PAH-contaminated Soil Research Articles

Characterization and degradation mechanism of bimetallic iron-based/AC activated persulfate for PAHs-contaminated soil remediation

In this research, a novel iron based bimetallic nanoparticles (Fe–Ni) supported on activated carbon (AC) were synthesized and employed as an activator of persulfate in polycyclic aromatic hydrocarbons (PAHs) polluted sites remediation. AC-supported Fe–Ni activator was prepared according to two-step reduction method: the liquid phase reduction and H2- reduction under high temperature (600 °C), which was defined as Fe–Ni/AC. Characterizations using micropore physisorption analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM) showed that the synthetic material had large specific surface area, nano-size and carbon-encapsulated metal particles, moreover, the lattice fringes of metals were clearly defined. The PAH compound types and their concentrations were determined by gas chromatography mass spectrometry (GC-MS) with SIM mode, the method detection limit (MDL) was estimated to about 0.21 μg/kg for PAHs, and the average recovery of PAHs was 96.3%. Mechanisms of PAH oxidation degradation with the reaction system of Fe–Ni/AC activated persulfate were discussed, the results showed that short-life free radicals, such as SO4−·, OH·, and OOH· were generated simultaneously, which acted as strong oxidizing radicals, resulting in the oxidation and almost complete opening of the PAH rings.

Bacterial community and PAH-degrading genes in paddy soil and rice grain from PAH-contaminated area

The significance of the bacterial communities and PAH-degrading genes (PDGs) in PAH-contaminated soil has received extensive attention, however, little attention was focused on those in plants grown on contaminated farmland soil. This study aimed to dissect the interactive relationships among PAHs, PDGs, and bacterial communities in the rhizosphere soil and rice grain. Although the concentrations and compositions of PAHs varied greatly, PAHs was the most critical factor in shifting of community in the soil and rice grain. Diversity of the potential PAH-degrading bacteria (PDB) in the rhizosphere soil was higher than that in the rice grain; however, the relative and absolute abundances of PDB in the rhizosphere soil were lower than those in the rice grain. Abundances of four PDGs in the soil were higher than those in the rice grain, and many species of bacteria, including Pseudomonas, Sphingomonas, and so on, which may harbor PDGs were detected. Bacteria in the soil had stronger relationships and were more centrally clustered within the network compared to bacteria in the rice grain. The keystone species (Actiobacteria, Betaproteobacteria, and Chloroflexi) in the soil were different from those (Pseudomonas, Sphingomonas, and Comamonadaceae) in the rice grain. Pseudomonas and Sphingomonas in the rice grain seemed to be the most important bacteria associated with PAH degradation. Overall, these findings provided novel insights into bacterial communities and PDGs in both the soil and plant from the PAH-contaminated paddy soil.

Biochar applications combined with paddy-upland rotation cropping systems benefit the safe use of PAH-contaminated soils: From risk assessment to microbial ecology

This study aimed to establish a method allowing the safe use of polycyclic aromatic hydrocarbon (PAH)-contaminated soils through the combination of biochar applications and different cropping systems. The impact of biochar applications under different cropping systems on the human health risks of PAHs and soil microbiology was elucidated. The residual PAHs were the lowest in rhizosphere soils amended with 2% corn straw-derived biochar pyrolyzed at 300 °C (CB300) under the paddy-upland rotation cropping (PURC) system. Human health risks resulting from the ingestion of PAH-contaminated carrot roots / rice grains under the PURC system were significantly lower than those under continuous upland cropping systems. The greatest diversity, richness and network complexity of soil microbial communities occurred under the PURC system combined with the 2% CB300 treatment. Soil microbial functions associated with soil health and PAH biodegradation were enhanced under this strategy, while the pathogen group was inhibited. Primarily owing to its high sorption capacity, bamboo-derived biochar pyrolyzed at 700 °C realized in the reduction of PAHs, but weakly influenced shifts in soil microbial communities. Overall, the combination of PURC systems and low-temperature-pyrolyzed nutrient-rich biochar could efficiently reduce the human health risks of PAHs and improve soil microbial ecology in agricultural fields.

