Development of bioreactors for comparative study of natural attenuation, biostimulation, and bioaugmentation of petroleum-hydrocarbon contaminated soil

Empirical relationship between vadose zone properties and diesel attenuation capacity: A complement for intrinsic vulnerability models

Evaluating and predicting the natural attenuation capacity (AC) of a vadose zone is essential for determining groundwater vulnerability to contamination from upper sources. However, it remains unclear how the physicochemical properties of vadose zone soils affect AC owing to their complexity and spatial heterogeneity. In this study, we developed a regression model for estimating the AC of a vadose zone against diesel using datasets from different soils with a wide range of physicochemical properties. Among the 17 properties, six (i.e., organic matter (OM), total phosphorous (TP), coefficient of uniformity, particle size (D30), van Genuchten's n, saturation degree (SD)) were selected as primary regressors. The results indicate that biogeochemical factors, including OM and TP, have decisive effects on the AC. Finally, the regression model was expanded to a GIS-based spatial model and applied to Namyangju, Korea using the index-overlay method. The produced AC map showed a nonmonotonic decrease along the depth, and the areas closer to the water bodies generally represented low AC values, most likely due to the lower OM, TP, and higher SD. This study provides an empirical basis for future research initiatives for spatial and temporal AC dynamics, which complements conventional intrinsic groundwater vulnerability models such as DRASTIC.

Low dose phosphorus supplementation is conducive to remediation of heavily petroleum-contaminated soil-From the perspective of hydrocarbon removal and ecotoxicity risk control

Biostimulation by supplementing of nitrogen and phosphorus nutrients is a common strategy for remediation of petroleum-polluted soils. However, the dosage influence of exogenous nitrogen or phosphorus on petroleum hydrocarbon removal and soil ecotoxicity and microbial function remain unclear. In this study, we compared the efficiencies of hydrocarbon degradation and ecotoxicity control by experiment conducted over addition of inorganic nitrogen or phosphorus at C/N ratio of 100/10, C/N/P ratio of 100/10/1, and C/P ratio of 100/1 in a heavily petroleum-contaminated loessal soil with 12,320 mg/kg of total petroleum hydrocarbon (TPH) content. A 90-day incubation study revealed that low-dose of phosphorus addition with the C/P ratio of 100/1 promoted hydrocarbon degradation and reduced soil ecotoxicity. Microbial community composition analysis suggested that phosphorus addition enriched hydrocarbon degrader Gordonia and Mycolicibacterium genus. The key enzymes EC 5.3.3.8, EC 6.2.1.20 and EC 6.4.1.1 which referred to degradation of long-chain hydrocarbons, unsaturated fatty acids and pyruvate metabolism were abundance by phosphorus supplementation. While nitrogen addition at C/N ratio of 100/10 or C/N/P ratio of 100/10/1 inhibited hydrocarbon degradation and exacerbated soil ecotoxicity due to promoting denitrification and coupling reactions with hydrocarbons. Our results suggested that low-dose phosphorus addition served as a favorable strategy to promote crude oil remediation and ecotoxicity risk control in heavily petroleum-contaminated soil. Hence, the application of suitable doses of exogenous biostimulants is an efficient approach to restore the ecological functions of organically contaminated soils.

Path to autonomous soil sampling and analysis by ground-based robots

Good site characterization is essential for the selection of remediation alternatives for impacted soils. The value of site characterization is critically dependent on the quality and quantity of the data collected. Current methods for characterizing impacted soils rely on expensive manual sample collection and off-site analysis. However, recent advances in terrestrial robotics and artificial intelligence offer a potentially revolutionary set of tools and methods that will help to autonomously explore natural environments, select sample locations with the highest value of information, extract samples, and analyze the data in real-time without exposing humans to potentially hazardous conditions. A fundamental challenge to realizing this potential is determining how to design an autonomous system for a given investigation with many, and often conflicting design criteria. This work presents a novel design methodology to navigate these criteria. Specifically, this methodology breaks the system into four components - sensing, sampling, mobility, and autonomy - and connects design variables to the investigation objectives and constraints. These connections are established for each component through a survey of existing technology, discussion of key technical challenges, and highlighting conditions where generality can promote multi-application deployment. An illustrative example of this design process is presented for the development and deployment of a robotic platform characterizing salt-impacted oil & gas reserve pits. After calibration, the relationship between the in situ robot chloride measurements and laboratory-based chloride measurements had a good linear relationship (R2-value = 0.861) and statistical significance (p-value = 0.003).

Biodegradation of the strobilurin fungicide pyraclostrobin by Burkholderia sp. Pyr-1: Characteristics, degradation pathway, water remediation, and toxicity assessment

Pyraclostrobin, a widely used fungicide, poses significant risks to both the environment and human health. However, research on the microbial degradation process of pyraclostrobin was scarce. Here, a pyraclostrobin-degrading strain, identified as Burkholderia sp. Pyr-1, was isolated from activated sludge. Pyraclostrobin was efficiently degraded by strain Pyr-1, and completely eliminated within 6 d in the presence of glucose. Additionally, pyraclostrobin degradation was significantly enhanced by the addition of divalent metal cations (Mn2+ and Cu2+). The degradation pathway involving ether bond and N-O bond cleavage was proposed by metabolite identification. The sodium alginate-immobilized strain Pyr-1 had a higher pyraclostrobin removal rate from contaminated lake water than the free cells. Moreover, the toxicity evaluation demonstrated that the metabolite 1-(4-chlorophenyl)-1H-pyrazol-3-ol significantly more effectively inhibited Chlorella ellipsoidea than pyraclostrobin, while its degradation products by strain Pyr-1 alleviated the growth inhibition of C. ellipsoidea, which confirmed that the low-toxic metabolites were generated from pyraclostrobin by strain Pyr-1. The study provides a potential strain Pyr-1 for the bioremediation in pyraclostrobin-contaminated aquatic environments.

Mechanisms of nanoscale zero-valent iron mediating aerobic denitrification in Pseudomonas stutzeri by promoting electron transfer and gene expression

Aerobic denitrification and its mechanism by P. stutzeri was investigated in the presence of nanoscale zero-valent iron (nZVI). The removal of nitrate and ammonia was accelerated and the nitrite nitrogen accumulation was reduced by nZVI. The particle size and dosage of nZVI were key factors for enhancing aerobic denitrification. nZVI reduced the negative effects of low carbon/nitrogen, heavy metals, surfactants and salts to aerobic denitrification. nZVI and its dissolved irons were adsorbed into the bacteria cells, enhancing the transfer of electrons from nicotinamide adenine dinucleotide (NADH) to nitrate reductase. Moreover, the activities of NADH-ubiquinone reductase involved in the respiratory system, and the denitrifying enzymes were increased. The expression of denitrifying enzyme genes napA and nirS, as well as the iron metabolism gene fur, were promoted in the presence of nZVI. This work provides a strategy for enhancing the biological denitrification of wastewater using the bio-stimulation of nanomaterials.

The main strategies for soil pollution apportionment: A review of the numerical methods

Nowadays, a large number of compounds with different physical and chemical properties have been determined in soil. Environmental behaviors and source identification of pollutants in soil are the foundation of soil pollution control. Identification and quantitative analysis of potential pollution sources are the prerequisites for its prevention and control. Many efforts have made to develop methods for identifying the sources of soil pollutants. These efforts have involved the measurement of source and receptor parameters and the analysis of their relationships via numerical statistics methods. We have comprehensively reviewed the progress made in the development of source apportionment methodologies to date and present our synthesis. The numerical methods, such as spatial geostatistics analysis, receptor models, and machine learning methods are addressed in depth. In most cases, however, the effectiveness of any single approach for source apportionment remains limited. Combining multiple methods to address soil quality problems can reduce uncertainty about the sources of soil pollution. This review also constructively highlights the key strategies of combining mathematical models with the assessment of chemical profiles to provide more accurate source attribution. This review intends to provide a comprehensive summary of source apportionment methodologies to help promote further development.

