Bioremediation Of PAH-contaminated Soil Research Articles

Dynamics of microbial community and functional genes during bioremediation of PAHs-contaminated soil by two biostimulants

Biostimulation is a favored approach in bioremediation strategies for polycyclic aromatic hydrocarbons (PAHs). However, the addition of some biostimulants can instead be counterproductive to the soil. In this study, rhamnolipid and leaf litter were added as aids to PAHs biodegradation in soil. Quantitative Real-time PCR (qPCR) and 16 S ribosomal RNA (16 S rRNA) techniques were used to investigate the structural-functional response of soil microbial communities and changes in PAHs functional genes during 82 days of the degradation process. The study reveals that rhamnolipid and leaf litter increase the degradation rate of Benzo(a)pyrene by 20.49% and 11.64%, respectively, while having little effect on the degradation rate of phenanthrene. During the degradation process, each biostimulant increases the number of different bacterial genera capable of degrading PAHs, which influences both the structure and function of the microbial community and alters microbial diversity. Additionally, functional gene abundance was enhanced during degradation and showed an inverse relationship with residual PAHs concentration in the soil. These results indicate that different biostimulants have varying effects on microorganisms. This study enhances the understanding of useing of two biostimulants to degrade soil PAHs.

The negative effects of the excessive nitrite accumulation raised by anaerobic bioaugmentation on bioremediation of PAH-contaminated soil

Nitrite accumulation in anaerobic bioaugmentation and its side effects on remediation efficiency of polycyclic aromatic hydrocarbon (PAH)-contaminated soil were investigated in this study. Four gradient doses of PAH-degrading inoculum (10^4, 10^5, 10^6 and 10^7 cells/g soil) were separately supplied to the actual PAH-contaminated soil combining with nitrate as the biostimulant. Although bioaugmented with higher dose of inoculum could effectively improve the biodegradation efficiencies in the initial stage than sole nitrate addition but also accelerated the accumulation of nitrite in soil. The inhibition effects of nitrite swiftly occurred following the rapid accumulation of nitrite in each experiment group, restraining the PAH-degrading functionality by inhibiting the growth of total biomass and denitrifying functions in soil. This study revealed the side effects of nitrite accumulation raised by bioaugmentation on soil microorganisms, contributing to further improving the biodegrading efficiencies in the actual site restoration.

Multi-Omic Profiling of a Newly Isolated Oxy-PAH Degrading Specialist from PAH-Contaminated Soil Reveals Bacterial Mechanisms to Mitigate the Risk Posed by Polar Transformation Products.

Polar biotransformation products have been identified as causative agents for the eventual increase in genotoxicity observed after the bioremediation of PAH-contaminated soils. Their further biodegradation has been described under certain biostimulation conditions; however, the underlying microorganisms and mechanisms remain to be elucidated. 9,10-Anthraquinone (ANTQ), a transformation product from anthracene (ANT), is the most commonly detected oxygenated PAH (oxy-PAH) in contaminated soils. Sand-in-liquid microcosms inoculated with creosote-contaminated soil revealed the existence of a specialized ANTQ degrading community, and Sphingobium sp. AntQ-1 was isolated for its ability to grow on this oxy-PAH. Combining the metabolomic, genomic, and transcriptomic analyses of strain AntQ-1, we comprehensively reconstructed the ANTQ biodegradation pathway. Novel mechanisms for polyaromatic compound degradation were revealed, involving the cleavage of the central ring catalyzed by Baeyer-Villiger monooxygenases (BVMO). Abundance of strain AntQ-1 16S rRNA and its BVMO genes in the sand-in-liquid microcosms correlated with maximum ANTQ biodegradation rates, supporting the environmental relevance of this mechanism. Our results demonstrate the existence of highly specialized microbial communities in contaminated soils responsible for processing oxy-PAHs accumulated by primary degraders. Also, they underscore the key role that BVMO may play as a detoxification mechanism to mitigate the risk posed by oxy-PAH formation during bioremediation of PAH-contaminated soils.