Hydroxylation at Multiple Positions Initiated the Biodegradation of Indeno[1,2,3-cd]Pyrene in Rhodococcus aetherivorans IcdP1.

Nowadays, contamination by polycyclic aromatic hydrocarbons (PAHs) has become a serious problem all over the world; in particular, high-molecular-weight PAHs (HWM PAHs, four to seven rings) are more harmful to human health and environment due to their more complex structure and metabolic pathway. Biodegradation of PAHs with six or more rings, such as indeno[1,2,3-cd]pyrene (IcdP), was rarely described. An IcdP-degrading strain, Rhodococcus aetherivorans IcdP1, was isolated from HWM PAH-contaminated soil. It could grow on and efficiently degrade various HWM PAHs, such as IcdP, benzo[a]pyrene, and benzo[j]fluoranthene. It showed highest degrading ability toward IcdP (> 70% within 10 days). The IcdP degradation was initiated by ring hydroxylation with multiple pathways, including the hydroxylation at the 1,2 and 7,8 positions, according to the relevant metabolites detected, e.g., cyclopenta[cd]pyrene-3,4-dicarboxylic acid and 2,3-dimethoxy-2,3-dihydrofluoranthene. The transcriptional patterns of the genes encoding ring-hydroxylating oxygenases (RHOs) and cytochrome P450 monooxygenases (CYP450s) under the induction of IcdP, pyrene, and benzo[b]fluoranthene (BbF) were compared to determine the key initial RHOs in the conversion of IcdP. The expression of genes encoding RHOs 1892–1894, 1917–1920, and 4740–4741 was induced strictly by IcdP, and the amino acid sequences of these proteins showed very low identities with their homologs. These results suggested that IcdP was degraded through a dioxygenation-initiated metabolism pattern, and RHOs 1892–1894, 1917–1920, and 4740–4741 responded to the initial ring cleavage of IcdP through 1,2-dihydrodiol or 7,8-dihydrodiol. The studies would contribute to the understanding of the molecular mechanism of initial degradation of IcdP.

Performance and potential mechanism of transformation of polycyclic aromatic hydrocarbons (PAHs) on various iron oxides

The abiotic transformation of polycyclic aromatic hydrocarbons (PAHs) is significantly impacted by soil components, especially inorganic redox species like iron oxides. In this study, the catalytic activities of three types of iron oxides in PAHs degradation without light irradiation were evaluated using a combination of experimental techniques. The results showed that α-Fe2O3 possessed the highest transformation rate for anthracene (ANT), with a reaction rate constant (Kobs) up to 0.28 d−1, followed by Fe3O4 (Kobs = 0.06 d−1) and α-FeOOH (Kobs = 0.06 d−1). X-ray photoelectron spectroscopy (XPS) characterization suggested that α-Fe2O3 had the highest oxygen vacancy concentration, which was conducive to the adsorption of O2 by α-Fe2O3, providing sufficient adsorbed oxygen species. Oxygen vacancy contributed to the exposure of Fe(III), and accordingly, more active sites were created that were responsible for ANT degradation. According to these results, two possible pathways for the degradation of PAHs on iron oxides can be concluded: (1) direct oxidation by Fe(III) and (2) oxidation by the O2•− generated onto oxygen vacancies. This study provides significant insights into the environmental fate of PAHs on iron oxides, and raises the possibility that iron oxides may be used as catalytic materials in the remediation PAHs-contaminated soil.

Genome Sequence of Trichoderma lixii MUT3171, A Promising Strain for Mycoremediation of PAH-Contaminated Sites.

Mono- and polycyclic aromatic hydrocarbons (PAHs) are widespread and recalcitrant pollutants that threaten both environmental and human health. By exploiting the powerful enzymatic machinery of fungi, mycoremediation in contaminated sites aims at removing a wide range of pollutants in a cost-efficient and environmentally friendly manner. Next-generation sequencing (NGS) techniques are powerful tools for understanding the molecular basis of biotransformation of PAHs by selected fungal strains, allowing genome mining to identify genetic features of biotechnological value. Trichoderma lixii MUT3171, isolated from a historically PAH-contaminated soil in Italy, can grow on phenanthrene, as a sole carbon source. Here, we report the draft genome sequence of T. lixii MUT3171 obtained with high-throughput sequencing method. The genome of T. lixii MUT3171 was compared with other 14 Trichoderma genomes, highlighting both shared and unique features that can shed a light on the biotransformation of PAHs. Moreover, the genes potentially involved in the production of important biosurfactants and bioactive molecules have been investigated. The gene repertoire of T. lixii MUT3171 indicates a high degrading potential and provides hints on putative survival strategies in a polluted environment.