Current trends in bioremediation and bio-integrated treatment of petroleum hydrocarbons

Petroleum hydrocarbons and their derivatives constitute the leading group of environmental pollutants worldwide. In the present global scenario, petroleum and natural gas production, exploration, petroleum refining, and other anthropogenic activities produce huge amounts of hazardous petroleum wastes that accumulate in the terrestrial and marine environment. Due to their carcinogenic, neurotoxic, and mutagenic characteristics, petroleum pollutants pose severe risks to human health and exert ecotoxicological effects on the ecosystems. To mitigate petroleum hydrocarbons (PHs) contamination, implementing "green technologies" for effective cleanup and restoration of an affected environment is considered as a pragmatic approach. This review provides a comprehensive outline of newly emerging bioremediation technologies, for instance; nanobioremediation, electrokinetic bioremediation, vermiremediation, multifunctional and sustainably implemented on-site applied biotechnologies such as; natural attenuation, biostimulation, bioaugmentation, bioventing, phytoremediation and multi-process hybrid technologies. Additionally, the scope of the effectiveness and limitations of individual technologies in treating the petroleum hydrocarbon polluted sites are also evaluated.

Enhanced degradation of petroleum in saline soil by nitrogen stimulation and halophilic emulsifying bacteria Bacillus sp. Z-13

Remediation of petroleum-contaminated soil is a widely concerned challenge. As an ecofriendly method, the performance improvement of indigenous microbial degradation is facing the bottleneck. In this study, a strain with high efficiency of petroleum degradation was isolated from the petroleum-contaminated soil and identified and named as Bacillus sp. Z-13. The strain showed the ability to produce lipopeptide surfactant which could improve 66% more petroleum hydrocarbons eluted. Strain Z-13 and its biosurfactant exhibited broad environmental adaptability to salinity (0-8%), pH (6-9) and temperature (15-45 °C). With the addition of strain Z-13 and the stimulation of NH4Cl, up to 59% of the petroleum in the contaminated soil was removed at the carbon to nitrogen ratio of 10. Microbial community analysis showed that petroleum-degrading bacteria, represented by Bacillus, became the dominant species at genus level and played an important role in the remediation. Additionally, ammonium stimulation facilitated both pathways of ammonium assimilation and nitrification in native microorganisms to achieve efficient degradation of petroleum hydrocarbons. This study could provide a promising approach for stable, environmental-friendly and efficient remediation of petroleum-contaminated soil.

Complex behavior of petroleum hydrocarbons in vadose zone: A holistic analysis using unsaturated soil columns

The migration of petroleum hydrocarbons in vadose zone involves complex coupled processes such as downward displacement and natural attenuation. Despite its significance in determining groundwater vulnerability to petroleum contamination and optimizing the remedial strategy, it has not been comprehensively studied in terms of overall processes under field-relevant conditions. In this study, a series of unsaturated soil column experiments were conducted by simulating subsurface diesel contamination within a vadose zone using different soil textures at different soil bulk densities and initial diesel concentrations, while partly exposing them to simulated precipitation. The results showed that the soil column with less fine fraction was favorable for the downward migration of diesel but unfavorable for its natural degradation. However, precipitation complicated the relative conductivities of multiple fluids (water, air, and diesel) through the pore network, therby decreasing diesel migration and degradation. For example, the downward migration of diesel in the SL column decreased by 8.4% under precipitation, while the overall attenuation rate dropped to almost 0.24% of its original state. Lowering bulk density (from 1.5 to 1.23 g/cm3), however, could enhance the attenuation rate presumably due to the secured void space for the incoming fluids. A high initial concentration of diesel (2%; w/w) inhibited its natural attenuation, while its influence on its vertical propagation after the precipitation was not significant. The present findings provide a mechanistic basis for approximating the behavior of petroleum hydrocarbons in a random vadose zone.

Efficient Bioremediation of Petroleum-Contaminated Soil by Immobilized Bacterial Agent of Gordonia alkanivorans W33

In this article, we report a method for preparing an immobilized bacterial agent of petroleum-degrading bacteria Gordonia alkanivorans W33 by combining high-density fermentation and bacterial immobilization technology and testing its bioremediation effect on petroleum-contaminated soil. After determining the optimal combination of MgCl₂, CaCl₂ concentration, and culture time in the fermentation conditions by conducting a response surface analysis, the cell concentration reached 7.48 × 10⁹ CFU/mL by 5 L fed-batch fermentation. The W33-vermiculite-powder-immobilized bacterial agent mixed with sophorolipids and rhamnolipids in a weight ratio of 9:10 was used for the bioremediation of petroleum-contaminated soil. After 45 days of microbial degradation, 56.3% of the petroleum in the soil with 20,000 mg/kg petroleum content was degraded, and the average degradation rate reached 250.2 mg/kg/d.

Effects of different carbon substrates on PAHs fractions and microbial community changes in PAHs-contaminated soils

Different types of carbon substrates were widely used in soil remediation. However, differences of their impacts and related mechanisms on degradation of polycyclic aromatic hydrocarbons (PAHs) and microbial community structures in contaminated soil still remain unclear. Here, we investigated the effects of corn straw (S), glucose (G), straw combined with glucose (SG), and sodium azide (N, as an abiotic control) on PAHs fractions and bacterial communities in soil. After 70 days' microcosm experiments, total PAHs concentrations were significantly reduced by 30.9%, 19.5% and 44.6% under S, G and SG treatments. Water soluble, acid soluble and residual PAHs under all treatments were significantly decreased after 70 days of incubation, while organically bound PAHs were increased by 11.4%, 22.7% and 36.1% under G, S and SG treatments. Additionally, straw and glucose application increased relative abundance related PAHs-degrading bacteria and the copy numbers of gram-negative (PAHs-RHDα GN) and gram-positive genes (PAHs-RHDα GP) in the contaminated soil. Redundancy analysis (RDA) and Random Forest (RF) indicated that PAHs fractions are crucial factors for biodegradation of PAHs in PAHs-contaminated soils amended with carbon substrates. These suggested that carbon substrates contributed to PAHs conversion from residual PAHs (nonlabile fractions) to organically bound PAHs and thus increased the potential for PAHs conversion to water-soluble and organic acid-soluble PAHs, which were more easy to be utilized by soil microorganisms. This study revealed the new insights of different carbon substrates on degradation and dynamic changes of PAHs fractions and the better potential of combined application of straw and glucose in enhancing degradation of PAHs in PAHs-contaminated soils.

Enhanced bioremediation of oil-contaminated soil in a slurry bioreactor by H2O2-stimulation of oil-degrading/biosurfactant-generating bacteria: performance optimization and bacterial metagenomics

Oil-contaminated soil is the main challenge for oil-rich countries, and this study aimed to investigate the performance of the H₂O₂-stimulated slurry bioreactor for the bioremediation of real oil-contaminated soil. The effect of biomass concentration, soil to water (S/W) ratio, slurry temperature, pH, and H₂O₂ concentration were optimized for the removal of total petroleum hydrocarbons (TPH) from oil-contaminated soil. TPH removal efficiency, biosurfactants production, and peroxidase and dehydrogenase activities were measured. The optimum conditions for the complete biodegradation of 32 [Formula: see text] in the slurry bioreactor during 6 days were biomass of 2250 mg/L, S/W ratio of 20%, the temperature of 30 °C, pH of 7, and an H₂O₂ concentration of 120 mg/L. The highest peroxidase, dehydrogenase, surfactin, and rhamnolipid formation were also obtained under optimum conditions. The results pointed out that complete biodegradation of 32 g/kg of TPH in oil-contaminated soil at a short reaction time of 6 days is achievable in the developed process operated under optimum conditions. The GC/FID analysis of solid and liquid phases showed that the bioprocess completely biodegraded the different TPH fractions. H₂O₂ efficiently stimulated the biosurfactant-generating bacteria to produce peroxidase and thereby accelerating the bioremediation rate. Accordingly, an H₂O₂-mediated slurry bioreactor inoculated with biosurfactant/peroxidase-generating bacteria is a promising technique for cleaning up oil-contaminated soils.

