Prepared Bed Land Treatment of Soils Containing Diesel and Crude Oil Hydrocarbons

An ex situ, field-scale, prepared bed land treatment unit (LTU) was used to bio-remediate soils containing petroleum hydrocarbons. Two soils were treated in side-by-side units to compare performance: (1) a clayey silt containing crude oil hydrocarbons from releases 30 to 40 years ago and (2) a silty sand containing diesel fuel hydrocarbons from a leak about three years prior to the bioremediation. The effectiveness of the bioremediation in the LTU was evaluated over a period of 18 months. The results indicated that: (1) prepared bed bioremediation reduced the hydrocarbon concentration, mobility, and relative toxicity in the soil with the diesel fuel, and (2) chemical bioavailability appeared to limit bioremediation of the soil containing the crude oil hydrocarbons. Although the soils containing the crude oil hydrocarbons contained an average of 10,000?mg TPH/kg dry soil, these soils had limited hydrocarbon availability, nontoxic conditions, and low potential for chemical migration. For the soils containing the diesel fuel, active prepared bed bioremediation of about 15 weeks was adequate to reach an environmentally acceptable endpoint. At that time, there was little further TPH loss, no Microtox^TM toxicity, and limited hydrocarbon mobility.     

Importance of soil-water relations in assessing the endpoint of bioremediated soils

This study was conducted to investigate water movement in hydrocarbon contaminated soils. Three soils were studied, a hydrocarbon contaminated soil, the same soil after 3 years of bioremediation, and a control soil from the same site. There was a critical soil water content around 18% (bioremediated soil) and 20% (contaminated soil), above which the sorptivity of the contaminated soil was near that of the control soil. For soils with water contents below this value, there was a strong divergence in sorptivity between contaminated and control or bioremediated soils. Results suggest that water availability in contaminated soils will be highly dependent on soil water properties as water potential approaches the permanent wilting point (-1.5 MPa matrix potential).Infiltration of water into air dry (2% m.c. w/w) hydrocarbon contaminated soils was up to three orders of magnitude slower than for the control soil. For air dried soils, the infiltration rate of the contaminated and bioremediated soils was constant with time. This was in contrast to the control soil where infiltration rate was a function of the reciprocal of the square root of time.     

Laboratory study on the bioremediation of petrochemical sludge-contaminated soil

This study evaluated by biological and chemical analyses the effectiveness of bioremediation of sludge from the petrochemical industry in systems containing artificially contaminated soil. The sludge–soil systems were prepared with three different initial concentrations of sludge, and during bioremediation 86–95% of the hydrocarbons was eliminated. Simultaneously, soil bacterial populations and inhibition of seed germination by aqueous extracts increased in all sludge–soil systems during the first 180 days of treatment. After 1 year of bioremediation, a loss in the catabolic capacity of the Gram-negative bacterial population was observed, but was not dependent on the initial sludge concentration. Furthermore, residual levels of hydrocarbons and seed germination inhibitory effect decreased sharply, but some level of toxicity remained in the systems containing the highest initial sludge concentration. Independent of the initial sludge concentration, the contaminated soils did not re-establish their original features even when residual hydrocarbon concentrations suggested the end of the process.     

Strong Impact on the Polycyclic Aromatic Hydrocarbon (PAH)-Degrading Community of a PAH-Polluted Soil but Marginal Effect on PAH Degradation when Priming with Bioremediated Soil Dominated by Mycobacteria

Bioaugmentation of soil polluted with polycyclic aromatic hydrocarbons (PAHs) is often disappointing because of the low survival rate and low activity of the introduced degrader bacteria. We therefore investigated the possibility of priming PAH degradation in soil by adding 2% of bioremediated soil with a high capacity for PAH degradation. The culturable PAH-degrading community of the bioremediated primer soil was dominated by Mycobacterium spp. A microcosm containing pristine soil artificially polluted with PAHs and primed with bioremediated soil showed a fast, 100- to 1,000-fold increase in numbers of culturable phenanthrene-, pyrene-, and fluoranthene degraders and a 160-fold increase in copy numbers of the mycobacterial PAH dioxygenase gene pdo1. A nonpolluted microcosm primed with bioremediated soil showed a high rate of survival of the introduced degrader community during the 112 days of incubation. A nonprimed control microcosm containing pristine soil artificially polluted with PAHs showed only small increases in the numbers of culturable PAH degraders and no pdo1 genes. Initial PAH degradation rates were highest in the primed microcosm, but later, the degradation rates were comparable in primed and nonprimed soil. Thus, the proliferation and persistence of the introduced, soil-adapted degraders had only a marginal effect on PAH degradation. Given the small effect of priming with bioremediated soil and the likely presence of PAH degraders in almost all PAH-contaminated soils, it seems questionable to prime PAH-contaminated soil with bioremediated soil as a means of large-scale soil bioremediation.     

