Removal Rate Of Polycyclic Aromatic Hydrocarbons Research Articles

Occurrence, removal, and risk assessment of polycyclic aromatic hydrocarbons and their derivatives in typical wastewater treatment plants

Wastewater treatment plants (WWTPs) have a certain removal capacity for polycyclic aromatic hydrocarbons (PAHs) and their derivatives, but some of them are discharged with effluent into the environment, which can affect the environment. Therefore, to understand the presence, sources, and potential risks of PAHs and their derivatives in WWTPs. Sixteen PAHs, three chlorinated polycyclic aromatic hydrocarbons (ClPAHs), three oxidized polycyclic aromatic hydrocarbons (OPAHs), and three methylated polycyclic aromatic hydrocarbons (MPAHs) were detected in the influent and effluent water of three WWTPs in China. The average concentrations of their influent ∑PAHs, ∑ClPAHs, ∑OPAHs, and ∑MPAHs ranged from 2682.50 to 2774.53 ng/L, 553.26–906.28 ng/L, 415.40–731.56 ng/L, and 534.04–969.83 ng/L, respectively, and the effluent concentrations ranged from 823.28 to 993.37 ng/L, 269.43–489.94 ng/L, 285.93–463.55 ng/L, and 376.25–512.34 ng/L, respectively. The growth of heat transport and industrial energy consumption in the region has a significant impact on the level of PAHs in WWTPs. According to the calculated removal efficiencies of PAHs and their derivatives in the three WWTPs (A, B, and C), the removal rates of PAHs and their derivatives were 69–72%, 62–71%, and 68–73%, respectively, and for the substituted polycyclic aromatic hydrocarbons (SPAHs), the removal rates were 41–49%, 31–40%, and 33–39%, respectively; moreover, the removal rates of PAHs were greater than those of SPAHs in the WWTPs. The results obtained via the ratio method indicated that the main sources of PAHs in the influent of WWTPs were the combustion of coal and biomass, and petroleum contamination was the secondary source. In risk evaluation, there were 5 compounds for which the risk quotient was considered high ecological risk. During chronic disease evaluation, there were 11 compounds with a risk quotient considered to indicate high risk. PAHs and SPAHs with high relative molecular masses in the effluent of WWTPs pose more serious environmental hazards than their PAHs counterparts.

Preliminary study on the enhanced bioremediation of PAH-contaminated soil in Beijing and assessment of remediation effects based on toxicity tests.

In this study, we focused on soil contaminated by polycyclic aromatic hydrocarbons (PAHs) at typical coking-polluted sites in Beijing, conducted research on enhanced PAH bioremediation and methods to evaluate remediation effects based on toxicity testing, and examined changes in pollutant concentrations during ozone preoxidation coupled with biodegradation in test soil samples. The toxicity of mixed PAHs in soil was directly evaluated using the Ames test, and the correlation between mixed PAH mutagenicity and benzo(a)pyrene (BaP) toxicity was investigated in an effort to establish a carcinogenic risk assessment model based on biological toxicity tests to evaluate remediation effects on PAH-contaminated soil. This study provides a theoretical and methodological foundation for evaluating the effect of bioremediation on PAH-contaminated soil at industrially contaminated sites. The results revealed that the removal rate of PAHs after 5min of O3 preoxidation and 4weeks of soil reaction with saponin surfactants and medium was 83.22%. The soil PAH extract obtained after remediation had a positive effect on the TA98 strain at a dose of 2000μg·dish-1, and the carcinogenic risk based on the Ames toxicity test was 8.98 times greater than that calculated by conventional carcinogenic PAH toxicity parameters. The total carcinogenic risk of the remediated soil samples was approximately one order of magnitude less than that of the original soil samples.

