive system were systematically studied. The results indicated that PAHs with higher molecular weight were more easily adsorbed on MPs, and the adsorption efficiency of PAHs on PE was 1.4–3.8 times higher than PMMA. The desorption experiments were conducted in simulated gastrointestinal fluid, the activity of enzymes directly affected the desorption of PAHs, and the desorption efficiency of PAHs from the surfaces of PMMA (0.7–41.6 %) was significantly higher than PE (0.8–27.7 %). For 15 PAHs, the desorption efficiency from the surfaces of PE decreased gradually with the number of PAHs rings, which was opposite to PMMA. Molecular dynamics simulation showed that enzymes in digestive fluid attenuated the interaction energy between MPs and PAHs, resulting in substantial desorption of PAHs from the surfaces of MPs. The risk assessment demonstrated that the carcinogenic risk of PAHs desorption from PMMA was higher than PE. This study helps understand the adsorption of PAHs on MPs and the potential health risks of accidental ingestion by humans.

Eucalyptus saponin- and sophorolipid-mediated desorption of polycyclic aromatic hydrocarbons from contaminated soil and sediment

The potential for biosurfactant-mediated desorption of polyaromatic hydrocarbons (PAHs) was evaluated using PAH-spiked soil and sediment. PAH desorption behaviors and toxicity of novel saponin biosurfactant extracted from Eucalyptus camaldulensis leaves and sophoro-lipid biosurfactant were investigated. Their PAH desorption efficiencies were compared with rhamnolipid biosurfactant and the industrial-chemical surfactant, Tween 20. Based on the emulsification indices, the salt tolerance of surfactants up to 30 g/L NaCl followed the order of saponin > Tween 20 > sophorolipid > rhamnolipid, while the thermal stability over the range of 15 to 50 °C was in the order of sophorolipid > rhamnolipid > saponin > Tween 20. The saponin biosurfactant emulsion demonstrated the highest stability under a wide range of acidic to basic pHs. PAH extraction percentages of saponin and sophorolipid under the optimized surfactant concentration, volume, and incubation time were 30–50% and 30–70%, respectively. PAH desorption capacities of saponin and sophorolipid were comparable to that of rhamnolipid and Tween 20 for all matrices. Sophorolipid more efficiently desorbed low molecular weight PAHs in soil and sediment compared to the other three surfactants. Microbial respiration was used to determine biosurfactant toxicity to the soil/sediment microbiome and indicated no inhibition of respiration during 60 days of incubation, suggesting that sophorolipid- and saponin-mediated remediation may be sustainable approaches to remove PAHs from contaminated soils and sediments.

Dissipation of a mix of priority PAHs in soils by using availability enhancers. Effect of aging and pollutant interactions.

A remediation strategy using three non-toxic availability enhancers (two cyclodextrins and a rhamnolipid biosurfactant) was applied to various soils artificially contaminated with a mix of Polycyclic Aromatic Hydrocarbons (PAHs) considered priority pollutants at two levels of contamination: only with 7 low molecular weight PAHs (LMW PAHs, 5 with 3-ring and 2 with 4-ring - fluoranthene and pyrene) or with 14 PAHs (from 3 to 6 rings). Natural attenuation of PAHs in all soils showed degradation capacity for the LMW PAHs, with a final content of LMW PAHs <5% of their initial concentration. Conversely, the rest of PAHs (high molecular weight PAHs, HMW) remained in the soils (61% - 83.5%), indicating abiotic dissipation of HMW PAHs due to formation of non-extractable residues in soils. The influence of the presence of HMW PAHs on the degradation of the 7 LMW PAHs was also tested, showing a general decrease in the time to obtain 50% dissipation (DT50), statistically significant for acenaphthene, acenaphthylene and fluorene. Availability enhancers showed different effects on PAHs dissipation. 2-hydroxypropyl-β-cyclodextrin (HP) decreased DT50 of some of the lighter PAHs, whereas the rhamnolipid (RL) caused a slight DT50 increase due to its initial toxicity on native soil microorganisms, but showing later high degradation rate for LMW PAHs. On the contrary, randomly methylated-β-cyclodextrin (RAMEB) slowed down PAHs degradation due to its high adsorption onto soil surface, blocking the desorption of PAHs from the soils. The high number of experimental factors not studied simultaneously before (soil type, co-contamination, availability enhancers and incubation time) allowed to conduct a statistical analysis which supported the conclusions reached. Principal Component Analysis separated the studied PAHs in 3 groups, in relation with their molecular weight and Kow. The first principal component was related with LMW PAHs, and separate the inefficient RAMEB from the other availability enhancers.