Microbe-aliphatic hydrocarbon interactions in soil: implications for biodegradation and bioremediation

Aliphatic hydrocarbons make up a substantial portion of organic contamination in the terrestrial environment. However, most studies have focussed on the fate and behaviour of aromatic contaminants in soil. Despite structural differences between aromatic and aliphatic hydrocarbons, both classes of contaminants are subject to physicochemical processes, which can affect the degree of loss, sequestration and interaction with soil microflora. Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe-contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight mechanisms controlling their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil.     

Strong impact on the polycyclic aromatic hydrocarbon (PAH)-degrading community of a PAH-polluted soil but marginal effect on PAH degradation when priming with bioremediated soil dominated by mycobacteria

Bioaugmentation of soil polluted with polycyclic aromatic hydrocarbons (PAHs) is often disappointing because of the low survival rate and low activity of the introduced degrader bacteria. We therefore investigated the possibility of priming PAH degradation in soil by adding 2% of bioremediated soil with a high capacity for PAH degradation. The culturable PAH-degrading community of the bioremediated primer soil was dominated by Mycobacterium spp. A microcosm containing pristine soil artificially polluted with PAHs and primed with bioremediated soil showed a fast, 100- to 1,000-fold increase in numbers of culturable phenanthrene-, pyrene-, and fluoranthene degraders and a 160-fold increase in copy numbers of the mycobacterial PAH dioxygenase gene pdo1. A nonpolluted microcosm primed with bioremediated soil showed a high rate of survival of the introduced degrader community during the 112 days of incubation. A nonprimed control microcosm containing pristine soil artificially polluted with PAHs showed only small increases in the numbers of culturable PAH degraders and no pdo1 genes. Initial PAH degradation rates were highest in the primed microcosm, but later, the degradation rates were comparable in primed and nonprimed soil. Thus, the proliferation and persistence of the introduced, soil-adapted degraders had only a marginal effect on PAH degradation. Given the small effect of priming with bioremediated soil and the likely presence of PAH degraders in almost all PAH-contaminated soils, it seems questionable to prime PAH-contaminated soil with bioremediated soil as a means of large-scale soil bioremediation.     

Effects of Bacillus subtilis O9 biosurfactant on the bioremediation of crude oil-polluted soils

The application of a surfactant from Bacillus subtilis O9 (Bs) on the bioremediation of soils polluted with crude oil was assayed in soil microcosms under laboratory conditions. Three concentrations of biosurfactant were assayed (1.9, 19.5, and 39 mg kg(-1) soil). Microcosms without biosurfactant were prepared as controls. During the experiment, the crude oil-degrading bacterial population, the aliphatic and aromatic hydrocarbons were monitored in each microcosm. The results indicated that applying Bs did not negatively affect the hydrocarbon-degrading microbial population Concentrations of 19 and 19.5mg (Bs) per kilogram of soil stimulated the growth of the population involved in the crude oil degradation, and accelerated the biodegradation of the aliphatic hydrocarbons. However, none of the assayed Bs concentrations stimulated aromatic hydrocarbon degradation.     

Characterisation of biodegradation capacities of environmental microflorae for diesel oil by comprehensive two-dimensional gas chromatography

In contaminated soils, efficiency of natural attenuation or engineered bioremediation largely depends on biodegradation capacities of the local microflorae. In the present study, the biodegradation capacities of various microflorae towards diesel oil were determined in laboratory conditions. Microflorae were collected from 9 contaminated and 10 uncontaminated soil samples and were compared to urban wastewater activated sludge. The recalcitrance of hydrocarbons in tests was characterised using both gas chromatography (GC) and comprehensive two-dimensional gas chromatography (GC×GC). The microflorae from contaminated soils were found to exhibit higher degradation capacities than those from uncontaminated soil and activated sludge. In cultures inoculated by contaminated-soil microflorae, 80% of diesel oil on an average was consumed over 4-week incubation compared to only 64% in uncontaminated soil and 60% in activated sludge cultures. As shown by GC, n-alkanes of diesel oil were totally utilised by each microflora but differentiated degradation extents were observed for cyclic and branched hydrocarbons. The enhanced degradation capacities of impacted-soil microflorae resulted probably from an adaptation to the hydrocarbon contaminants but a similar adaptation was noted in uncontaminated soils when conifer trees might have released natural hydrocarbons. GC×GC showed that a contaminated-soil microflora removed all aromatics and all branched alkanes containing less than C₁₅. The most recalcitrant compounds were the branched and cyclic alkanes with 15–23 atoms of carbon.     