Comparative analysis of remediation efficiency and ultrastructural translocalization of polycyclic aromatic hydrocarbons in Medicago sativa, Helianthus annuus, and Tagetes erecta

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile anthropogenic contaminants that can damage soil fertility and threaten the environment due to their hazardous effects on various ecological parameters. The experimental objective was divided into two parts because PAHs are always present in mixtures. The toxicity of anthracene, phenanthrene, pyrene, and fluoranthene was examined and investigated the potential of three phytoremediator plants species viz Tagetes erecta, Helianthus annuus, and Medicago sativa for remediation and translocation of individual PAH. PAHs were shown to have inhibitory or stimulating effects on growth, antioxidant properties, and impact on the structure of plant cells. The result showed that M. sativa significantly enhances the removal rate of PAHs in the soil. The dissipation rate reached 96.2% in M. sativa planted soil, followed by H. annuus and T. erecta. Among the plant species, M. sativa exhibited the highest root and shoot concentrations (314.37 and 169.55 mg kg−1), while the lowest concentration was 187.56 and 76.60 mg kg−1 in T. erecta. SEM-EDX and fluorescence micrographs confirmed that pyrene altered plant tissue’s ultrastructure and cell viability and was found to be the most toxic and resistant. M. sativa was proven to be the most effective plant for the mitigation of PAHs.

Effects of deodorization on the content of polycyclic aromatic hydrocarbons (PAHs), 3-monochloropropane-1,2-diol esters (3-MCPDE) and glycidyl esters (GE) in rapeseed oil using ethanol steam distillation at low temperature

High temperature is beneficial for the removal of polycyclic aromatic hydrocarbons (PAHs) from oil via steam, but leads to an increase in the content of 3-monochloropropane-1,2-diol esters (3-MCPDE) and glycidyl esters (GE). To inhibit the production of 3-MCPDE and GE during the removal of PAHs, rapeseed oil was deodorized using ethanol steam at low-temperature (140–220 °C) (L-ESD) and the content changes were studied for PAHs, 3-MCPDE and GE, and compared with conventional high-temperature water steam deodorization (H-WSD) (250 °C for 60 min). The removal rates of PAHs in L-ESD oil can be higher than those in conventional H-WSD oil, and the contents of 3-MCPDE and GE in L-ESD oil (140–180 °C for 60–100 min) ranged from 48.32 to 73.65 % and 50.49–69.90 %, respectively, in H-WSD oil due to the lower temperature of ethanol steam deodorization. These results indicate that L-ESD is beneficial in minimizing the contents of PAHs, 3-MCPDE and GE in vegetable oil.

Biochar reduces uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in winter wheat on a PAH-contaminated soil

Biochar has been used previously for remediation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils for years, which has achieved remarkable results in improving removal of soil PAHs and reducing PAHs uptake in crops. However, the underlying mechanism of biochar application in reducing the uptake and accumulation of PAHs in winter wheat remains unclear. Pot trials using PAHs-contaminated soils were conducted for whole plant growth period of winter wheat, which were amended with 2% (w/w) bamboo biochar (BB), coconut shell biochar (CB) and maize straw biochar (MSB) or not (CK). Compared with CK, application of the three types of biochar significantly (p < 0.01) reduced grain PAHs concentration, the total equivalent concentration (TEC) values and the incremental lifetime cancer risk (ILCR) of grain PAHs, indicating that application of biochar reduced the exposure risk of PAHs in wheat grain, especially for MSB. Consistently, application of the three types of biochar significantly (p < 0.05) reduced uptake and accumulation of PAHs in root and stem of wheat, which may be due to that application of biochar enhanced the degradation of PAHs in the rhizosphere soil. Compared with CK, application of the three types of biochar significantly (p < 0.05) reduced the concentration of PAHs in the rhizosphere soil by 15.9%, 26.1% and 33.7%, respectively. It was found that the degradation rate of HMW PAHs (high molecular weight PAHs, 5-6 ring PAHs) was significantly (p < 0.05) higher than that of LMW PAHs (low molecular weight PAHs, 2-4 ring PAHs) regardless of types of biochar used. Additionally, application of the three types of biochar significantly increased the relative abundance of dominant bacterial phyla and genera in soil. Redundancy analysis and correlation analysis results also showed that there was a strong correlation between the removal rate of PAHs and dominant bacteria in the rhizosphere soil. The present study indicated that biochar could reduce dietary risk of PAHs in wheat grains mainly by increasing the abundance of bacteria related to PAHs degradation, promoting the biodegradation of PAHs in the rhizosphere soil and consequently reducing PAHs uptake in wheat.

