Recovery of phenanthrene-degrading bacteria after simulated in situ persulfate oxidation in contaminated soil

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 5 min of O3 preoxidation and 4 weeks 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 2000 μg·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.

Overestimate of remediation efficiency due to residual sodium persulfate in PAHs contaminated soil and a solution

Oxidation remediation is a commonly used technology for PAHs contaminated soil presently, but the overestimate of efficiency due to ongoing remediation by residual oxidants during extraction and testing has not been paid enough attention. In this study, persulfate was activated by Fe(II) to investigate the effects of residual oxidants on PAHs removal during detection process and the elimination effects of adding Na₂SO₃ and extending sampling time on residual oxidants. Results verified that the residual oxidants removed PAHs in extraction process, making the results lower than the actual values: the detection recovery rate η of ∑PAHs and 3-6 ring PAHs ranged from 24.3% (25% Na₂S₂O₈ treatment) to 87.4% (5% Na₂S₂O₈+4/4Fe²⁺ treatment), 20.1%-99.0%, 28.9%-87.9%, 20.8%-89.4%, and 18.6%-76.9%, respectively. After adding Na₂SO₃, the accuracy of detection results increased significantly: the η of ∑PAHs and 3-6 ring PAHs increased to 64.1%-96.5%, 58.8%-95.5%, 73.8%-114.4%, 60.6%-95.6%, and 45.4%-77.1%, respectively. After 49 days of adding oxidants, residual oxidants had no considerable effect on the detection of PAHs, indicating it was appropriate to start soil remediation verification sampling49 days after the remediation was completed. The observed results will help scientific evaluation of the remediation effects of chemical oxidation on organic contaminated soil.

Degradation of organic contaminants in marine sediments by peroxymonosulfate over LaFeO3 nanoparticles supported on water caltrop shell-derived biochar and the associated microbial community responses

Sediment is an important final repository of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Herein, a novel catalyst of LaFeO₃ nanoparticles supported on biochar was synthesized from water caltrop shell by chemical precipitation. The composite (LFBC) was used as peroxymonosulfate (PMS) activator to oxidize PAHs in real marine sediments. Systematic surface characterization confirmed the immobilization of well crystalline nano LaFeO₃ particles onto the biochar surface. Under optimal conditions, i.e., [PMS] = 3 × 10^-4 M, [LFBC] = 0.75 g/L, pH 6.0, and seawater, the total PAH degradation efficiency was 90%, while that of 2-, 3-, 4-, 5-, and 6-ring PAHs was 52%, 61%, 66%, 56%, and 29%, respectively, in 24 h. The Langmuir-Hinshelwood equation better predicted the PAHs degradation kinetics over LFBC by PMS. Interactions between surface oxygen species at LaFeO₃ defective sites and the graphitized biochar network facilitated the PAHs degradation. Furthermore, changes in the bacterial community during the LFBC/PMS treatment were highlighted to assess the sustainable development of the sediment ecosystem. The LFBC/PMS process enhanced the biological richness and diversity of sediment eco-systems. The major phylum was Proteobacteria initially, while Hyphomonas was the genera after LFBC/PMS treatment of the sediment.

Remediation of polycyclic aromatic hydrocarbons by sulfate radical advanced oxidation: Evaluation of efficiency and ecological impact

Remediation of polycyclic aromatic hydrocarbon (PAH) contamination in soil remains expensive and difficult. Sulfate radical advanced oxidation processes (SR-AOPs) can be used for in situ PAH oxidation but their efficiency and ecological impacts require evaluation. Here, we tested the remediation efficiency and ecological impacts of an SR-AOP combining sodium persulfate and ferrous sulfate (FS), the FS SR-AOP with the chelating agent citric acid (FS+CA), and the FS SR-AOP with chelating agent and the surfactant IGEPALCA-720 (FS+CA+IG) compared with natural attenuation (control, CK). We measured PAH, soil physicochemical properties (pH, soil organic matter [SOM]), and soil biological properties (polyphenol oxidase [PPO] activity, peroxidase [POD] activity, soil microbes) in contaminated soil samples after incubation with FS, FS+CA, FA+CA+IG, or CK for 1, 15, and 30 d. Compared with CK, all SR-AOPs significantly decreased PAH after 1 d, with FS+CA+IG showing the highest efficiency (80.8%) and PAH removal peaking at 15 d. FS+CA+IG treatment reduced SOM the least and soil pH the most; after 30 d, SOM recovered to ~80% of the level observed in CK, but soil pH decreased further. PPO and POD activities were highest after 15 and 30 d of FS+CA+IG treatment. Real-time quantitative PCR demonstrated that SR-AOPs significantly decreased quantities of PAH-degrading bacteria, soil bacteria, fungi, and actinobacteria at 1 d, but after 30 d, the microbes recovered to levels similar to those observed in CK, with no significant differences among SR-AOPs. SR-AOPs reduced bacterial diversity and changed the dominant phylum from Acidobacteria to Firmicutes. In summary, SR-AOP treatment with both the chelating agent and the surfactant produced the best PAH removal and least SOM destruction but the largest pH decrease, although some factors recovered with longer incubation. This study provides key information for improving PAH remediation and evaluating its ecological impact.

Enhancing remediation of PAH-contaminated soil through coupling electrical resistance heating using Na2S2O8

Soil polycyclic aromatic hydrocarbons (PAHs) contamination caused by factory relocations is a serious environmental issue across the world. Electrical resistance heating (ERH) and chemical oxidation are two promising in-situ methods for treating volatile and semi-volatile organic pollutants in contaminated soil. Coupling of ERH and chemical oxidation technologies to improve the remediation efficiency for PAH-contaminated soil was estimated in this study. PAH removal ratio in contaminated soils using ERH treatment were significantly negatively correlated with the boiling point of the pollutants (P = 0.002), and 21.63% (DBA high boiling point) to 71.53% (Nap low boiling point) of PAHs in the contaminated soil were removed in 120 min. With oxidant Na₂S₂O₈ coupling, the removal ratio were increased as more oxidant was added. For one Phe, 35.90% was removed by ERH treatment and increased to 52.90% and 79.42% when 0.05 or 2.5 mmol/g oxidant was added, respectively. PAHs with higher boiling points had more obvious removal ratio, such as Bap, which increased from 23.50% to 85.47% when coupling ERH with Na₂S₂O₈, and Phe which increased from 35.90% to 79.42%. Relationships between boiling points and PAH removal ratio changed with coupled oxidants, indicating a change of mechanism from volatilization to coupling effects of volatilization and oxidation with the introduction of Na₂S₂O₈. A dynamic experiment showed that Na₂S₂O₈ can accelerate 45.50% of the treatment process. The results of this research demonstrated a novel, cost-effective coupling approach for remediating soil contaminated by organic pollutants.