Influence of electrode configuration on electrokinetic-enhanced persulfate oxidation remediation of PAH-contaminated soil.

Electrokinetic (EK) remediation combined with in situ chemical oxidation (ISCO) can be applied to low permeability organic contaminated soil. However, the effects of electrode configuration on EK-oxidation remediation remain unclear. In this study, EK-ISCO remediation of real polycyclic aromatic hydrocarbon (PAH)-contaminated soil under different electrode configurations was conducted. The results showed that increasing the number of anodes and electrode pairs in one-dimensional (1D) and two-dimensional (2D) electrode configuration was conducive to migration of oxidants into the system. The change in soil pH after remediation in 2D electrode configuration was not obvious, but the increase of soil electrical conductivity (EC) was higher than that of the 1D electrode configuration. The removal rates of PAHs in 2D electrode configurations (35.9-40.9%) were relatively higher than those of the 1D electrode configurations (0.54-31.6%), and the hexagonal electrode configuration yielded the highest pollutant removal efficiency, reaching 40.9%. The energy consumption under 2D electrode configuration was smaller than that under 1D electrode configuration, and the energy consumption of per gram removed PAHs in the hexagon configuration (66.74kWh (g PAHs)-1) was lowest in all electrode configurations. Overall, the results of this study suggest that 2D electrode configuration is better than 1D and hexagonal electrode configuration is an optimal electrode configuration.

Remediation of Anthracene-Contaminated Soil with Sophorolipids-SDBS-Na2SiO3 and Treatment of Eluting Wastewater

The soil pollution of polycyclic aromatic hydrocarbons (PAHs) is serious in China, which not only affects the living and growing environment of plants and animals but also has a great impact on people’s health. The use of hydrophobic organic compounds to make use of surfactant ectopic elution processing is more convenient and cheaper as a repair scheme and can effectively wash out the polycyclic aromatic hydrocarbons in the soil. Therefore, we mixed sophorolipids:sodium dodecylbenzene sulfonate (SDBS):Na2SiO3 according to the mass ratio of 1:15:150. We explored the influencing factors of high and low concentrations of PAH-contaminated soil using a single factor test and four factors at a two-level factorial design. Then, the elution wastewater was treated by ultrasonic oxidation technology and the alkali-activated sodium persulfate technology. The results showed that: (1) In the single factor test, when the elution time is 8 h, the concentration of the compounded surfactant is 1200 mg/L, the particle size is 60 mesh, the concentration of NaCl is 100 mmol/L, and the concentration of KCl is 50 mmol/L, and the effect of the PAH-contaminated soil eluted by the composite surfactant is the best. Externally added NaCl and KCl salt ions have a more obvious promotion effect on the polycyclic aromatic hydrocarbon-contaminated soil; (2) in the interaction experiment, single factor B (elution time) and D (NaCl concentration) have a significant main effect. There is also a certain interaction between factor A (concentration agent concentration) and factor D, factor B, and factor C (KCl concentration); (3) the treatment of anthracene in the eluate by ultrasonic completely mineralizes the organic pollutants by the thermal and chemical effects produced by the ultrasonic cavitation phenomenon, so that the organic pollutants in the eluate are oxidized and degraded into simple environmentally friendly small molecular substances. When the optimal ultrasonic time is 60 min and the ratio of oxidant to activator is 1:2, the removal rate of contaminants in the eluent can reach 63.7%. At the same time, the turbidity of the eluent is significantly lower than that of the liquid after centrifugal separation, indicating that oxidants can not only remove the pollutants in elution water but also remove the residual soil particulate matter; and (4) by comparing the infrared spectrum of the eluted waste liquid before and after oxidation, it can be seen that during the oxidation process, the inner part of eluent waste liquid underwent a ring-opening reaction, and the ring-opening reaction also occurred in the part of the cyclic ester group of the surfactant, which changed from a ring to non-ring.