Advances in bioremediation of polycyclic aromatic hydrocarbons contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent pollutants that are widely distributed in the environment. Due to their stable structure and poor degradability, PAHs exhibit carcinogenic, teratogenic, and mutagenic toxicity to the ecological environment and organisms, thus increasing attentions have been paid to their removals and remediation. Green, safe and economical technologies are widely used in the bioremediation of PAHs-contaminated soil. This article summarizes the present status of PAHs pollution in soil of China from the aspects of origin, migration, fate, and pollution level. Meanwhile, the types of microorganisms and plants capable of degrading PAHs, as well as the underlying mechanisms, are summarized. The features of three major bioremediation technologies, i.e., microbial remediation, phytoremediation, and joint remediation, are compared. Analysis of the interaction mechanisms between plants and microorganisms, selection and cultivation of stress-resistant strains and plants, as well as safety and efficacy evaluation of practical applications, are expected to become future directions in this field.

Enhanced bioremediation of PAH-contaminated soil by wheat bran and microbial community response

ABSTRACT Microcosms were set up containing a PAH polluted soil to investigate biostimulation (addition of wheat bran and fertilizer) and bioaugmentation (inoculation with Pseudomonas sp. SB). After 60 d the fertilizer + wheat bran gave the highest PAH degradation. The degradation rate was 42.2%, significantly higher than the 18.7% in the fertilizer only treatment. Principal coordinate analysis (PCoA) indicates that wheat bran treatment can significantly alter soil bacterial and fungal communities. In addition, wheat bran promoted the enrichment of some soil bacteria such as Bacillaceae, Xanthomonadaceae, Streptomycetaceae, and Chitinophagaceae, and the fungi Talaromyces, Humicola, unclassified_Chaetomiaceae and Mortierella. These results highlight the potential of wheat bran application to reduce the PAHs detected in soil.

Effect of Bioaugmentation by Bacterial Consortium and Methyl-β-cyclodextrin on Soil Functional Diversity and Removal of Polycyclic Aromatic Hydrocarbons

ABSTRACTThe low biological effectiveness of polycyclic aromatic hydrocarbons (PAHs) is the main limiting factor of in-situ bioremediation of PAH-contaminated soil. The purpose of the present study was to assess the effects of methyl-β-cyclodextrin (MCD) and microbial consortia on the PAHs degradation rate and microbial ecology and functional diversity and stability in soil. The results show that MCD and microorganisms significantly increased the degradation rate of pyrene and benzo[a]pyrene by 30.1% and 9.1%, respectively, (p < 0.05) after 4 weeks. The average well color development (AWCD) values and diversity indices of bioaugmentation (B) and MCD- and bacterial-assisted bioaugmentation (MB) were significantly higher than that in control (CK). The Shannon–Weaver index (H) and McIntosh index (U) in the MB treatment were significantly higher than those observed in other treatments, which indicated that its species richness and individuals were distributed evenly. The soil microbial activity and community structure were the most abundant in the MB treatment. Compared to the CK treatment, MB significantly promoted soil dehydrogenase activity (DHA) and fluorescein diacetate hydrolysis (FDAH) enzyme activity, which were increased by 96.3% and 994.3%, respectively. According to the results of principal component analysis, the physiological functions of microbial communities in the MB and B treatments were different from the other treatments. Therefore, the combination of the microorganisms with MCD can stimulate the remediation efficiency of PAHs and the physiological functions of microbial communities.

Importance of organic amendment characteristics on bioremediation of PAH-contaminated soil.

This study investigates the importance of the organic matter characteristics of several organic amendments (i.e., buffalo manure, food and kitchen waste, fruit and vegetables waste, and activated sewage sludge) and their influence in the bioremediation of a polycyclic aromatic hydrocarbons (PAH)-contaminated soil. The removal of low molecular weights (LMW) and high molecular weights (HMW) PAHs was monitored in four bioremediation reactors and used as an indicator of the role of organic amendments in contaminant removal. The total initial concentration of LMW PAHs was 234mgkg(-1) soil (dry weight), while the amount for HMW PAHs was 422mgkg(-1) soil (dry weight). Monitoring of operational parameters and chemical analysis was performed during 20weeks. The concentrations of LMW PAH residues in soil were significantly lower in reactors that displayed a mesophilic phase, i.e., 11 and 15%, compared to reactors that displayed a thermophilic phase, i.e., 29 and 31%. Residual HMW PAHs were up to five times higher compared to residual LMW PAHs, depending on the reactor. This demonstrated that the amount of added organic matter and macronutrients such as nitrogen and phosphorus, the biochemical organic compound classes (mostly soluble fraction and proteins), and the operational temperature are important factors affecting the overall efficiency of bioremediation. On that basis, this study shows that characterization of biochemical families could contribute to a better understanding of the effects of organic amendments and clarify their different efficiency during a bioremediation process of PAH-contaminated soil.