Degradation of poly(butylene adipate-co-terephthalate) by Stenotrophomonas sp. YCJ1 isolated from farmland soil

In recent years, poly (butylene adipate-co-terephthalate) (PBAT) has been widely used. However, PBAT-degrading bacteria have rarely been reported. PBAT-degrading bacteria were isolated from farmland soil and identified. The effects of growth factors on the degradation of PBAT and the lipase activity of PBAT-degrading bacteria were assessed. The degradation mechanism was analyzed using scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, X-ray diffraction, and liquid chromatography-mass spectrometry. The results showed that Stenotrophomonas sp. YCJ1 had a significant degrading effect on PBAT. Under certain conditions, the strain could secrete 10.53 U/mL of lipase activity and degrade 10.14 wt.% of PBAT films. The strain secreted lipase to catalyze the degradation of the ester bonds in PBAT, resulting in the production of degradation products such as terephthalic acid, 1,4-butanediol, and adipic acid. Furthermore, the degradation products could participate in the metabolism of YCJ1 as carbon sources to facilitate complete degradation of PBAT, indicating that the strain has potential value for the bioremediation of PBAT in the environment.

Remediation of PBDEs-metal co-contaminated soil by the combination of metal stabilization, persulfate oxidation and bioremediation

Laboratory experiments were performed to investigate the efficiency of a simultaneous metal stabilization, persulfate oxidation and bioremediation for decontaminating polybrominated diphenyl ethers (PBDEs) and toxic metals from an actual soil polluted by the recycling activity of electronic waste. Biochar and bentonite were applied to the soil for immobilizing heavy metals (Cu, Pb, Zn and Ni). It was found that the toxicity level declined most significantly in the case of 20 g/kg biochar +20 g/kg bentonite. A low dose of persulfate (20 mmol/kg soil) was found to be suitable for oxidizing soil PBDEs and enhancing the bioavailability of PBDEs residue. Persulfate oxidation reduced the soil organic matter content, and caused dramatic decrease of bacterial density. Nevertheless, microbial activity and number recovered on the whole during 90 days of bioremediation. Finally, a degradation efficiency of 94.6% and a mineralization efficiency of 60.3% were obtained by the hybrid treatment scheme. The pyrosequencing analysis indicates that soil bacterial community changed obviously during the treatments, and there was an enrichment of PBDE-degrading populations during bioremediation relative to that of oxidized soil.

Removal of polycyclic aromatic hydrocarbons (PAHs) and the response of indigenous bacteria in highly contaminated aged soil after persulfate oxidation

Integrated chemical-biological treatment is a promising alternative to remove PAHs from contaminated soil, wherein indigenous bacteria is the key factor for the biodegradation of residual PAHs after the application of chemical oxidation. However, systematical study on the impact of persulfate (PS) oxidation on indigenous bacteria as well as PAHs removal is still scarce. In this study, the influences of different PS dosages (1%, 3%, 6%, and 10% [w/w]), as well as various activation methods (native iron, H₂O₂, alkaline, ferrous iron, and heat) on PAHs removal and indigenous bacteria in highly contaminated aged soil were investigated. Apparent degradation of PAHs in the soil treated with PS oxidation was observed, and the removal efficiency of total PAHs in the soil ranged from 38.28% to 79.97%. The removal efficiency of total PAHs in the soil increased with increasing consumption of PS. However, the bacterial abundance in soil was negatively affected following oxidation for all of the treatments added with PS, with bacterial abundance in the soil decreased by 0.89-2.93 orders of magnitude compared to the untreated soil. Moreover, the number of total bacteria in the soil decreased as PS consumption increased. Different PS activation methods and PS dosages exhibited different influences on the bacterial community composition. Bacteria capable of degrading PAHs under anoxic conditions were composed predominantly by Proteobacteria and Firmicutes. The total amount of Proteobacteria and Firmicutes also decreased with increasing consumption of PS. The results of this study provide important insight for the design of PAHs contaminated soil remediation projects.

Response of sulfate-reducing bacteria and supporting microbial community to persulfate exposure in a continuous flow system

Coupling of chemical oxidation using persulfate with bioremediation has been proposed as a method to increase remedial efficacy at petroleum hydrocarbon contaminated sites. To support this integrated treatment approach, an understanding of persulfate impact on the indigenous microbial community is necessary for system design. As sulfate-reducing bacteria (SRB) are active in most aquifer systems and can utilize the sulfate generated from the degradation of persulfate, this study assessed the impact on SRB and the supporting anaerobic microbial community when exposed to persulfate in a continuous flow system. A series of bioreactors (1000 L) packed with anaerobic aquifer material were operated for an 8 month acclimatization period before being continuously subjected to benzene, toluene, ethylbenzene and xylenes (total BTEX 3 mg L-1). After 2 months, the bioreactors were then exposed to an unactivated persulfate solution (20 g L-1), or an alkaline-activated persulfate solution (20 g L-1, pH 12) then effluent-sampled for 60 days following. A combination of culture and molecular-based techniques were used to monitor SRB presence and structural profiles in the anaerobic SRB-specific and broader microbial community. Post-exposure, the rate of BTEX mass removal remained below pre-exposure values; however, trends suggest that full recovery would be expected. Rebound of SRB-specific and the associated microbial community to pre-exposure levels were observed in all exposed bioreactors. Structural community profiles identified recovery in both microbial species and diversity indices. Findings from this investigation demonstrate robustness of SRB in the presence of a supporting microbial community and, thus, are suitable organisms for target use during bioremediation in an integrated system with persulfate.

Effect of various chemical oxidation reagents on soil indigenous microbial diversity in remediation of soil contaminated by PAHs

Chemical oxidation is a promising pretreatment step coupled with bioremediation for removal of polycyclic aromatic hydrocarbons (PAHs). The effectiveness of Fenton, modified Fenton, potassium permanganate and activated persulfate oxidation treatments on the real contaminated soils collected from a coal gas plant (263.6 ± 73.3 mg kg^-1 of the Σ16 PAHs) and a coking plant (385.2 ± 39.6 mg kg^-1 of the Σ16 PAHs) were evaluated. Microbial analyses showed only a slight impact on indigenous microbial diversity by Fenton treatment, but showed the inhibition of microbial diversity and delayed population recovery by potassium permanganate reagent. After potassium permanganate treatment, the microorganism mainly existed in the soil was Pseudomonas or Pseudomonadaceae. The results showed that total organic carbon (TOC) content in soil was significantly increased by adding modified Fenton reagent (1.4%-2.3%), while decreased by adding potassium permanganate (0.2%-1%), owing to the nonspecific and different oxidative properties of chemical oxidant. The results also demonstrated that the removal efficiency of total PAHs was ordered: permanganate (90.0%-92.4%) > activated persulfate (81.5%-86.54%) > modified Fenton (81.5%-85.4%) > Fenton (54.1%-60.0%). Furthermore, the PAHs removal efficiency was slightly increased on the 7th day after Fenton and modified Fenton treatments, about 14.6%, and 14.4% respectively, and the PAHs removal efficiency only enhanced 4.1% and 1.3% respectively from 1st to 15th day after potassium permanganate and activated persulfate treatments. The oxidants greatly affect the growth of soil indigenous microbes, which cause further influence for PAHs degradation by bioremediation.