Integration of soil washing and cork permeable reactive barriers for the remediation of soil contaminated with polycyclic aromatic hydrocarbons

AbstractBACKGROUNDSoil washing is a well‐known technology for the remediation of soils polluted by organic contaminants, including polycyclic aromatic hydrocarbons (PAHs). This study aimed to go further by integrating soil washing and permeable reactive barriers (PRBs) made of cork granules to remove PAHs from the soil. While PAHs may be transferred from the soil to the washing solution in the soil washing step, the cork PRB may provide the removal of PAHs from the washing solution, ultimately leading to the reuse of this solution.RESULTSThe integrated approach was tested by means of packed bed column experiments in the absence and presence of cork PRBs. Two PAHs were under focus: fluorene (FLU) and phenanthrene (PHE). In soil with 0.5 mmol L−1 kgsoil−1 of FLU and PHE, the soil washing technique employing thermally treated cork granules and a solution of 70%/30% water/acetonitrile (v/v) flowing at 2.2 mL min−1 promoted the transfer of ~58% of PAHs from the soil to the washing solution, while the cork PRB retained ~98% of the PAHs from the washing solution. The acetonitrile content of the water/acetonitrile washing solutions contributed to the soil washing since it was responsible for PAH desorption and elution, however it was unfavorable for PAH sorption onto the cork as acetonitrile competed with PAHs for cork sorption sites.CONCLUSIONCork PRBs were able to retain PAHs from soil washing solutions and provide final solutions free of PAHs, demonstrating the viability of integrating solvent‐aided soil washing with cork PRBs. © 2022 Society of Chemical Industry (SCI).

Desorption of polycyclic aromatic hydrocarbons by cosmic rays

Context. The rate of sputtering and release of condensed species is an important aspect of interstellar chemistry, as is photodesorption for the most volatile species, because in the absence of such mechanisms the whole gas phase would have to condense in times often shorter than the lifetime of the considered medium, in particular for dense clouds. The recent detection of cyclic aromatic molecules by radioastronomy requires an understanding of the potential mechanisms supporting the rather high abundances observed. Aims. We perform experiments to advance our understanding of the sputtering yield due to cosmic rays for very large carbonaceous species in the solid phase. Methods. Thin films of perylene and coronene were deposited on a quartz cell microbalance and exposed to a 1.5 MeV N+ ion beam at the Laboratoire de Physique des 2 Infinis Irène Joliot-Curie (IJCLab, Orsay, France) and a 230 MeV 48Ca10+ ion beam at the GSI Helmholtzzentrum für Schwerionenforschung (GSI, Darmstadt, Germany). The mass loss was recorded as a function of the fluence for the N+ beam. The microbalance response was calibrated using Fourier transform infrared (FTIR) reflectance measurements of the produced films. In addition, the destruction cross-section of the same species was measured with the 48Ca10+ ion beam by in situ monitoring of the evolution of the infrared spectra of the bombarded films. Results. We deduced the sputtering yield for perylene and coronene and their radiolysis destruction cross-sections. Combining these results with a cosmic ray astrophysical spectrum, we discuss the impact on the possible abundance that may originate from the sputtering of dust grains with these molecules as well as from polycyclic aromatic molecules when they are trapped in ice mantles.