The collaborative monitored natural attenuation (CMNA) of soil and groundwater pollution in large petrochemical enterprises: A case study

A large in-service petrochemical enterprises in Northeast China was taken as the research object, and the Collaborative Monitored Natural Attenuation (CMNA) for soil and groundwater pollution was carried out to remedy combined pollution and reduce environmental risks. The pollutants distributions were obtained based on detailed regional investigation (Mar. 2019), and feature pollutants in soil and groundwater were then screened. The spatiotemporal variations of feature pollutants and relative microbial responses were explored during the CMNA process. Furthermore, the CMNA efficiency of the contaminated site at initial stage was evaluated by calculation of natural attenuation rate constant. The results showed that the feature pollutants in soil were 2,2',5,5'-tetrachlorobiphenyl (2,2',5,5'-TCB) and petroleum hydrocarbons (C₁₀∼C₄₀), and the feature pollutant in groundwater was 1,2-dichloroethane (1,2-DCA). The concentrations of all feature pollutants decreased continuously during four years of monitoring. Feature pollutants played a dominant role in the variability of microbial species both in soil and groundwater, increasing the relative abundance of petroleum tolerant/biodegradation bacteria, such as Actinobacteria, Proteobacteria and Acidobacteriota. The average natural attenuation rate constant of 2,2',5,5'-TCB and C₁₀∼C₄₀ in soil was 0.0012 d^-1 and 0.0010 d^-1, respectively, meeting the screening value after four years' attenuation. The average natural attenuation rate constant of 1,2-DCA was 0.0004 d^-1, which need strengthening measures to improve the attenuation efficiency.

Bacterial strains diversity in contaminated soils and their potential for bioremediation of total petroleum hydrocarbons in south west of Iran

PURPOSE

The main purpose of this research was investigating of bioremediation potential oily contaminated soils using native bacterial strains in an oil field.

METHODS

In this research, total bacterial consortium were identified in oily soils with sandy loam texture as case and non-contaminated soils as controls during six months. The dominant strains present on contaminated soil were identified by DNA extraction using 16S rDNA gene sequencing via NGS technique and compared with bacteria present in non-contaminated soil as control samples. Furthermore, quantitative variations of bacterial count along with total petroleum hydrocarbons (TPH) removal was performed in oily (case) samples to investigate the relation between TPH removal and changes in bacterial density. The TPH values were determined with gas chromatography equipped with a flame ionization detector (GC-FID).

RESULTS

The dominant identified bacteria in oily soil were as follows: Halomonas, Moraxellaceae, Thalassobacillus, Zhihengliuella and Enterobacteriaceae which varied significantly from those identified in control soil. The bacterial diversity was higher in contaminated soil and a TPH removal of 50.9% was observed over a period of six months monitoring.

CONCLUSION

Indigenous bacteria in oil-contaminated soils of an oilfield in south west of Iran were found to be able to degrade Total Petroleum Hydrocarbons. Our results showed that bioremediation of oil-contaminated soils can be implemented without need to amplification of heterogeneous bacteria. Considering sandy loam texture of soil samples, the identified strains of bacteria could be introduced as sufficient consortium for biodegradation of this soils with similar texture.

A starch-based controlled-release targeted nutrient agent to stimulate the activity of volatile chlorinated hydrocarbon-degrading indigenous microflora present in groundwater

Volatile chlorinated hydrocarbons (VCHs) contaminated groundwater has a low indigenous microorganism population, and lack of nutrient substrates involved in degradation reactions, resulting in a weak natural remediation ability of groundwater ecosystems. In this study, based on the principle of degradation of VCHs by indigenous microorganisms in groundwater, and combined with biostimulation and controlled-release technology, we developed a starch-based encapsulated targeted bionutrient (YH-1) with easy uptake, good stability, controllable slow-release migration, and long timeliness for the remediation of groundwater contaminated by VCHs by indigenous microorganisms. The results showed that YH-1 is easily absorbed by microorganisms and can rapidly initiate itself to stimulate the microbial degradation of VCHs, and the degradation rate of various VCH components within 7 days was 82.38-92.38 %. The release rate of nutrient components in YH-1 increases with increasing VCH concentrations in groundwater; this could effectively prolong the action time of nutrient components, while also improving the degradation efficiency of pollutants with a sustained effect of more than 15 days. Simultaneously, owing to the fluidity, water solubility, and biodegradability of YH-1 in lithologic media, YH-1 injection did not cause blockage of the lithologic media in the aquifer. Through YH-1 stimulation, indigenous microorganisms grew rapidly in the underground environment, the diversity of microbial communities and the total number of species increased, and the correlation between genera strengthened. Simultaneously, YH-1 improved the ability of microbial community to convert inorganic electron donors/acceptors, thereby strengthening the co-metabolic mechanism between microorganisms. Additionally, there was a significant increase in the percentage of many microorganisms (e.g., Sphingomonas, Janthinobacterium, Duganella, etc.) that mediated the reductive dechlorination process and were redox inorganic electron donors/acceptors. This was conducive to the reductive dechlorination process of VCHs and achieved the efficient degradation of VCHs.

Supramolecular bioamphiphile facilitated bioemulsification and concomitant treatment of recalcitrant hydrocarbons in petroleum refining industry oily waste

Bioremediation of real-time petroleum refining industry oily waste (PRIOW) is a major challenge due to the poor emulsification potential and oil sludge disintegration efficiency of conventional bioamphiphile molecules. The present study was focused on the design of a covalently engineered supramolecular bioamphiphile complex (SUBC) rich in hydrophobic amino acids for proficient emulsification of hydrocarbons followed by the concomitant degradation of total petroleum hydrocarbons (TPH) in PRIOW using the hydrocarbonoclastic microbial bio-formulation system. The synthesis of SUBC was carried out by pH regulated microbial biosynthesis process and the yield was obtained to be 450.8 mg/g of petroleum oil sludge. The FT-IR and XPS analyses of SUBC revealed the anchoring of hydrophilic moieties of monomeric bioamphiphilic molecules, resulting in the formation of SUBC via covalent interaction. The SUBC was found to be lipoprotein in nature. The maximum loading capacity of SUBC onto surface modified rice hull (SMRH) was achieved to be 45.25 mg/g SMRH at the optimized conditions using RSM-CCD design. The SUBC anchored SMRH was confirmed using SEM, FT-IR, XRD and TGA analyses. The adsorption isotherm models of SUBC onto SMRH were performed. The integrated approach of SUBC-SMRH and hydrocarbonoclastic microbial bio-formulation system, emulsified oil from PRIOW by 92.86 ± 2.26% within 24 h and degraded TPH by 89.25 ± 1.75% within 4 days at the optimum dosage ratio of SUBC-SMRH (0.25 g): PRIOW (1 g): mass of microbial-assisted biocarrier material (0.05 g). The TPH degradation was confirmed by SARA fractional analysis, FT-IR, ¹H NMR and GC-MS analyses. The study suggested that the application of covalently engineered SUBC has resulted in the accelerated degradation of real-time PRIOW in a very short duration without any secondary sludge generation. Thus, the SUBC integrated approach can be considered to effectively manage the hydrocarbon contaminants from petroleum refining industries under optimal conditions.

Coupled effect of porous network and water content on the natural attenuation of diesel in unsaturated soils

The natural attenuation potential of a vadose zone against diesel is critical for optimizing remedial actions and determining groundwater vulnerability to contamination. Here, diesel attenuation in unsaturated soils was systematically examined to develop a qualitative relationship between physical soil properties and the natural attenuation capacity of a vadose zone against diesel. The uniformity coefficient (C_u) and water saturation (S_w, %) were considered as the proxies reflecting the degree of effects by porous network and water content in different soils, respectively. These, in turn, are related to the primary diesel attenuation mechanisms of volatilization and biodegradation. The volatilization of diesel was inversely proportional to C_u and S_w, which could be attributed to effective pore channels facilitating gas transport. Conversely, biodegradation was highly proportional to C_u under unsaturated conditions (S_w = 35-71%), owing to nutrients typically associated with fine soil particles. The microbial community in unsaturated soils was affected by S_w rather than C_u. The overall diesel attenuation including volatilization and biodegradation was optimized at S_w = 35% for all tested soils.

Nitrogen addition enhanced the polycyclic aromatic hydrocarbons dissipation through increasing the abundance of related degrading genes in the soils

High concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in the soils cause significant threats to human health. Since nitrogen plays a crucial role in controlling microbial composition and functions in terrestrial ecosystems, bio-stimulation based on nitrogen has been used in PAHs contaminated environments remediation. Recent studies show that microbial community composition and organic pollutants dissipation correlate with nitrogen addition. Here, we investigated the effect of nitrogen addition on the abundance of microbial community, degrading genes, and their relationship to PAHs dissipation. After a 32-day experiment, PAHs residues in nitrogen treatment soil were reduced by 23.23%-34.21%. The application of 80 mg·kg^-1 nitrate and ammonium nitrogen resulted in higher PAHs removal efficiency, and the dissipation rate of PAHs was 59.61% and 62.09%, respectively. Nitrogen application could improve the abundance and the diversity of soil microbial community. Degrading genes involved in PAH detoxification were enhanced after nitrogen addition, particularly those encoding ring-hydroxylating and catechol dioxygenases such as nahAc and nidA, thus, accelerating PAH dissipation in the soil. The results will facilitate the development of beneficial microbiome-based remediation strategies and improve agricultural production safety in PAHs-contaminated soils.

