Plant-assisted Bioremediation Research Articles

Microbial Bioremediation of Petroleum Contaminated Soil: Structural Complexity, Degradation Dynamics and Advanced Remediation Techniques

Soil contamination with petroleum hydrocarbons poses a significant environmental challenge, necessitating effective remediation strategies to mitigate ecological risks. This review paper systematically examines the current state of knowledge regarding soil contamination with petroleum hydrocarbons, focusing on diverse sources and the extent of contamination. The investigation encompasses a range of hydrocarbon compounds, including aliphatic and aromatic fractions, emphasizing the dynamic nature of the contamination scenarios. A thorough review of bioremediation techniques, which have shown promise and sustainability as methods for cleaning up soil contaminated with petroleum hydrocarbons are also involved in order to solve these issues. Each of the three microbial processes, biodegradation, bioaugmentation, and biostimulation, is covered in detail in the paper, along with the complex mechanics underlying each technique. The report also emphasises new developments in genetics and molecular biology that add to our understanding of the metabolic pathways and microbial interactions involved in hydrocarbon breakdown. The effectiveness of plant-assisted bioremediation coupled with bioaugmentation and stimulation, specifically phytoremediation, is also explored, emphasizing the potential of certain plant species to enhance the removal of petroleum hydrocarbons from contaminated soils through rhizosphere interactions and plant-associated microbial activities. Furthermore, the paper evaluates the influence of environmental variables including soil composition, temperature, and moisture content on the effectiveness of bioremediation techniques, offering valuable perspectives on enhancing remediation efficiency through optimal conditions. The possibility for enhancing conventional bioremediation techniques through the incorporation of cutting-edge technology like nano-remediation is also explored.

Ex situ bioremediation of diesel fuel-contaminated soil in two different climates

The petroleum industry is often faced with accidental spills and discharges that pollute valuable natural resources such as soil. The purpose of this study was to assess bioremediation potential of an on-site landfarming unit (LU), a highly economical solution that complies with the zero-waste policy, for bioremediation of the contaminated soil after an actual diesel fuel leakage in a fuel depot. The first aim was to evaluate the effects of different climates on hydrocarbon bioremediation. For this reason, a part of the contaminated soil was moved from the initial location with a sub-Mediterranean climate to an LU at another location with a temperate continental climate. Our results demonstrated that remediation in sub-Mediterranean climate is less effective than the remediation in a temperate continental climate. The second aim of this study was to evaluate the effect of different plant species on the microbial population during bioremediation. For that purpose, 365-day monitoring of phospholipid fatty acids (PLFA) was performed. Our results support the hypothesis that plant-assisted bioremediation can diminish toxic effects of diesel-polluted soil and that the changes in plant species during bioremediation cause changes in the microbial population.

Performic acid pre-treatment of poplar biomasses grown on a contaminated area for enhanced enzymatic digestibility: A viable route to obtain fine-products and recovery of contaminants

Biomasses obtained from green remediation strategies can represent a new valuable feedstock for obtaining fine chemicals and/or next generation liquid fuels. A sustainable chain of technologies for recovering chemicals from poplar grown in a multi-contaminated area is presented here in this work. A pre-treatment based on the use of performic acid (generated in situ from formic acid and hydrogen peroxide) was designed and tested. The effect of this pre-treatment was measured in terms of delignification, the increased enzymatic digestibility of the solid residues, and final destination of the mineral components initially present in poplar biomass. Upon treatment with performic acid at 1.75, 3.5 and 7 M, the content of lignin in the residual biomasses resulted as being significantly reduced: 28.5, 92.8 and 100% of initial lignin were removed and dissolved. After this pre-treatment, most of minerals initially present in poplar biomass were dissolved during the generated aqueous phase. In concomitance, a large part of the initial lignin and xylose were also dissolved. The solid residues obtained from the pre-treatment phase were then subjected to hydrolysis. Enzymatic digestibility was proven to be already effective on samples pre-treated with 3.5 M performic acid at 55 °C. Indeed, even when lignin was not completely removed (>75%), the cellulose in the residual biomasses was completely hydrolysed in glucose through a commercial cellulase (from Trichoderma reesei). Finally, the aqueous solution obtained from enzymatic hydrolysis was effectively reacted in presence of AlCl3·6H2O (1%) and sulphuric acid (0.5%) at 150 °C for 45 min. A final yield of 68.2% of levulinic acid and 4.8% of hydroxymethyl furfural were eventually obtained. Through this process, not only were the majority of metals coming from the plant-assisted bioremediation process/strategy confined to an aqueous solution, but also residual poplar biomasses were valorised by generating platform molecules which might find applications in the production of fine-chemicals.

