Assessment of soil pollution based on total petroleum hydrocarbons and individual oil substances

Metagenomic analyses of a consortium for the bioremediation of hydrocarbons polluted soils

A bacterial consortium was isolated from a soil in Noblejas (Toledo, Spain) with a long history of mixed hydrocarbons pollution, by enrichment cultivation. Serial cultures of hydrocarbons polluted soil samples were grown in a minimal medium using diesel (1 mL/L) as the sole carbon and energy source. The bacterial composition of the Noblejas Consortium (NC) was determined by sequencing 16S rRNA gene amplicon libraries. The consortium contained around 50 amplicon sequence variants (ASVs) and the major populations belonged to the genera Pseudomonas, Enterobacter, Delftia, Stenotrophomonas, Achromobacter, Acinetobacter, Novosphingobium, Allorhizobium-Neorhizobium-Rhizobium, Ochrobactrum and Luteibacter. All other genera were below 1%. Metagenomic analysis of NC has shown a high abundance of genes encoding enzymes implicated in aliphatic and (poly) aromatic hydrocarbons degradation, and almost all pathways for hydrocarbon degradation are represented. Metagenomic analysis has also allowed the construction of metagenome assembled genomes (MAGs) for the major players of NC. Metatranscriptomic analysis has shown that several of the ASVs are implicated in hydrocarbon degradation, being Pseudomonas, Acinetobacter and Delftia the most active populations.

Wood ash application for crop production, amelioration of soil acidity and contaminated environments

Agriculture is vital to human life and economic development even though it may have a detrimental influence on soil quality. Agricultural activities can deteriorate the soil quality, endangers the ecosystem health and functioning, food safety, and human health. To resolve the problem of soil degradation, alternative soil conditioners such as wood ash are being explored for their potential to improve soil-plant systems. This study provides an overview of the production, properties, and effects of wood ash on soil properties, crop productivity, and environmental remediation. A comprehensive search of relevant databases was conducted in order to locate and assess original research publications on the use of wood ash in agricultural and environmental management. According to the findings, wood ash, a byproduct of burning wood, may improve the structure, water-holding capacity, nutrient availability, and buffering capacity of soil as well as other physico-chemical, and biological attributes of soil. Wood ash has also been shown to increase agricultural crop yields and help with the remediation of polluted regions. Wood ash treatment, however, has been linked to several adverse effects, such as increased trace element concentrations and altered microbial activity. The examination found that wood ash could be a promising material to be used as soil conditioner and an alternative supply of nutrients for agricultural soils, while, wood ash contributes to soil improvement and environmental remediation, highlighting its potential as a sustainable solution for addressing soil degradation and promoting environmental sustainability in agricultural systems.

Assessing petroleum contamination in parts of the Niger Delta based on a sub-catchment delineated field assessment

The Niger Delta in Nigeria is a complex and heavily contaminated area with over 150,000 interconnected contaminated sites. This intricate issue is compounded by the region's strong hydrological processes and high-energy environment, necessitating a science-based approach for effective contamination assessment and management. This study introduces the concept of sub-catchment contamination assessment and management, providing an overarching perspective rather than addressing each site individually. A description of the sub-catchment delineation process using the digital elevation model data from an impacted area within the Delta is provided. Additionally, the contamination status from the delineated sub-catchment is reported. Sediment, surface water and groundwater samples from the sub-catchment were analyzed for total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs), respectively. Surface sediment TPH concentrations ranged from 129 to 20,600 mg/kg, with subsurface (2-m depth) concentrations from 15.5 to 729 mg/kg. PAHs in surface and subsurface sediment reached 9.55 mg/kg and 0.46 mg/kg, respectively. Surface water exhibited TPH concentrations from 10 to 620 mg/L, while PAHs ranged from below detection limits to 1 mg/L. Groundwater TPH concentrations spanned 3 to 473 mg/L, with total PAHs varying from below detection limits to 0.28 mg/L. These elevated TPH and PAH levels indicate extensive petroleum contamination in the investigated sediment and water environment. Along with severe impacts on large areas of mangroves and wetlands, comparison of TPH and PAH concentrations with sediment and water quality criteria found 54 to 100% of stations demonstrated exceedances, suggesting adverse biological effects on aquatic and sediment biota are likely occurring.

Utilizing machine learning for reactive material selection and width design in permeable reactive barrier (PRB)

Permeable reactive barrier (PRB) is an important groundwater treatment technology. However, selecting the optimal reactive material and estimating the width remain critical and challenging problems in PRB design. Machine learning (ML) has advantages in predicting evolution and tracing contaminants in temporal and spatial distribution. In this study, ML was developed to design PRB, and its feasibility was validated through experiments and a case study. ML algorithm showed a good prediction about the Freundlich equilibrium parameter (R2 0.94 for KF, R2 0.96 for n). After SHapley Additive exPlanation (SHAP) analysis, redefining the range of the significant impact factors (initial concentration and pH) can further improve the prediction accuracy (R2 0.99 for KF, R2 0.99 for n). To mitigate model bias and ensure comprehensiveness, evaluation index with expert opinions was used to determine the optimal material from candidate materials. Meanwhile, the ML algorithm was also applied to predict the width of the mass transport zone in the adsorption column. This procedure showed excellent accuracy with R2 and root-mean-square-error (RMSE) of 0.98 and 1.2, respectively. Compared with the traditional width design methodology, ML can enhance design efficiency and save experiment time. The novel approach is based on traditional design principles, and the limitations and challenges are highlighted. After further expanding the data set and optimizing the algorithm, the accuracy of ML can make up for the existing limitations and obtain wider applications.

Groundwater-level fluctuation effects on petroleum hydrocarbons in vadose zones and their potential risks: Laboratory studies

Despite the role of the vadose zone protecting groundwater from contamination, the non-stationarity in this zone makes it difficult to predict the behavior of petroleum hydrocarbons (PH) therein. In laboratory soil columns with sandy and sandy loam soils, we simulated a vadose zone subjected to repeated groundwater-level fluctuation (GLF) to evaluate the behavior of PH under hydrodynamic conditions. The GLF vertically redistributed the PH, the extent of which was pronounced in the sandy soil with a high initial concentration due to the enhanced transport of the immiscible PH through the larger pores. The frequency of GLF did not show a substantial effect on the extent of PH redistribution but largely affected their attenuation. The greater GLF hindered PH volatilization by maintaining a high degree of water saturation, while the subsequent development of a local anaerobic regime inhibited biodegradation, which was more apparent in the sandy loam. Finally, a specific potential risk index was introduced to quantitatively compare the potential risk of PH contamination in different vadose zones exposed to GLF. Overall, the sandy soil contaminated with the higher total PH (TPH) concentration showed markedly higher potential risk indices (i.e., 18.4-29.0%), while the ones comprised of the sandy loam showed 0.6-4.9%, which increased under the greater number of GLF cycles.

The potential of multicylindrical dielectric barrier discharge plasma for diesel-contaminated soil remediation and biocompatibility assessment

This study explored the use of multicylindrical dielectric barrier discharge (MC-DBD) plasma technology to eliminate diesel fuel contamination from the soil. This study also assessed the environmental impact of plasma-generated reactive species on soil properties, plant growth, and the safety of microbial and human skin cells using various analytical methods. MC-DBD plasma was characterized using the current-voltage analysis and optical emission spectroscopy (OES). Gas Fourier transform infrared spectroscopy was employed to detect reactive species, such as O3, NO, NO2, N2O, and HNO3, in the plasma-treated air. The diesel fuel concentration in the soil was measured before and after plasma treatment using a gas chromatography-flame ionization detector. The efficacy of the MC-DBD plasma treatment was evaluated based on soil characteristics (pH and moisture), discharge parameters (power), and reactive species (O3 and NOx). Using only power of 30 W, the MC-DBD achieved a 94.19% removal of diesel fuel from the soil and yielded an energy efficiency of 1.78 × 10-2 m3/kWh within a 60-min treatment period. Neutral soil with a moisture content of 2% proved more effective in diesel fuel removal compared with acidic or alkaline soil with higher moisture content. O3 was the most efficient plasma-generated reactive species for diesel fuel removal and is involved in oxidation-induced fragmentation and volatilization. Overall, the potential of the MC-DBD plasma technology for remediating diesel fuel-contaminated soils is highlighted, and valuable insights for future applications are provided.