Differences in geological conditions have reshaped the structure and diversity of microbial communities in oily soils

High-throughput sequencing was used to study the microbial community structure diversity changes in oil-contaminated soils under different spatial distances and environmental conditions. 239 Phyla, 508 Classes, 810 Orders, 1417 Families, 2048 Genera, 511 Species of microbial communities were obtained from 16 samples in three regions. The physicochemical properties of the soil, microorganisms' community structure has been changed by Petroleum hydrocarbon (PHA). Alpha diversity results showed that the soil contained high bacterial diversity, especially in Qingyang's loess soil. The bacterial abundance was in the order of loess soil > black soil > sandy soil. Beta diversity revealed that spatial distance limitation and random variation of repeated samples may be the main factors leading to soil heterogeneity and microbial community structure differences. The dominant bacteria phyla with broad petroleum hydrocarbon degradation ability such as Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were identified. Pseudomonas, Bacillus, Nocardioides, Oceanobacillus, Sphingomonas, Alkanindiges and Streptomyces were identified as functional microbial for the PHA degradation. The microbial communities manifested the co-exclusion under different geological conditions, and played the key role in the soil PHA degradation through amino acid metabolism, energy metabolism and carbohydrate metabolism. The correlation results of amos structural equation showed that the diversity and abundance of soil microorganisms in different regions were controlled by soil PHA content and environmental factors. Altitude, annual average temperature and annual rainfall were positively correlated with microbial diversity. Annual rainfall and soil physical and chemical factors exhibited the most significant influence on it. Microbial diversity indirectly affected the PHA content in different type soil. We believe that reshape the structure and diversity of microbial communities in soil could be changed and reshaped by different geological conditions, pollutants and soil type. This study can provide helps for understanding the ecological effect of geomicrobiology formation under the driving force of geographic environment and other factors.

A metagenomic portrait of the microbial community responsible for two decades of bioremediation of poly-contaminated groundwater

Biodegradation of pollutants is a sustainable and cost-effective solution to groundwater pollution. Here, we investigate microbial populations involved in biodegradation of poly-contaminants in a pipeline for heavily contaminated groundwater. Groundwater moves from a polluted park to a treatment plant, where an aerated bioreactor effectively removes the contaminants. While the biomass does not settle in the reactor, sediment is collected afterwards and used to seed the new polluted groundwater via a backwash cycle. The pipeline has successfully operated since 1999, but the biological components in the reactor and the contaminated park groundwater have never been described. We sampled seven points along the pipeline, representing the entire remediation process, and characterized the changing microbial communities using genome-resolved metagenomic analysis. We assembled 297 medium- and high-quality metagenome-assembled genome sequences representing on average 46.3% of the total DNA per sample. We found that the communities cluster into two distinct groups, separating the anaerobic communities in the park groundwater from the aerobic communities inside the plant. In the park, the community is dominated by members of the genus Sulfuricurvum, while the plant is dominated by generalists from the order Burkholderiales. Known aromatic compound biodegradation pathways are four times more abundant in the plant-side communities compared to the park-side. Our findings provide a genome-resolved portrait of the microbial community in a highly effective groundwater treatment system that has treated groundwater with a complex contamination profile for two decades.

Phytoremediation of soil contaminated with weathered petroleum hydrocarbons by applying mineral fertilization, an anionic surfactant, or hydrocarbonoclastic bacteria

This study evaluated the effect of the application of mineral fertilization (F), the anionic surfactant Triton X-100 (TX100), or the inoculation with a hydrocarbooclastic bacterial consortium (BCons) on the growth of Clitoria ternatea during the phytoremediation of a Gleysol contaminated with weathered petroleum hydrocarbons (39,000 mg kg^-1 WPH) collected from La Venta, Tabasco (Mexico). The experiment consisted of a completely randomized design with seven treatments and four replications each under greenhouse conditions. The application of F (biostimulation) increased plant growth and biomass production; in contrast, TX100 only favored root biomass (11%) but significantly favored WPH degradation. Bioaugmentation with BCons did not show significant effects on plant growth. Nevertheless, the combination of biostimulation with bioaugmentation (BCons + F, BCons + TX100, and BCons + F+TX100) enhanced plant growth, hydrocarbonoclastic bacteria population, and WPH degradation when compared to treatments with the single application of bioaugmentation (BCons) or biostimulation (F).

Organic wastes bioremediation and its changing prospects

Increasing inappropriate anthropogenic activities and industrialization have resulted in severe environmental pollution worldwide. Their effective treatment is vital for general health concerns. Depending on the characteristics of pollutants, the severity of pollution may differ. For sustainable treatment of polluted environments, bioremediation is accepted as the most efficient, economical, and environmentally friendly method hence largely preferred. However, every bioremediation technique has its own unique advantages and limitations due to its defined applications criteria. In bioremediation, microorganisms play a decisive role in detoxification by degrading, mineralizing and accumulating various forms of harmful and biodegradable pollutants from the surroundings and transforming them into less lethal forms. Bioremediation is performed ex-situ or in-situ, based on location of polluted site as well as characteristics, type and strength of the pollutants. Furthermore, the most popular methodologies for bioremediation include bioaugmentation, biostimulation, bioattenuation among others which depend on the prevailing environmental factors into the microbial system. Implementing them appropriately and effectively under ex-situ or in-situ method is extremely important not only for obtaining efficient treatment but also for the best economic, environmental, and social impacts. Therefore, this review aims to analyze various bioremediation methods for organic pollutants remediation from soil/sediments and wastewater, their strength, limitation, and insights for the selection of appropriate bioremediation techniques based on nature, types, degree, and location of the pollution. The novelty aspect of the article is to give updates on several key supporting technologies which have recently emerged and exhibited great potential to enhance the present bioremediation efficiency such as nanobubble, engineered biochar, mixotrophic microalgae, nanotechnology etc. Moreover, amalgamation of these technologies with existing bioremediation facilities are significantly changing the scenario and scope of environmental remediation towards sustainable bioremediation.

Evaluation of the Effectiveness of the Biopreparation in Combination with the Polymer γ-PGA for the Biodegradation of Petroleum Contaminants in Soil

Biodegradation is a method of effectively removing petroleum hydrocarbons from the natural environment. This research focuses on the biodegradation of aliphatic hydrocarbons, monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and all three xylene isomers (BTEX) and polycyclic aromatic hydrocarbons (PAHs) as a result of soil inoculation with a biopreparation A1 based on autochthonous microorganisms and a biopreparation A1 with the addition of γ-PGA. The research used biopreparation A1 made of the following strains: Dietzia sp. IN133, Gordonia sp. IN138 Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN119, Rhodococcus sp. IN136 and Pseudomonas sp. IN132. The experiments were carried out in laboratory conditions (microbiological tests, respirometric tests, and in semi-technical conditions (ex-situ prism method). The biodegradation efficiency was assessed on the basis of respirometric tests, chromatographic analyses and toxicological tests. As a result of inoculation of AB soil with the biopreparation A1 within 6 months, a reduction of total petroleum hydrocarbons (TPH) (66.03%), BTEX (80.08%) and PAHs (38.86%) was achieved and its toxicity was reduced. Inoculation of AB soil with the biopreparation A1 with the addition of γ-PGA reduced the concentration of TPH, BTEX and PAHs by 79.21%, 90.19%, and 51.18%, respectively, and reduced its toxicity. The conducted research has shown that the addition of γ-PGA affects the efficiency of the biodegradation process of petroleum pollutants, increasing the degree of TPH biodegradation by 13.18%, BTEX by 10.11% and PAHs by 12.32% compared to pure biopreparation A1.