Response and recovery of microbial communities subjected to oxidative and biological treatments of 1,4-dioxane and co-contaminants

Microbial community dynamics were characterized following combined oxidation and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Bioremediation is generally inhibited by co-contaminate CVOCs; with only a few specific bacterial taxa reported to metabolize or cometabolize 1,4-dioxane being unaffected. Chemical oxidation by hydrogen peroxide (H₂O₂) as a non-selective treatment demonstrated 50-80% 1,4-dioxane removal regardless of the initial CVOC concentrations. Post-oxidation bioaugmentation with 1,4-dioxane metabolizer Pseudonocardia dioxanivorans CB1190 removed the remaining 1,4-dioxane. The intrinsic microbial population, biodiversity, richness, and biomarker gene abundances decreased immediately after the brief oxidation phase, but recovery of cultivable microbiomes and a more diverse community were observed during the subsequent 9-week biodegradation phase. Results generated from the Illumina Miseq sequencing and bioinformatics analyses established that generally oxidative stress tolerant genus Ralstonia was abundant after the oxidation step, and Cupriavidus, Pseudolabrys, Afipia, and Sphingomonas were identified as dominant genera after aerobic incubation. Multidimensional analysis elucidated the separation of microbial populations as a function of time under all conditions, suggesting that temporal succession is a determining factor that is independent of 1,4-dioxane and CVOCs mixtures. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase, in line with the shifts of predominant genera and various developing directions during different steps of the treatment train. Collectively, this study demonstrated that chemical oxidation followed by bioaugmentation is effective for treating 1,4-dioxane, even in the presence of high levels of CVOC mixtures and residual peroxide, a disinfectant, and enhanced our understanding of microbial ecological impacts of the treatment train. These results will be valuable for predicting treatment synergies that lead to cost savings and improved remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

Realistic expectations for the treatment of FMGP residuals by chemical oxidants

Methods to remediate soil and groundwater contamination at former manufactured gas plant (FMGP) sites are scarce. The objective of this study was to investigate the ability of two chemical oxidants (persulfate and permanganate) to degrade FMGP residuals in a dynamic system representative of in situ conditions. A series of physical model trials supported by aqueous and slurry batch experiments using impacted sediments collected from a FMGP site were conducted. To explore treatment expectations a screening model constrained by the experimental data was employed. The results from the aqueous experiments showed that dissolved components (except for benzene) were readily degraded by persulfate or permanganate. In the well-mixed slurry systems, when contact with the oxidant was achieved, 95%, 45% and 30% of the initial mass quantified was degraded by permanganate, unactivated persulfate, and alkaline activated persulfate, respectively. In stark contrast, the total mass removed in the physical model trials was negligible for both permanganate and persulfate irrespective of the bleb or lense architecture used. Hence the net benefit of flushing 6 pore volumes of permanganate or persulfate at a concentration of 30 g/L under the physical model operating conditions was minimal. To achieve a substantial degradation of mass within the treatment system (>40%), results from the screening model indicated that the hydraulic resident time would need to be >10 days and the average lumped mass transfer coefficient increased by two orders-of-magnitude. Results from long-term (5 years) simulations showed that the dissolved concentrations of organic compounds are reduced temporarily as a result of the presence of permanganate but then rebound to a profile that is essentially coincident with a no-treatment scenario following exposure to permanganate. Neither a lower velocity nor higher permanganate dosing affected the long-term behavior of the dissolved phase concentrations; however, increasing the mass transfer rate coefficient had an impact. The findings from this investigation indicate that the efficiency of permanganate or persulfate to treat for FMGP residuals is mass transfer limited.

Remediation of aged diesel contaminated soil by alkaline activated persulfate

The present work studies the efficiency of alkaline activated persulfate (PS) to remediate an aged diesel fuel contaminated soil from a train maintenance facility. The Total Petroleum Hydrocarbon (TPH) concentration in soil was approximately 5000mgkg^-1 with a ratio of aliphatic:aromatic compounds of 70:30. Aromatic compounds were mainly naphtalenes and phenanthrenes. The experiments were performed in batch mode where different initial concentrations of persulfate (105mM, 210mM and 420mM) and activator:persulfate ratios (2 and 4) were evaluated, with NaOH used as activator. Runs were carried out during 56days. Complete TPH conversion was obtained with the highest concentration of PS and activator, whereas in the other runs the elimination of fuel ranged between 60 and 77%. Besides, the abatement of napthalenes and phenantrenes was faster than aliphatic reduction (i. e. after 4days of treatment, the conversions of the aromatic compounds were around 0.8 meanwhile the aliphatic abatements were 0.55) and no aromatic oxidation intermediates from naphtalenes or phenantrenes were detected. These results show that this technology is effective for the remediation of aged diesel in soil with alkaline pH.

Remediation of a soil chronically contaminated with hydrocarbons through persulfate oxidation and bioremediation

The impact of remediation combining chemical oxidation followed by biological treatment on soil matrix and microbial community was studied, of a chronically hydrocarbon contaminated soil sourced from a landfarming treatment. Oxidation by ammonium persulfate produced a significant elimination of polycyclic aromatic hydrocarbons (PAHs) and an increase in PAH bioavailability. Organic-matter oxidation mobilized nutrients from the soil matrix. The bacterial populations were affected negatively, with a marked diminution in the diversity indices. In this combined treatment with oxidation and bioremediation working in tandem, the aliphatic-hydrocarbon fractions were largely eliminated along with additional PAHs. The chemical and spectroscopic analyses indicated a change in soil nutrients. In spite of the high residual-sulfate concentration, a rapid recovery of the cultivable bacterial population and the establishment of a diverse and equitable microbial community were obtained. Pyrosequencing analysis demonstrated a marked succession throughout this twofold intervention in accordance with the chemical and biologic shifts observed. These remediation steps produced different effects on the soil physiology. Spectroscopic analysis became a useful tool for following and comparing those treatments, which involved acute changes in a matrix of such chronically hydrocarbon-contaminated soil. The combined treatment increased the elimination efficiency of both the aliphatic hydrocarbons and the PAHs at the expense of the mobilized organic matter, thus sustaining the recovery of the resilient populations throughout the treatment. The high-throughput-DNA-sequencing techniques enabled the identification of the predominant populations that were associated with the changes observed during the treatments.

Remediation of trichloroethene (TCE)-contaminated groundwater by persulfate oxidation: a field-scale study

This study uses a trichloroethene (TCE)-contaminated site to determine the efficacy of persulfate oxidation for the treatment of TCE-contaminated groundwater.

Contrasting dual (C, Cl) isotope fractionation offers potential to distinguish reductive chloroethene transformation from breakdown by permanganate

cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollutants in groundwater systems. They are both conducive to reductive dehalogenation and to oxidation by permanganate. In this study, the potential of dual element (C, Cl) compound specific isotope analyses (CSIA) for distinguishing between chemical oxidation and anaerobic reductive dechlorination of cis-DCE and TCE was investigated. Well-controlled cis-DCE degradation batch tests gave similar carbon isotope enrichment factors ε_C (‰), but starkly contrasting dual element isotope slopes Δδ¹³C/Δδ³⁷Cl for permanganate oxidation (ε_C=-26‰±6‰, Δδ¹³C/Δδ³⁷Cl≈-125±47) compared to reductive dechlorination (ε_C=-18‰±4‰, Δδ¹³C/Δδ³⁷Cl≈4.5±3.4). The difference can be tracked down to distinctly different chlorine isotope fractionation: an inverse isotope effect during chemical oxidation (ε_Cl=+0.2‰±0.1‰) compared to a large normal isotope effect in reductive dechlorination (ε_Cl=-3.3‰±0.9‰) (p≪0.05). A similar trend was observed for TCE. The dual isotope approach was evaluated in the field before and up to 443days after a pilot scale permanganate injection in the subsurface. Our study indicates, for the first time, the potential of the dual element isotope approach for distinguishing cis-DCE (and TCE) concentration drops caused by dilution, oxidation by permanganate and reductive dechlorination both at laboratory and field scale.