Enhancing Salix viminalis L.-mediated phytoremediation of polycyclic aromatic hydrocarbon-contaminated soil by inoculation with Crucibulum laeve (white-rot fungus).

Although plant-white-rot fungi (WRF) remediation is considered efficient in improving polycyclic aromatic hydrocarbon (PAH)-contaminated soil, the prospects for using it remain poorly known. Therefore, we evaluated whether the WRF Crucibulum laeve could improve the phytoremediation of PAH-contaminated soil by Salix viminalis L. A 60-day pot experiment was conducted to investigate the effects of C. laeve inoculation (using two inoculation treatments and a non-inoculated control) on the phytoremediation potential, growth, and antioxidant metabolism of S. viminalis cultivated in PAH-contaminated soil. The S. viminalis-C. laeve association synergistically caused the highest PAH removal rate. Under the S. viminalis-C. laeve treatment, 80% of the biological concentration and translocation factors for all tissues of S. viminalis were > 1, whereas only 20% of these factors were > 1 when S. viminalis was used alone. C. laeve inoculation remarkably enhanced phytoremediation by promoting S. viminalis-based phytoextraction of PAHs from soils. Furthermore, although C. laeve inoculation altered the antioxidant metabolism of S. viminalis by inducing oxidative stress, thereby inhibiting plant growth, the plant's hardiness enabled it to survive and grow normally for 60days after treatment. Therefore, phytoremediation using S. viminalis inoculated with C. laeve can be considered a feasible approach for the phytoremediation of PAH-contaminated soil.

Microbial diversity and co-occurrence patterns in deep soils contaminated by polycyclic aromatic hydrocarbons (PAHs)

Numerous studies have enriched our knowledge of the microbial community composition and metabolic versatility of contaminated soil. However, there remains a substantial gap regarding the bioassembly patterns of the indigenous microbial community distribution in contaminated deep soils. Herein, the indigenous microbial community structure diversity, function, and co-occurrence relationships in aged PAH-contaminated deep soil collected from an abandoned chemical facility were investigated using high-throughput sequencing. The results showed that the dominant phyla in all samples were responsible for PAH degradation and included Proteobacteria (20.86%–81.37%), Chloroflexi (2.03%–28.44%), Firmicutes (3.06%–31.16%), Actinobacteria (2.92%–11.91%), Acidobacteria (0.41%–12.68%), and Nitrospirae (0.81%–9.21%). Eighty biomarkers were obtained by linear discriminant analysis of effect size (LEfSe), and most of these biomarkers were PAH degraders. Functional predictions using Tax4Fun indicated that the aged contaminated soil has the potential for PAH degradation. Statistical analysis showed that in contrast with the PAH concentration, edaphic properties (nutrients and pH) were significantly correlated (r > 0.25, P < 0.01) with the bacterial community and functional composition. Co-occurrence network analysis (modularity index of 0.781) revealed non-random assembly patterns of the bacterial communities in the PAH-contaminated soils. The modules in the network were mainly involved in carbon and nitrogen cycles, organic substance degradation, and biological electron transfer processes. Microbes from the same module had strong ecological linkages. Additionally, SAR202 clade, Thermoanaerobaculum, Nitrospira, and Xanthomonadales, which were identified as keystone species, played an irreplaceable role in the network. Overall, our results suggested that environmental factors such as nutrients and pH, together with ecological function, are the main factors driving the assembly of microbial communities in aged PAH-contaminated deep soils.