Factors Influencing the Bacterial Bioremediation of Hydrocarbon Contaminants in the Soil: Mechanisms and Impacts

The discharge of hydrocarbons and their derivatives to environments due to human and/or natural activities cause environmental pollution (soil, water, and air) and affect the natural functioning of an ecosystem. To minimize or eradicate environmental pollution by hydrocarbon contaminants, studies showed strategies including physical, chemical, and biological approaches. Among those strategies, the use of biological techniques (especially bacterial biodegradation) is critically important to remove hydrocarbon contaminants. The current review discusses the insights of major factors that enhance or hinder the bacterial bioremediation of hydrocarbon contaminants (aliphatic, aromatic, and polyaromatic hydrocarbons) in the soil. The key factors limiting the overall hydrocarbon biodegradation are generally categorized as biotic factors and abiotic factors. Among various environmental factors, temperature range from 30 to 40°C, pH range from 5 to 8, moisture availability range from 30 to 90%, carbon/nitrogen/phosphorous (C/N/P; 100:20:1) ratio, and 10–40% of oxygen for aerobic degradation are the key factors that show positive correlation for greatest hydrocarbon biodegradation rate by altering the activities of the microbial and degradative enzymes in soil. In addition, the formation of biofilm and production of biosurfactants in hydrocarbon-polluted soil environments increase microbial adaptation to low bioavailability of hydrophobic compounds, and genes that encode for hydrocarbon degradative enzymes are critical for the potential of microbes to bioremediate soils contaminated with hydrocarbon pollutants. Therefore, this review works on the identification of factors for effective hydrocarbon biodegradation, understanding, and optimization of those factors that are essential and critical.

Oil bioremediation in soils contaminated with oil spills in tropical environments

Bioremediation techniques like bioaugmentation and/or biostimulation are an economical and environmentally friendly procedure which emerged as the most advantageous methodology for treatment of contaminated sites by oil spills pollutants. This research uses a tropical soil contaminated with oil based drilling fluids (OBMs) and drill cuttings were evaluating at laboratory scale. Seven treatments were implemented separately: (C) control; (A) natural attenuation; (B) compost (Bs) nutrients; (BsT) nutrients and tween 80; (BsTL) nutrients, tween 80, leonardite, and (BL) nutrients, tween 80, leonardite and d-limonene. For three months, changes in Total Petroleum Hydrocarbons (TPH) soil microbial counts and activity were monitored as indicators of biodegradation. In order to evaluate the efficiency of treatments in the microcosm experiments. After 90 days of incubation hydrocarbon biodegradation is 76.2% (C), 28.6% (A), 76.2% (B), 66.7% (Bs), 83.3% (BsT), 69% (BsTL) and 88.1% (BL), respectively. Scanning electron microscopy (SEM) of OBMs evidenced absence of heavy metals. Biodiversity analysis showed a decrease in bacterial diversity and a rise in tolerant genus of hydrocarbons such as Nocardiodes, Streptomyces, Dietzia and Advenella. The co-substrate and stimulants had synergistic effect on the biological degradation of hydrocarbons. This research suggests that the implementation of bioaugmentation and biostimulation methods will be used a larger scale in contaminated sites.

Potential biodegradation of Tapis Light Crude Petroleum Oil, using palm oil mill effluent final discharge as biostimulant for isolated halotolerant Bacillus strains

Petroleum hydrocarbon pollution in marine waters has been an extremely significant environmental and health issue worldwide. This study aims at constructing an efficient indigenous bacterial consortium to biodegrade Tapis Light Crude Petroleum Oil (TLCO). The local agro-industrial wastewater of palm oil mill effluent final discharge (POME FD) was used as biostimulant to enhance the biodegradation efficiency. In this study, three TLCO degrading bacteria were isolated from seawater samples collected. Molecular identification using 16S rRNA genes sequencing was done and results show that these isolated strains belong to: Bacillus tropicus, Bacillus licheniformis and Bacillus subtilis. Bacterial consortium tested using four different concentrations of POME FD (0.1, 0.25, 0.5, and 1%) as biostimulant and TLCO (0.5 and 1.0%) degradation capability was investigated. The residual TLCO in culture medium after 40 days was analysed. The results confirmed that POME FD dosage of 0.25% is optimum for the bacterial consortium and can degrade 99.85% of TLCO at 0.5%. However, TLCO degradation with POME FD dosage (0.25%) in TLCO (1.0%) was found optimum, with biodegradation reaching up to 95.23% in 40 days. This study is a beginning for the future development of a consortium of petroleum hydrocarbon degrading bacteria to mitigate oil spills in the Malaysian shoreline.

Managing soils of environmental significance: A critical review

Globally, environmentally significant soils (ESSs) mainly include acid sulfate, heavy metal(loid)-contaminated, petroleum hydrocarbon-contaminated, pesticide-contaminated, and radionuclide-contaminated soils. These soils are interrelated and have many common characteristics from an environmental management perspective. In this review, we critically evaluate the available literature on individual ESSs, aiming to identify common problems related to environmental quality/risk assessment, remediation approaches, and environmental regulation for these soils. Based on these findings, we highlight the challenges to, and possible solutions for sustainable ESS management. Contaminated land has been rapidly expanding since the first industrial revolution from the industrialized Western countries to the emerging industrialized Asia and other parts of the world. Clean-up of contaminated lands and slowdown of their expansion require concerted international efforts to develop advanced cleaner production and cost-effective soil remediation technologies in addition to improvement of environmental legislation, regulatory enforcement, financial instruments, and stakeholder involvement to create enabling environments. Two particular areas require further action and research efforts: developing a universal system for assessing ESS quality and improving the cost-effectiveness of remediation technologies. We propose an integrated framework for deriving ESS quality indicators and make suggestions for future research directions to improve the performance of soil remediation technologies.

Corksorb Enhances Alkane Degradation by Hydrocarbonoclastic Bacteria

Biosorbent materials are effective in the removal of spilled oil from water, but their effect on hydrocarbonoclastic bacteria is not known. Here, we show that corksorb, a cork-based biosorbent, enhances growth and alkane degradation by Rhodococcus opacus B4 (Ro) and Alcanivorax borkumensis SK2 (Ab). Ro and Ab degraded 96 ± 1% and 72 ± 2%, respectively, of a mixture of n-alkanes (2 g L-1) in the presence of corksorb. These values represent an increase of 6 and 24%, respectively, relative to the assays without corksorb. The biosorbent also increased the growth of Ab by 51%. However, no significant changes were detected in the expression of genes involved in alkane uptake and degradation in the presence of corksorb relative to the control without the biosorbent. Nevertheless, transcriptomics analysis revealed an increased expression of rRNA and tRNA coding genes, which confirms the higher metabolic activity of Ab in the presence of corksorb. The effect of corksorb is not related to the release of soluble stimulating compounds, but rather to the presence of the biosorbent, which was shown to be essential. Indeed, scanning electron microscopy images and downregulation of pili formation coding genes, which are involved in cell mobility, suggest that cell attachment on corksorb is a determinant for the improved activity. Furthermore, the existence of native alkane-degrading bacteria in corksorb was revealed, which may assist in situ bioremediation. Hence, the use of corksorb in marine oil spills may induce a combined effect of sorption and stimulated biodegradation, with high potential for enhancing in situ bioremediation processes.

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.

Simulated Ageing of Crude Oil and Advanced Oxidation Processes for Water Remediation since Crude Oil Pollution

Crude oil can undergo biotic and abiotic transformation processes in the environment. This article deals with the fate of an Italian crude oil under simulated solar irradiation to understand (i) the modification induced on its composition by artificial ageing and (ii) the transformations arising from different advanced oxidation processes (AOPs) applied as oil-polluted water remediation methods. The AOPs adopted were photocatalysis, sonolysis and, simultaneously, photocatalysis and sonolysis (sonophotocatalysis). Crude oil and its water-soluble fractions underwent analysis using GC-MS, liquid-state 1H-NMR, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), and fluorescence. The crude oil after light irradiation showed (i) significant modifications induced by the artificial ageing on its composition and (ii) the formation of potentially toxic substances. The treatment produced oil oxidation with a particular effect of double bonds oxygenation. Non-polar compounds present in the water-soluble oil fraction showed a strong presence of branched alkanes and a good amount of linear and aromatic alkanes. All remediation methods utilised generated an increase of C5 class and a decrease of C6–C9 types of compounds. The analysis of polar molecules elucidated that oxygenated compounds underwent a slight reduction after photocatalysis and a sharp decline after sonophotocatalytic degradation. Significant modifications did not occur by sonolysis.