Nontarget Analysis Reveals a Bacterial Metabolite of Pyrene Implicated in the Genotoxicity of Contaminated Soil after Bioremediation

Bioremediation is an accepted technology for cleanup of soil contaminated with polycyclic aromatic hydrocarbons (PAHs), but it can increase the genotoxicity of the soil despite removal of the regulated PAHs. Although polar biotransformation products have been implicated as causative genotoxic agents, no specific product has been identified. We pursued a nontarget analytical approach combining effect-directed analysis (EDA) and metabolite profiling to compare extracts of PAH-contaminated soil from a former manufactured-gas plant site before and after treatment in a laboratory-scale aerobic bioreactor. A compound with the composition C₁₅H₈O₂ and four methylated homologues were shown to accumulate as a result of bioreactor treatment, and the C₁₅H₈O₂ compound purified from soil extracts was determined to be genotoxic. Its structure was established by nuclear magnetic resonance and mass spectroscopy as a heretofore unidentified α,β-unsaturated lactone derived from dioxygenation of pyrene at an apical ring, 2H-naphtho[2,1,8-def]chromen-2-one (NCO), which was confirmed by synthesis. The concentration of NCO in the bioreactor was 11 μg g^-1 dry soil, corresponding to 13% of the pyrene removed. It also accumulated in aerobically incubated soil from two additional PAH-contaminated sites and was formed from pyrene by two pyrene-degrading bacterial cultures known to be geographically widespread, underscoring its potential environmental significance.

Description of Immundisolibacter cernigliae gen. nov., sp. nov., a high-molecular-weight polycyclic aromatic hydrocarbon-degrading bacterium within the class Gammaproteobacteria, and proposal of Immundisolibacterales ord. nov. and Immundisolibacteraceae fam. nov

The bacterial strain TR3.2T was isolated from aerobic bioreactor-treated soil from a polycyclic aromatic hydrocarbon (PAH)-contaminated site in Salisbury, NC, USA. Strain TR3.2T was identified as a member of 'Pyrene Group 2' or 'PG2', a previously uncultivated cluster of organisms associated with the degradation of high-molecular-weight PAHs by stable-isotope probing. Based on its 16S rRNA gene sequence, the strain was classified as a member of the class Gammaproteobacteria but possessed only 90.5 % gene identity to its closest described relative, Methylococcus capsulatus strain Bath. Strain TR3.2T grew on the PAHs pyrene, phenanthrene, anthracene, benz[a]anthracene and fluorene, as well as the azaarene carbazole, and could additionally metabolize a limited number of organic acids. Optimal growth occurred aerobically under mesophilic temperature, neutral pH and low salinity conditions. Strain TR3.2T was catalase and oxidase positive. Predominant fatty acids were C17 : 0 cyclo and C16 : 0. Genomic G+C content of the single chromosome was 67.79 mol% as determined by complete genome sequencing. Due to the high sequence divergence from any cultivated species and its unique physiological properties compared to its closest relatives, strain TR3.2T is proposed as a representative of a novel order, family, genus and species within the class Gammaproteobacteria, for which the name Immundisolibacter cernigliae gen. nov., sp. nov. is proposed. The associated order and family are therefore proposed as Immundisolibacteralesord. nov. and Immundisolibacteraceaefam. nov. The type strain of the species is TR3.2T (=ATCC TSD-58T=DSM 103040T).

Rugosibacter aromaticivorans gen. nov., sp. nov., a bacterium within the family Rhodocyclaceae, isolated from contaminated soil, capable of degrading aromatic compounds

A bacterial strain designated Ca6T was isolated from polycyclic aromatic hydrocarbon (PAH)-contaminated soil from the site of a former manufactured gas plant in Charlotte, NC, USA, and linked phylogenetically to the family Rhodocyclaceae of the class Betaproteobacteria. Its 16S rRNA gene sequence was highly similar to globally distributed environmental sequences, including those previously designated 'Pyrene Group 1' demonstrated to grow on the PAHs phenanthrene and pyrene by stable-isotope probing. The most closely related described relative was Sulfuritalea hydrogenivorans strain sk43HT (93.6 % 16S rRNA gene sequence identity). In addition to a limited number of organic acids, Ca6T was capable of growth on the monoaromatic compounds benzene and toluene, and the azaarene carbazole, as sole sources of carbon and energy. Growth on the PAHs phenanthrene and pyrene was also confirmed. Optimal growth was observed aerobically under mesophilic temperature, neutral pH and low salinity conditions. Major fatty acids present included summed feature 3 (C16 : 1ω7c or C16 : 1ω6c) and C16 : 0. The DNA G+C content of the single chromosome was 55.14  mol% as determined by complete genome sequencing. Due to its distinct genetic and physiological properties, strain Ca6T is proposed as a member of a novel genus and species within the family Rhodocyclaceae, for which the name Rugosibacter aromaticivorans gen. nov., sp. nov. is proposed. The type strain of the species is Ca6T (=ATCC TSD-59T=DSM 103039T).

Combined remediation of pyrene-contaminated soil with a coupled system of persulfate oxidation and phytoremediation with ryegrass

The in situ chemical oxidation technology (ISCO) and phytoremediation for PAHs have been studied respectively, but few focus on the feasibility of combining persulfate with ryegrass. This literature revealed the effect of persulfate oxidation on the growth of ryegrass and the removal ratios of pyrene in the couple system of persulfate oxidation and phytoremediation. The results demonstrated that half of pyrene in test soil was oxidized by persulfate in 7 days and then the residual pyrene concentration was decreased to a lower level by ryegrass in the following 2 months in oxidation treatment and drip washing and plants (OWP) and oxidation treatment and drip washing and plants and fertilization (OWFP) treatment. Ryegrass could grow well after persulfate oxidation with the oxidized soil washed by water. Ryegrass in OWP and OWFP treatments had higher ratios of overground and underground biomass. However, the seeds of ryegrass cannot germinate when drip washing was omitted. Pyrene together with residual persulfate changed soil enzyme activities. Drip washing and the growth of ryegrass made soil enzyme activities tend to returned to normal levels. Persulfate oxidation and phytoremediation were compatible to make contributions to the dissipation of pyrene. Persulfate oxidation activated by heat had higher removal efficiency of PAHs and phytoremediation could further decrease the pyrene concentration in spiked soil.