Remediation of Petroleum Contaminated Tidal Flat Sediments by Co-bioremediation System

ABSTRACT The remediation effects of oil-degrading bacteria, Nereis succinea and Suaeda heteroptera, on oil-contaminated sediments were studied by laboratory pot experiments under simulated conditions of intertidal zone. Three concentrations of oil-contaminated sediments (I: 500 mg/Kg, II: 1500 mg/Kg, III: 3000 mg/kg) and four bioremediation treatment groups (bacteria group, bacteria-N. succinea group, bacteria-S. heteroptera group, bacteria-N. succinea-S. heteroptera group) were set up, and the oil removal efficiency was measured after 15, 30, 45, 60, and 70 days of the experiment, respectively. The results showed that the percent removals of total petroleum content, linear hydrocarbons, and polycyclic aromatic hydrocarbons (PAHs) of each sediment under all bioremediation treatments were significantly higher than those of the control groups (P < .05). The bacteria – N. succinea – S. heteroptera synergistic model performed best, after 70 days of remediation tests, the percent removals of total petroleum content reached 51.9%, 47.8%, and 40.6% under I, II, and III oil concentration conditions, respectively, indicating the biological disturbance caused by N. succinea and the rhizosphere effect of S. heteroptera can effectively promote the oil removal of the bioremediation system. In addition, the oil degradation speed in each bioremediation combination showed an increasing trend in the began month, peaked during 15–30 d period, and then decreased obviously at 30–70 d in all bioremediation treatments. We also found that the synergistic bioremediation models promoted the removal of petroleum linear hydrocarbons and PAHs, and the percent removals of linear hydrocarbons were negatively related to their carbon chain length, and the removal rates of PAHs decreased significantly as the number of benzene rings increases. The above results demonstrated the feasibility of co-bioremediation technology in the remediation of petroleum contaminated tidal flat sediments.

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

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

Enhanced remediation of PAHs-contaminated site soil by bioaugmentation with graphene oxide immobilized bacterial pellets

Bioaugmentation is considered as a promising technology for cleanup of polycyclic aromatic hydrocarbons (PAHs) from contaminated site soil, however, available high-efficiency microbial agents remain very limited. Herein, we explored graphene oxide (GO)-immobilized bacterial pellets (JGOLB) by embedding high-efficiency degrading bacteria Paracoccus aminovorans HPD-2 in alginate-GO-Luria-Bertani medium (LB) composites. Microcosm culture experiments were performed with contaminated site soil to assess the effect of JGOLB on the removal of PAHs. The results showed that JGOLB exhibited greatly improved mechanical strength, larger specific surface area and more enriched mesopores, compared with traditional immobilized bacterial pellets. They significantly increased the removal rate of PAHs by 18.51% compared with traditional bacterial pellets, reaching the removal rate at 62.86% over 35 days of incubation. Moreover, the increase mainly focused on high-molecular-weight PAHs. JGOLB not only greatly increased the abundance of embedded degrading bacteria in soil, but also significantly enhanced the enrichment of potential indigenous degrading bacteria (Pseudarthrobacter and Arthrobacter), the functional genes involved in PAHs degradation and a number of ATP transport genes in the soil. Overall, such nanocomposite bacterial pellets provide a novel microbial immobilization option for remediating organic pollutants in harsh soil environment.