Potential natural attenuation of petroleum hydrocarbons in fuel contaminated soils: Focusing on anaerobic fuel biodegradation involving microbial Fe(III) reduction

Liquid fossil fuels, collectively known as total petroleum hydrocarbons (TPHs), are highly toxic and frequently leak into subsurface environments due to anthropogenic activities. As an in-situ biological remedial option for TPH contamination, aerobic TPH biodegradation is limited due to oxygen's low solubility in water, and because it is consumed quickly by aerobic bacteria. Thus, we investigated the potential of anaerobic TPH degradation by indigenous fermenting bacteria and Fe(III)-reducing bacteria. Twenty 6-10 m soil cores were collected from a closed military base subject to ongoing TPH contamination since the 1980s. Physicochemical and microbial properties were determined at 0.5-m intervals in each core. To assess the relationship between TPH degradation and microbial Fe(III) reduction, soil samples were grouped into high-TPH (>500 mg kg-1) and high-Fe(II) (>450 mg kg-1), high-TPH and low-Fe(II), low-TPH and high-Fe(II), and low-TPH and low-Fe(II) groups. Alpha diversity was significantly lower in high-TPH groups than in low-TPH groups, suggesting that high TPH concentrations exerted a strong selective pressure on bacterial communities. In the high-TPH and low-Fe(II) group, fermenting bacteria, including Microgenomatia and Chlamydiae, were more abundant, suggesting that TPH biodegradation occurred via fermentation. In the high-TPH and high-Fe(II) group, Fe(III)-reducing bacteria, including Geobacter and Zoogloea, were more abundant, suggesting that microbial Fe(III) reduction enhances TPH biodegradation. In contrast, the fermenting and/or Fe(III)-reducing bacteria were not statistically abundant in the low-TPH groups.

Strategies for cost-effective remediation of widespread oil-contaminated soils in Kuwait, an environmental legacy of the first Gulf War

The Kuwaiti oil fire during the first Gulf War resulted in the formation of approximately 300 "oil lakes" of varying sizes that covered over 110 km2 of the desert land. This threatens the fragile desert ecosystems and human health. Following the award of over US$2 billion to the State of Kuwait by the United Nations, large-scale remediation of the oil-contaminated soils has now been on the agenda. However, how to implement the remediation program in a cost-effective way represents a major challenge. In this study, cost-effective remediation strategies were developed based on field and laboratory investigations in a typical oil lake area. Overall, most of the lighter petroleum hydrocarbons (PHCs) were lost due to evaporation. Long-chain aliphatic PHCs dominated the PHCs in the investigated oil lake area. This has implications for developing remediation strategies. Toxicity assessment results showed that the majority of soils pose a low environmental risk with a hazard index <1. Therefore, intensive treatment of these PHCs may not be necessary for these soils. Although active treatment methods are needed to remove the contaminants as soon as practical for the relatively small areas of high contamination, more cost-effective passive methods should be considered to minimize the remedial costs for the larger area of the non-hotspot areas. Given the extremely low risk in terms of groundwater contamination by the contaminated soils, it may not be necessary to remove the soils from the contaminated sites. A low-cost capping method should be sufficient to minimize human exposure to the PHC-contaminated soils.

Short-term arsenic mobilization, labilization, and microbiological aspects after gasoline and diesel addition in tropical soils

The effect of the presence of gasoline and diesel on the speciation and mobility of inorganic arsenic species in tropical topsoils was investigated. Topsoil samples (n = 25) were contaminated with gasoline and diesel (500 mg kg^-1) in laboratory and were incubated under unsaturated conditions and regular aeration for 21 days. Speciation analysis and chemical fractionation were performed in the pore water from control, gasoline, and diesel-contaminated soil samples. Arsenic concentrations were compared to microbiological parameters (microbial metabolic quotient and soil basal breathing) and the presence of ArsM-harboring bacteria. The spike of gasoline and diesel to the topsoils increased pore water As³⁺ (H₃AsO₃) concentration. Arsenic mobilization was lower compared to previously reported data for other sources of organic matter (biochar, litter, and a mixture of sphagnum peat moss and composted poultry manure). However, gasoline or diesel addition mobilized As fractions that were adsorbed to the solid phase, in approximately 60% of the soils. Methylation presented an important role in the As³⁺ regulation in control soils, which was no longer observed after gasoline or diesel addition. The quantification of the labile fractions sampled by the diffusive gradients in thin films technique showed that the increased As concentration in the gasoline or diesel-contaminated soils mostly included inert species. Dissolved organic carbon content seems to be an important control mechanism of the labile As concentration. The increase in As mobility seems to pose a more concerning scenario due to As leaching than to plant uptake.

Monitoring of in-situ chemical oxidation for remediation of diesel-contaminated soil with electrical resistivity tomography

In-situ chemical oxidation (ISCO) with persulfate, an electrically conductive oxidant, provides a powerful signal for noninvasive geophysical techniques to characterize the remediation process of hydrocarbon contaminants. In this study, remediation with ISCO is conducted in laboratory sandboxes to evaluate the ability of electrical resistivity tomography (ERT) for monitoring the base-activated persulfate remediation process of diesel-contaminated soil. It was found that the resistivity of contaminated sand significantly decreased from 846 Ω·m to below 10 Ω·m after persulfate injection, and all measured chemical parameters showed a noticeable increase. Natural degradation and contamination plume migration were not evident in a reference sandbox without treatment. The area with a resistivity ratio < 0.95 based on imaging before and after injection indicated downward migration of the oxidation plume due to density-driven flow. A comparison between remediation and reference sandboxes showed that the observed resistivity decrease can be due to both contaminant degradation as well as the oxidation plume itself in the contaminated source zone. In contrast, the resistivity decrease in the area with low contamination concentration is attributed to the oxidation plume alone. The derived relationships between resistivity and contaminant indicators further emphasize that the contribution of contaminant consumption to resistivity change in the source area is 25.6%, while it is <16% in the low or non-contaminated area. Although this study showed that resistivity is not solely affected by the chemical transformation of diesel components, it can be combined with sampling data to allow an assessment of the effectiveness of ISCO treatment and to identify target areas for subsequent treatment.

Diesel removal and recovery from heavily diesel-contaminated soil based on three-liquid-phase equilibria of diesel + 2-butyloxyethanol + water

Diesel contamination poses a serious threat to ecosystem and human health. This study proposes a novel method for simultaneous diesel removal and recovery from heavily diesel-contaminated soil by washing based on three-liquid-phase equilibria of diesel+2-butoxyethanol+water. This work covers both theoretical-cum-experimental explorations. For this brand-new ternary three-liquid-phase system (TPS), Ternary-Gibbs and Fish-Shaped phase diagrams were constructed through the phase behavior investigation to provide theoretical support for diesel removal/recovery. As the experiment demonstrated, the removal efficiency was up to 87.5 % for the contaminated soil with diesel content of 226,723 mg/kg, and the recovery rate reached 73.8 %. In addition, the TPS could also be used continuously during the washing process while avoiding solution purification, and the detached diesel would automatically float into the top phase without complicated separation. The mechanism of diesel removal was determined as the surface "stripping" effect based on ultralow interfacial tension, and the enhanced process involved "stripping+dissolution". The treated soil contained almost negligible organic solvent residue and was therefore appropriate for plant cultivation. The recovered diesel exhibited less variation from commercial diesel in composition and properties, possessing a higher potential for reuse. Moreover, this study also provided key insights into the residual mechanisms of recalcitrant hydrocarbons in the soil.