Desorption of polycyclic aromatic hydrocarbons from polyethylene microplastics in two morphologically different digestive tracts of marine teleosts: Gastric red seabream (Pagrus major) and agastric mummichog (Fundulus heteroclitus)

In this study, we elucidated the desorption potency of polycyclic aromatic hydrocarbons (PAHs) sorbed on microplastics (MP; polyethylene) in the digestive tract of two fish species: gastric red seabream and agastric mummichog. In our in vitro assay system using the real gut sample of unexposed fish, the digestive tract was firstly removed from the fish and divided into three parts. Then, MP that had previously been sorbed with 16 PAHs were incubated with extracts of the gut contents or tissue with buffer or only a buffer. The desorption potency of PAHs was individually assessed for gut contents and tissue, which revealed that PAH desorption from MP was elevated in extracts of the gut contents compared with that in the buffer alone for both fish species. PAH desorption potency was the highest in the midgut for gastric red seabream and in the foregut for agastric mummichog, which indicates that PAH desorption from MP varies among different parts of the digestive tract and among fish with distinct gut morphology. In the midgut contents of red seabream and foregut contents of mummichog, the desorption fraction was 5.6% and 8.1% of the total PAHs sorbed on MP, respectively. The desorption fraction enhancement achieved by adding gut contents extracts tended to be greater with an increase in the n-octanol/water partition ratio, suggesting that enhancement of the desorption fraction in the digestive tract depends on the physicochemical properties of PAHs. Thus, morphological differences in digestive tracts and PAH properties should be considered when evaluating the effect of MP vector on pollutant exposure in fish.

Kill two birds with one stone: Ceramisite production using organic contaminated soil

Disposal of organic-contaminated soil through ceramsite production can not only generate ceramsite with acceptable properties but also completely remediate the organic-contaminated soil owing to high treatment temperature. However, the removal mechanism of organic pollutants and the gas-solid phase distribution of the pollutants remain unclear. In this study, coking contaminated soils with high concentrations of polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbon (PHC) were used to prepare ceramsite at 1160 °C. The quality of ceramsite met the required product standard when the disposal ratio of contaminated soil was up to 60%. The concentration of PAHs and PHC in the soil was 57.7 mg kg-1 and 255 mg kg-1. After the experiment, almost no PAHs and PHC were found in the ceramsite. High-ring PAHs were dominant in the flue gas when using model soil spiked with PAHs. Computed tomography scanning indicated that cracks developed in the ceramsite when the temperature was higher than 200 °C. High-temperature in-situ thermal analysis showed that when the temperature was increased to 400 °C, the pollutant from the interior of ceramsite would flow into the flue gas with the released volatile matter. Thermal desorption and degradation of PAHs were the main mechanisms of pollutant removal.

Inhalation Bioaccessibility of Polycyclic Aromatic Hydrocarbons in PM2.5 under Various Lung Environments: Implications for Air Pollution Control during Coronavirus Disease-19 Outbreak.

Global spread of coronavirus disease-19 (COVID-19) is placing an unprecedented pressure on the environment and health. In this study, a new perspective is proposed to assess the inhalation bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 for people with various lung health conditions. In vitro bioaccessibility (IVBA) was measured using modified epithelial lung fluids simulating the extracellular environment of patients with severe and mild lung inflammation. The average PAH IVBA in PM2.5 of 24.5 ± 4.52% under healthy conditions increased (p = 0.06) to 28.6 ± 3.17% and significantly (p < 0.05) to 32.3 ± 5.32% under mild and severe lung inflammation conditions. A mechanistic study showed that lung inflammation decreased the critical micelle concentrations of main pulmonary surfactants (i.e., from 67.8 (for dipalmitoyl phosphatidylcholine) and 53.3 mg/L (for bovine serum albumin) to 44.5 mg/L) and promoted the formation of micelles, which enhanced the solubilization and competitive desorption of PAHs from PM2.5 in the lung fluids. In addition, risk assessment considering different IVBA values suggested that PAH contamination levels in PM2.5, which were safe for healthy people, may not be acceptable for patients with lung inflammation. Because of the large number of COVID-19 infections, and the fact that some survivors of COVID-19 were observed to still show symptoms of interstitial lung inflammation, the finding here can provide important implications for both the scientific community and policy makers in addressing health risk and air pollution control during the COVID-19 outbreak.