Biological stimulation with Fe(III) promotes the growth and aerobic denitrification of Pseudomonas stutzeri T13

Certain metal ions can contribute to the functional microorganisms becoming dominant by stimulating their metabolism and activity. Therefore, Pseudomonas stutzeri T13 was used to investigate the impacts of biological stimulation with certain metal ions on aerobic denitrifying bacteria. Results showed that with the addition of 0.036 mmol/L Fe³⁺ ions, the nitrogen-assimilation capacity of P. stutzeri T13 significantly increased by 43.99% when utilizing ammonium as the sole nitrogen source. Kinetic models were applied to analyze the role of Fe³⁺ ions in the growth, and results indicated that increasing Fe³⁺ ion concentrations decreased the decay rate. The maximum nitrate reduction rate increased from 9.55 mg-N L^-1 h^-1 to 19.65 mg-N L^-1 h^-1 with Fe³⁺ ion concentrations increasing from 0.004 to 0.036 mmol/L, which was due to the increased level of napA gene transcription and activity of nitrate reductase. This study provides a theoretical foundation for further understanding of the mechanism of Fe³⁺ ion stimulation of aerobic denitrification, benefiting the practicable application of aerobic denitrifiers.

Functional potential of sewage sludge digestate microbes to degrade aliphatic hydrocarbons during bioremediation of a petroleum hydrocarbons contaminated soil

Sewage sludge digestate is a valuable organic waste which can be used as fertilizer in soil bioremediation. Sewage sludge digestate is not only a good source of nutrients but is also rich in bacteria carrying alkB genes, which are involved in aliphatic hydrocarbons metabolism. Increase of alkB genes ratio in polluted soils has been observed to improve bioremediation efficiency. In this study, for the first time, the genetic potential of indigenous microorganisms of digestate to degrade petroleum products was assessed. The objectives were to study petroleum hydrocarbons (PHCs) removal together with shifts in soil taxa and changes in the concentration of alkB genes after digestate application. Initial alkB genes concentration in contaminated soils and digestate was 1.5% and 4.5%, respectively. During soil incubation with digestate, alkB genes percentage increased up to 11.5% and after the addition of bacteria immobilized onto biochar this value increased up to 60%. Application of digestate positively affected soil respiration and bacterial density, which was concomitant with enhanced PHCs degradation. Incubation of soil amended with digestate resulted in 74% PHCs decrease in 2 months, while extra addition of bacteria immobilized onto biochar increased this value up to 95%. The use of digestate affected the microbial community profiles by increasing initial bacterial density and diversity, including taxa containing recognized PHCs degraders. This study reveals the great potential of digestate as a soil amendment which additionally improves the abundance of alkB genes in petroleum contaminated soils.

Advances in research on petroleum biodegradability in soil

With the increased demand for petroleum and petroleum products from all parts of the society, environmental pollution caused by petroleum development and production processes is becoming increasingly serious. Soil pollution caused by petroleum seriously affects environmental quality in addition to human lives and productivity. At present, petroleum in soil is mainly degraded by biological methods. In their natural state, native bacteria in the soil spontaneously degrade petroleum pollutants that enter the soil; however, when the pollution levels increase, the degradation rates decrease, and it is necessary to add nutrients, dissolved oxygen, biosurfactants and other additives to improve the degradation ability of the native bacteria in the soil. The degradation process can also be enhanced by adding exogenous petroleum-degrading bacteria, microbial immobilization technologies, and microbial fuel cell technologies.

Toluene induces hormetic response of soil alkaline phosphatase and the potential enzyme kinetic mechanism

Hormesis of soil enzyme that involved in heavy metal has been attracting much more attention for risk assessment of heavy metal toxicity, but insufficient studies were conducted to define the hormetic responses induced by toluene or other organic pollutions. The objectives of this study were to investigate the hormetic responses of soil enzyme induced by toluene and explore the potential enzyme kinetic mechanism. Soil alkaline phosphatase (ALP) activity was regarded as the endpoint to explore the hormetic responses under different doses of toluene (0.0, 0.1, 0.5, 1.0, 2.0, 3.0, 5.0, 10.0, 50.0 and 100.0 μL g^-1). Subsequently, we conducted the experiments of enzymatic reaction kinetics and pure enzyme to further verify the potential mechanisms of soil ALP's hormesis. Results showed that ALP activities at 0.1-1.0 μL g^-1 toluene were significantly increased in contrast to the control (0 μL g^-1 toluene) (P < 0.05) at the exposure time of 30, 36, 48 and 54 h, with the maximum stimulation magnitudes of 24-43%. ALP activities were almost not affected by toluene (2-100 μL L^-1) in the whole experimental period (6-54 h). Meanwhile, the values of catalytic efficiency (the radio V_max/K_m, V_max: maximum reaction velocity and K_m: Michaelis constant) and V_max significantly increased compared with the control, but the value of K_m decreased from 2.5 to 1.6. Overall, low dose toluene can induce hormesis of soil ALP. The potential reason is that low-dose toluene could enhance the combination of soil ALP and substrates. We believe that this study will provide a new viewpoint for ecological risk assessment of toluene contaminated soils.

Enhanced degradation of total petroleum hydrocarbons in real soil by dual-frequency ultrasound-activated persulfate

Ultrasound (US) can be employed to activate persulfate (PS) for degrading total petroleum hydrocarbons (TPH). In this study, to improve the degradation efficiency, PS is combined with dual-frequency US (DFUS) towards synergistic degradation of TPH in real soil. After 180 min, the degradation percentages for DFUS/PS, DFUS, high-frequency US and high-frequency US/PS are around 88.9%, 38.7%, 7.3% and 54.2%, respectively. Additionally, the influence of US power, PS content, slurry pH and temperature, and TPH components on the degradation percentage in the DFUS/PS process are explored. Scanning electron microscopy (SEM) images and the results of specific surface area verify that the DFUS can break the soil aggregates more effectively than the single-frequency US, and thus enhance the TPH desorption and accelerate the oxidant diffusion. Moreover, the investigation of the mechanism is further evaluated through quenching and electron spinning resonance spectrum (ESR) tests. The results indicate that the generation of SO₄^- and OH in DFUS/PS is ~1.6 times and ~2.5 times as much, respectively, as in high frequency US/PS. The relative contributions to the synergistic TPH degradation in the DFUS/PS system are: SO₄^- (PS activation via the heat induced by US) > pyrolysis inside the bubbles (hydrophobicity of TPH) > SO₄^- (PS activation via US cavitation) >OH. Finally, the hypothesis is confirmed via the evaluation of the degradation kinetics, which shows that the combined process of DFUS/PS is not a simple addition of the US and PS, but provides a highly effective process of synergistic degradation.

Groundwater quality

Groundwater is a vital component of water supply for residential, industrial, and agricultural purposes. However, many groundwater basins are being used unsustainably and groundwater contamination is a growing water quality problem. Although anthropogenic activities and natural processes have been increasing the contamination in this valuable water resource, several remediation techniques have been developed in the last few decades to reduce these contamination levels. This review paper focuses on the recent studies developed on groundwater pollutions, remediation practices, and groundwater quality management. PRACTITIONER POINTS: Groundwater pollution is mainly due to anthropogenic activities and it is considered as a growing water quality problem. Groundwater bioremediation is one of the sustainable long-term solutions that uses the microorganisms to degrade the complex environmental pollutants. Groundwater quality management techniques play a significant role to restore or maintain water quality, which is critical for the sustainable development.