Fluidized bed gasification of biomass from plant-assisted bioremediation: Fate of contaminants

Fluidized-bed gasification (FBG) of Phyto-assisted Bioremediation (PABR) biomass is analyzed focusing on the contaminants’ dispersion. Poplar pruning coming from an area contaminated by polychlorinated biphenyls (PCBs) and heavy metals (HM) are considered. The biomass analysis showed relevant contents in HMs, especially Cd and Cr, and no significant PCB content. FBG process was analyzed to: a) track pollutants, b) detect contaminants in the FBG and c) investigate the HMs concentration in the produced streams. The results showed that most of the metals are concentrated in the ashes collected in the bottom of the reactor (Pb, Cd, Cu, Cr), or in the cyclone (B, Na, Mg, Al, K and Fe). Interestingly, metals are also released by the olivine bed (Mg, Fe, Ni and Al) and transported downstream. Consistent fractions of Zn and Fe (also Cu) were detected in the fugitive ashes. As for the Volatile Organic Compounds (VOC) concentration, we noted similarities between PABR and virgin biomass syngas streams. A reduced-scale process was carried out in TGA-DTA to investigate the potential of such technique in reproducing the main features of the FBG process. Comparable results were obtained, thus suggesting its possible application for small-scale preliminary assessment of FBG process.

Fluidized bed gasification of biomass from plant assisted bioremediation (PABR): Lab-scale assessment of the effect of different catalytic bed material on emissions

The interaction between biomass from plant assisted bioremediation processes PABR contaminated with heavy metals and the bed materials used in Fluidized Bed Gasifier FBG systems was experimentally studied to identify the origin of the metals detected in syngas and/or solid residues, and affecting the quality of the produced fuels and biochar. The characteristics of an arboreal (poplar pruning) and an herbaceous biomass (Arundo Donax), both previously used in phytoremediation processes, were evaluated. The bed materials have been identified among those most used in pyrogasification processes, such as olivine, K-feldspar, kaolinite and calcite. The simulation of the process and the sampling of the syngas was carried out by means of an instrumental apparatus composed of TGA-DSC connected with a system of bubblers for the capture of heavy metals HM. The analysis of the matrices and the bubbled solutions in ICP-MS allowed to experimentally evaluate quantity and composition of HM released. The analyses showed that calcite gives the best results for both arboreal and herbaceous biomass but it has the disadvantage of losing about 55 % in weight during the process, releasing CO and CO2 and becoming CaO. The criteria for choosing the most suitable material for the bed of an arboreal or herbaceous biomass gasification were carried out mainly on the basis of the heavy metals released during the process. The study provides useful results for the assessment of the bed materials in FBG conversion process using PABR biomass. From a comparison between all the parameters considered and the Principal Component Analysis (PCA) results, it emerges that K-feldspar represent the best optimization for the materials that can be used in FBG beds both in the case of arboreal and herbaceous plants, while olivine is particularly effective only with arboreal biomass.

Cadmium-Tolerant Plant Growth-Promoting Bacteria Curtobacterium oceanosedimentum Improves Growth Attributes and Strengthens Antioxidant System in Chili (Capsicum frutescens)