Sampling and concentration of particulate matter bound polycyclic aromatic hydrocarbons (PAHs) basing on polystyrene nanofibers followed a determination by gas chromatography-mass spectrometry

Electrospun polystyrene (PS) nanofibers as an effective particulate filter and a sorbent in a packed-fiber solid phase extraction (PFSPE) were used to develop a novel method for the sampling and concentration of sixteen polycyclic aromatic hydrocarbons (PAHs) in the atmospheric particulate matter (PM). The PAHs were quantified by gas-chromatography-mass spectrometry (GC–MS). The main factors (the shape of PFSPE devices, the leaching solvents, and the elution methods) affecting the adsorption and desorption of PAHs on PS nanofibers were evaluated in detail. Under the optimized conditions (sampling of particulate matter bound PAHs basing on PS nanofibers filter following the release of them with ultrsound for 20 min in ethanol, the concentration of PAHs by adsorption of them on PS nanofibers again in a disk PFSPE-column, eluting of PAHs in ethanol at 75 ○C for 10 min), PS nanofibers displayed excellent properties in the sampling of PM bound PAHs and in the concentration of PAHs in the leaching solution with the recoveries ranging from 79.2 to 104.5%. The linear calibration curves were in the range of 0.17 to 64.9 ng m−3, and relative standard deviations (RSDs) were 3.8–11.6% for intra-day, 4.3–10.2% for inter-day. The method was fast, sensitive, cost-effective, with less harmful reagents, and has great potential for analyzing PAHs in atmospheric particulate matter.

Biodegradation dynamics disparity between n‐alkanes and polycyclic aromatic hydrocarbons in the vadose zone: A critical review

AbstractIn the shallow terrestrial subsurface, bioavailability often controls biodegradation rates of various hydrophobic organic pollutants, such as hydrocarbons. Microorganism‐mediated depletion of n‐alkanes and polycyclic aromatic hydrocarbons (PAHs) in the vadose zone proceeds with distinctively different rates and kinetics. The observed disparity in biodegradation dynamics between these two classes of hydrocarbons are described here in terms of the Best equation, which allows for a complex process of hydrocarbon contaminant depletion to be explained in terms of the physically relevant processes. This equation combines terms describing contributions of two key elements of hydrocarbon biodegradation—the intrinsic catabolic activity of microorganisms and the mass transfer process delivering substrate to active microorganisms. If substrate supply is slow, biodegradation process is availability‐limited because microorganisms consume the substrate faster than it can be delivered. Conversely, when the mass transfer of substrate is faster than the microbial consumption, biodegradation rate tends to be controlled by metabolic kinetics.The evaluation conducted in this study ascertains that the critical factor limiting the rate and extent of PAH biodegradation is the mass transfer rather than the intrinsic microbial activity that appears to govern the rate of n‐alkane biodegradation. The specifics of mass transfer are determined by the magnitude of the substrate–soil interactions. Whereas sorption of n‐alkanes is controlled by weak hydrophobic and van der Waals forces, PAHs tend to bind to the soil matrix by much stronger electron‐donor–acceptor interactions. Stronger interactions between aromatic compounds and soil components translate into the higher activation energies for desorption of PAHs and therefore a slower mass transfer process. This aspect of the substrate–soil interaction explains a more prominent effect of mass transfer limitation on biodegradation dynamics of PAHs compared to that of the corresponding n‐alkanes.

Polycyclic aromatic hydrocarbons in sediment–porewater system from the East China Sea: Occurrence, partitioning, and diffusion

The distribution, partitioning behavior, and diffusion of polycyclic aromatic hydrocarbons (PAHs) within sediment–porewater system were determined in two cores obtained from the Min-Zhe coastal mud of the East China Sea (ECS). Depth profiles of apparently dissolved PAH levels exhibited greater variabilities, with their elevated levels at depth and a high abundance of two-to three-ring PAHs observed. These distribution and composition patterns were inconsistent with the corresponding sediment PAHs, indicating differences in controlling factors for PAHs present in the system. In addition to compound's hydrophobicity, low detection of heavier PAHs in porewater was possibly correlated with the sediment transport process, as indicated by a relatively high weathering ratio in southern Min-Zhe coastal mud. PAH sorption affinity to the collected core sediments exhibited a generally decreasing trend downcore, as expressed by sediment–porewater partition coefficients. This was consistent with the higher content of porewater PAHs in deep core sediment. The established sediment total organic carbon (TOC)–porewater partitioning profiles in cores were predicted with amorphous organic carbon (AOC)-, coal tar-, and TOC-based distribution models, suggesting a dominant nonlinear sorption of PAHs to AOC. Through activity determinations, PAH diffusion within porewater was elucidated, with significant upward and downward mass transfer for PAHs occurring in both cores. The upward diffusion in the core collected from northern Min-Zhe coastal mud was in significant association with sediment TOC. This suggests that sediment TOC (especially AOC)-desorption of lighter PAHs into porewater, and therefore the possibility of their participation in environmental cycling. Baseline toxicity potential and toxic unit calculations indicated a relatively low exposure risk for benthic organisms to porewater PAHs.