Aerobic Bioremediation of PAH Contaminated Soil Results in Increased Genotoxicity and Developmental Toxicity.

The formation of more polar and toxic polycyclic aromatic hydrocarbon (PAH) transformation products is one of the concerns associated with the bioremediation of PAH-contaminated soils. Soil contaminated with coal tar (prebioremediation) from a former manufactured gas plant (MGP) site was treated in a laboratory scale bioreactor (postbioremediation) and extracted using pressurized liquid extraction. The soil extracts were fractionated, based on polarity, and analyzed for 88 PAHs (unsubstituted, oxygenated, nitrated, and heterocyclic PAHs). The PAH concentrations in the soil tested, postbioremediation, were lower than their regulatory maximum allowable concentrations (MACs), with the exception of the higher molecular weight PAHs (BaA, BkF, BbF, BaP, and IcdP), most of which did not undergo significant biodegradation. The soil extract fractions were tested for genotoxicity using the DT40 chicken lymphocyte bioassay and developmental toxicity using the embryonic zebrafish (Danio rerio) bioassay. A statistically significant increase in genotoxicity was measured in the unfractionated soil extract, as well as in four polar soil extract fractions, postbioremediation (p < 0.05). In addition, a statistically significant increase in developmental toxicity was measured in one polar soil extract fraction, postbioremediation (p < 0.05). A series of morphological abnormalities, including peculiar caudal fin malformations and hyperpigmentation in the tail, were measured in several soil extract fractions in embryonic zebrafish, both pre- and postbioremediation. The increased toxicity measured postbioremediation is not likely due to the 88 PAHs measured in this study (including quinones), because most were not present in the toxic polar fractions and/or because their concentrations did not increase postbioremediation. However, the increased toxicity measured postbioremediation is likely due to hydroxylated and carboxylated transformation products of the 3- and 4-ring PAHs (PHE, 1MPHE, 2MPHE, PRY, BaA, and FLA) that were most degraded.

Insight into the Modulation of Dissolved Organic Matter on Microbial Remediation of PAH-Contaminated Soils.

Microorganisms play a key role in degradation of polycyclic aromatic hydrocarbons (PAHs) in environments. Dissolved organic matter (DOM) can enhance microbial degradation of PAHs in soils. However, it is not clear how will the soil microbial community respond to addition of DOM during bioremediation of PAH-contaminated soils. In this study, DOMs derived from various agricultural wastes were applied to remediate the aging PAH-contaminated soils in a 90-day microcosm experiment. Results showed that the addition of DOMs offered a more efficient and persistent elimination of soil PAHs compared to the control which had no DOM addition. PAH removal effects were different among treatments with various DOMs; the addition of DOMs with high proportion of hydrophobic fraction could remove PAHs more efficiently from the soil. Low-molecular-weight (LMW) PAHs were more easily eliminated than that with high-molecular-weight (HMW). Addition of DOMs significantly increased abundance of 16S ribosomal RNA (rRNA), pdo1, nah, and C12O genes and obviously changed community compositions of nah and C12O genes in different ways in the PAH-contaminated soil. Phylogenetic analyses of clone libraries exhibited that all of nah sequences and most of C12O sequences were affiliated into Gammaproteobacteria and Betaproteobacteria. These results suggested that external stimuli produced by DOMs could enhance the microbial degradation of PAHs in soils through not only solubilizing PAHs but also altering abundance and composition of indigenous microbial degraders. Our results reinforce the understanding of role of DOMs in mediating degradation of PAHs by microorganims in soils.

Bioremediation of PAH-contaminated soil with fungi – From laboratory to field scale

The purpose of this study was to develop a fungal bioremediation method that could be used for soils heavily contaminated with persistent organic compounds, such as polyaromatic hydrocarbons (PAHs). Sawmill soil, contaminated with PAHs, was mixed with composted green waste (1:1) and incubated with or without fungal inoculum. The treatments were performed at the laboratory and field scales. In the laboratory scale treatment (starting concentration 3500 mg kg−1, sum of 16 PAH) the high molecular weight PAHs were degraded significantly more in the fungal-inoculated microcosms than in the uninoculated ones. In the microcosms inoculated with Phanerochaete velutina, 96% of 4-ring PAHs and 39% of 5- and 6-ring PAHs were removed in three months. In the uninoculated microcosms, 55% of 4-ring PAHs and only 7% of 5- and 6-ring PAHs were degraded. However, during the field scale (2 t) experiment at lower starting concentration (1400 mg kg−1, sum of 16 PAH) the % degradation was similar in both the P. velutina-inoculated and the uninoculated treatments: 94% of the 16 PAHs were degraded in three months. In the field scale experiment the copy number of gram-positive bacteria PAH-ring hydroxylating dioxygenase genes was found to increase 1000 fold, indicating that bacterial PAH degradation also played an important role.