Surfactant-induced bacterial community changes correlated with increased polycyclic aromatic hydrocarbon degradation in contaminated soil

Bioremediation as a method for removing polycyclic aromatic hydrocarbons (PAHs) from contaminated environments has been criticized for poor removal of potentially carcinogenic but less bioavailable high molecular weight (HMW) compounds. As a partial remedy to this constraint, we studied surfactant addition at sub-micellar concentrations to contaminated soil to enhance the biodegradation of PAHs remaining after conventional aerobic bioremediation. We demonstrated increased removal of four- and five-ring PAHs using two nonionic surfactants, polyoxyethylene(4)lauryl ether (Brij 30) and polyoxyethylene sorbitol hexaoleate (POESH), and analyzed bacterial community shifts associated with those conditions. Eight groups of abundant bacteria were implicated as potentially being involved in increased HMW PAH removal. A group of unclassified Alphaproteobacteria and members of the Phenylobacterium genus in particular showed significantly increased relative abundance in the two conditions exhibiting increased PAH removal. Other implicated groups included members of the Sediminibacterium, Terrimonas, Acidovorax, and Luteimonas genera, as well as uncharacterized organisms within the families Chitinophagaceae and Bradyrhizobiaceae. Targeted isolation identified a subset of the community likely using the surfactants as a growth substrate, but few of the isolates exhibited PAH-degradation capability. Isolates recovered from the Acidovorax and uncharacterized Bradyrhizobiaceae groups suggest the abundance of those groups may have been attributable to growth on surfactants. Understanding the specific bacteria responsible for HMW PAH removal in natural and engineered systems and their response to stimuli such as surfactant amendment may improve bioremediation efficacy during treatment of contaminated environmental media.

Improving Polycyclic Aromatic Hydrocarbon Biodegradation in Contaminated Soil Through Low-Level Surfactant Addition After Conventional Bioremediation

Efficacy of bioremediation for soil contaminated with polycyclic aromatic hydrocarbons (PAHs) may be limited by the fractions of soil-bound PAHs that are less accessible to PAH-degrading microorganisms. In previous test-tube-scale work, submicellar doses of nonionic surfactants were screened for their ability to enhance the desorption and biodegradation of residual PAHs in soil after conventional bioremediation in a laboratory-scale, slurry-phase bioreactor. Polyoxyethylene sorbitol hexaoleate (POESH) was the optimum surfactant for enhancing PAH removal, especially the high-molecular weight PAHs. This work extends that concept by treating the effluent from the slurry-phase bioreactor in a second-stage batch reactor, to which POESH was added, for an additional 7 or 12 days. Surfactant amendment removed substantial amounts of the PAHs and oxy-PAHs remaining after conventional slurry-phase bioremediation, including more than 80% of residual 4-ring PAHs. Surfactant-amended treatment decreased soil cytotoxicity, but often increased the genotoxicity of the soil as measured using the DT-40 chicken lymphocyte DNA damage response assay. Potential ecotoxicity, measured using a seed germination assay, was reduced by bioreactor treatment and was reduced further after second-stage treatment with POESH. Of bacteria previously implicated as potential PAH degraders under POESH-amended conditions in a prior study, members of the Terrimonas genus were associated with differences in high-molecular weight PAH removal in the current study. Research using submicellar doses of surfactant as a second-stage treatment step is limited and these findings can inform the design of bioremediation systems at field sites treating soil contaminated with PAHs and other hydrophobic contaminants that have low bioaccessibility.

Screening Nonionic Surfactants for Enhanced Biodegradation of Polycyclic Aromatic Hydrocarbons Remaining in Soil After Conventional Biological Treatment

A total of five nonionic surfactants (Brij 30, Span 20, Ecosurf EH-3, polyoxyethylene sorbitol hexaoleate, and R-95 rhamnolipid) were evaluated for their ability to enhance PAH desorption and biodegradation in contaminated soil after treatment in an aerobic bioreactor. Surfactant doses corresponded to aqueous-phase concentrations below the critical micelle concentration in the soil-slurry system. The effect of surfactant amendment on soil (geno)toxicity was also evaluated for Brij 30, Span 20, and POESH using the DT40 B-lymphocyte cell line and two of its DNA-repair-deficient mutants. Compared to the results from no-surfactant controls, incubation of the bioreactor-treated soil with all surfactants increased PAH desorption, and all except R-95 substantially increased PAH biodegradation. POESH had the greatest effect, removing 50% of total measured PAHs. Brij 30, Span 20, and POESH were particularly effective at enhancing biodegradation of four- and five-ring PAHs, including five of the seven carcinogenic PAHs, with removals up to 80%. Surfactant amendment also significantly enhanced the removal of alkyl-PAHs. Most treatments significantly increased soil toxicity. Only the no-surfactant control and Brij 30 at the optimum dose significantly decreased soil genotoxicity, as evaluated with either mutant cell line. Overall, these findings have implications for the feasibility of bioremediation to achieve cleanup levels for PAHs in soil.

A novel three-stage treatment train for the remediation of trichloroethylene-contaminated groundwater

The proposed treatment train removed TCE and its by-products effectively and there was no problem with the connection of chemical oxidation and anaerobic bioremediation in the novel treatment train technology.

Combining in situ chemical oxidation, stabilization, and anaerobic bioremediation in a single application to reduce contaminant mass and leachability in soil

Laboratory batch reactors were maintained for 32 weeks to test the potential for an in situ remedy that combines chemical oxidation, stabilization, and anaerobic bioremediation in a single application to treat soil from a manufactured gas plant, contaminated with polycyclic aromatic hydrocarbons (PAH) and benzene, toluene, ethylbenzene, and xylenes (BTEX). Portland cement and slaked lime were used to activate the persulfate and to stabilize/encapsulate the contaminants that were not chemically oxidized. Native sulfate-reducing bacteria degraded residual contaminants using the sulfate left after persulfate activation. The ability of the combined remedy to reduce contaminant mass and leachability was compared with NaOH-activated persulfate, stabilization, and sulfate-reducing bioremediation as stand-alone technologies. The stabilization amendments increased pH and temperature sufficiently to activate the persulfate within 1 week. Activation with both stabilization amendments and NaOH removed between 55% and 70% of PAH and BTEX. However, combined persulfate and stabilization significantly reduced the leachability of residual BTEX and PAH compared with NaOH activation. Sulfide, 2-naphthoic acid, and the abundance of subunit A of the dissimilatory sulfite reductase gene (dsrA) were used to monitor native sulfate-reducing bacteria, which were negatively impacted by activated persulfate, but recovered completely within weeks.

Identification of anthraquinone-degrading bacteria in soil contaminated with polycyclic aromatic hydrocarbons

Quinones and other oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are toxic and/or genotoxic compounds observed to be cocontaminants at PAH-contaminated sites, but their formation and fate in contaminated environmental systems have not been well studied. Anthracene-9,10-dione (anthraquinone) has been found in most PAH-contaminated soils and sediments that have been analyzed for oxy-PAHs. However, little is known about the biodegradation of oxy-PAHs, and no bacterial isolates have been described that are capable of growing on or degrading anthraquinone. PAH-degrading Mycobacterium spp. are the only organisms that have been investigated to date for metabolism of a PAH quinone, 4,5-pyrenequinone. We utilized DNA-based stable-isotope probing (SIP) with [U-(13)C]anthraquinone to identify bacteria associated with anthraquinone degradation in PAH-contaminated soil from a former manufactured-gas plant site both before and after treatment in a laboratory-scale bioreactor. SIP with [U-(13)C]anthracene was also performed to assess whether bacteria capable of growing on anthracene are the same as those identified to grow on anthraquinone. Organisms closely related to Sphingomonas were the most predominant among the organisms associated with anthraquinone degradation in bioreactor-treated soil, while organisms in the genus Phenylobacterium comprised the majority of anthraquinone degraders in the untreated soil. Bacteria associated with anthracene degradation differed from those responsible for anthraquinone degradation. These results suggest that Sphingomonas and Phenylobacterium species are associated with anthraquinone degradation and that anthracene-degrading organisms may not possess mechanisms to grow on anthraquinone.