Synthesis and evaluation of recoverable activated carbon/Fe3O4 composites for removal of polycyclic aromatic hydrocarbons from aqueous solution

Three different synthesis methods were employed to prepare magnetic powder and granular activated carbons (MPAC and MGAC) as recoverable adsorbents to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. The MPAC and MGAC composites were characterized by XRD, and the XRD patterns confirmed the presence of Fe 3 O 4 particles with cubic crystal structure on the adsorbents surface. FE-SEM images showed that the magnetic composites had spherical morphologies, with clusters of iron oxide nanoparticles formed in the ACs pores and distributed evenly on their surface. FTIR spectra of the PAH-loaded adsorbents revealed that the analytes were attached to the surfaces of MPACs and MGACs by π - π and H- π interactions formed between the PAHs and functional groups of the adsorbents. All the synthesized magnetic ACs were very effective in removing PAH compounds from aqueous solution with removal percentages between 87.2% to 99.3%. The precipitation method of magnetization resulted in the highest PAHs removal efficiency (99.3%) using PAC as the base AC, while the co-precipitation method of magnetization provided the highest PAHs removal efficiency (98.3%) using GAC as the base AC. The PAHs desorption tests indicated that low molecular weight PAHs were more easily desorbed from the magnetic ACs ranging from 38.1 to 60.1%, compared with high molecular PAHs ranging from 23.4 to 57.2%. This shows that the increase in the number of PAH rings would lead to the formation of more covalent bonds between the adsorbate and the adsorbent. • Six types of magnetic activated carbon particles were successfully synthesized and characterized. • All the synthesized magnetic adsorbents were able to strongly remove PAHs from the aqueous solutions. • The adsorption results indicated that the PAHs have a strong affinity to the surface of the magnetic activated carbons. • All the magnetic activated carbons could be rapidly and efficiently separated from the solutions by a magnetic field. • Desorption of five- and six-ring PAHs from the magnetic activated carbons were lower than three- and four-ring PAHs.

Thermally enhanced anoxic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in a highly contaminated aged soil

During the application of in situ thermal desorption technology (ISTD), heat in some areas often can not be effectively utilized. Nevertheless, the heat in these areas might promote the biodegradation of polycyclic aromatic hydrocarbons (PAHs). However, few studies have concentrated on the effect of temperature on biodegradation of PAHs, especially under anoxic conditions. The effects of temperature on the abundance and community characteristics of indigenous bacteria in soil are also unclear. Consequently, thermally enhanced anoxic biodegradation of PAHs in subsurface soil was investigated in this study. After 150 days of anoxic incubation, both the bacterial abundance and the removal rates of PAHs in soil were positively affected by temperature. The total number of potential PAH-degrading bacteria (Proteobacteria and Firmicutes) was increased by 0.11–0.72 orders of magnitude compared to the untreated soil in different temperature treatment groups (20 °C, 30 °C, 40 °C, and 50 °C). Firmicutes was more adaptable to higher temperatures than Proteobacteria. The removal rates of total PAHs increased from 28.85% to 50.44% with increasing temperature. The degradation rates of three- and four-ring PAHs were significantly higher than those of five- and six-ring PAHs. These findings provide a more applicable and economical way to treat with PAHs contaminated subsurface soil where the temperature is lower than the target temperature needed for the desorption of PAHs from the soil when ISTD is used.