An overview on heavy metal resistant microorganisms for simultaneous treatment of multiple chemical pollutants at co-contaminated sites, and their multipurpose application

Anthropogenic imbalance of chemical pollutants in environment raises serious threat to all life forms. Contaminated sites often possess multiple heavy metals and other types of pollutants. Elimination of chemical pollutants at co-contaminated sites is imperative for the safe ecosystem functions, and simultaneous removal approach is an attractive scheme for their remediation. Different conventional techniques have been applied as concomitant treatment solution but fall short at various parameters. In parallel, use of microorganisms offers an innovative, cost effective and ecofriendly approach for simultaneous treatment of various chemical pollutants. However, microbiostasis due to harmful effects of heavy metals or other contaminants is a serious bottleneck facing remediation practices in co-contaminated sites. But certain microorganisms have unique mechanisms to resist heavy metals, and can act on different noxious wastes. Considering this significant, my review provides information on different heavy metal resistant microorganisms for bioremediation of different chemical pollutants, and other assistance. In this favour, the integrated approach of simultaneous treatment of multiple heavy metals and other environmental contaminants using different heavy metal resistant microorganisms is summarized. Further, the discussion also intends toward the use of heavy metal resistant microorganisms associated with industrial and environmental applications, and healthcare. PREFACE: Simultaneous treatment of multiple chemical pollutants using microorganisms is relatively a new approach. Therefore, this subject was not well received for review before. Also, multipurpose application of heavy metal microorganisms has certainly not considered for review. In this regard, this review attempts to gather information on recent progress on studies on different heavy metal resistant microorganisms for their potential of treatment of co-contaminated sites, and multipurpose application.

Multilevel changes in bacterial properties on long-term exposure to hydrocarbons and impact of these cells on fresh-water communities

To handle the impact of habitat transformations, the microbial cells developed mechanisms aimed at adjustment of their biological processes in response to signals indicating environmental changes. One of the first changes in their properties is observed on their surface, which has direct contact with the dynamically varying surroundings. In this study, we present results of changes in the cell surface properties which may have a decisive impact on the xenobiotics' bioavailability and microbial cell survival. These changes influence their ability to remove xenobiotics by accelerating and empowering this process. Moreover, the application of microorganisms exposed for long-term to hydrocarbons in bioremediation processes might have positive impact on biodegradation of the latter in the natural environment as well as natural microbial community diversity. This study demonstrates a variety of microbial cell mechanisms of adaptation to long-term exposure to hydrocarbons and their potential as the bioremediation tools.

Performance and Kinetics of Bioaugmentation, Biostimulation, and Natural Attenuation Processes for Bioremediation of Crude Oil-Contaminated Soils

Bioremediation of contaminated sites is usually limited due to the inadequate availability of nutrients and microorganisms. This study was conducted to assess the impact of bioaugmentation (BA) and biostimulation (BS) on petroleum hydrocarbon degradation efficiency. In addition, treatment performance and kinetics of different remediation processes were investigated. For this purpose, four tanks containing oil-contaminated soils were tested. Tank 1 was operated as the natural attenuation process. Then, a microbial inoculum and nutrients were added to tank 2 to promote BA and BS. In tank 3, only the BA process was adopted, whereas in tank 4, only the BS process was adopted. After 63 days of operation, the total petroleum hydrocarbon (TPH) in tank 2 was reduced from 1674 to 430 mg/kg, with 74% reduction. Tank 1, tank 3, and tank 4 indicated TPH reductions of 35%, 41%, and 66%, respectively. Microbiological analysis of the inoculum indicated that Alcanivorax was the dominant bacterium. The population of TPH degrader bacteria in tank 2 soil was two orders of magnitude higher than in the control tank. Reaction rate data were fitted with a first-order reaction rate model. The Monod kinetic constants, maximum specific growth rate (µmax), and substrate concentration at half-velocity constant (Ks) were also estimated. This study showed that the TPH removal efficiency in the combined BA and BS process was higher than in other processes tested. The populations of TPH degrading microorganisms in soil tanks were positively related to TPH removal efficiency during bioremediation of petroleum-contaminated soils.

Application of alkyl polyglycosides for enhanced bioremediation of petroleum hydrocarbon-contaminated soil using Sphingomonas changbaiensis and Pseudomonas stutzeri

Bioremediation is considered a cost-effective and environmentally sound method for degradation of petroleum hydrocarbons in contaminated soils. This study investigated the effects of biosurfactant alkyl polyglycosides (APG) on enhanced biodegradation of petroleum hydrocarbon-contaminated soils using Sphingomonas changbaiensis and Pseudomonas stutzeri and explored the mechanism responsible for the enhanced petroleum hydrocarbon degradation. To accomplish this, the following treatments were evaluated: (1) bioaugmentation with Sphingomonas changbaiensis; (2) bioaugmentation with Pseudomonas stutzeri; (3) a combination of Sphingomonas changbaiensis and APG; and (4) a combination of Pseudomonas stutzeri and APG. The results showed that the degradation rates of total petroleum hydrocarbons (TPH) in contaminated soil samples bioaugmented with S. changbaiensis and P. stutzeri for 30 days were 39.2 ± 1.9% and 47.2 ± 1.2%, respectively. The addition of biosurfactant APG enhanced the bioremediation processes and improved the biodegradation rates. The biodegradation rate at 1.5 g/kg APG in soil samples bioaugmented with S. changbaiensis was 52.1 ± 2.0%, while the rate at 1.5 g/kg APG in soil samples bioaugmented with P. stutzeri was 59.0 ± 1.8%. The half-life decreased from 39.7 d to 24.5 d and from 29.6 to 20.1 d when the dosage of APG was 1.5 g/kg in contaminated soil samples bioaugmented with S. changbaiensis and P. stutzeri, respectively. Mechanism studies showed that the addition of APG can increase the TPH solubility, promote the sorption of TPH onto microbial cells and subsequent trans-membrane transport by APG-induced structural changes, stimulate microbial activities and participate in the co-metabolism. Therefore, the combination of bioaugmentation and APG is an effective method for remediation of petroleum hydrocarbon-contaminated soil.

Nutrient drip irrigation for refractory hydrocarbon removal and microbial community shift in a historically petroleum-contaminated soil

An adequate amount of nutrients is required to enable biodegradation of refractory hydrocarbons in petroleum-contaminated soil. In this study, a microcosm experiment was conducted using a drip fertigation method for petroleum-contaminated soil remediation. Nitrogen and phosphorus were homogeneously and periodically sprayed into a historically contaminated soil using a modified horticultural drip irrigation device. Various petroleum hydrocarbon fraction contents were then determined by gravimetry and gas chromatography (GC), and changes in the soil microbial community were analyzed by high throughput sequencing. After 90 days of remediation, the removal efficiencies of total petroleum hydrocarbon (TPH), saturates, aromatics, C7-C30 n-alkanes, and 16 PAHs were respectively enhanced by 21.5%, 25.5%, 12.4%, 10.4%, and 19.6% compared with the use of a single nutrient amendment application. The high throughput sequencing result showed that obvious changes had occurred in the soil microbial community compositions during drip fertigation; however, fungi were more sensitive to drip fertigation than bacteria. The resulting predominant bacterial and fungal genera were Dietzia, Nocardioides, Mycobacterium, Sphaerobacter, Leifsonia, and Aspergillus, Scolecobasidium, and Fusarium, respectively. Remediating polluted soils by regular fertigation ensures the automatic addition of even amounts of nutrients, which achieves high refractory hydrocarbon removal efficiencies. It is expected that this method can be applied in the in-situ remediation of petroleum-contaminated soil on a large scale.

Metabolic Exchange with Non-Alkane-Consuming Pseudomonas stutzeri SLG510A3-8 Improves n-Alkane Biodegradation by the Alkane Degrader Dietzia sp. Strain DQ12-45-1b