Sphingobacterium sp. SW-09에 의한 토양환경에서의 다환 방향족탄화수소인 페난스렌의 분해

We isolated a potent phenanthrene-degrading bacterium from oil-contaminated soils of Suzhou, China, and assessed the potential use of these bacteria for bioremediation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs) in a microcosm. Based on 16S rDNA sequencing, we identified this bacteria as Sphigobacterium sp. SW-09. By PCR amplification, we also identified catechol 2,3-dioxygenase genes (nahH genes) mediating PAH degradation. Staphylococcus sp. KW-07, which has been identified in our previous study, showed potential for use in bioremediation of oil-contaminated soils. In this experiment, we compared the rate of phenanthrene-degradation between Staphylococcus sp. KW-07 and Sphingobacterium sp. SW-09 in a microcosm condition. Newly isolated Sphingobacterium sp. SW-09 showed a higher phenanthrene-degradation rate than that of Staphylococcus sp. KW-07 in soil microcosms. Together, our results suggest that the Sphingobacterim sp. SW-09 strain isolated from the Suzhou area may also be useful in bioremediation of PAH-contaminated soils.

Bioremediation of PAHs-contaminated soil through composting: Influence of bioaugmentation and biostimulation on contaminant biodegradation

The degradation of several polycyclic aromatic hydrocarbons (PAHs) in soil through composting was investigated. The selected PAHs included: fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, and chrysene, with concentrations simulating a real creosote sample. The degradation of PAHs (initial concentration 1 g of total PAHs kg −1 dry soil) was assessed applying bioaugmentation with the white-rot fungi Trametes versicolor and biostimulation using compost of the source-selected organic fraction of municipal solid waste (OFMSW) and rabbit food as organic co-substrates. The process performance during 30 days of incubation was evaluated through different analyses including: dynamic respiration index (DRI), cumulative oxygen consumption during 5 days (AT 5), enzymatic activity, and fungal biomass. These analyses demonstrated that the introduced T. versicolor did not significantly enhance the degradation of PAHs. However, biostimulation was able to improve the PAHs degradation: 89% of the total PAHs were degraded by the end of the composting period (30 days) compared to the only 29.5% that was achieved by the soil indigenous microorganisms without any co-substrate (control, not amended). Indeed, the results showed that stable compost from the OFMSW has a greater potential to enhance the degradation of PAHs compared to non-stable co-substrates such as rabbit food.

Staphylococcus sp. KW-07 contains nahH gene encoding catechol 2,3-dioxygenase for phenanthrene degradation and a test in soil microcosm

We isolated three species of phenanthrene-degrading bacteria from oil-contaminated soils and marine sediment, and assessed the potential use of these bacteria for bioremediation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs). Based on 16S rDNA sequences, these bacteria were Staphylococcus sp. KW-07 and Pseudomonas sp. CH-11 from soil, and Ochrobactrum sp. CH-19 from the marine sediment. By PCR amplification, catechol 2,3-dioxygenase genes (nahH genes) mediating PAH degradation in the chromosome of Staphylococcus sp. KW-07 and Ochrobactrum sp. CH-19, and in plasmid DNA of Pseudomonas sp. CH-11 were detected. All isolates had a similar optimal growth temperature (25°C) and optimal growth pH (7.0) in a minimal salt medium (MSM) with 0.1% (w/v) phenanthrene as the sole source of carbon and energy. Pseudomonas sp. CH-11 and Staphylococcus sp. KW-07 degraded 90% of added phenanthrene in 3 days and Ochrobactrum sp. CH-19 degraded 90% of the phenanthrene in 7 days under laboratory batch culture conditions. However, Staphylococcus sp. KW-07 was the most effective among the three strains in degradation of phenanthrene in soil. After inoculation of 1×1011 cells of Staphylococcus sp. KW-07, over 90% degradation of 0.1% phenanthrene (0.1g/100g soil) was achieved after 1 month at 25°C. The results collectively suggest that the Staphylococcus sp. KW-07 strain isolated may be useful in bioremediation of PAH-contaminated soils.