Field scale biodegradation of total petroleum hydrocarbons and soil restoration by Ecopiles: microbiological analysis of the process

Ecopiling is a method for biodegradation of hydrocarbons in soils. It derives from Biopiles, but phytoremediation is added to biostimulation with nitrogen fertilization and bioaugmentation with local bacteria. We have constructed seven Ecopiles with soil heavily polluted with hydrocarbons in Carlow (Ireland). The aim of the study was to analyze changes in the microbial community during ecopiling. In the course of 18 months of remediation, total petroleum hydrocarbons values decreased in 99 and 88% on average for aliphatics and aromatics, respectively, indicating a successful biodegradation. Community analysis showed that bacterial alfa diversity (Shannon Index), increased with the degradation of hydrocarbons, starting at an average value of 7.59 and ending at an average value of 9.38. Beta-diversity analysis, was performed using Bray-Curtis distances and PCoA ordination, where the two first principal components (PCs) explain the 17 and 14% of the observed variance, respectively. The results show that samples tend to cluster by sampling time instead of by Ecopile. This pattern is supported by the hierarchical clustering analysis, where most samples from the same timepoint clustered together. We used DSeq2 to determine the differential abundance of bacterial populations in Ecopiles at the beginning and the end of the treatment. While TPHs degraders are more abundant at the start of the experiment, these populations are substituted by bacterial populations typical of clean soils by the end of the biodegradation process. Similar results are found for the fungal community, indicating that the microbial community follows a succession along the process. This succession starts with a TPH degraders or tolerant enriched community, and finish with a microbial community typical of clean soils.

Correlation of soil microbiome with crude oil contamination drives detection of hydrocarbon degrading genes which are independent to quantity and type of contaminants

The impacts of crude oil contamination on soil microbial populations were explored in seven different polluted areas near oil and gas drilling sites and refineries of Assam, India. Using high-throughput sequencing techniques, the functional genes and metabolic pathways involved in the bioconversion of crude oil contaminants by the indigenous microbial community were explored. Total petroleum hydrocarbon (TPH) concentrations in soil samples ranged from 1109.47 to 75,725.33 mg/kg, while total polyaromatic hydrocarbon (PAH) concentrations ranged from 0.780 to 560.05 mg/kg. Pyrene, benzo[a]anthracene, naphthalene, phenanthrene, and anthracene had greater quantities than the maximum permitted limits, suggesting a greater ecological risk, in comparison to other polyaromatic hydrocarbons. According to the metagenomic data analysis, the bacterial phyla Proteobacteria, Actinobacteria, Acidobacteria, and Bacteroides were the most prevalent among all polluted areas. The most prominent hydrocarbon degraders in the contaminated sites included Burkholderia, Mycobacterium, Polaromonas, and Pseudomonas. However, the kinds of pollutants and their concentrations did not correlate with the abundances of respective degrading genes for all polluted locations, as some of the sites with little to low PAH contamination had significant abundances of corresponding functional genes for degradation. Thus, the findings of this study imply that the microbiome of hydrocarbon-contaminated areas, which are biologically involved in the degradation process, has various genes, operons and catabolic pathways that are independent of the presence of a specific kind of contaminant.

Pollution level and health risk assessment of the total petroleum hydrocarbon in marine environment and aquatic products: a case of China

To evaluate the pollution level and health risk of total petroleum hydrocarbon (TPH), seawater, sediments, and aquatic organisms were sampled from the southern sea area of Zhejiang Province (Yangtze River Delta, China) between 2017 and 2019. TPH was widely present in the aquatic environment and products, and its concentration was highly variable. The average value of pollution index (PI) exceeded 1 from 2017 to 2018, and 45.46-69.19% of seawater samples and 56.87-50.00% of sediment samples were polluted. The results showed significant differences in the TPH concentration in various species of aquatic organisms. The average TPH value in aquatic organisms could be ranked in the order as follows: bivalve > shrimp > crab > fish, further reflecting that the ability to accumulate and metabolize TPH existed differently among aquatic organisms within the same pond aquaculture environment. It was relatively safe to eat aquatic products since the exposure risk index was found to be far below the threshold value in this study. Therefore, it would be prudent to undertake regular monitoring of TPH to ensure effective ecosystem functioning and seafood safety in the southern Zhejiang ocean.

Evaluation of biostimulation, bioaugmentation, and organic amendments application on the bioremediation of recalcitrant hydrocarbons of soil

In the present work, the operational conditions for improving the degradation rates of Total Petroleum Hydrocarbons (TPHs) in contaminated soil from a machinery park were optimized at a microcosms scale along a 90-days incubation period. In this study, bioremediation strategies and an organic amendment have been tested to verify the remediation of soil contaminated with different hydrocarbons, mineral oils, and heavy metals. Specifically, designed biostimulation and bioaugmentation strategies were compared with and without adding vermicompost. The polluted soil harboring multiple contaminants, partially attenuated for years, was used. The initial profile showed enrichment in heavy linear alkanes, suggesting a previous moderate weathering. The application of vermicompost increased five and two times the amounts of available phosphorus (P) and exchangeable potassium (K), respectively, as a direct consequence of the organic amendment addition. The microbial activity increased due to soil acidification, which influenced the solubility of P and other micronutrients. It also impacted the predominance and variability of the different microbial groups and the incubation, as reflected by phospholipid fatty acid (PLFA) results. An increase in the alkaline phosphatases and proteases linked to bacterial growth was displayed. This stimulation of microbial metabolism correlated with the degradation rates since TPHs degradation' efficiency after vermicompost addition reached 32.5% and 34.4% of the initial hydrocarbon levels for biostimulation and bioaugmentation, respectively. Although Polycyclic Aromatic Hydrocarbons (PAHs) were less abundant in this soil, results also decreased, especially for the most abundant, the phenanthrene. Despite improving the degradation rates, results revealed that recalcitrant and hydrophobic petroleum compounds remained unchanged, indicating that mobility, linked to bioavailability, probably represents the limiting step for further soil recovery.

Ecological risk assessment of priority PAHs pollutants in crude oil contaminated soil and its impacts on soil biological properties

Polycyclic aromatic hydrocarbons (PAHs) are one of the major toxic constituents of crude oil and therefore, an understanding on PAHs associated risks and their relationship with soil biological parameters are necessary for adopting effective risk-based and site specific remediation strategies in the contaminated soil. Here, risks evaluation of eight detected PAHs in terms of toxic equivalent concentration (TEQ_C), benzo(a)pyrene equivalent (BaPeq), contamination factor (CF), pollution load index (PLI), hazard quotient (HQ), hazard index (HI), toxic unit for individual PAHs (TU) and PAHs mixture (TU_m) have been evaluated. Besides, the effect of PAHs contamination on soil biological properties has also been investigated and correlated with PAHs concentrations. The TEQc of eight PAHs was recorded in the range of 0.06-5.0 mg kg^-1 soil_, whereas the BaPeq value was 25.3 mg kg^-1 soil which exceed the permissible limit. Similarly, CF (85.5-1668.2), PLI (322.8), HQ (311.7-8340.9), HI (26,443.8), TU (227.9-3821.6) and TU_m(7916.2) also exceed the permissible values for non-toxic conditions indicating carcinogenic risk for humans. Besides, activities of soil dehydrogenase, urease, alkaline-phosphatase, catalase, amylase and cellulase were decreased by 1.5-2.3 folds in the contaminated soil than control. The results of Pearson's correlation matrix also established negative impact of PAHs on the soil's biological properties.