Association of Growth Substrates and Bacterial Genera with Benzo[a]pyrene Mineralization in Contaminated Soil

Benzo[a]pyrene (BaP) is a carcinogenic polycyclic aromatic hydrocarbon (PAH) that is not known to be a bacterial growth substrate. Organisms capable of cometabolizing BaP in complex field-contaminated systems have not previously been identified. We evaluated BaP mineralization by a bacterial community from a bioreactor treating PAH-contaminated soil during coincubation with or after pre-enrichment on various PAHs as growth substrates. Pyrosequence libraries of 16S rRNA genes were used to identify bacteria that were enriched on the added growth substrate as a means of associating specific organisms with BaP mineralization. Coincubating the bioreactor-treated soil with naphthalene, phenanthrene, or pyrene inhibited BaP mineralization, whereas pre-enriching the soil on the same three PAHs enhanced BaP mineralization. Combined, these results suggest that bacteria in the bioreactor community that are capable of growing on naphthalene, phenanthrene, and/or pyrene can metabolize BaP, with coincubation competitively inhibiting BaP metabolism. Anthracene, fluoranthene, and benz[a]anthracene had little effect on BaP mineralization compared to incubations without an added growth substrate under either coincubation or pre-enrichment conditions. Substantial increases in relative abundance after pre-enrichment with phenanthrene, naphthalene, or pyrene, but not the other PAHs, suggest that members of the genera Cupriavidus and Luteimonas may have been associated with BaP mineralization.

A comparison of physicochemical methods for the remediation of porous medium systems contaminated with tar

The remediation of former manufactured gas plant (FMGP) sites contaminated with tar DNAPLs (dense non-aqueous phase liquids) presents a significant challenge. The tars are viscous mixtures of thousands of individual compounds, including known and suspected carcinogens. This work investigates the use of combinations of mobilization, solubilization, and chemical oxidation approaches to remove and degrade tars and tar components in porous medium systems. Column experiments were conducted using several flushing solutions, including an alkaline-polymer (AP) solution containing NaOH and xanthan gum (XG), a surfactant-polymer (SP) solution containing Triton X-100 surfactant (TX100) and XG, an alkaline-surfactant-polymer (ASP) solution containing NaOH, TX100, and XG, and base-activated sodium persulfate both with and without added TX100. The effectiveness of the flushing solutions was assessed based on both removal of polycyclic aromatic hydrocarbon (PAH) mass and on the reduction of dissolved-phase PAH concentrations. SP flushes of 6.6 to 20.9 PV removed over 99% of residual PAH mass and reduced dissolved-phase concentrations by up to two orders of magnitude. ASP flushing efficiently removed 95-96% of residual PAH mass within about 2 PV, and significantly reduced dissolved-phase concentrations of several low molar mass compounds, including naphthalene, acenaphthene, fluorene, and phenanthrene. AP flushing removed a large portion of the residual tar (77%), but was considerably less effective than SP and ASP in terms of the effect on dissolved PAH concentrations. Persulfate was shown to oxidize tar components, primarily those with low molar mass, however, the overall degradation was relatively low (30-50% in columns with low initial tar saturations), and the impact on dissolved-phase concentrations was minimal.

Remediation of phenanthrene-contaminated soil by simultaneous persulfate chemical oxidation and biodegradation processes

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds with carcinogenic and/or mutagenic potential. To address the limitations of individual remediation techniques and to achieve better PAH removal efficiencies, the combination of chemical and biological treatments can be used. The degradation of phenanthrene (chosen as a model of PAH) by persulfate in freshly contaminated soil microcosms was studied to assess its impact on the biodegradation process and on soil properties. Soil microcosms contaminated with 140 mg/kgDRY SOIL of phenanthrene were treated with different persulfate (PS) concentrations 0.86-41.7 g/kgDRY SOIL and incubated for 28 days. Analyses of phenanthrene and persulfate concentrations and soil pH were performed. Cultivable heterotrophic bacterial count was carried out after 28 days of treatment. Genetic diversity analysis of the soil microcosm bacterial community was performed by PCR amplification of bacterial 16S rDNA fragments followed by denaturing gradient gel electrophoresis (DGGE). The addition of PS in low concentrations could be an interesting biostimulatory strategy that managed to shorten the lag phase of the phenanthrene biological elimination, without negative effects on the physicochemical and biological soil properties, improving the remediation treatment.

Bioavailability of (Geno)toxic Contaminants in Polycyclic Aromatic Hydrocarbon-Contaminated Soil Before and After Biological Treatment

Contaminated soil from a former manufactured-gas plant site was treated in a laboratory-scale bioreactor. Desorbability and biodegradability of 14 polycyclic aromatic hydrocarbons (PAHs) and 4 oxygenated PAHs (oxy-PAHs) were investigated throughout a treatment cycle. Desorbability was determined using a mixed-function sorbent (Oasis^® HLB) or a hydrophobic sorbent (Tenax^®) in dialysis tubing suspended in the soil slurry. Toxicity and genotoxicity of the whole soil and the desorbable fractions were determined by DNA damage response analysis with the chicken DT40 B-lymphocyte isogenic cell line and its DNA repair-deficient mutant Rad54^-/-. Biological treatment significantly removed both PAHs and oxy-PAHs, and their desorbability decreased throughout the bioreactor treatment cycle. Collectively, oxy-PAHs were more desorbable and biodegradable than the corresponding PAHs; for example, the oxy-PAH present at the highest concentration, 9,10-anthraquinone, was more desorbable and biodegradable than anthracene. For both PAHs and oxy-PAHs, the percentage removed in the bioreactor significantly exceeded the percentage desorbed from untreated soil, indicating that desorption did not control the extent of biodegradation. Consistent with previous results on the same soil, genotoxicity of the whole soil slightly increased after biological treatment. However, both toxicity and genotoxicity of the desorbable constituents in the soil decreased after treatment, suggesting that any genotoxic constituents that may have formed during treatment were primarily associated with less accessible domains in the soil.

Geochemical and microbiological characteristics during in situ chemical oxidation and in situ bioremediation at a diesel contaminated site

While in situ chemical oxidation with persulfate has seen wide commercial application, investigations into the impacts on groundwater characteristics, microbial communities and soil structure are limited. To better understand the interactions of persulfate with the subsurface and to determine the compatibility with further bioremediation, a pilot scale treatment at a diesel-contaminated location was performed consisting of two persulfate injection events followed by a single nutrient amendment. Groundwater parameters measured throughout the 225 day experiment showed a significant decrease in pH and an increase in dissolved diesel and organic carbon within the treatment area. Molecular analysis of the microbial community size (16S rRNA gene) and alkane degradation capacity (alkB gene) by qPCR indicated a significant, yet temporary impact; while gene copy numbers initially decreased 1-2 orders of magnitude, they returned to baseline levels within 3 months of the first injection for both targets. Analysis of soil samples with sequential extraction showed irreversible oxidation of metal sulfides, thereby changing subsurface mineralogy and potentially mobilizing Fe, Cu, Pb, and Zn. Together, these results give insight into persulfate application in terms of risks and effective coupling with bioremediation.