Electrochemically reversible foam enhanced flushing for PAHs-contaminated soil: Stability of surfactant foam, effects of soil factors, and surfactant reversible recovery

Although surfactant foams enhanced-remediation for PAHs-contaminated soil has been proved to be an effective method, lack of simple/economic surfactant recovery methods from the eluent solutions limit its further remediation application for organic contaminated soil. Here, we prepared a electrochemically reversible ferrocene surfactant FcCH2N+(CH3)C12H25 (Fc12), then investigated the foaming ability and foam stability of Fc12 under its reduced (active state) and oxidation (inactive state) states and explored the flushing efficiency of reduced Fc12 foam for PAHs-contaminated soil and the recovery efficiency of collected eluent solution. The results showed that the foaming ability and foam stability of reduced Fc12 are greatly higher than those of oxidized Fc12, which is indicative of a well reversibly switchable characteristic of Fc12. The contaminated soil flushing efficiencies of reduced Fc12 for phenanthrene and pyrene were 65.28% and 46.45%. The respective desorption efficiency of phenanthrene and pyrene from collected eluent solutions were calculated to be 74.94% and 72.75% by electrochemical oxidation control, which indicates that Fc12 can be well recovered by simple electrochemical control. This study provides a feasible method for the recovery of surfactants from surfactant-enhanced remediation processes by simply electrochemical control.

Enhanced cometabolism of benzo(a)anthracene by the lignin monomer vanillate is related to structural and functional responses of the soil microbiome

Lignin is a natural polymer composed of phenolic units. The structural similarity between lignin monomers and recalcitrant aromatic pollutants raises the possibility of their cometabolism by soil microorganisms. Here, we explored the links between polycyclic aromatic hydrocarbon (PAH) degradation and microbiome responses in soil microcosms amended with lignin or one of its phenolic units, vanillate, by coupled amplicon and metagenomic shotgun sequencing. The transformation of the four-ring model PAH benzo(a)anthracene (BaA) was monitored by using a radiolabelled tracer. The results demonstrated that vanillate significantly promoted 14CO2 production during incubation, suggesting activation of BaA biodegradation in the soil microcosms. Lignin changed the fate of BaA mainly by increasing its adsorption to soil organic matter. In contrast to the control microcosms, the mineralization and formation of nonextractable residue (NER) from BaA in the presence of vanillate were sensitive to the fungicide cycloheximide. Lignin and vanillate consistently enriched bacterial methyl utilization and aromatic ring cleavage genes at the two sampling times, which, however, did not result in BaA mineralization. The distinct responses of the fungal community to vanillate as well as the coupled cycloheximide-induced inhibition of BaA mineralization and 18S rRNA gene abundance suggest an essential contribution of fungi to BaA biodegradation in the vanillate-amended microcosms. Overall, these findings reveal a cometabolic mechanism between vanillate and PAHs, which contributed to the detoxification of BaA in the soil. This study also provides a scientific basis for the bioremediation of PAH-contaminated soil by priming the soil microbiome with phenolic monomers of lignin.

Mechanism of biochar as a biostimulation strategy to remove polycyclic aromatic hydrocarbons from heavily contaminated soil in a coking plant

Twelve types of biochars were applied in a heavily contaminated soil from a coking plant to gain insights into the mechanism responsible for the microbial response to the addition of different biochar types into soil and biodegradation removal of polycyclic aromatic hydrocarbons (PAHs). The biochars primarily influenced the bacterial community at the genus level, while they strongly affected the fungal community not only at the genus level but also at the class and phylum levels. Principal component analysis (PCA) indicated that the inorganic minerals in biochars played a key role in stimulating microbial abundance (bacteria) and diversity (bacteria and fungi) in soil from the coking plant, and significantly negative correlations between the residual concentrations of PAHs in biochar-treated soils and the ash contents in biochars (generally, p < 0.05 for PAHs with 3–6 rings) were observed. These findings further suggested a positive effect of the inorganic minerals of biochars on stimulating changes in microorganisms, which could contribute to the biodegradation of PAHs in soil from the coking plant. Generally, the addition of biochars to the soils increased the biodegradation percentages of individual PAHs by 3.0–60.3% compared to those of the control. Among these biochars, rice straw-derived biochar pyrolyzed at 600 °C (RS6) effectively degraded PAHs from soil, with increasing biodegradation percentages of individual PAHs from 40.00% to 58.84%. This result was likely attributed to that the substantially specific Acidobacteria-related genera in RS6-treated soil were detected, which contributed to the effective biodegradation of PAHs. Accordingly, biochars pyrolyzed at a relatively high heating temperature with rice straw feedstock containing relatively high mineral nutrients are recommended for application to heavily PAH-contaminated soils.