Development and characterization of chlorophyll-amended montmorillonite clays for the adsorption and detoxification of benzene

After disasters, such as forest fires and oil spills, high levels of benzene (> 1 ppm) can be detected in the water, soil, and air surrounding the disaster site, which poses a significant health risk to human, animal, and plant populations in the area. While remediation methods with activated carbons have been employed, these strategies are limited in their effectiveness due to benzene's inherent stability and limited retention to most surfaces. To address this problem, calcium and sodium montmorillonite clays were amended with a mixture of chlorophyll (a) and (b); their binding profile and ability to detoxify benzene were characterized using in vitro, in silico, and well-established ecotoxicological (ecotox) bioassay methods. The results of in vitro isothermal analyses indicated that chlorophyll-amended clays showed an improved binding profile in terms of an increased binding affinity (Kf = 668 vs 67), increased binding percentage (52% vs 11%), and decreased rates of desorption (28% vs 100%), compared to the parent clay. In silico simulation studies elucidated the adsorption mechanism and validated that the addition of the chlorophyll to the clays increased the adsorption of benzene through Van der Waals forces (i.e., aromatic π-π stacking and alkyl-π interactions). The sorbents were also assessed for their safety and ability to protect sensitive ecotox organisms (Lemna minor and Caenorhabditis elegans) from the toxicity of benzene. The inclusion of chlorophyll-amended clays in the culture medium significantly reduced benzene toxicity to both organisms, protecting C. elegans by 98-100% from benzene-induced mortality and enhancing the growth rates of L. minor. Isothermal analyses, in silico modeling, and independent bioassays all validated our proof of concept that benzene can be sequestered, tightly bound, and stabilized by chlorophyll-amended montmorillonite clays. These novel sorbents can be utilized during disasters and emergencies to decrease unintentional exposures from contaminated water, soil, and air.

Study on the Enhanced Remediation of Petroleum-Contaminated Soil by Biochar/g-C3N4 Composites

This work developed an environmentally-friendly soil remediation method based on BC and g-C3N4, and demonstrated the technical feasibility of remediating petroleum-contaminated soil with biochar/graphite carbon nitride (BC/g-C3N4). The synthesis of BC/g-C3N4 composites was used for the removal of TPH in soil via adsorption and photocatalysis. BC, g-C3N4, and BC/g-C3N4 have been characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface area analyzer (BET), FT-IR, and X-ray diffraction (XRD). BC/g-C3N4 facilitates the degradation due to reducing recombination and better electron-hole pair separation. BC, g-C3N4, and BC/g-C3N4 were tested for their adsorption and photocatalytic degradation capacities. Excellent and promising results are brought out by an apparent synergism between adsorption and photocatalysis. The optimum doping ratio of 1:3 between BC and g-C3N4 was determined by single-factor experiments. The removal rate of total petroleum hydrocarbons (TPH) by BC/g-C3N4 reached 54.5% by adding BC/g-C3N4 at a dosing rate of 0.08 g/g in a neutral soil with 10% moisture content, which was 2.12 and 1.95 times of BC and g-C3N4, respectively. The removal process of TPH by BC/g-C3N4 conformed to the pseudo-second-order kinetic model. In addition, the removal rates of different petroleum components in soil were analyzed in terms of gas chromatography–mass spectrometry (GC-MS), and the removal rates of nC13-nC35 were above 90% with the contaminated soil treated by BC/g-C3N4. The radical scavenger experiments indicated that superoxide radical played the major role in the photocatalytic degradation of TPH. This work definitely demonstrates that the BC/g-C3N4 composites have great potential for application in the remediation of organic pollutant contaminated soil.

Bacterial community and chemical profiles of oil-polluted sites in selected cities of Uganda: potential for developing a bacterial-based product for remediation of oil-polluted sites

Background

Oil spills are ranked among the greatest global challenges to humanity. In Uganda, owing to the forthcoming full-scale production of multi-billion barrels of oil, the country’s oil pollution burden is anticipated to escalate, necessitating remediation. Due to the unsuitability of several oil clean-up technologies, the search for cost-effective and environmentally friendly remediation technologies is paramount. We thus carried out this study to examine the occurrence of metabolically active indigenous bacterial species and chemical characteristics of soils with a long history of oil pollution in Uganda that can be used in the development of a bacterial-based product for remediation of oil-polluted sites.

Results

Total hydrocarbon analysis of the soil samples revealed that the three most abundant hydrocarbons were pyrene, anthracene and phenanthrene that were significantly higher in oil-polluted sites than in the control sites. Using the BIOLOG EcoPlate™, the study revealed that bacterial species richness, bacterial diversity and bacterial activity (ANOVA, p < 0.05) significantly varied among the sites. Only bacterial activity showed significant variation across the three cities (ANOVA, p < 0.05). Additionally, the study revealed significant moderate positive correlation between the bacterial community profiles with Zn and organic contents while correlations between the bacterial community profiles and the hydrocarbons were largely moderate and positively correlated.

Conclusions

This study revealed largely similar bacterial community profiles between the oil-polluted and control sites suggestive of the occurrence of metabolically active bacterial populations in both sites. The oil-polluted sites had higher petroleum hydrocarbon, heavy metal, nitrogen and phosphorus contents. Even though we observed similar bacterial community profiles between the oil polluted and control sites, the actual bacterial community composition may be different, owing to a higher exposure to petroleum hydrocarbons. However, the existence of oil degrading bacteria in unpolluted soils should not be overlooked. Thus, there is a need to ascertain the actual indigenous bacterial populations with potential to degrade hydrocarbons from both oil-polluted and unpolluted sites in Uganda to inform the design and development of a bacterial-based oil remediation product that could be used to manage the imminent pollution from oil exploration and increased utilization of petroleum products in Uganda.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02541-x.

Geotechnical properties of oil-polluted soil: a review

Soil polluted by oil and its derivatives is a critical environmental issue worldwide that jeopardizes ecological systems and causes geotechnical problems. This review paper focuses on the previous studies concerning the impacts of oil pollution on soil geotechnical properties. To this end, related academic literature on this topic was investigated and discussed. The findings of this study demonstrated that the addition of oil pollution in coarse-grained soils significantly reduces particle surface roughness. On the other hand, in fine-grained soils, it results in flocculation and secondary aggregation of clay particles, less aggregated and loose packing in the soil matrix, the formation of isometric pores, the formation of fissure-like pores, and an increase in mesoporosity. In general, it was found that the geotechnical properties of oil-polluted soils are mostly determined by the physicochemical and/or physical interactions between the soil and contaminant. Additionally, previous research has demonstrated that oil pollutants alter the geotechnical properties of cohesive and non-cohesive soils significantly, including the Atterberg limits, particle-size distribution, compaction behavior, unconfined compressive strength, friction angle, cohesion, hydraulic conductivity, and consolidation characteristics. However, no general pattern could be established for the majority of them. Besides, it was found that the degree of geotechnical property alteration of oil-polluted soil is strongly influenced by the soil type and features, as well as the quantity, type, and chemical composition of oil pollutants.

Efficient removal of heavily oil-contaminated soil using a combination of fenton pre-oxidation with biostimulated iron and bioremediation

Crude oil contamination severely deteriorates soils quality. Bioremediation utilizing soil indigenous organisms could be employed to decompose petroleum hydrocarbons thanks to its low cost and minor environmental disturbance. However, slow kinetics limit the successful application of this biotechnique. Pretreating oil-contaminated soils with Fenton pre-oxidation could accelerate the subsequent bioremediation process. This study was to explore the mechanisms behind the rapid propagation of indigenous petroleum-degrading bacteria (IPDB) and the efficient degradation of total petroleum hydrocarbons (TPH) in soil after Fenton pre-oxidation with biostimulated iron. Biostimulated iron and non-biostimulated iron were used in the experiments, where Fenton pre-oxidation was combined with the bioremediation of oil-contaminated soil (TPH = 13221 mg/kg). Although the amount of Fenton pre-oxidized TPH (3331-3775 mg/kg) was similar with biostimulated and non-biostimulated irons, the biodegradation of TPH after Fenton pre-oxidation with biostimulated iron (5840 mg/kg) was much higher than that with non-biostimulated iron (3034-4034 mg/kg). Moreover, abundant nutrients and a high population of residual IPDB were found after Fenton pre-oxidation with biostimulated iron, which benefited stable consumption of NH₃-N and dissolved organic carbon (DOC) by IPDB during the subsequent bioremediation. However, Fenton pre-oxidation with non-biostimulated iron either resulted in greater damage to IPDB or produced fewer nutrients, thereby failing to ensure the continuous propagation of IPDB during the subsequent bioremediation. Therefore, we propose that Fenton pre-oxidation with biostimulated iron should be applied to heavily oil-contaminated soils prior to bioremediation.