Incomplete Hydrocarbon Biodegradation in Contaminated Soils: Limitations in Bioavailability or Inherent Recalcitrance?

Bioremediation has been used to treat soils contaminated with complex mixtures of organic compounds such as total petroleum hydrocarbons (TPH), oil and grease (O&G), or polycyclic aromatic hydrocarbons (PAHs). Despite the common use and cost-effectiveness of bioremediation for treating hydrocarbon-contaminated soils, it has been observed that a residual fraction remains undegraded in the soil even when optimal biodegradation conditions have been provided. This paper provides a brief review of the two major conceptual models that have been used to explain why a residual hydrocarbon fraction remains in the soil after bioremediation treatment. The contaminant sequestration model is based on the assumption that a certain fraction of hydrocarbons is “locked up” in small soil pores within soil particles or aggregates. These sorbed hydrocarbons are believed to be inaccessible to soil microorganisms. Consequently, limitations in bioavailability are thought to be the major reason for incomplete hydrocarbon biodegradation, particularly in aged or weathered soils. Alternatively, according to the inherent recalcitrance model, incomplete TPH biodegradation may be caused by the presence of certain hydrocarbons that are inherently recalcitrant to biodegradation or are only extremely slowly degradable even under optimal conditions. Each conceptual model provides different explanations regarding the potential risks of the residual hydrocarbon fraction. If the residual TPH is truly sequestered within the soil pore space, it is unlikely that these compounds will pose any significant risk to human or environmental receptors. By contrast, these risks may be considerably greater if the residual TPH fraction consists of inherently recalcitrant compounds that reside mostly on the surface of soil particles and therefore are much more available to potential receptors. Both conceptual models and their implications for the potential risk of the residual TPH fraction are discussed.     

Soil lipase activity – a useful indicator of oil biodegradation

The evaluation of soil lipase activity as a tool to monitor the decontamination of a freshly oil-polluted soil was tested in a laboratory study. An arable soil was experimentally contaminated with diesel oil at 5 mg hydrocarbons g^–1 soil dry weight and incubated with and without fertilization (N-P-K) for 116 days at 20°C. Lipase activity and counts of oil-degrading microorganisms were measured at regular time intervals, and the correlations with the levels of hydrocarbon concentrations in soil were investigated. The residual soil hydrocarbon concentration correlated significantly negatively with soil lipase activity and with the number of oil-degrading microorganisms, independent of fertilization. The induction of soil lipase activity is a valuable indicator of oil biodegradation in naturally attenuated (unfertilized) and bioremediated (fertilized) soils.     

Bioremediation of oil-polluted soils: Using the [13C]/[12C] ratio to characterize microbial products of oil hydrocarbon biodegradation

We compared data on the extent of bioremediation in soils polluted with oil. The data were obtained using conventional methods of hydrocarbon determination: extraction gas chromatography-mass spectrometry, extraction IR spectroscopy, and extraction gravimetry. Due to differences in the relative abundances of the stable carbon isotopes (¹³C/¹²C) in oil and in soil organic matter, these ratios could be used as natural isotopic labels of either substance. Extraction gravimetry in combination with characteristics of the carbon isotope composition of organic products in the soil before and after bioremediation was shown to be the most informative approach to an evaluation of soil bioremediation. At present, it is the only method enabling quantification of the total petroleum hydrocarbons in oil-polluted soil, as well as of the amounts of hydrocarbons remaining after bioremediation and those microbially transformed into organic products and biomass.     

Relationship between soil microbial diversity and bioremediation process at an oil refinery

Microbial diversity in hydrocarbon-contaminated soil was characterized during a bioremediation project at an oil refinery. The project consisted of isolation and cultivation of microbes on laboratory media and the subsequent characterization of pure isolates. In a lagoon at the Czechowice Oil Refinery, Poland, a biopile with actively and passively aerated sections was constructed and has been operated since 1997. The bioremediation process has been continuously monitored by physical, chemical, and microbiological methods. One hundred and forty nine bacterial and fungal strains were isolated from site soils by standard procedures. Analysis of cultivable microorganisms revealed a diverse microbial population within the cultured isolates. Among isolated strains, Pseudomonas and Chryseomonas genera predominated in the bacterial population while Candida, Fusarium, and Trichophyton dominated the fungal population. This paper describes the application of traditional microbiological methods (plating and microscopic methods) to evaluate cultivable microbial diversity in bioremediated soil.     