Responses of oil degrader enzyme activities, metabolism and degradation kinetics to bean root exudates during rhizoremediation of crude oil contaminated soil

During rhizoremediation process, plant roots secrete the specific exudates which enhance or stimulate growth and activity of microbial community in the rhizosphere resulting in effective degradation of pollutants. The present study characterized cowpea (CP) and mung bean (MB) root exudates and examined their influences on the degradation of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) by the two oil degraders Micrococcus luteus WN01 and Bacillus cereus W2301. The effects of root exudates on soil microbial population dynamic and their enzymes dehydrogenase (DHA), and catechol 2,3 dioxygenase (C23O) activities were assessed. Both root exudates enhanced the degradation by both oil degraders. Cowpea root exudates maximized the removal of TPHs and PAHs by M. luteus WN01. Both bacterial population and DHA increased significantly in the presence of both root exudates. However, the C23O activities were significantly higher in WN01 treated. No significant influence of root exudates was observed on the C23O activities of W2301 treated. By using gas chromatography -mass spectroscopy, the dominant compounds found in cowpea and mung bean root exudates were 4-methoxy-cinnamic acid and terephthalic acid. Found in lower amount were propionic, malonic acid, and citric acid which were associated with enhanced PAHs desorption from soil and subsequent degradation. Novelty statement This is the first study to characterize the low molecular weight organic acids from root exudates of cowpea and mung bean and their influences on hydrocarbon desorption and hence enhancing the biodegradation process. The findings of the present study will greatly contribute to a better understanding of plant-microbe interaction in total petroleum hydrocarbons contaminated soil.

Surfactant‐aided mycoremediation of soil contaminated with polycyclic aromatic hydrocarbon (PAHs): progress, limitation, and countermeasures

AbstractSoil contaminated with hydrophobic organic hydrocarbons, such as polycyclic aromatic hydrocarbons (PAHs), pose a serious threat to the ecosystem and human health. Moreover, the sorption and desorption of the PAHs, due to the interaction with the soil organic matter (SOM) and other contaminants, greatly affect the fate and mycoremediation efficiency of the contaminated soil. On the other hand, the application of surfactants with or without additives for the mobilization of PAHs from contaminated soil has garnered increasing attention for soil remediation. In this context, several commercial surfactants and biosurfactants were reported either as soil flushing agents or soil additives, followed by either in situ or ex situ mycoremediation of the PAHs from contaminated soil. Hence, for a successful implementation of surfactants for mycoremediation of contaminated soil, a comprehensive introspection on its chemistry and mechanism is necessary. Thus, this review focuses primarily on understanding the effect of surfactants and the mechanism of desorption of PAHs from the soil. This work also emphasizes the effect of surfactants on the efficiency of mycoremediation of contaminated soil. Further, the review summarizes various surfactant‐assisted mycoremediation strategies of contaminated soil. Finally, the limitations of surfactant‐assisted mycoremediation, precipitative, and partitioning loss, along with toxicity of the surfactants, were reviewed. Thus, this review will aid in understanding the underlying mechanism and efficiency of surfactant‐assisted mycoremediation and it also proposes current research trends to improve the efficiency and enhance the bioremediation of PAHs‐contaminated soil. © 2021 Society of Chemical Industry (SCI).

Assessment of the effects of soil organic matter and iron oxides on the individual sorption of two polycyclic aromatic hydrocarbons

Soils are the ultimate sink for environmental pollutants like polycyclic aromatic hydrocarbons (PAHs), but the roles of major soil constituents in this process are still unclear. The fate of PAHs is governed by sorption processes which in turn affect transport, chemical and biological reactivity of these PAHs. Thus, the effects and contributions of two major soil constituents (organic matter-OM and iron oxides-IOs) on pyrene and fluorene sorption on soils were assessed by removal of both constituents. The whole soils had higher sorption than the treated OM/IOs soils. Pyrene sorption on OM-rich soils was high and nearly instantaneous, while on the IOs-rich soils, it was lower with delayed equilibrium. The IOs contributed IOR > OMR soils. Though, removal of any of these soil constituents usually reduced sorption and enhanced sorbed PAHs desorption, the presence of IOs masked some PAHs sorption sites, thus its removal resulted in higher sorption. In general, this study highlights the contributions of soil OM and IOs on the sorption of pyrene and fluorene.