Ecological criteria for assessing the content of petroleum hydrocarbons in the main soils of coniferous-deciduous forests and forest steppe

The effect of pollution of Albicluvisols/Retisols, Calcaric Leptosols, Luvic Phaeozems, Greyzamic Phaeozems and Folic Fluvisols with oil (Solovatovsky oil field, Perm region) added in amounts of 1, 2, 3 and 5 g oil/kg of soil on the organisms was studied in a model laboratory experiment. Oil addition showed phytotoxic effects on root length in Triticum aestivum L., Lepidium sativum L., Picea obovata Ledeb. and Pinus sylvestris L. in all soils. However, oil contamination of Calcaric Leptosols and Greyzamic Phaeozems led to growth stimulation in Picea obovata seedlings. A remarkable shift in the diversity and number of colony-forming units of heterotrophic and oil-oxidizing bacteria was detected in all soil types. The maximum decrease in biodiversity (45%) was noted for heterotrophic bacteria in Luvic Phaeozems. Aqueous extracts from all oil-contaminated soils had a toxic effect on Chlorella vulgaris Beijer, causing an increase in biomass by more than 30%, but did not show acute toxicity on Daphnia magna Straus. Oil addition in the range of 1-3 g oil/kg soil posed no environmental risk to human health. However, oil addition at 5 g oil/kg of soil led to an increase in the level of carcinogenic risk to children to the threshold values of acceptable risk and ranged from 0.95 × 10^-4 for Greyzamic Phaeozems and Folic Fluvisols to 1.098 × 10^-4 for Luvic Phaeozems. Our results suggest that the reaction of test organisms to oil pollution depends on the soil type, and their complex application makes it possible to identify the most sensitive factor and assess the dangerous level of pollution.

Planted mangroves cap toxic petroleum-contaminated sediments

Mangroves are known to provide many ecosystem services, however there is little information on their potential role to cap and immobilise toxic levels of total petroleum hydrocarbons (TPH). Using an Australian case study, we investigated the capacity of planted mangroves (Avicennia marina) to immobilise TPH within a small embayment (Stony Creek, Victoria, Australia) subjected to minor oil spills throughout the 1980s. Mangroves were planted on the oil rich strata in 1984 to rehabilitate the site. Currently the area is covered with a dense mangrove forest. One-meter-long sediment cores revealed that mangroves have formed a thick (up to 30 cm) organic layer above the TPH-contaminated sediments, accumulating on average 6.6 mm of sediment per year. Mean TPH levels below this organic layer (30-50 cm) are extremely toxic (30,441.6 mg kg^-1), exceeding safety thresholds up to 220-fold which is eight times higher when compared to top layer (0-10 cm).

Mitigation of petroleum-hydrocarbon-contaminated hazardous soils using organic amendments: A review

The term "Total petroleum hydrocarbons" (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research.

Investigating the potential of bioremediation in aged oil-polluted hypersaline soils in the south oilfields of Iran

To date, studies for bioremediation of oil-polluted hypersaline soils have been neglected or limited to specific spots. Hence, in this study, ten samples of oil field soils in the Khuzestan province of Iran were collected to evaluate bioremediation's feasibility. These samples were analyzed for their physicochemical properties as well as the most probable number of total and hydrocarbon-degrading bacteria. Thirty-nine hydrocarbon-degrading bacteria were isolated from these soils over a 1-month incubation in an MSM medium enriched with diesel oil as the sole source of carbon. As revealed by 16S-rRNA analysis, the identified strains belonged to the genera Ochrobactrum, Microbacterium, and Bacillus with a high frequency of Ochrobactrum species. Additionally, by using degenerate primers, the third group of alkB gene was detected in Ochrobactrum and Microbacterium isolates through the touchdown nested PCR method for the first time. Ochrobactrum species possessing the alkB gene showed the highest population, and therefore, the highest adaptation to harsh environmental conditions. Most isolates showed outstanding results in the ability to grow with crude and diesel oil and tolerate high salt percentages, biosurfactant production, and emulsification activity, which are considered the most effective factors in bioremediation of such environments. Considering the soil analysis, limiting factors in bioremediation like available phosphorous, and the abundance of bacteria with remediation traits in these soils, these extremely polluted environments can be refined.

Assessment of groundwater safety surrounding contaminated water storage sites using multivariate statistical analysis and Heckman selection model: a case study of Kazakhstan

Petrochemical enterprises in Kazakhstan discharge polluted wastewater into special recipients. Contaminants infiltrate through the soil into the groundwater, which potentially affects public health and environment safety. This paper presents the evaluation of a 7-year monitoring program from one of the factories and includes nineteen variables from nine wells during 2013-2019. Several multivariate statistical techniques were used to analyse the data: Pearson's correlation matrix, principal component analysis and cluster analysis. The analysis made it possible to specify the contribution of each contaminant to the overall pollution and to identify the most polluted sites. The results also show that concentrations of pollutants in groundwater exceeded both the World Health Organization and Kazakhstani standards for drinking water. For example, average exceedance for total petroleum hydrocarbons was 4 times, for total dissolved solids-5 times, for chlorides-9 times, for sodium-6 times, and total hardness was more than 6 times. It is concluded that host geology and effluents from the petrochemical industrial cluster influence the groundwater quality. Heckman two-step regression analysis was applied to assess the bias of completed analysis for each pollutant, especially to determine a contribution of toxic pollutants into total contamination. The study confirms a high loading of anthropogenic contamination to groundwater from the petrochemical industry coupled with natural geochemical processes.

A new foam-based method for the (bio)degradation of hydrocarbons in contaminated vadose zone

An innovative foam-based method for Fenton reagents (FR) and bacteria delivery was assessed for the in situ remediation of a petroleum hydrocarbon-contaminated unsaturated zone. The surfactant foam was first injected, then reagent solutions were delivered and propagated through the network of foam lamellae with a piston-like effect. Bench-scale experiments demonstrated the feasibility of the various treatments with hydrocarbon (HC) removal efficiencies as high as 96 %. Compared to the direct injection of FR solutions, the foam-based method led to larger radii of influence and more isotropic reagents delivery, whereas it did not show any detrimental effect regarding HC oxidation. Despite 25 % of HCs were expelled from the treated zone because of high foam viscosity, average degradation rates were increased by 20 %. At field-scale, foam and reagent solutions injections in soil were tracked both using visual observation and differential electric resistivity tomography. The latter demonstrated the controlled delivery of the reactive solutions using the foam-based method. Even if the foam-based method duration is about 5-times longer than the direct injection of amendment solutions, it provides important benefits, such as the confinement of harmful volatile hydrocarbons during Fenton treatments, the enhanced reagents delivery and the 30 % lower consumption of the latter.

Rhizoremediation as a green technology for the remediation of petroleum hydrocarbon-contaminated soils

Rhizoremediation is increasingly becoming a green and sustainable alternative to physico-chemical methods for remediation of contaminated environments through the utilization of symbiotic relationship between plants and their associated soil microorganisms in the root zone. The overall efficiency can be enhanced by identifying suitable plant-microbe combinations for specific contaminants and supporting the process with the application of appropriate soil amendments. This approach not only involves promoting the existing activity of plants and soil microbes, but also introduces an adequate number of microorganisms with specific catabolic activity. Here, we reviewed recent literature on the main mechanisms and key factors in the rhizoremediation process with a particular focus on soils contaminated with total petroleum hydrocarbon (TPH). We then discuss the potential of different soil amendments to accelerate the remediation efficiency based on biostimulation and bioaugmentation processes. Notwithstanding some successes in well-controlled environments, rhizoremediation of TPH under field conditions is still not widespread and considered less attractive than physico-chemical methods. We catalogued the major pitfalls of this remediation approach at the field scale in TPH-contaminated sites and, provide some applicable situations for the future successful use of in situ rhizoremediation of TPH-contaminated soils.