Phytoremediation potential of Bermuda grass (Cynodon dactylon (L.) pers.) in soils co-contaminated with polycyclic aromatic hydrocarbons and cadmium

Soils co-contaminated with polycyclic aromatic hydrocarbons (PAHs) and cadmium (Cd) have serious environmental impacts and are highly toxic to humans and ecosystems. Phytoremediation is an effective biotechnology for the remediation and restoration of PAH- and Cd-polluted soils. Pot experiments were conducted to investigate the individual and combined effects of PAHs (1238.62 mg kg−1) and Cd (23.1 mg kg−1) on the phytoremediation potential of Bermuda grass grown in contaminated soils. Bermuda grass exhibited a significant decrease in plant growth rate, leaf pigment content, root activity, plant height and biomass and a remarkable increase in malondialdehyde content and electrolyte leakage when grown in PAH- and Cd-contaminated soils compared with grass grown in uncontaminated soils. The activity of soil enzymes, including urease, alkaline phosphatase, sucrose, and fluorescein diacetate hydrolysis, were reduced in soil with PAH and Cd stress. Furthermore, the toxicity of combined PAHs and Cd on Bermuda grass growth and soil enzyme activity was much higher than that of PAH or Cd stress alone, suggesting a synergistic effect of PAHs and Cd on cytotoxicity. To scavenge redundant reactive oxygen species and avoid oxidative damage, Bermuda grass increased plant catalase, superoxide dismutase, and peroxidase activity and soluble sugar and proline content. The bioconcentration factor of Cd in Bermuda grass grown under Cd alone and combined PAH and Cd exposure was greater than 1 for both, suggesting that Bermuda grass has a high Cd accumulation ability. Under PAH alone and combined PAH and Cd exposure conditions, a higher PAH removal rate (41.5–56.8%) was observed in soils planted with Bermuda grass than in unplanted soils (24.8–29.8%), indicating that Bermuda grass has a great ability to degrade PAHs. Bermuda grass showed great phytoremediation potential for the degradation of PAHs and phytoextraction of Cd in co-contaminated soils.

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.

Enhanced oxidative activation of chlorine dioxide by divalent manganese ion for efficient removal of PAHs in industrial soil

Chlorine dioxide (ClO2) takes effect as a promising chemical oxidant to remove polycyclic aromatic hydrocarbons (PAHs) from contaminated soil in situ. However, the conventional ClO2 degradation procedure is limited by its reaction selectivity to organic pollutants, as well as its low economic efficiency with huge dosage. Systematical study of activated ClO2 oxidation which is more efficient to remove PAHs in soil is still scarce. Herein, the impact of divalent manganese ion [Mn(Ⅱ)] on activating ClO2 to oxidize PAHs in real contaminated soil was currently studied, including the kinetics, degradation products, mechanisms, and biological toxicity. The results revealed that the PAHs removal rate constants (k1) had a quadratic relationship with Mn(II) concentrations (k1 = -0.005 × [Mn(Ⅱ)]2 + 0.0033 × [Mn(Ⅱ)] + 0.0222, R2 = 0.9084, [Mn(Ⅱ)] = 0 ∼ 5 mM), the best degradation performance was obtained when the molar ratio of Mn(II)/ClO2 was 1/20. Furthermore, the optimal initial ClO2 concentration of 2500 mg/L could satisfy the comprehensive considerations of efficiency and economy. At the pH range of 3 ∼ 11, the removal efficiency decreased with increasing pH. Four representative PAH congeners (anthracene, phenanthrene, pyrene, and fluoranthene) had been chlorine substituted and oxygenated, but benzene ring rupture was observed only in fluoranthene simultaneously. XPS spectra, EPR analysis, and quenching experiments indicated the mechanisms that HOCl and •OH were the principal active species in the oxidation reaction. The toxicity evaluation by earthworms Eisenia fetida resulted out that high toxic effect to organism still remained in remediated soil which should be paid attention to.

