Bioremediation of petroleum hydrocarbons by vermicomposting process bioaugmentated with indigenous bacterial consortium isolated from petroleum oily sludge

Bioaugmentation and vermicompost facilitated the hydrocarbon bioremediation: scaling up from lab to field for petroleum-contaminated soils

The biodegradation of total petroleum hydrocarbon (TPH) in soil is very challenging due to the complex recalcitrant nature of hydrocarbon, hydrophobicity, indigenous microbial adaptation and competition, and harsh environmental conditions. This work further confirmed that limited natural attenuation of petroleum hydrocarbons (TPHs) (15% removal) necessitates efficient bioremediation strategies. Hence, a scaling-up experiment for testing and optimizing the use of biopiles for bioremediation of TPH polluted soils was conducted with three 500-kg pilots of polluted soil, and respective treatments were implemented: including control soil (CT), bioaugmentation and vermicompost treatment (BAVC), and a combined application of BAVC along with bioelectrochemical snorkels (BESBAVC), all maintained at 40% field capacity. This study identified that at pilot scale level, a successful application of BAVC treatment can achieve 90.3% TPH removal after 90 days. BAVC's effectiveness stemmed from synergistic mechanisms. Introduced microbial consortia were capable of TPH degradation, while vermicompost provided essential nutrients, enhanced aeration, and, potentially, acted as a biosorbent. Hence, it can be concluded that the combined application of BAVC significantly enhances TPH removal compared to natural attenuation. While the combined application of a bioelectrochemical snorkel (BES) with BAVC also showed a significant TPH removal, it did not differ statistically from the individual application of BAVC, under applied conditions. Further research is needed to optimize BES integration with BAVC for broader applicability. This study demonstrates BAVC as a scalable and mechanistically sound approach for TPH bioremediation in soil.

Vermiremediation of heavy metals (HMs)-contaminated agricultural land: synergistic changes in soil enzyme activities and earthworm's growth parameters

In this investigation the heavy metals (Cu, Zn, Mn, Cr and Ni) remediation potential of Eisenia fetida was studied in the crude oil polluted soil. The potential of E. fetida was evaluated based on the decrease in concentrations of Cu, Zn, Mn, Cr and Ni, and improvement in the soil enzyme activities at the end of 90 days of experimental trials. Moreover, soil health quality, inter-relationship between the enzyme activities and the growth parameters of E. fetida and synergistic relation among the enzyme activities were also evaluated through G-Mean and T-QSI indices, chord plot analysis and principal component analysis (PCA) to confirm the performance of E. fetida during vermiremediation. The results revealed that the soil treated with E. fetida showed a reduction in the concentration of Cu, Zn, Mn, Cr and Ni by 17.4% 19.45%, 9.44%, 23.8% and 9.6% respectively by end of the experimental trials. The cellulase, amylase, polyphenol oxidase, peroxidase, urease, dehydrogenase and catalase activities in the E. fetida-treated soil were enhanced by 89.83%, 99.17%, 142%, 109.9%, 92.9%, 694.3% and 274.5% respectively. The results of SEM-EDS revealed enhancement in the O, K, Na, Mg and P content by 62.36%, 96.2%, 97.9%, 93.7% and 98.2% respectively by the end of the experimental trial. The G-Mean and T-QSI indices also confirmed the improvement in soil enzyme activities thereby indicating the positive influence of E. fetida on soil decontamination process. The chord plot indicated the interrelationship between the earthworm's growth parameters and enzyme activities of the soil as indicated by the high linkage between the nodes. Finally, the PCA confirmed the negative effect of the heavy metals on the soil enzyme activities and synergistic interrelationship between the enzyme activities during the vermiremediation process. Thus, this study demonstrated the changes in the soil enzyme activities and their interconnected influences during vermiremediation of crude oil sourced heavy metals from polluted soil.

Bioremediation of polycyclic aromatic hydrocarbons in crude oil by bacterial consortium in soil amended with Eisenia fetida and rhamnolipid