Application of enhanced electrokinetic remediation by coupling surfactants for kerosene-contaminated soils: Effect of ionic and nonionic surfactants

Electrokinetic (EK) by coupling surfactants is an enhanced promising remediation technology to eliminate hydrophobic organic contaminants (HOC_s) from low-permeable soils. It is also applied to remediate kerosene-contaminated soils using anionic (SDS) and non-ionic (Tween 80) surfactants at different concentrations. There was negligible removal efficiency (40%) of kerosene during traditional EK without any enhancement technique. In the present study, the application of 0.005M and 0.01M SDS in EK-SDS-1 and EK-SDS-2 improved the removal efficiency to 50 and 55%, respectively towards the anode. Furthermore, the use of Tween 80 in EK-Tw80-1 and EK-Tw80-2 at 0.1 and 1% concentrations was able to raise kerosene removal gradually from 45% to 52% towards the cathode. These findings suggest that higher concentrations of SDS and Tween 80 contribute to the more effective elimination of kerosene. Thus, in EK-SDS-Tw80-V1.5 and EK-SDS-Tw80-V2, SDS and Tween 80 were used simultaneously at higher concentrations, which led to 63 and 67% kerosene removal, respectively. Considering the maximum removal in EK-SDS-Tw80-V2, the energy consumption in EK-SDS-Tw80-V2 was 178 KWh/m³ due to the higher voltage gradient; whereas without increased voltage in EK-SDS-Tw80-V1.5, this amount was decreased to 84 KWh/m³. It is to be mentioned that the electro-osmotic flow (EOF) played a significant role in minimizing kerosene concentration during the EK process, particularly when combined with surfactants.

Assessment of European and hybrid aspen clones efficiency based on height growth and removal percentage of petroleum hydrocarbons-a field trial

Soils polluted by organic or inorganic pollutants are an emerging global environmental issue due to their toxic effects. A phytoremediation experiment was conducted to evaluate the extraction potential of three European aspen clones (R2, R3, and R4) and seven hybrid aspen clones (14, 27, 34, 134, 172, 191, and 291) grown in soils polluted with hydrocarbons (includes polycyclic aromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH)). Height growth, plant survival rates, and .hydrocarbon removal efficiencies were investigated over a 4-year period at a site in Somerharju, Luumaki Finland, to assess the remediation potential of the clones. Hydrocarbon content in the soil was determined by gas chromatography and mass spectrometry. The results revealed that hybrid aspen clones 14 and 34 and European aspen clone R3 achieved greater height growth (171, 171, and 114 cm, respectively) than the other clones in the study. Further, the greatest removals of PAH (90% at depth 10-50 cm) and (86% at depth 5-10 cm) were observed in plot G15 planted with clone R2. Furthermore, the greatest TPH removal rate at 5-10 cm depth (C₂₂-C₄₀, 97%; C₁₀-C₄₀, 96%; and C₁₀-C₂₁, 90%) was observed in plot 117 with clone 134. However, other clones demonstrated an ability to grow in soils with elevated levels of TPH and PAH, which indicates their tolerance to hydrocarbons and their potential capacity for phytoremediation of hydrocarbon-polluted soils. Our study suggests that European aspen and hybrid aspen clones could be used for the remediation of soils polluted with PAH and TPH.

Removal of Total Petroleum Hydrocarbons from Contaminated Soil through Microwave Irradiation

In this study, we investigated the removal mechanism of total petroleum hydrocarbons (TPH) from soil by microwave heating. TPH contaminated soil was investigated to determine the desorption behavior of five carbon number-based fractions of TPH. The applied operating microwave power density influenced the final temperature that was reached during heating. For low operating power density applications, microwave effectiveness was limited due to the soil’s dielectric properties, which exhibited a direct relationship with temperature variation. Soil particle distribution could be attributed to permeability, which significantly influenced the evaporation of contaminated soil during the microwave treatment. The results indicate that the activation energy was correlated with the influence of particle size. The removal efficiency of the coarse soil reached 91.1% at 15 min, whereas that of fine soil was low. A total of 30 min had passed, and a removal efficiency of 71.2% was found for the fine soil. Residual TPH concentration was decreased when irradiation time was increased with a removal rate dependent on soil temperature variation. The surface functional groups of the contaminated soil were influenced by microwave irradiation, and changes in the hydrocarbon fraction affected contaminant removal.

Ecotoxicological effects of petroleum-contaminated soil on the earthworm Eisenia fetida

Petroleum is an important industrial raw material that enters the soil during production and use and is harmful to soil organisms. To evaluate the toxicity of petroleum-contaminated soil, earthworms (Eisenia fetida) were used as model organisms for soil ecotoxicity studies. We found that earthworm weight and cocoon production decreased significantly after exposure to petroleum-contaminated soil. In addition, soil contaminated with high concentrations of petroleum can cause damage to the DNA within earthworm seminal vesicles. Superoxide dismutase (SOD), catalase, and peroxidase activities were significantly inhibited when earthworms were exposed to petroleum-contaminated soil, indicating that oxidative stress was induced by petroleum pollutants. The mRNA levels of annetocin precursor, a reproduction-related gene, was significantly inhibited after petroleum exposure. The mRNA levels of translationally controlled tumour protein (TCTP) and SOD exhibited a concentration-dependent relationship, and their relative expression increased with petroleum concentration.

Aerobic degradation of BTEX compounds by Streptomyces species isolated from activated sludge and agricultural soils

In this study, we tested the ability of Streptomyces to use for their growth benzene, toluene, ethylbenzene, and o-, m-, p-xylenes as sole source of carbon and energy. These bacteria were isolated from agricultural soils and activated sludge samples from a wastewater treatment plant. The results show that Streptomyces are capable of degrading at least one of the BTEX compounds. Among them, 3 isolates from activated sludge called (U, F and V) and a single isolate (SA13) isolated from an agricultural soil, can use as the sole source of carbon and energy, all of these BTEX compounds at concentrations of 1500 mg/L. Based on the analysis of the 16S rRNA gene sequence, two active strains were identified as Streptomyces fimicarius, Streptomyces cavourensis, Streptomyces flavogriseus and Streptomyces pratensis. These strains can be excellent candidates for the bioremediation of the telluric and aquatic sites polluted by these xenobiotics.

Effect of Heat-Treatment Remediation on the Mechanical Behavior of Oil-Contaminated Soil

The heat treatment of oil-contaminated sites is widely carried out for the purposes of remediation. However, heat treatment changes the physical and chemical properties of soil. Before the soil can be reused as a construction material in civil engineering, such as in backfill or road base materials, the changes to its physical properties must be understood. Therefore, this study investigates the changes in the physical and chemical properties of oil-contaminated soil after heat treatment. In this investigation, experimental samples of soil with added oil from a refinery plant are used to investigate the removal rate of total petroleum hydrocarbons (TPHs) by thermal desorption and incineration. The physical properties of the soil, including water permeability and mechanical properties, are compared before and after heat treatment. The results of this study are as follows. (1) Particle size analysis reveals that heat treatment makes soil particles finer. (2) In the burning reduction test, heat treatment at 900 °C removes more than 90% of THP. (3) In the direct shear test, the friction angle (ϕ) increases with the removal rate. (4) In the hydraulic test, as the removal rate increases, the permeability coefficient increases after heat treatment.