Photocatalytic Degradation of Polycyclic Aromatic Hydrocarbons in Water by 3D Printed TiO2 Composites

Recent progress in developing composites embedded with photocatalysts indicates application for wastewater treatment. However, significant gaps remain in developing effective photocatalyst–polymer composites for use as customizable, deployable, and retrievable structures for mitigating environmental contamination. The goal of this study was to generate and evaluate the performance of 3D printed TiO2 composites for degrading polycyclic aromatic hydrocarbons (PAHs) in waters affected by contaminated sediment. Photocatalytic structures were fabricated using polylactic acid (PLA) compounded with TiO2 nanoparticles as filament feedstock and printed using a benchtop 3D printer. Photocatalysis and photolysis experiments were conducted in controlled environmental chambers under full spectrum light (λ = 280–750 nm). 3D printed PLA-TiO2 disks increased the degradation kinetics (compared to photolysis) of a complex mixture of 4- to 5-ring PAHs achieving nondetectable concentrations within hours to days. The PAH removal rate was relatively rapid, with 3D printed PLA-TiO2 treatments achieving degradation half-lives within ∼6 to ∼24 h. After 48 h of treatment, both photolysis and photocatalysis eliminated toxicity to Ceriodaphnia dubia. These data indicate the potential application of 3D printable photocatalytic polymers to mitigate problematic organic constituents in water and highlight the benefits of additive manufacturing to rapidly prototype and optimize innovative structures.

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.

Co-metabolic Effect of Glucose on Methane Production and Phenanthrene Removal in an Enriched Phenanthrene-Degrading Consortium Under Methanogenesis.

Anaerobic digestion is used to treat diverse waste classes, and polycyclic aromatic hydrocarbons (PAHs) are a class of refractory compounds that common in wastes treated using anaerobic digestion. In this study, a microbial consortium with the ability to degrade phenanthrene under methanogenesis was enriched from paddy soil to investigate the cometabolic effect of glucose on methane (CH4) production and phenanthrene (a representative PAH) degradation under methanogenic conditions. The addition of glucose enhanced the CH4 production rate (from 0.37 to 2.25mg⋅L−1⋅d−1) but had no influence on the degradation rate of phenanthrene. Moreover, glucose addition significantly decreased the microbial α-diversity (from 2.59 to 1.30) of the enriched consortium but showed no significant effect on the microbial community (R2=0.39, p=0.10), archaeal community (R2=0.48, p=0.10), or functional profile (R2=0.48, p=0.10). The relative abundance of genes involved in the degradation of aromatic compounds showed a decreasing tendency with the addition of glucose, whereas that of genes related to CH4 synthesis was not affected. Additionally, the abundance of genes related to the acetate pathway was the highest among the four types of CH4 synthesis pathways detected in the enriched consortium, which averagely accounted for 48.24% of the total CH4 synthesis pathway, indicating that the acetate pathway is dominant in this phenanthrene-degrading system during methanogenesis. Our results reveal that achieving an ideal effect is diffcult via co-metabolism in a single-stage digestion system of PAH under methanogenesis; thus, other anaerobic systems with higher PAH removal efficiency should be combined with methanogenic digestion, assembling a multistage pattern to enhance the PAH removal rate and CH4 production in anaerobic digestion.

Pilot-scale bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil using an indigenous bacterial consortium in soil-slurry bioreactors

Soil-slurry bioreactor based bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil was studied through laboratory and pilot-scale trials, in which the degradation mechanism was explored. Indigenous PAH-degrading consortium was firstly screened out and it degraded 80.5% of total PAHs in lab-scale bioreactors. Then a pilot-scale trial lasting 410 days was conducted in two bioreactors of 1.5 m3 to examine the operating parameters and validate the optimum running conditions. During the initial 200 days, the crucial running parameters affecting PAH removal were evaluated and selected. Subsequently, an average PAH removal rate of 93.4% was achieved during 15 consecutive batches (210 days) under the optimum running conditions. The kinetic analysis showed that the reactor under optimum conditions achieved the highest PAH degradation rate of 0.1795 day−1 and the shortest half-life of 3.86 days. Notably, efficient mass transfer of PAHs and high biodegradation capability by bioaugmented consortia in soil-slurry bioreactors were two key mechanisms for appreciable PAH removal performance. Under the optimal operating conditions, the degradation rate of low-molecular-weight (LMW) PAHs was significantly higher than high-molecular-weight (HMW) PAHs; when the mass transfer was limited, there was no significant difference between their degradation behaviors. Both microbial co-metabolism and collaborative metabolism might occur when all PAHs demonstrated low degradation rates. The findings provide insightful guidance on the future assessment and remediation practices of PAH-contaminated sites.