The remediation of potentially toxic element-polluted soils can be accomplished through the use of microbial and plant-assisted bioremediation. A total of 32 bacteria were isolated from soil samples contaminated with potentially toxic elements. The isolated bacterial strain DG-20 showed high tolerance to cadmium (up to 18 mM) and also showed bioaccumulative Cd removal properties, as demonstrated by atomic absorption spectroscopy studies. By sequencing the 16S rRNA gene, this strain was identified as Curtobacterium oceanosedimentum. Under stress and normal conditions, isolate DG-20 also produced a wide range of plant growth promoting traits, including ammonia production (51–73 µg/mL) and IAA production (116–183 µg/mL), alongside siderophore production and phosphate solubilization. Additionally, pot experiments were conducted to determine whether the strain could promote Chili growth when Cd salts are present. Over the control, bacterial colonization increased root and shoot lengths significantly up to 58% and 60%, respectively. Following inoculation with the Cd-tolerant strain, the plants also increased in both fresh and dry weight. In both the control and inoculated plants, Cd was accumulated more in roots than in shoots, indicating that Chili was phytostabilizing Cd levels. Besides improving the plant attributes, Cd-tolerant bacteria were also found to increase the amount of total chlorophyll, proline, total phenol, and ascorbic acid in the soil when added to the soil. These results suggest that the inoculant provides protection to plants from negative effects. The results of the present study predict that the combined properties of the tested strain in terms of Cd tolerance and plant growth promotion can be exploited for the purpose of the bioremediation of Cd, and for the improvement of Chili cultivation in soils contaminated with Cd.

Reflections and Insights on the Evolution of the Biological Remediation of Contaminated Soils

The field of soil biological remediation was initially focused on the use of microorganisms. For organic contaminants, biostimulation and bioaugmentation were the strategies of choice. For heavy metals, bioremediation was centered on the feasibility of using microorganisms to reduce metal toxicity. Partly due to the impossibility to degrade metals, phytoremediation emerged proposing the use of plants to extract them (phytoextraction) or reduce their bioavailability (phytostabilization). Later, microbial-assisted phytoremediation addressed the inoculation of plant growth-promoting microorganisms to improve phytoremediation efficiency. Similarly, plant-assisted bioremediation examined the stimulatory effect of plant growth on the microbial degradation of soil contaminants. The combination of plants and microorganisms is nowadays often recommended for mixed contaminated soils. Finally, phytomanagement emerged as a phytotechnology focused on the use of plants and associated microorganisms to decrease contaminant linkages, maximize ecosystem services, and provide economic revenues. Although biological remediation methods have been in use for decades, the truth is that they have not yet yielded the expected results. Here, we claim that much more research is needed to make the most of the many ways that microorganisms have evolutionary developed to access the contaminants and to better understand the soil microbial networks responsible, to a great extent, for soil functioning.

Fluidized Bed Gasification of Biomass from Plant-Assisted Bioremediation - Fate of Contaminants

Fluidized Bed Gasification of Biomass from Plant-Assisted Bioremediation - Fate of Contaminants

Gasification treatment of poplar biomass produced in a contaminated area restored using plant assisted bioremediation

Remediation of polluted soils using phytoremediation techniques is an effective strategy. However, the use of the biomass from these soils for energy purposes may raise efficiency and pollution emission problems and there is currently little research on this issue.In this work, the main results of a fluidized-bed gasification treatment conducted on poplar biomass pruning residues from a multi-contaminated area are presented. The samples were collected from an experimental site in which a plant-assisted bioremediation (PABR) technology has been applied since 2013 to reduce the soil heavy metal (HM) and polychlorinated biphenyl (PCB) contents. The main goal of this study was to identify the specific treatment necessary, in addition to conventional tar reforming, for trapping possible residues of HMs and PCBs in ashes during the gasification process. In our study, we demonstrate that gasification of contaminated biomass coming from PABR (where contaminant residues are concentrated mainly in the roots and are insignificant in the shoots) produces syngas whose characteristics are similar to those obtained using non-contaminated biomass. The results showed that contaminant concentrations in the prunings were negligible; the total amount of PCBs was 1.63 ng/g, while HMs ranged from 0.01 to 0.70 mg/kg, except for Cu and Zn (∼20 mg/kg). Furthermore, the presence in the biomass of Ca and traces of other metals showed a possible catalytic effect with an improvement in the tar conversion in the gasifier leading to a reduction of 5–10% in tar content. The overall results suggest that a specific treatment for pollutant capture is necessary only when the roots, the part of the plants where these contaminants are concentrated, are sampled and used for the gasification process. Although energy from biomass produced on a contaminated site is currently considered waste and involves disposal costs, this paper shows that the poplar biomass grown on a multi-contaminated soil can be used for energy purposes without any impact on the environment.

Microbial and Plant-Assisted Bioremediation of Heavy Metal Polluted Environments: A Review.