Biomonitoring of aromatic hydrocarbons in clam Meretrix meretrix from an emerging urbanization area, and implications for human health

Pollution with total petroleum hydrocarbons (TPHs) is a global concern and particularly in coastal environments. Polycyclic aromatic hydrocarbons (PAHs) are regarded as the most toxic components of TPHs and they can also be derived from other sources. Fangcheng Port is considered as a representative emerging coastal city in China, but the status, sources, and hazards to organisms and humans with respect to contamination with PAHs and TPHs are unknown in the coastal regions of this area. Therefore, in this study, we cloned cytochrome P450 family genes (CYP1A1, CYP3A, and CYP4) and heat shock protein 70 gene (HSP70) in the clam Meretrix meretrix as well as optimizing the method for measuring the 7-ethoxyresorufin O-deethylase activity. These molecular indicators and four specific physiological indexes were found to be appropriate biomarkers for indicating the harmful effects of PAHs and TPHs on clams after exposure to the crude oil water-soluble fraction. In field monitoring surveys, we found that the 2- and 3-ring PAHs were dominant in the clams whereas the 4- to 6-ring PAHs were dominant in the sediments at each site. The PAH levels (3.63-12.77 ng/g wet weight) in wild clams were lower, whereas the TPH levels (13.25-70.50 μg/g wet weight) were higher compared with those determined previous in China and elsewhere. The concentrations of PAHs and TPHs in the sediments (19.20-4215.76 ng/g and 3.65-866.40 μg/g dry weight) were moderate compared with those in other global regions. Diagnostic ratio analysis demonstrated that the PAHs were derived mainly from pyrogenic sources. The TPHs may have come primarily from industrial effluents, land and maritime transportation, or fishing activities. The Integrated Biomarker Response version 2 indexes indicated that the clams collected from site S5 exhibited the most harmful effects due to contamination by PAHs and TPHs. Human health risk assessments demonstrated that the risks due to PAHs and TPHs following the consumption of clams can be considered acceptable. Our results suggest that continuous monitoring of contamination by PAHs and TPHs is recommended in this emerging coastal city as well as assessing their human health risks.

Remediation of Crude Oil-Polluted Soil by the Bacterial Rhizosphere Community of Suaeda salsa Revealed by 16S rRNA Genes

Crude oil pollution of soil is a serious environmental issue, and bioremediation using plants and microorganisms is a natural and sustainable method for its restoration. Pot incubation of a two-factor randomized block (plants with two levels, and crude oil with three levels) was designed to investigate the rhizosphere bacterial community of Suaeda salsa (L.) Pall. Crude oil contamination of soil was studied at different levels: 2 g/kg (low), 4 g/kg (medium), and 6 g/kg (high) levels. In this study, the physicochemical properties of the collected rhizosphere soil were analyzed. Moreover, the soil bacteria were further identified using the 16S rRNA gene. The effects of S. salsa and crude oil and their interaction on the physiochemical properties of the soil and crude oil degradation were found to be significant. Crude oil significantly influenced the diversity and evenness of bacteria, while the effects of S. salsa and interaction with crude oil were not significant. Proteobacteria were found to be dominant at the phylum level. Meanwhile, at the genera level, Saccharibacteria and Alcanivorax increased significantly in the low and medium contamination treatment groups with S. salsa, whereas Saccharibacteria and Desulfuromonas were prevalent in the high contamination treatment group. High crude oil contamination led to a significant decrease in the bacterial diversity in soil, while the effects of S. salsa and its interaction were not significant. Despite the highest abundance of crude oil degradation bacteria, S. salsa reduced crude oil degradation bacteria and increased bacteria related to sulfur, phosphorus, and nitrogen cycling in the low and high contamination group, whereas the opposite effect was observed for the medium contamination treatment group. The abundance of most crude oil degradation bacteria is negatively correlated with crude oil content. Nitrogen cycling bacteria are sensitive to the total nitrogen, total phosphorus, ammonia nitrogen, and nitrate nitrogen, and pH of the soil. Sulfur cycling bacteria are sensitive to aromatic hydrocarbons, saturated hydrocarbons, and asphaltene in soil. This research is helpful for further studying the mechanism of synergistic degradation by S. salsa and bacteria.

Toxic Site Identification Program in Azerbaijan

The need to protect communities from hazardous waste is an important agenda for any nation. Although pollutant management and policy development are attempted in many developing countries, it is not always successful due to limited funds, project resources, and access to trained experts to conduct toxic site identification projects. For this reason, Pure Earth created the Toxic Site Identification Program (TSIP). The goal of the TSIP program is to provide reliable information and data that identifies location of toxic sites and the level of toxic severity. TSIP is significant because it provides developing countries a database of ranked toxic sites identified as hazardous risk to human health. For example, Azerbaijan is one of the most polluted post-Soviet nations, but has limited resources to address and manage its polluted sites. The Azerbaijani TSIP database is the first reliable data source that identifies hazardous pollutants in the country. Our study is significant because it discusses how the TSIP labels and ranks the level of toxic severity to human health. It is also the first data source in Azerbaijan that identifies which Soviet legacy toxic sites are affecting local communities. Although our study is specific to Azerbaijan, the TSIP method can be applied to nations with similar data limitations and the need for a database that identifies country specific environmental and hazardous locations. The data sampling method and results are mapped and accompanied by tables of the collected pollutant types to identify communities at greatest health-risk to legacy toxic sites.

Bio-based remediation of petroleum-contaminated saline soils: Challenges, the current state-of-the-art and future prospects

Exploiting synergism between plants and microbes offers a potential means of remediating soils contaminated with petroleum hydrocarbons (PHCs). Salinity alters the physicochemical characteristics of soils and suppresses the growth of both plants and soil microbes, so the bioremediation of saline soils requires the use of plants and in microbes which can tolerate salinity. This review focuses on the management of PHC-contaminated saline soils, surveying what is currently known with respect to the potential of halophytes (plants adapted to saline environments) acting in concert with synergistic microbes to degrade PHCs. The priority is to identify optimal combinations of halophyte(s) and the bacteria present as endophytes and/or associated with the rhizosphere, and to determine what are the factors which most strongly affect their viability.

The application of a handheld mid-infrared spectrometry for rapid measurement of oil contamination in agricultural sites

Rapid analysis of oil-contaminated soils is important to facilitate risk assessment and remediation decision-making process. This study reports on the potential of a handheld mid-infrared (MIR) spectrometer for the prediction of total petroleum hydrocarbons (TPH), including aliphatic (alkanes) and polycyclic aromatic hydrocarbons (PAH) in limited number of fresh soil samples. Partial least squares regression (PLSR) and random forest (RF) modelling techniques were compared for the prediction of alkanes, PAH, and TPH concentrations in soil samples (n = 85) collected from three contaminated sites located in the Niger Delta, Southern Nigeria. Results revealed that prediction of RF models outperformed the PLSR with coefficient of determination (R²) values of 0.80, 0.79 and 0.72, residual prediction deviation (RPD) values of 2.35, 1.96, and 2.72, and root mean square error of prediction (RMSEP) values of 63.80, 83.0 and 65.88 mg kg^-1 for TPH, alkanes, and PAH, respectively. Considering the limited dataset used in the independent validation (18 samples), accurate predictions were achieved with RF for PAH and TPH, while the prediction for alkanes was less accurate. Therefore, results suggest that RF calibration models can be used successfully to predict TPH and PAH using handheld MIR spectrophotometer under field measurement conditions.