The effects of exogenous application of melatonin on the degradation of polycyclic aromatic hydrocarbons in the rhizosphere of Festuca.

The study aimed to assess the effects of melatonin, a plant growth regulator, on the degradation of phenanthrene (Phe) and pyrene (Py), in the rhizosphere of the Festuca grass. The experiments were divided into the following groups: 1) soil contaminated with Phe and Py, without the Festuca, 2) contaminated soil+Festuca, 3-5), contaminated soil+Festuca+ the application of melatonin in three separate doses: 10, 50, or 100μM. After 90 days, the effects of melatonin supplementation on the degradation of polycyclic aromatic hydrocarbons (PAHs) were analyzed by evaluating the rate of PAHs degradation, the expression of genes encoding salicylaldehyde dehydrogenase (SDH) and glutathione peroxidase (GPX) enzymes in Pseudomonas putida, as well as by measuring the total activity of dehydrogenase and peroxidase enzymes. Our results have shown that in soil contaminated by 300mgkg-1 PAHs, application of melatonin (10, 50, 100μM), resulted in the following increase in the dehydrogenase and peroxidase activity in all three applied doses (19% and 5.7%), (45.3% and 34.3%), (40.9% and 14.3%), respectively in comparison to the control group. The experiment showed that soil supplementation with melatonin at 50μM, resulted in the highest removal rate of PAHs. According to our results, melatonin demonstrated a potentially favorable role in enhancing plant biomass, as well as an increase in soil bacterial population, and the activity of antioxidative enzymes in P.putida, causing all tested parameters of the soil and the expression of desired genes to be advantageously altered for the degradation of the chosen PAHs.

Assessment of PAH degradation potential of native species from a coking plant through identifying of the beneficial bacterial community within the rhizosphere soil

Understanding the mechanisms underlying plant–rhizobacteria interactions in field-contaminated soils is crucial for designing effective rhizoremediation strategies. This study aimed to test the ability of four native herb species to remove polycyclic aromatic hydrocarbons (PAHs) and to analyze their associated bacterial community structures and functional genes within the rhizosphere from the abandoned site of a former Shenyang coking plant in China; the bulk soil was collected as control. All four species removed PAHs, of which the rhizosphere of Kochia scoparia had the highest PAH removal rate (almost 30.2%). Although the composition of the bacterial community within the rhizosphere varied among plant species, all plant species could promote the growth of Sphingomonas, Pedomicrobium, Rhodoplanes, Blastoccus, Mycobacterium, Devosia, and Pseudomonas, and their relative abundance positively correlated with the removal rates of PAHs, soil moisture, and total carbon/total nitrogen in the rhizosphere. Moreover, the activities of 1-aminocyclopropane-1 -carboxylic deaminase gene and Gram-negative ring-hydroxylating dioxygenase gene significantly (P < 0.05) increased compared with those in the control, and these activities had a strong positive correlation with the removal rates of PAHs [r = 0.759 (P < 0.01) and 0.87 (P < 0.01), respectively]. The findings of this study indicated that PAHs were the main factor driving the composition of beneficial bacteria in PAH rhizodegradation, and the PAH rhizoremediation of native plants grown in coking plant can be controlled though altering soil properties.

Comparison of the Fe2+/H2O2 and Fe2+/PMS systems in simulated sludge: Removal of PAHs, migration of elements and formation of chlorination by-products