Microbial dechlorination activity during and after chemical oxidant treatment

Potassium permanganate (PM) and sodium persulfate (PS) are used in soil remediation, however, their compatibility with a coinciding or subsequent biotreatment is poorly understood. In this study, different concentrations of PM (0.005-2g/L) and PS (0.01-4.52 g/L) were applied and their effects on the abundance, activity, and reactivation potential of a dechlorinating enrichment culture were investigated. Expression of the tceA, vcrA and 16S rRNA genes of Dehalococcoides spp. were detected at 0.005-0.01 g/L PM and 0.01-0.02 g/L PS. However, with 0.5-2g/L PM and 1.13-4.52 g/L PS no gene expression was recorded, neither were indicator molecules for total cell activity (Adenosine triphosphate, ATP) detected. Dilution did not promote the reactivation of the microbial cells when the redox potential was above -100 mV. Similarly, inoculated cells did not dechlorinate trichloroethene (TCE) above -100 mV. When the redox potential was decreased to -300 mV and the reactors were bioaugmented for a second time, dechlorination activity recovered, but only in the reactors with 1.13 and 2.26 g/L PS. In conclusion, our results show that chemical oxidants can be combined with a biotreatment at concentrations below 0.5 g/L PM and 1g/L PS.

Biostimulation Reveals Functional Redundancy of Anthracene-Degrading Bacteria in Polycyclic Aromatic Hydrocarbon-Contaminated Soil

Stable-isotope probing was previously used to identify bacterial anthracene-degraders in untreated soil from a former manufactured gas plant site. However, subsequent pyrosequence analyses of total bacterial communities and quantification of 16S rRNA genes indicated that relative abundances of the predominant anthracene-degrading bacteria (designated Anthracene Group 1) diminished as a result of biological treatment conditions in lab-scale, aerobic bioreactors. This study identified Alphaproteobacterial anthracene-degrading bacteria in bioreactor-treated soil which were dissimilar to those previously identified. The largest group of sequences was from the Alterythrobacter genus while other groups of sequences were associated with bacteria within the order Rhizobiales and the genus Bradyrhizobium. Conditions in the bioreactor enriched for organisms capable of degrading anthracene which were not the same as those identified as dominant degraders in the untreated soil. Further, these data suggest that identification of polycyclic aromatic hydrocarbon-degrading bacteria in contaminated but untreated soil may be a poor indicator of the most active degraders during biological treatment.

Recovery of microbial diversity and activity during bioremediation following chemical oxidation of diesel contaminated soils

To improve the coupling of in situ chemical oxidation and in situ bioremediation, a systematic analysis was performed of the effect of chemical oxidation with Fenton's reagent, modified Fenton's reagent, permanganate, or persulfate, on microbial diversity and activity during 8 weeks of incubation in two diesel-contaminated soils (peat and fill). Chemical oxidant and soil type affected the microbial community diversity and biodegradation activity; however, this was only observed following treatment with Fenton's reagent and modified Fenton's reagent, and in the biotic control without oxidation. Differences in the highest overall removal efficiencies of 69 % for peat (biotic control) and 59 % for fill (Fenton's reagent) were partially explained by changes in contaminant soil properties upon oxidation. Molecular analysis of 16S rRNA and alkane monooxygenase (alkB) gene abundances indicated that oxidation with Fenton's reagent and modified Fenton's reagent negatively affected microbial abundance. However, regeneration occurred, and final relative alkB abundances were 1-2 orders of magnitude higher in chemically treated microcosms than in the biotic control. 16S rRNA gene fragment fingerprinting with DGGE and prominent band sequencing illuminated microbial community composition and diversity differences between treatments and identified a variety of phylotypes within Alpha-, Beta-, and Gammaproteobacteria. Understanding microbial community dynamics during coupled chemical oxidation and bioremediation is integral to improved biphasic field application.

Pyrosequence analyses of bacterial communities during simulated in situ bioremediation of polycyclic aromatic hydrocarbon-contaminated soil

Barcoded amplicon pyrosequencing was used to generate libraries of partial 16S rRNA genes from two columns designed to simulate in situ bioremediation of polycyclic aromatic hydrocarbons (PAHs) in weathered, contaminated soil. Both columns received a continuous flow of artificial groundwater but one of the columns additionally tested the impact of biostimulation with oxygen and inorganic nutrients on indigenous soil bacterial communities. The penetration of oxygen to previously anoxic regions of the columns resulted in the most significant community changes. PAH-degrading bacteria previously determined by stable-isotope probing (SIP) of the untreated soil generally responded negatively to the treatment conditions, with only members of the Acidovorax and a group of uncharacterized PAH-degrading Gammaproteobacteria maintaining a significant presence in the columns. Additional groups of sequences associated with the Betaproteobacterial family Rhodocyclaceae (including those associated with PAH degradation in other soils), and the Thiobacillus, Thermomonas, and Bradyrhizobium genera were also present in high abundance in the biostimulated column. Similar community responses were previously observed during biostimulated ex situ treatment of the same soil in aerobic, slurry-phase bioreactors. While the low relative abundance of many SIP-determined groups in the column libraries may be a reflection of the slow removal of PAHs in that system, the similar response of known PAH degraders in a higher-rate bioreactor system suggests that alternative PAH-degrading bacteria, unidentified by SIP of the untreated soil, may also be enriched in engineered systems.

Long-term simulation of in situ biostimulation of polycyclic aromatic hydrocarbon-contaminated soil

A continuous-flow column study was conducted to evaluate the long-term effects of in situ biostimulation on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil from a manufactured gas plant site. Simulated groundwater amended with oxygen and inorganic nutrients was introduced into one column, while a second column receiving unamended groundwater served as a control. PAH and dissolved oxygen (DO) concentrations, as well as microbial community profiles, were monitored along the column length immediately before and at selected intervals up to 534 days after biostimulation commenced. Biostimulation resulted in significantly greater PAH removal than in the control condition (73% of total measured PAHs vs. 34%, respectively), with dissolution accounting for a minor amount of the total mass loss (~6%) in both columns. Dissolution was most significant for naphthalene, acenaphthene, and fluorene, accounting for >20% of the total mass removed for each. A known group of PAH-degrading bacteria, 'Pyrene Group 2' (PG2), was identified as a dominant member of the microbial community and responded favorably to biostimulation. Spatial and temporal variations in soil PAH concentration and PG2 abundance were strongly correlated to DO advancement, although there appeared to be transport of PG2 organisms ahead of the oxygen front. At an estimated oxygen demand of 6.2 mg O(2)/g dry soil and a porewater velocity of 0.8 m/day, it took between 374 and 466 days for oxygen breakthrough from the 1-m soil bed in the biostimulated column. This study demonstrated that the presence of oxygen was the limiting factor in PAH removal, as opposed to the abundance and/or activity of PAH-degrading bacteria once oxygen reached a previously anoxic zone.