The present study investigated the concerted effort of Eisenia fetida and rhamnolipid JBR-425 in combination with a five-member bacterial consortium exhibiting elevated degradation levels of low and high molecular weight polycyclic aromatic hydrocarbons (PAH) from soil contaminated with Digboi crude oil. Application of bacterial consortium (G2) degraded 30-89% of selected PAH from the artificial soil after a 45-day post-exposure, in which chrysene showed the highest level of degradation with 89% and benzo(a)pyrene is the lowest with 30%, respectively. Moreover, an acute exposure study observed that earthworm biomass decreased, and mortality rates increased with increasing crude oil concentrations (0.25 to 2%). Earthworms with a 100% survival rate at 1% crude oil exposure suggest the tolerance potential and its mutual involvement in the bioremediation of crude oil with selected bacterial consortia. Bacterial consortium assisted with E. fetida (G3) showed 98% chrysene degradation with a slight change in benzo(a)pyrene degradation (35%) in crude oil spiked soil. Besides, the most dominant PAH in crude oil found in the current work, fluoranthene, undergoes 93% and 70% degradation in G3 and G5 groups, respectively. However, rhamnolipid JBR-425 coupled with the bacterial consortium (G5) has resulted in 97% degradation of chrysene and 33% for benzo(a)pyrene. Overall, bacterial consortium assisted with earthworm group has shown better degradation of selected PAH than bacterial consortium with biosurfactant. Catalase (CAT), glutathione reductase (GST) activity and MDA content was found to be reduced in earthworms after sub-lethal exposure, suggesting oxidative stress prevalence via reactive oxygen species (ROS). Hence, the findings of the present work suggest that the application of a bacterial consortium, along with earthworm E. fetida, has huge potential for field restoration of contaminated soil with PAH and ecosystem sustainability.

Bioremediation of heavy oily sludge: a microcosms study

Oily sludge is a residue from the petroleum industry composed of a mixture of sand, water, metals, and high content of hydrocarbons (HCs). The heavy oily sludge used in this study originated from Colombian crude oil with high density and low American Petroleum Institute (API) gravity. The residual waste from heavy oil processing was subject to thermal and centrifugal extraction, resulting in heavy oily sludge with very high density and viscosity. Biodegradation of the total petroleum hydrocarbons (TPH) was tested in microcosms using several bioremediation approaches, including: biostimulation with bulking agents and nutrients, the surfactant Tween 80, and bioaugmentation. Select HC degrading bacteria were isolated based on their ability to grow and produce clear zones on different HCs. Degradation of TPH in the microcosms was monitored gravimetrically and with gas chromatography (GC). The TPH removal in all treatments ranged between 2 and 67%, regardless of the addition of microbial consortiums, amendments, or surfactants within the tested parameters. The results of this study demonstrated that bioremediation of heavy oily sludge presents greater challenges to achieve regulatory requirements. Additional physicochemical treatments analysis to remediate this recalcitrant material may be required to achieve a desirable degradation rate.

Mixed polyaromatic hydrocarbon degradation by halotolerant bacterial strains from marine environment and its metabolic pathway

Accidents involving diesel oil spills are prevalent in sea- and coastal regions. Polycyclic aromatic hydrocarbons (PAHs) can be adsorbed in soil and constitute a persistent contaminant due to their poor water solubility and complex breakdown. PAHs pollution is a pervasive environmental concern that poses serious risks to human life and ecosystems. Thus, it is the need of the hour to degrade and decontaminate the toxic pollutant to save the environment. Among all the available techniques, microbial degradation of the PAHs is proving to be greatly beneficial and effective. Bioremediation overcomes the drawbacks of most physicochemical procedures by eliminating numerous organic pollutants at a lower cost in ambient circumstances and has therefore become a prominent remedial option for pollutant removal, including PAHs. In the present study, we have studied the degradation of Low molecular Weight and High Molecular Weight PAH in combination by bacterial strains isolated from a marine environment. Optimum pH, temperature, carbon, and nitrogen sources, NaCl concentrations were found for efficient degradation using the isolated bacterial strains. At 250 mg/L concentration of the PAH mixture an 89.5% degradation was observed. Vibrio algiolytcus strains were found to be potent halotolerant bacteria to degrade complex PAH into less toxic simple molecules. GC-MS and FTIR data were used to probe the pathway of degradation of PAH.

Earthworm Eisenia fetida potential for sewage sludge amended soil valorization by heavy metal remediation and soil quality improvement

Sewage sludge reuse in agriculture is increasing, however it can be an important route for contaminants to enter the environment. The aim of this study was to evaluate earthworm Eisenia fetida capability to reduce heavy metal content in the sewage sludge (SS) amended soil and increase soil fertility in terms of soil nutrients content. Adult earthworms were introduced into aged SS amended soil (0-200 Mg ha^-1) and left for 65 days. Earthworms have stabilized soil pH and accelerated organic matter mineralization. The concentrations of most heavy metals during the vermiremediation sharply decreased, K and Mg decreased to a moderate extent, whereas Ca content has increased. The highest removal efficiency was detected for Ni, Co and Mn (> 80%), bioconcentration factors were as follows Zn > Co > Cu > Ni > Mn > Cr. The content of major nutrients (S, P) was substantially higher compared to the initial values. The most efficient remediation and soil quality improvement was achieved under the doses of 25-50 Mg ha^-1. Higher (≥ 100 Mg ha^-1) doses might restrict this technique application because of earthworm mortality and retarded growth. Overall, the study shows that vermiremediation might be a sustainable technique for ecological stabilization of SS amended soil and converting to usable for agricultural needs.