Pitfalls of Wastewater Treatment in Oil Refinery Enterprises in Kazakhstan—A System Approach

The present article is an assessment of wastewater treatment processes in the oil refinery sector in Kazakhstan by comparing relevant experience of developed and developing countries. The legislation in this sphere, the treatment methods, the discharge process and the effect on the environment were evaluated following international and national regulations. In our study, the wastewater systems in three factories in Kazakhstan were assessed. Results show that, even though the environmental regulation in Kazakhstan promotes the polluter pays principle and follows the World Health Organization (WHO) recommendations, the oil refinery plants in Kazakhstan still contain exceeding concentrations of pollutants in their effluents. One issue is that the local legislation allows disposal of wastewater to natural or artificial ponds as long as the concentrations of pollutants in effluents are less than the already existing concentrations in the pond. Consequently, the factories can use ponds with an initially high concentration of contaminants. The high initial concentration of pollutants in the pond water is due to wastewater discharged before the implementation of current environmental regulations. This issue in the current legislation leads to the situation where there is no incentive for efficient wastewater treatment. The national law also lacks regulations regarding which methodology should be used to assess the pollutants in the wastewater. Thus, the control by national environmental office for each enterprise is negotiated separately between the factory and the governmental body. This gives the factory a strong position to define the parameters assessing the effluents. This has led to none of the factories measuring, e.g., heavy metals in discharged wastewater. Total petroleum hydrocarbons (TPH) concentration in wastewater is often exceeded at each factory and there is no analysis done for different hydrocarbon fraction. To overcome the issues described in the present study, we strongly recommended a unified and transparent methodology for the country’s oil refinery industry to assess important pollutants in discharged wastewater.

Microwave (MW) remediation of hydrocarbon contaminated soil using spent graphite - An approach for waste as a resource

In this study, we have explored the possibility of using an industrial waste for remediation of heavy fuel oil contaminated soil. Microwave (MW) heating in the presence of spent graphite (SG) from an auto forging industry has been used for the remediation. The physico-chemical characterization of SG and contaminated soil were done. Microwave remediation experiments were conducted in a lab scale unit and the effect of different parameters like microwave power, susceptor loading and treatment time were studied and optimized. The contaminated and decontaminated soils were analysed using GC-MS for total petroleum hydrocarbons (TPH), Total Organic Carbon and CHNS analyzers. Batch experiments of soil remediation showed that the TPH removal efficiencies (%) of 41.25, 87.77 and 91.18 at 300, 450 and 600 W respectively at SG concentration of 2.5 (wt. %) for a reaction time of 60 min. The addition of SG as susceptor enhanced the desorption of long chain hydrocarbons (C12-C29) present in the soil. Desorption of hydrocarbons from the soil fits well with first order kinetic model. This study successfully demonstrated the reuse of spent graphite (a lubricant waste) recovered from metal forging operations for remediating the fuel oil contaminated soil.

Bioremediation capability evaluation of benzene and sulfolane contaminated groundwater: Determination of bioremediation parameters

Benzene and sulfolane are commonly used but hazardous chemicals in the petrochemical industry and their leakage and inappropriate disposal certainly causes serious soil and groundwater contamination. In this research, the bioremediation potential of groundwater contaminated with benzene and sulfolane was evaluated, and the operating parameters for bioremediation were established through laboratory batch experiments. Among the various bacterial consortia, the bacterial population of monitoring well c (MWc) contained the highest sulfolane and benzene removal efficiencies. When the dissolved oxygen (DO) level was >1 mg L^-1, the bacterial population of MWc showed excellent removal efficiencies toward high and low concentrations of benzene and sulfolane. The C:N:P ratio of 100:10:1 in media facilitated sulfolane and benzene biodegradation, and the degradation time was greatly reduced. Adding additional phosphate into real groundwater could slightly increase benzene removal efficiency. Trace elements only slightly enhanced benzene degradation. On the contrary, additional phosphate and trace elements supplementary did not enhance sulfolane degradation. However, sulfolane removal efficiency could be significantly improved through bioaugmentation of specific sulfolane degrading bacterium and 100% sulfolane removal efficiency was achieved.

Comparison of Petroleum Hydrocarbons Degradation by Klebsiella pneumoniae and Pseudomonas aeruginosa

: The aim of this work was to develop bacterial communities to effectively degrade petroleum hydrocarbons (PHs). We investigated the biotic and abiotic contributors to differences in PHs degradation efficacy between two bacterial strains, Klebsiella pneumoniae (Kp) and Pseudomonas aeruginosa (Pa), screened out from the activated sludge of a petroleum refinery. We characterized the temporal variations in degradation efficacy for diesel and its five major constituents as a sole carbon source and identified more constituents they degraded. The growth characteristics, surface tension, hydrophobicity and emulsifiability of these two strains were measured. We further estimated the relationships between their degradation efficacy and all the biotic and abiotic factors. Results showed that the Pa strain had higher diesel degradation efficacy (58% on Day 14) and utilized more diesel constituents (86%) compared to Kp. Additionally, the growth of the Pa strain in diesel medium was faster than that of the Kp strain. The Pa strain had a lower surface tension and higher hydrophobicity and emulsifiability than Kp, while the surfactant produced by Pa was identified as rhamnolipids. Degradation of PHs was positively related to bacterial growth, hydrophobicity and emulsification but negatively related to surface tension. Overall, differences in degrading capacity for diesel constituents, relative growth rate, and biosurfactant production contributed to the variation in the PHs degradation efficacy of these two bacterial strains.

Effects of Phytoremediation Treatment on Bacterial Community Structure and Diversity in Different Petroleum-Contaminated Soils

Increased exploitation and use of petroleum resources is leading to increased risk of petroleum contamination of soil and groundwater. Although phytoremediation is a widely-used and cost-effective method for rehabilitating soils polluted by petroleum, bacterial community structure and diversity in soils undergoing phytoremediation is poorly understood. We investigate bacterial community response to phytoremediation in two distinct petroleum-contaminated soils (add prepared petroleum-contaminated soils) from northwest China, Weihe Terrace soil and silty loam from loess tableland. High-throughput sequencing technology was used to compare the bacterial communities in 24 different samples, yielding 18,670 operational taxonomic units (OTUs). The dominant bacterial groups, Proteobacteria (31.92%), Actinobacteria (16.67%), Acidobacteria (13.29%) and Bacteroidetes (6.58%), increased with increasing petroleum concentration from 3000 mg/kg–10,000 mg/kg, while Crenarchaeota (13.58%) and Chloroflexi (4.7%) decreased. At the order level, RB41, Actinomycetales, Cytophagales, envOPS12, Rhodospirillales, MND1 and Xanthomonadales, except Nitrososphaerales, were dominant in Weihe Terrace soil. Bacterial community structure and diversity in the two soils were significantly different at similar petroleum concentrations. In addition, the dominant genera were affected by available nitrogen, which is strongly associated with the plants used for remediation. Overall, the bacterial community structure and diversity were markedly different in the two soils, depending on the species of plants used and the petroleum concentration.

Microbe and plant assisted-remediation of organic xenobiotics and its enhancement by genetically modified organisms and recombinant technology: A review

Environmental problems such as the deterioration of groundwater quality, soil degradation and various threats to human, animal and ecosystem health are closely related to the presence of high concentrations of organic xenobiotics in the environment. Employing appropriate technologies to remediate contaminated soils is crucial due to the site-specificity of most remediation methods. The limitations of conventional remediation technologies include poor environmental compatibility, high cost of implementation and poor public acceptability. This raises the call to employ biological methods for remediation. Bioremediation and microbe-assisted bioremediation (phytoremediation) offer many ecological and cost-associated benefits. The overall efficiency and performance of bio- and phytoremediation approaches can be enhanced by genetically modified microbes and plants. Moreover, phytoremediation can also be stimulated by suitable plant-microbe partnerships, i.e. plant-endophytic or plant-rhizospheric associations. Synergistic interactions between recombinant bacteria and genetically modified plants can further enhance the restoration of environments impacted by organic pollutants. Nevertheless, releasing genetically modified microbes and plants into the environment does pose potential risks. These can be minimized by adopting environmental biotechnological techniques and guidelines provided by environmental protection agencies and other regulatory frameworks. The current contribution provides a comprehensive overview on enhanced bioremediation and phytoremediation approaches using transgenic plants and microbes. It also sheds light on the mitigation of associated environmental risks.

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.