Evaluating the effects of bioremediation on genotoxicity of polycyclic aromatic hydrocarbon-contaminated soil using genetically engineered, higher eukaryotic cell lines

Bioremediation is one of the commonly applied remediation strategies at sites contaminated with polycyclic aromatic hydrocarbons (PAHs). However, remediation goals are typically based on removal of the target contaminants rather than on broader measures related to health risks. We investigated changes in the toxicity and genotoxicity of PAH-contaminated soil from a former manufactured-gas plant site before and after two simulated bioremediation processes: a sequencing batch bioreactor system and a continuous-flow column system. Toxicity and genotoxicity of the residues from solvent extracts of the soil were determined by the chicken DT40 B-lymphocyte isogenic cell line and its DNA-repair-deficient mutants. Although both bioremediation processes significantly removed PAHs from the contaminated soil (bioreactor 69% removal, column 84% removal), bioreactor treatment resulted in an increase in toxicity and genotoxicity over the course of a treatment cycle, whereas long-term column treatment resulted in a decrease in toxicity and genotoxicity. However, when screening with a battery of DT40 mutants for genotoxicity profiling, we found that column treatment induced DNA damage types that were not observed in untreated soil. Toxicity and genotoxicity bioassays can supplement chemical analysis-based risk assessment for contaminated soil when evaluating the efficacy of bioremediation.

Characterization of the bacterial archaeal diversity in hydrocarbon-contaminated soil

A polyphasic approach combining culture-based methods with molecular methods is useful to expand knowledge on microbial diversity in contaminated soil. Microbial diversity was examined in soil samples from a former industrial site in the European Alps (mainly used for aluminum production and heavily contaminated with petroleum hydrocarbons) by culture-dependent and culture-independent methods. The physiologically active eubacterial community, as revealed by fluorescence-in-situ-hybridization (FISH), accounted for 6.7% of the total (DAPI-stained) bacterial community. 4.4% and 2.0% of the DAPI-stained cells could be attributed to culturable, heterotrophic bacteria able to grow at 20°C and 10°C, respectively. The majority of culturable bacterial isolates (34/48) belonged to the Proteobacteria (with a predominance of Alphaproteobacteria and Gammaproteobacteria), while the remaining isolates were affiliated with the Actinobacteria, Cytophaga-Flavobacterium-Bacteroides and Firmicutes. A high fraction of the culturable, heterotrophic bacterial population was able to utilize hydrocarbons. Actinobacteria were the most versatile and efficient degraders of diesel oil, n-alkanes, phenol and PAHs. The bacterial 16S rRNA gene clone library contained 390 clones that grouped into 68 phylotypes related to the Proteobacteria, Bacteroidetes, Actinobacteria and Spirochaetes. The archaeal 16S rRNA gene library contained 202 clones and 15 phylotypes belonging to the phylum Euryarchaeota; sequences were closely related to those of methanogenic archaea of the orders Methanomicrobiales, Methanosarcinales, Methanobacteriales and Thermoplasmatales. A number of bacterial and archaeal phylotypes in the clone libraries shared high similarities with strains previously described to be involved in hydrocarbon biodegradation. Knowledge of the bacterial and archaeal diversity in the studied soil is important in order to get a better insight into the microbial structure of contaminated environments and to better exploit the bioremediation potential by identifying potential hydrocarbon degraders and consequently developing appropriate bioremediation strategies.

Heterologous expression of polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase genes from a novel pyrene-degrading betaproteobacterium

A betaproteobacterium within the family Rhodocyclaceae previously identified as a pyrene degrader via stable-isotope probing (SIP) of contaminated soil (designated pyrene group 1 or PG1) was cultivated as the dominant member of a mixed bacterial culture. A metagenomic library was constructed, and the largest contigs were analyzed for genes associated with polycyclic aromatic hydrocarbon (PAH) metabolism. Eight pairs of genes with similarity to the α- and β-subunits of ring-hydroxylating dioxygenases (RHDs) associated with aerobic bacterial PAH degradation were identified and linked to PG1 through PCR analyses of a simplified enrichment culture. In tandem with a ferredoxin and reductase found in close proximity to one pair of RHD genes, six of the RHDs were cloned and expressed in Escherichia coli. Each cloned RHD was tested for activity against nine PAHs ranging in size from two to five rings. Despite differences in their predicted protein sequences, each of the six RHDs was capable of transforming phenanthrene and pyrene. Three RHDs could additionally transform naphthalene and fluorene, and these genotypes were also associated with the ability of the E. coli constructs to convert indole to indigo. Only one of the six cloned RHDs was capable of transforming anthracene and benz[a]anthracene. None of the tested RHDs were capable of significantly transforming fluoranthene, chrysene, or benzo[a]pyrene.

Desorption and bioavailability of polycyclic aromatic hydrocarbons in contaminated soil subjected to long-term in situ biostimulation

The distribution and potential bioavailability of polycyclic aromatic hydrocarbons (PAHs) in soil from a former manufactured-gas plant (MGP) site were examined before and after long-term biostimulation under simulated in situ conditions. Treated soil was collected from the oxygenated zones of two continuous-flow columns, one subjected to biostimulation and the other serving as a control, and separated into low- and high-density fractions. In the original soil, over 50% of the total PAH mass was associated with lower density particles, which made up <2% of the total soil mass. However, desorbable fractions of PAHs were much lower in the low-density material than in the high-density material. After more than 500 d of biostimulation, significant removal of total PAHs occurred in both the high- and low-density materials (77 and 53%, respectively), with three- and four-ring PAHs accounting for the majority of the observed mass loss. Total PAHs that desorbed over a 28-d period were substantially lower in treated soil from the biostimulated column than in the original soil for both the high-density material (23 vs. 63%) and the low-density material (5 vs. 20%). The fast-desorbing fractions quantified by a two-site desorption model ranged from 0.1 to 0.5 for most PAHs in the original soil but were essentially zero in the biostimulated soil. The fast-desorbing fractions in the original soil underestimated the extent of PAH biodegradation observed in the biostimulated column and thus was not a good predictor of PAH bioavailability after long-term, simulated in situ biostimulation.

Cosolvent flushing for the remediation of PAHs from former manufactured gas plants

Cosolvent flushing is a technique that has been proposed for the removal of hydrophobic organic contaminants in the subsurface. Cosolvents have been shown to dramatically increase the solubility of such compounds compared to the aqueous solubility; however, limited data are available on the effectiveness of cosolvents for field-contaminated media. In this work, we examine cosolvent flushing for the removal of polycyclic aromatic hydrocarbons (PAHs) in soil from a former manufactured gas plant (FMGP). Batch studies confirmed that the relationship between the soil-cosolvent partitioning coefficient (K(i)) and the volume fraction of cosolvent (f(c)) followed a standard log-linear equation. Using methanol at an fc of 0.95, column studies were conducted at varying length scales, ranging from 11.9 to 110 cm. Removal of PAH compounds was determined as a function of pore volumes (PVs) of cosolvent flushed. Despite using a high f(c), rate and chromatographic effects were observed in all the columns. PAH effluent concentrations were modeled using a common two-site sorption model. Model fits were improved by using MeOH breakthrough curves to determine fitted dispersion coefficients. Fitted mass-transfer rates were two to three orders of magnitude lower than predicted values based on published data using artificially contaminated sands.