Study on Occurrence Characteristics and Natural Degradation of Polycyclic Aromatic Hydrocarbons in Mined-out Area of Northern Shaanxi Coal Mine

The rapid economic development is accompanied by the rapid consumption of energy. Coal plays an important role in China’s energy production. With the continuous exploitation of coal resources, the mined-out area of coal mines has continued to increase. PAHs are common organic pollutants in coal mines. With the gradual deepening of the research on PAHs, the natural degradation of indigenous dominant bacteria has become the best choice. The application of microbial treatment to repair PAHs-contaminated soil, and the research on the relationship between PAHs and degrading microorganisms are great significance to the bioremediation of PAHs pollution.

Bioremediation of PAH-Contaminated Soils: Process Enhancement through Composting/Compost

Bioremediation of contaminated soils has gained increasing interest in recent years as a low-cost and environmentally friendly technology to clean soils polluted with anthropogenic contaminants. However, some organic pollutants in soil have a low biodegradability or are not bioavailable, which hampers the use of bioremediation for their removal. This is the case of polycyclic aromatic hydrocarbons (PAHs), which normally are stable and hydrophobic chemical structures. In this review, several approaches for the decontamination of PAH-polluted soil are presented and discussed in detail. The use of compost as biostimulation- and bioaugmentation-coupled technologies are described in detail, and some parameters, such as the stability of compost, deserve special attention to obtain better results. Composting as an ex situ technology, with the use of some specific products like surfactants, is also discussed. In summary, the use of compost and composting are promising technologies (in all the approaches presented) for the bioremediation of PAH-contaminated soils.

Concentrations, distributions, sources, and risk assessment of polycyclic aromatic hydrocarbons in topsoils around a petrochemical industrial area in Algiers (Algeria)

Fifty-five samples were collected from topsoils around a petrochemical industrial area at the east of Algiers (Algeria) and analyzed for 16EPA priority PAHs in the aim to determine the concentrations, the distributions, and the possible sources of polycyclic aromatic hydrocarbons (PAHs). The results of the quantification are then devoted to the assessment of the potential risks as the toxicity, the risk for the ecosystem, and the risk for the human health. The sampling sites were classified into four categories: rural, suburban, urban, and industrial-urban. A new extraction method based on the insertion of a preliminary step, using hot water, was proposed to improve the extraction efficiency. Principal component analysis (PCA) and selected diagnostic ratio of PAHs were used to investigate the source apportionment of these PAHs. The potential toxicity, the ecological, and human health risk of PAHs in soil were estimated using the toxic equivalent quotient, the risk quotient, and the total lifetime cancer risk (TLCR) methods, respectively. The proposed new protocol gave improved recovery rates for the sixteen EPA PAHs particularly for low molecular weight PAHs, with satisfactory repeatability (RSD < 10%). The Σ16PAHs concentrations were varied from 143.73 to 4575.65μgkg-1 with a mean value of 1209.56μgkg-1. Σ16PAH concentrations found for the industrial areas would be 2 times higher than for urban soils and 3 times higher than for the rural soils. The biplots of PCA and the five diagnostic ratios suggested that the most sources of PAHs in the rural, the suburban, and the urban areas are traffic emissions, biomass burning, and coal combustion sources. Some points of the urban-industrial area are from the petroleum source. The found Σ16PAH concentrations and theirs calculated TEQs showed the following trend: industrial-urban > urban > suburban >rural. The potential cancer of human health risks calculated through TLCR results indicated that the exposure to the 7EPA PAH-contaminated soils produces negligible cancer risk to human health.

Peculiar attenuation of soil toluene at contaminated coking sites

In the soil of contaminated coking sites, polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene (BTEX) are typical indicator compounds. Generally, PAHs are enriched in the topsoil layer. BTEX, with higher water solubilities and lower organic carbon-water partitioning coefficients (Koc), are distributed deeper than PAHs. However, current models have employed predictions using single compounds to mimic the migration of BTEX at contaminated coking sites. Such models have not considered the influence of the upper soil layer, where PAHs are enriched. An attempt to fill this gap was made by setting up a control soil column experiment in this study. One column was filled with undisturbed soil (column #1) and the other with PAH-contaminated soil (column #2) to simulate the theoretical and actual surface soil layers, respectively. The results showed that in column #2, the toluene gas concentration of the headspace and time required to reach steady state were notably greater than those in column #1. High-throughput sequencing revealed that there were large microbial community structure differences between the two soil columns throughout the experiment, while some genera that degrade toluene with high efficiency emerged noteworthily in column #2. This implied that the upper soil layer enriched with PAHs was conducive to the degradation of toluene vapor. Applying this finding to human health exposure assessment of toluene suggests that the potential exposure level should be reduced from the current predicted level given the unanticipated attenuation at contaminated coking sites.