Profiling of Indigenous Biosurfactant-Producing Bacillus Isolates in the Bioremediation of Soil Contaminated by Petroleum Products and Olive Oil

Petroleum is, up to this date, an inimitable nonrenewable energy resource. Petroleum leakage, which arises during transport, storage, and refining, is the most important contaminant in the environment, as it produces harm to the surrounding ecosystem. Bioremediation is an efficient method used to treat petroleum hydrocarbon-contaminated soil using indigenous microorganisms. The degradation characteristics for a variety of hydrocarbons (hexane, benzene, gasoline, and diesel) were qualitatively and quantitatively investigated using Bacillus isolates. Microbiological and biochemical methods have been used including isolation of oil-degrading bacteria, enzymatic activities, the determination of physicochemical parameters, biosurfactant production and extraction assay, oil displacement assay, antimicrobial assay of the biosurfactants, and bioremediation kinetics. Consequently, of the 60 isolates capable of degrading different hydrocarbons at fast rates, 34 were suspected to be Bacillus isolates capable of growing in 24 h or 48 h on BH medium supplemented with 2% of hexane, benzene, gasoline, diesel, and olive oil, respectively. Among the 34 isolates, 61% (21/34) are capable of producing biosurfactant-like molecules by using gasoline, 70% (24/34) with diesel oil, 85% (29/34) with hexane, and 82% (28/34) with benzene. It was found that biosurfactant-producing isolates are extractable with HCl (100%), ammonium sulphate (95%), chloroform (95%), and ethanol (100%). Biosurfactants showed stability at 20°C, 37°C, 40°C, and 60°C. Biosurfactant secreted by Bacillus strains has shown an antagonistic effect in Escherichia coli, Shigella flexneri 5a M90T, and Bacillus cereus. The selected isolates could therefore be safely used for biodegradation. Substrate biodegradation patterns by individual isolates were found to significantly differ. The study shows that benzene was degraded faster, followed by hexane, gasoline, and finally diesel. The Bacillus consortium used can decrease hydrocarbon content from 195 to 112 (g/kg) in 15 days.

Impact of kerosene pollution on ground vegetation of southern taiga in the Amur Region, Russia

The present study is the field experiment on kerosene pollution impact on southern taiga plant communities. Experimental sites were located in a mixed forest, a deciduous forest, a sedge fen and a wet meadow within the Amur Region of the Russian Far East. Kerosene loads from 1 to 500 g/kg of soil were applied to 50 × 50 cm plots in three replications and their effects on number of species and projective cover of ground vegetation were analysed in 1.5 months and 1 year after exposure. Statistical analyses of data included Student's t-test, Friedman ANOVA and correlation coefficient (r). Phylogenetic analysis was carried out for herbaceous plants on experimental plots. The highest susceptibility to kerosene pollution was found in the mixed forest, where the edificator species (Pteridium aquilinum subsp. pinetorum) was significantly suppressed by the kerosene load of only 1 g/kg of soil. Wetland communities regenerated faster than ground vegetation of forests, especially, in tests with high (>25 g/kg) kerosene loads. The wet meadow community was the most resistant to kerosene pollution, i.e., despite significant decreases in projective cover and number of species after exposure to kerosene loads of 5 and 25 g/kg in the first season, it had the highest regeneration success in the next season. In our study, the kerosene load of 25 g/kg of soil was the threshold level of pollution, above which there were significant structural changes in the studied plant communities. Depending on their abilities to resist kerosene pollution and to regenerate in the next year, dominant species of the studied plant communities were arranged in the following ascending order: Pteridium aquilinum ssp. pinetorum, Convallaria keiskei < Carex cespitosa, Calamagrostis purpurea < Lespedeza bicolor < Vaccinium uliginosum.

Facilitating the natural semi-drying of oily sludge by changing the form of water

Reducing the water content of oily sludge is essential for the disposal of it. Despite conditioning and solid-liquid separation, the water content of oily sludge generally exceeds 65%. A large amount of this water exists in the form of emulsified and bound water, reducing the efficiency of water removal during the natural semi-drying process of oily sludge. To shorten the time required for natural semi-drying, this study applied an orthogonal test to screen an oily sludge modified material (OSM). The effect and mechanism of OSM on the natural semi-drying of oily sludge were studied using a thermal gravimetric analyzer (TGA), scanning electron microscope (SEM), surface tension measurement, and microscopic observations. The results show that when the ambient temperature exceeded 10°C, the OSM increased in mass by 8-10%, and the time required for the natural semi-drying of oily sludge was shortened from 15 days to less than 5 days. OSM can rupture the emulsion, reduce the surface tension, convert the emulsion and bound water in the oily sludge into free water, and accelerate the rate of water migration, diffusion, and natural evaporation from the inside of the oily sludge to the surface and air. The research results show that changing the form of water can speed up the drying of oily sludge, creating positive economic benefits in the process of oily sludge reduction and recycling.