Effects of compost stability and contaminant concentration on the bioremediation of PAHs-contaminated soil through composting

The objective of this study was to investigate the effect of two factors: the stability degree (0.37–4.55 mg O 2 g −1 Organic Matter h −1) of different composts derived from the organic fraction of municipal solid wastes and the concentration of a complex mixture of PAHs including flourene, phenanthrene, anthracene, flouranthene, pyrene and benzo(a)anthracene in the bioremediation of soil. The two factors were systematically studied applying central composite design methodology. The obtained results demonstrated that compost stability degree was particularly important during the first stage of the process. Stable composts enhanced the levels of degradation in soil–compost mixture and a degradation rate of 92% was achieved in this period, but only 40% was degraded with the least stable compost. The PAHs concentration was also important during the process, since the degradation rates increased with the increase in the PAHs concentration. Moreover, all the individual PAHs demonstrated a notable decrease in their concentrations after the incubation period, but pyrene was degraded to lower levels in some treatments compared to others PAHs.

Binding of polycyclic aromatic hydrocarbons by humic acids formed during composting

Binding of two model polycyclic aromatic hydrocarbons (PAHs), phenanthrene and pyrene, by humic acids (HAs) isolated from an organic substrate at different stages of composting and a soil was investigated using a batch fluorescence quenching method and the modified Freundlich model. With respect to soil HA, the organic substrate HA fractions were characterized by larger binding affinities for both phenanthrene and pyrene. Further, isotherm deviation from linearity was larger for soil HA than for organic substrate HAs, indicating a larger heterogeneity of binding sites in the former. The composting process decreased the binding affinity and increased the heterogeneity of binding sites of HAs. The changes undergone by the HA fraction during composting may be expected to contribute to facilitate microbial accessibility to PAHs. The results obtained also suggest that bioremediation of PAH-contaminated soils with matured compost, rather than with fresh organic amendments, may result in faster and more effective cleanup.

Bioremediation of PAH-contaminated soil by composting: a case study.

Composting technique was used for bioremediation of industrial soil originating from a former tar-contaminated site. The composting process was regulated by aeration to keep optimal temperature gradient and concentrations of O2 and CO2 inside the composting pile. The efficiency of bioremediation was evaluated by performing analysis of 11 individual three- to six-ring unsubstituted aromatic hydrocarbons (PAH) and estimating of changes in ecotoxicity of the contaminated soil. After 42 d of composting, PAH with 3-4 rings were removed from 42 to 68%, other higher-molar mass PAH from 35 to 57%. Additional 100 d of compost maturation in open-air field did not result in a further decrease of PAH. Ecotoxicity tests performed with bioluminescent bacteria Vibrio fischerii showed a decrease in toxicity both after composting and maturation phases. However, toxicity tests on mustard-seed germination did not reveal any significant changes during composting and maturation phases.

Bioremediation of PAH-Contaminated Soil via In-Vessel Composting

This study is being conducted to investigate the biodegradation of polycyclic aromatic hydrocarbons (PAHs) present in contaminated soil using composting technology. Pyrene, a four-ring aromatic hydrocarbon, was chosen as a model PAH compound for the study. Preliminary investigations were carried out to assess the feasibility of soil composting by monitoring (a) carbon to nitrogen (C/N) ratio, (b) microbial consortia diversity, (c) coefficient of permeability and (d) moisture content. The soil was augmented with composted sludge, which was used as a bulking agent and nutrient supplement, in quantities ranging from 0-50% dry weight basis. Tests were conducted in both batch and continuous composters. In the batch composter, forty grams of soil/sludge mixtures in different proportions were spiked with 13.5 mg/kg (dry weight basis) of unlabeled pyrene. The batch composters were aerated and placed in a constant temperature water bath for a period of 21 days. Samples were soxhelet extracted and analyzed on the High Performance Liquid Chromatograph to determine the reduction in pyrene concentration. Analysis of these samples is in progress. In the continuous composter, the soil/sludge mixtures are spiked with both labeled and un-labclcd pyrene to obtain a total radioactivity of 13.5 µci. This process is being monitored for temperature, moisture content, volatile solids and microbial population. Mineralization of pyrene is assessed by quantifying 14CO2 produced.