Biodegradation of alkanes by microbial communities is ubiquitous in nature. Interestingly, the microbial communities with high hydrocarbon-degrading performances are sometimes composed of not only hydrocarbon degraders but also nonconsumers, but the synergistic mechanisms remain unknown. Here, we found that two bacterial strains isolated from Chinese oil fields, Dietzia sp. strain DQ12-45-1b and Pseudomonas stutzeri SLG510A3-8, had a synergistic effect on hexadecane (C₁₆ compound) biodegradation, even though P. stutzeri could not utilize C₁₆ individually. To gain a better understanding of the roles of the alkane nonconsumer P. stutzeri in the C₁₆-degrading consortium, we reconstructed a two-species stoichiometric metabolic model, iBH1908, and integrated in silico prediction with the following in vitro validation, a comparative proteomics analysis, and extracellular metabolomic detection. Metabolic interactions between P. stutzeri and Dietzia sp. were successfully revealed to have importance in efficient C₁₆ degradation. In the process, P. stutzeri survived on C₁₆ metabolic intermediates from Dietzia sp., including hexadecanoate, 3-hydroxybutanoate, and α-ketoglutarate. In return, P. stutzeri reorganized its metabolic flux distribution to fed back acetate and glutamate to Dietzia sp. to enhance its C₁₆ degradation efficiency by improving Dietzia cell accumulation and by regulating the expression of Dietzia succinate dehydrogenase. By using the synergistic microbial consortium of Dietzia sp. and P. stutzeri with the addition of the in silico-predicted key exchanged metabolites, diesel oil was effectively disposed of in 15 days with a removal fraction of 85.54% ± 6.42%, leaving small amounts of C₁₅ to C₂₀ isomers. Our finding provides a novel microbial assembling mode for efficient bioremediation or chemical production in the future.IMPORTANCE Many natural and synthetic microbial communities are composed of not only species whose biological properties are consistent with their corresponding communities but also ones whose chemophysical characteristics do not directly contribute to the performance of their communities. Even though the latter species are often essential to the microbial communities, their roles are unclear. Here, by investigation of an artificial two-member microbial consortium in n-alkane biodegradation, we showed that the microbial member without the n-alkane-degrading capability had a cross-feeding interaction with and metabolic regulation to the leading member for the synergistic n-alkane biodegradation. Our study improves the current understanding of microbial interactions. Because "assistant" microbes showed importance in communities in addition to the functional microbes, our findings also suggest a useful "assistant-microbe" principle in the design of microbial communities for either bioremediation or chemical production.

Evaluation of accelerated biodegradation of oil-SPM aggregates (OSAs)

The studies of the formation of oil-Suspended Particulate Matter (SPM) aggregates (OSAs) have advanced significantly in the scientific community, however there is a need to accelerate oil biodegradation that was dispersed by the formation of OSAs. The present research presents a pioneering character regarding the addition of nutrients as biostimulus for autochthonous hydrocarboclastic bacteria in the biodegradation of Total Petroleum Hydrocarbons (TPH) dispersed by the formation of OSAs. Water aliquots were taken over 60 days from eight bioreactors to perform ionic species analysis, pH, salinity and temperature monitoring, liquid/liquid extraction, serial dilution methodology and filter membrane. TPH quantification was performed on the gas chromatograph with a flame ionisation detector (GC-FID). The addition of nutrients contributed positively to the rate and extent of biodegradation of TPH in association with field-collected SPM. The best result found was with the lowest nutrient concentration (Bio 1) with an average of 98.65% of TPH reduction.

Microbial Degradation of Hydrocarbons-Basic Principles for Bioremediation: A Review

Crude oil-derived hydrocarbons constitute the largest group of environmental pollutants worldwide. The number of reports concerning their toxicity and emphasizing the ultimate need to remove them from marine and soil environments confirms the unceasing interest of scientists in this field. Among the various techniques used for clean-up actions, bioremediation seems to be the most acceptable and economically justified. Analysis of recent reports regarding unsuccessful bioremediation attempts indicates that there is a need to highlight the fundamental aspects of hydrocarbon microbiology in a clear and concise manner. Therefore, in this review, we would like to elucidate some crucial, but often overlooked, factors. First, the formation of crude oil and abundance of naturally occurring hydrocarbons is presented and compared with bacterial ability to not only survive but also to utilize such compounds as an attractive energy source. Then, the significance of nutrient limitation on biomass growth is underlined on the example of a specially designed experiment and discussed in context of bioremediation efficiency. Next, the formation of aerobic and anaerobic conditions, as well as the role of surfactants for maintaining appropriate C:N:P ratio during initial stages of biodegradation is explained. Finally, a summary of recent scientific reports focused on the removal of hydrocarbon contaminants using bioaugmentation, biostimulation and introduction of surfactants, as well as biosurfactants, is presented. This review was designed to be a comprehensive source of knowledge regarding the unique aspects of hydrocarbon microbiology that may be useful for planning future biodegradation experiments. In addition, it is a starting point for wider debate regarding the limitations and possible improvements of currently employed bioremediation strategies.

Kinetics and Optimization by Response Surface Methodology of Aerobic Bioremediation. Geoelectrical Parameter Monitoring

This study aimed to investigate the kinetics of an aerobic bioremediation process of diesel oil removal by indigenous microorganisms, and to define the optimal operative conditions by means of response surface methodology. This was carried out by setting up a series of microcosms (200 g of soil), polluted with the same diesel oil concentration (70 g·kg−1 of soil), but with different water contents (u%) and carbon to nitrogen (C/N) ratios. The process was monitored by: (1) residual diesel oil concentration, to measure the removal efficiency, and (2) fluorescein production, to check the microbial activity. These two parameters were the objective variables used for the analysis of variance (ANOVA) and response surface methodology (RSM). The results allowed the interactions between u% and C/N to be defined and the optimal range to be adopted for each. The process kinetics was modeled with first- and second-order reaction rates; slightly better results were achieved for the second-order model in terms of parameter variability. Biological processes like degradation may have effects on dielectric properties of soil; an open-ended coaxial cable was used to measure the dielectric permittivity of microcosm matrices at the start and after 130 days of bioremediation. The evolution of the real and the imaginary components of dielectric permittivity provided results that supported the evidence of a biodegradation process in progress.

Kinetic modelling of total petroleum hydrocarbon in spent lubricating petroleum oil impacted soil under different treatments

The integration of first and second order kinetic model in parameter estimation for the degradation pattern of total petroleum hydrocarbon (TPH) in spent lubricating petroleum oil (SLPO) over a four-month period was the subject of the present investigation. Study design considered four treatment microcosms notably; sewage sludge (SB), monitored natural recovery (MNR), surfactant (SA) and control (SO). The rate of TPH degradation using sewage sludge as amendment material depicted effective TPH removal within ten weeks. A maximum allowable concentration of residual TPH (4300 mg kg^-1) was obtained through an amendment with sewage sludge. Degradation constant (k) produced by both first and second order rates significantly demonstrated the performance of sewage sludge biomass over the other three treatments applied, however, experimental data adequately fitted into the first order kinetics (k = 0.27 d^-1, t½ = 3.0 d). TPH removal efficiency of sewage sludge and detergent were 96.0% and 81.0% respectively. The use of sewage sludge biomass significantly (p < .05) improved soil biological characteristics and produced optimum dehydrogenase activity (DHA ≥ 8.8 TPFg^-1 d), germination index (%IG ≥ 88%), and chlorophyll content (chl ≥ 100 µg cm^-2), thus, recommended for field scale application in soil hydrocarbon pollution remediation.

Simultaneous Bioaugmentation and Biostimulation to Remediate Soil Contaminated by Ship Dismantling in Bangkalan District, Indonesia

BACKGROUND

High concentrations of total petroleum hydrocarbons (TPH), iron (Fe), and manganese (Mn) were identified in soil samples from two shipyards where vessel dismantling activities take place in Tanjungjati Village, Indonesia, and subjected to bioremediation.

OBJECTIVES

The aim of the present study was to determine whether the combination of surfactant solution, bioaugmentation (a consortium of Bacillus subtilis and Acinetobacter lwoffii), and biostimulation (nutrient amendment and aeration intermittent) would reduce TPH, Fe, and Mn levels from soil contaminated from ship dismantling activities.

METHODS

Iron and Mn bioavailability were examined according to the Indonesian technical guidelines for soil chemical analysis with the help of atomic absorption spectrophotometry. The n-hexane solvent soil was extracted using the ultrasonic water bath method for TPH analysis.

RESULTS

The highest removal results achieved were TPH (69.62%), Fe (87.10%), and Mn (29%) for Soil 1 samples and elimination of TPH (28.80%), Fe (65.10%), and Mn (57.38%) for Soil 2 samples using a combination of surfactant solution, bioaugmentation, and biostimulation (nutrient amendment and without aeration intermittent). Iron and Mn removal in the controls was higher than in the treated soils, which showed that Fe and Mn could decrease naturally in both contaminated soils.

CONCLUSIONS

The present study showed that bioremediation using a combination of surfactant solution, a consortium of Bacillus subtilis, and Acinetobacter lwoffii, as well as a nutrient amendment, has the potential to degrade hydrocarbons in contaminated soil. Furthermore, Bacillus subtilis and Acinetobacter lwoffii consortium used for bioaugmentation have the potential to enhance the degradation of hydrocarbons in soil.

COMPETING INTERESTS

The authors declare no competing financial interests.