In this study, polycyclic aromatic hydrocarbons (PAHs) at practical concentrations in the simulated sludge treated by the Fe2+/H2O2 and Fe2+/peroxymonosulfate (PMS) systems were evaluated in terms of the PAHs (phenanthrene, anthracene, fluoranthene) removal, element migration, Cl− effect, and chlorination by-product formation. The results indicated that according to the removal rate of PAHs, the optimal dosage of the Fe2+/PMS system (∑PAHs removal rate was 64.66 ± 2.82 %) was 1/30 of that for the Fe2+/H2O2 system (∑PAHs removal rate was 78.63 ± 0.38 %). The elemental contents in the simulated sludge were mainly affected by the extent of advanced oxidation and the amount of generated iron flocs. By studying the PAHs removal, free chlorine formation, total organochlorine content, and PAHs products in Fe2+/H2O2/Cl- and Fe2+/PMS/Cl- systems, it was found that chlorine radicals (·Cl) had high reactivity with phenanthrene and fluoranthene, whereas dichloride anion radicals (Cl2·-) exhibited the opposite behavior. Furthermore, PAHs were oxidized by ·Cl and hydroxyl radical in the Fe2+/H2O2/Cl- system, whereas PAHs and their products were chlorinated by free chlorine and ·Cl in the Fe2+/PMS/Cl- system to six chlorinated by-products such as Cl-PAHs (9-Cl-phenanthrene, 2-Cl-anthracene, 9,10-Cl2-anthracene, 3-Cl-fluoranthene). These results provide some useful suggestions for the safe advanced oxidation process treatment of textile dyeing sludge.

Biodegradation of polyaromatic hydrocarbons and the influence of environmental factors during the co-composting of sewage sludge and green forest waste

The main aim of this research was to study the biodegradation of polycyclic aromatic hydrocarbons (PAHs) and the influence of environmental factors during composting in order to realize the utilization of PAHs contaminated sewage sludge. A production scale compost experiment was conducted with three mixtures of sewage sludge (SS): green forest waste (GFW) at quality ratios of 3:1 (T1), 3:2 (T2) and 3:3 (T3). The residual concentration of PAHs in the three treatments met the permissible limit prescribed by the Agricultural Sludge Pollutant Control Standard (GB 4284-2018). The biodegradation rates of PAHs were 0.0280, 0.0281 and 0.0218 mg/d, and removal efficiencies were 70.7%, 75.2% and 62.4% in T1, T2, T3, respectively, which followed the first-order rate kinetics. The residual concentration of PAHs in T2 was the lowest (1.81 mg/kg), while the germination index (GI) of Tall Fescues (~0.9) was the highest during 50 days of co-composting. The bacterial diversity negatively correlated with the residual PAHs content. The main genus, Bacillus, Pseudomonas and Methylotenera, with cellulose-degrading and PAHs co-metabolizing functions contributed significantly to sludge maturation and PAHs degradation. The dominant microorganisms, Pseudomonas, Sphingobacterium and Chitinophagaceae_uncultured, could support the high removal rate of PAHs in T2. Temperature, pH, total organic carbon (TOC), total nitrogen (TN) and carbon/nitrogen (C/N) ratio had significant positive effect on the compost maturity and quality, and these parameters correlated with the PAHs biodegradation efficiency during composting, especially in T2.

Effects of biochar and organic substrates on biodegradation of polycyclic aromatic hydrocarbons and microbial community structure in PAHs-contaminated soils

A incubation experiment was conducted to investigate whether combined amendment of biochar (B) and compost (CP), mushroom residue (M) and corn straw (Y) could enhance biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. After 77 days of incubation, both B + M and B + Y significantly (p < 0.01) increased removal rate of PAHs compared with amendment of biochar alone. However, B+CP resulted in a significant (p < 0.01) decreasing of PAHs removal. Compared with no biochar and no organic substrates addition (CK) and B, both B+M and B+Y significantly (p < 0.01) enhanced concentrations of dissolved organic carbon (DOC) and were favorable for the microbial growth reflected by microbial biomass carbons (MBC) and emission of carbon dioxide. Redundancy analysis (RDA) indicated that B + CP, B + M and B + Y separated the bacterial community compared with CK and B. However, the community composition structure in B + CP was different from that of B + M and B + Y. Moreover, the abundance of some PAHs degraders and PAH degradation genes predicted by PICRUSt software was promoted by B + M or B + Y, whereas that was inhibited under B + CP. The present study suggested that both B + M and B + Y could accelerate biodegradation of PAHs mainly through increasing the concentration of DOC and the abundances of microbial PAH degraders in soils.