Insights into the removal efficiencies of aged polycyclic aromatic hydrocarbons in humic acids of different soil aggregate fractions by various oxidants

Chemically oxidative removal of polycyclic aromatic hydrocarbons (PAHs) in soil is related to their occurrence state. Whether the heterogeneity of natural organic matter has an effect on the occurrence of PAHs in soil and, if there is an effect, on the oxidative removal efficiency of PAHs remains unknown. In this study, the removal efficiencies of 16 priority PAHs aged in humic acids (HAs) of different soil aggregate fractions by various oxidants were investigated by combining soil fractionation and microreaction experiments. Results showed that the accumulations of PAHs in particulate HA (P-HA) and microaggregate occluded HA (MO-HA) mainly occurred in the early period of the aging time frame. In contrast, PAH accumulation in non-aggregated silt and clay associated HA (NASCA-HA) was relatively slow and tended to saturate in the late period of the aging time frame. The cumulative contents of PAHs throughout the entire aging period in MO-HA and NASCA-HA were significantly greater than that in P-HA. The aged PAHs in P-HA and NASCA-HA exhibited the highest and lowest removal efficiencies, respectively. This ranking was mainly governed by the molecular size and polarity of HAs. Sodium persulfate and potassium permanganate had the highest removal efficiencies in total PAHs in HAs, with average efficiencies of 85.8% and 79.1%, respectively, in P-HA. Hydrogen peroxide had the lowest degradation efficiency in PAHs. In particular, the degradation efficiency of total PAHs in NASCA-HA was lowered to 31.0%. PAH congeners in HAs showed a large difference in oxidative removal efficiency. Low-ring PAH was more easily degraded than medium- and high-ring PAHs, and in most treatments, fluoranthene and pyrene in the medium ring and benzo[a]pyrene in the high ring demonstrated higher efficiencies than other PAHs with the same number of rings. Our findings are useful in promoting the accurate and green remediation of PAH-contaminated soils.

Changes of microbial community and activity under different electric fields during electro-bioremediation of PAH-contaminated soil

Electro-bioremediation is a promising technology for remediation of soil contaminated with persistent organic compounds such as polycyclic aromatic hydrocarbons (PAHs). During electro-bioremediation, electrical fields have been shown to increase pollutant degradation. However, it remains unclear whether there is an optimal strength for the electrical field applied that is conductive to the maximum role played by microbes. This study aimed to determine the optimal strength of electric field through the analysis of the effects of different voltages on the microbial community and activity. Four bench-scale experiments with voltages of 0, 1, 2 and 3 V cm−1 were conducted for 90 days in an aged PAH-contaminated soil. The spatiotemporal changes of the soil pH, moisture content and temperature, microbial biomass and community structure, and the degradation extent of PAHs were researched over 90 days. The results indicated that the total microbial biomass and degradation activity were highest at voltages of 2 V cm−1. The concentration of total phospholipid fatty acids, used to quantify soil microbial biomass, reached 65.7 nmol g−1 soil, and the mean degradation extent of PAHs was 44.0%. Similarly, the maximum biomass of actinomycetes, bacteria and fungus also occurred at the voltage of 2 V cm−1. The Gram-positive/Gram-negative and (cy17:0+cy 19:0)/(16:1ω7+18:1ω7) ratios also showed that the intensity of electric field and electrode reactions strongly influenced the microbial community structure. Therefore, to optimize the electro-bioremediation of PAH-contaminated soil, the strength of electric field needs to be selected carefully. This work provides reference for the development of novel electrokinetically enhanced bioremediation processes.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters βm and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (Km) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.