Environmental pollution from hazardous waste materials, organic pollutants and heavy metals, has adversely affected the natural ecosystem to the detriment of man. These pollutants arise from anthropogenic sources as well as natural disasters such as hurricanes and volcanic eruptions. Toxic metals could accumulate in agricultural soils and get into the food chain, thereby becoming a major threat to food security. Conventional and physical methods are expensive and not effective in areas with low metal toxicity. Bioremediation is therefore an eco-friendly and efficient method of reclaiming environments contaminated with heavy metals by making use of the inherent biological mechanisms of microorganisms and plants to eradicate hazardous contaminants. This review discusses the toxic effects of heavy metal pollution and the mechanisms used by microbes and plants for environmental remediation. It also emphasized the importance of modern biotechnological techniques and approaches in improving the ability of microbial enzymes to effectively degrade heavy metals at a faster rate, highlighting recent advances in microbial bioremediation and phytoremediation for the removal of heavy metals from the environment as well as future prospects and limitations. However, strict adherence to biosafety regulations must be followed in the use of biotechnological methods to ensure safety of the environment.

Plant-assisted bioremediation of a historically PCB and heavy metal-contaminated area in Southern Italy

A plant-assisted bioremediation strategy was applied in an area located in Southern Italy, close to the city of Taranto, historically contaminated by polychlorinated biphenyls (PCBs) and heavy metals. A specific poplar clone (Monviso) was selected for its ability to promote organic pollutant degradation in the rhizosphere, as demonstrated elsewhere. Chemical and microbiological analyses were performed at the time of poplar planting in selected plots at different distances from the trunk (0.25–1m) and at different soil depths (0–20 and 20–40cm), at day 420. A significant decrease in PCB congeners and a reduction in all heavy metals was observed where the poplar trees were present. No evidence of PCB and heavy metal reduction was observed in the non poplar-vegetated soil. Microbial analyses (dehydrogenase activity, cell viability, microbial abundance) of the autochthonous microbial community showed an improvement in soil quality. In particular, microbial activity generally increased in the poplar-rhizosphere and a positive effect was observed in some cases at up to 1m distance from the trunk and up to 40cm depth. The Monviso clone was effective in promoting both a general decrease in contaminant occurrence and an increase in microbial activity in the chronically polluted area a little more than one year after planting.

Enhanced bioremediation of BTEX contaminated groundwater in pot-scale wetlands.

Pot-scale wetlands were used to investigate the role of plants in enhancing the performance of engineered bioremediation techniques like biostimulation, bioaugmentation, and phytoremediation collectively. Canna generalis plants were grown hydroponically in BTEX contaminated groundwater supplied in wetland mesocosms. To quantify the contaminant uptake by the plants, wetlands with and without shoot biomass along with unplanted gravel bed were used under controlled conditions. The residual concentration of the selected BTEX compound, toluene, in the rhizosphere water was measured over the entire period of the experiment along with the water lost by evapotranspiration. The rate of biodegradation in all wetland mesocosms fitted best with the first-order kinetics. The total removal time of the BTEX compound was found to be highest in the unplanted gravel bed mesocosm followed by wetlands without and with shoot biomass. The cumulative uptake of toluene in shoot biomass of the wetland plants initially increased rapidly and started to decrease subsequently till it reached a peak value. Continuity equations integrated with biodegradation and plant uptake sink terms were developed to simulate residual concentration of toluene in rhizospheric water for comparison with the measured data for entire period of the experiments. The results of this research can be used to frame in situ plant-assisted bioremediation techniques for hydrocarbon-contaminated soil-water resources.

Phytoremediation and Plant-Assisted Bioremediation in Soil and Treatment Wetlands: A Review

Phytoremediation is a technology that is based on the combined action of plants and their associated microbial communities to degrade, remove, transform, or immobilize toxic compounds located in soils, sediments, and more recently in polluted ground water and wastewater in treatment wetlands. Phytoremediation could be used to treat different types of contaminants including petroleum hydrocarbons, chlorinated solvents, pesticides, explosives, heavy metals and radionuclides in soil and water. The advantages of phytoremediation compared to conventional techniques are lower cost, low disruptiveness to the environment, public acceptance, and potentiality to remediate various pollutants. The use of plants in conjunction with plant associated bacteria (rhizosphere or endophytic) offers greater potential for bioremediation of organic compounds, and in some cases inorganic pollutants than using plants alone in bioremediation. The implementation of treatment wetlands for phytoremediation of wastewater or polluted water originating from various sources allows removing organic and inorganic pollutants from water in an environmentally friendly and economically feasible way. Presently, different processes of phytoremediation in treatment wetlands are less studied compared to phytoremediation of polluted soils. Further research is needed to advance the understanding of the pollutant removal mechanisms in treatment wetlands with vegetation, and how based on this information to improve treatment wetland design and operational parameters to achieve more efficient treatment processes. This review covers basic processes of phytoremediation with special emphasis on rhizoremediation and plant-microbe interactions in plant–assisted biodegradation in soil and treatment wetlands.

Rhizoremediation of Diesel-Contaminated Soil with Two Rapeseed Varieties and Petroleum degraders Reveals Different Responses of the Plant Defense Mechanisms

Plant-assisted bioremediation (rhizoremediation) stands out as a potential tool to inactivate or completely remove xenobiotics from the polluted environment. Therefore, it is of key importance to find an adequate combination of plant species and microorganisms that together enhance the clean-up process. To understand the response of plants upon bioaugmentation, the antioxidative and detoxification system was analyzed in high and low erucic acid rapeseed varieties (HEAR and LEAR, respectively), after 8 weeks of their treatment with petroleum degraders and 6000 mg diesel oil/kg dry soil. The oxidative stress was enhanced in LEAR being exposed to sole diesel oil, in comparison with HEAR. However, when LEAR plants were additionally inoculated with bacteria, suppression of total catalase (CAT) and ascorbate peroxidase (APX) activity were observed. Interestingly, glutathione transferase (GST) activity was found in these plants at a much higher level than in HEAR, which correlated with a more efficient diesel removal performed by LEAR in the polluted soil and upon bioaugmentation. A distinct profile of polycyclic aromatic hydrocarbons (PAH) was detected in leaves of these plants. Neither LEAR nor HEAR experienced any changes in the photosynthetic capacity upon diesel pollution and presence of petroleum degraders, which supports the usefulness of rhizoremediation with rapeseed.

Remediation of LNAPL Contaminated Groundwater Using Plant-Assisted Biostimulation and Bioaugmentation Methods

Different cases of bioremediation technique were experimentally investigated here for decontaminating light non-aqueous phase liquid (LNAPL)-polluted groundwater collected from Panipat oil refinery situated in Haryana, India. Natural biodegradation of toluene, the selected LNAPL, was studied first under different varying substrate concentrations at room temperature (21.6 ± 0.3 °C). Biostimulation was then studied by mixing the polluted groundwater with a primary treated domestic wastewater for providing nutrients and other supplementary components to the native microbial population. For studying the remaining cases, small-scale wetland having plants of Canna generalis was developed in the laboratory with and without the presence of toluene in the rhizosphere. The wetland system in the presence of toluene was used here for developing the pre-grown microbial cultures to enhance the degradation rate of the LNAPL (bioaugmentation). The plant-assisted biostimulation was studied in the third case by adding the polluted groundwater with the root zone water of the wetland system developed without the presence of toluene. In the fourth case, the biostimulation was coupled with the bioaugmentation strategy by mixing the groundwater with the root zone water of the wetland system developed in the presence of toluene. A comparative account of these four different bioremediation techniques was prepared for their respective rates of biodegradation, duration of lag phases, and the total time of degradation. It was observed that the plant-assisted bioremediation techniques had better performance over the natural biodegradation and biostimulation methods of the considered LNAPL. The plant-assisted biostimulation coupled with the bioaugmentation technique needed almost no acclimatization time and accelerated the rate of degradation almost twofold compared to the natural bioremediation and, hence, is proved to be the best one among the other bioremediation techniques for decontaminating the LNAPL-polluted groundwater. The results of the conducted experiments can be used to obtain vital information on framing the engineered bioremediation planning for LNAPL-contaminated sites.

Multivariate data analysis for bioremediation of contaminated soil through Interactions between heavy metals, microbes and plants

Plant-assisted bioremediation (phytoremediation) is a promising technique for in-situ remediation of contaminated soils. Enhancement of phytoremediation processes requires a sound understanding of the complex interactions in the rhizosphere. This work presents a Pot experiment was conducted under green house conditions to test the effect of fungal inoculation on remediating heavy metal (HM) contaminated soil treated with sewage effluent for several years. Canola crop was used as accumulator plants. Results demonstrated that the dry matter yield of tested crops were significantly higher in soil irrigated for 50 years with sewage effluent than that in 20 years sewage effluent irrigated soil. Metal uptake and accumulation in different plant parts (shoot and root) was enhanced after inoculation with Aspergillus parasiticus (F1) and Fusarium oxysporum (F2). The reate of HM accumulation as higher in in soil treated irrigated sewage effluent for 50 years than that in 20 years sewage irrigated soil.

Multivariate data analysis for bioremediation of contaminated soil through Interactions between heavy metals, microbes and plants

Plant-assisted bioremediation (phytoremediation) is a promising technique for in-situ remediation of contaminated soils. Enhancement of phytoremediation processes requires a sound understanding of the complex interactions in the rhizosphere. This work presents a Pot experiment was conducted under green house conditions to test the effect of fungal inoculation on remediating heavy metal (HM) contaminated soil treated with sewage effluent for several years. Canola crop was used as accumulator plants. Results demonstrated that the dry matter yield of tested crops were significantly higher in soil irrigated for 50 years with sewage effluent than that in 20 years sewage effluent irrigated soil. Metal uptake and accumulation in different plant parts (shoot and root) was enhanced after inoculation with Aspergillus parasiticus (F1) and Fusarium oxysporum (F2). The reate of HM accumulation as higher in in soil treated irrigated sewage effluent for 50 years than that in 20 years sewage irrigated soil.

Synergism of Wild Grass and Hydrocarbonoclastic Bacteria in Petroleum Biodegradation

Synergism of Wild Grass and Hydrocarbonoclastic Bacteria in Petroleum Biodegradation

Rhizosphere processes and management in plant-assisted bioremediation (phytoremediation) of soils

Plant-assisted bioremediation or phytoremediation holds promise for in situ treatment of polluted soils. Enhancement of phytoremediation processes requires a sound understanding of the complex interactions in the rhizosphere. Evaluation of the current literature suggests that pollutant bioavailability in the rhizosphere of phytoremediation crops is decisive for designing phytoremediation technologies with improved, predictable remedial success. For phytoextraction, emphasis should be put on improved characterisation of the bioavailable metal pools and the kinetics of resupply from less available fractions to support decision making on the applicability of this technology to a given site. Limited pollutant bioavailability may be overcome by the design of plant–microbial consortia that are capable of mobilising metals/metalloids by modification of rhizosphere pH (e.g. by using Alnus sp. as co-cropping component) and ligand exudation, or enhancing bioavailability of organic pollutants by the release of biosurfactants. Apart from limited pollutant bioavailability, the lack of competitiveness of inoculated microbial strains (in particular degraders) in field conditions appears to be another major obstacle. Selecting/engineering of plant–microbial pairs where the competitiveness of the microbial partner is enhanced through a “nutritional bias” caused by exudates exclusively or primarily available to this partner (as known from the “opine concept”) may open new horizons for rhizodegradation of organically polluted soils. The complexity and heterogeneity of multiply polluted “real world” soils will require the design of integrated approaches of rhizosphere management, e.g. by combining co-cropping of phytoextraction and rhizodegradation crops, inoculation of microorganisms and soil management. An improved understanding of the rhizosphere will help to translate the results of simplified bench scale and pot experiments to the full complexity and heterogeneity of field applications.

Fuzzy Geographic Information Systems for Phytoremediation Plant Selection

Geographic information systems (GIS) technology was combined with fuzzy logic to construct a phytoremediation plant selection tool. Phytoremediation involves the use of vegetation for treatment of contaminated soils, sediments, and water. In this paper, the focus is on one particular phytoremediation mechanism plant-assisted bioremediation of polycyclic aromatic hydrocarbon (PAH) soil contamination. Many plants show potential for PAH remediation, but factors such as growth requirements, climate, and soil conditions need to be considered. Given the spatial nature of the data involved, GIS was chosen as the basis for the plant selection tool. Eight candidate plants were selected because of their PAH phytoremediation potential, and their growth requirements were represented using fuzzy membership functions to account for parameters’ uncertainty. Vermont and South Carolina were selected as case studies, and calculations were performed to determine the suitability ratings for each of the candidate plants in th...