不同类型原油污染土壤生物修复技术研究

对不同类型原油污染土壤在实用规模的预制床上采用堆制技术进行生物修复 .通过投加肥料、菌剂、控制水分和pH ,可使微生物获得较好的生态环境 .当稀油、高凝油、特稠油和稠油污染的土壤中原油总量为 2 5 .8～ 77.2 g·kg-1土时 ,经过近 2个月的运行 ,石油总量的去除率可达 38.37%～ 5 6 .74 % .石油中芳烃、沥青和胶质混合物是制约石油快速降解的主要因素 .在处理过程中筛选出石油降解的优势菌株 ,其中有 6株真菌、6株细菌和 1株放线菌 .研究结果为石油污染土壤异位生物修复技术实用化提供了理论依据 .     

Bacterial Community Dynamics during Bioremediation of Diesel Oil-Contaminated Antarctic Soil

The effect of nutrient and inocula amendment in a bioremediation field trial using a nutrient-poor Antarctic soil chronically contaminated with hydrocarbons was tested. The analysis of the effects that the treatments caused in bacterial numbers and hydrocarbon removal was combined with the elucidation of the changes occurring on the bacterial community, by 16S rDNA-based terminal restriction fragment length polymorphism (T-RFLP) typing, and the detection of some of the genes involved in the catabolism of hydrocarbons. All treatments caused a significant increase in the number of bacteria able to grow on hydrocarbons and a significant decrease in the soil hydrocarbon content, as compared to the control. However, there were no significant differences between treatments. Comparison of the soil T-RFLP profiles indicated that there were changes in the structure and composition of bacterial communities during the bioremediation trial, although the communities in treated plots were highly similar irrespective of the treatment applied, and they had a similar temporal dynamics. These results showed that nutrient addition was the main factor contributing to the outcome of the bioremediation experiment. This was supported by the lack of evidence of the establishment of inoculated consortia in soils, since their characteristic electrophoretic peaks were only detectable in soil profiles at the beginning of the experiment. Genetic potential for naphthalene degradation, evidenced by detection of nahAc gene, was observed in all soil plots including the control. In treated plots, an increase in the detection of catechol degradation genes (nahH and catA) and in a key gene of denitrification (nosZ) was observed as well. These results indicate that treatments favored the degradation of aromatic hydrocarbons and probably stimulated denitrification, at least transiently. This mesocosm study shows that recovery of chronically contaminated Antarctic soils can be successfully accelerated using biostimulation with nutrients, and that this causes a change in the indigenous bacterial communities and in the genetic potential for hydrocarbon degradation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Bioremediation of Pb-contaminated soil based on microbially induced calcite precipitation

To remediate lead (Pb)-contaminated soils, it is proposed that microbially induced calcite precipitation (MICP) would provide the best alternative to other remediation technologies. In this study, Pb bioremediation in soils was investigated using the calcite-precipitating bacterium Kocuria flava. Results indicate that the Pb is primarily associated with the carbonate fraction in bioremediated soil samples. The bioavailability of Pb in contaminated soil was reduced so that the potential stress of Pb was alleviated. This research provides insight into the geochemistry occurring in the MICP-based Pb-remediated soils, which will help in remediation decisions.     

Biodegradation of Aliphatic vs. Aromatic Hydrocarbons in Fertilized Arctic Soils

The objectives of this study were to (1) test a simple bioremediation treatment strategy in the Arctic and (2) examine the effect of fertilization on the degradation of aliphatic and aromatic hydrocarbons. The site is a coarse sand pad that once supported fuel storage tanks. Concentrations of diesel-range organics at the beginning of the study (July 1996) ranged from 250 to 860 mg/kg soil. Replicate field plots treated with fertilizer yielded final concentrations of 0, 50, 100, or 200 mg N/kg soil. Soil samples were collected three times during the thaw season and analyzed for physical and chemical properties, microbial populations and activities, and concentrations of semivolatile hydrocarbons. Soil pH and soil-water potentials declined as a result of fertilizer application. Addition of fertilizer significantly increased soil respiration potentials, but not the populations of microorganisms measured. Fertilizer addition also resulted in ∼50% loss of measured aliphatic and aromatic hydrocarbons in surface and subsurface soils. For fertilized plots, hydrocarbon loss was not related to the amount of fertilizer added. Losses of aliphatic hydrocarbons were attributed to biotic processes, whereas losses of aromatic hydrocarbons likely were a result of both biotic and abiotic processes.     

Release of Chemicals from Contaminated Soils

At sites that contain contaminated soils, there can be questions about the magnitude of risk posed by the chemicals in the soils and about the cleanup levels that should be achieved. Knowledge about the rate of release of chemicals is important to answers to such questions. This article: (1) describes a laboratory protocol to obtain rate of release information for chemicals in soils, and (2) provides estimates of the rate of release of individual polyaromatic hydrocarbon (PAH) compounds from several manufactured gas plant (MGP) site soils. The data were analyzed using an empirical two-site model. Different fractions of PAH were released rapidly from these soils. For one soil, this fraction was less than 20%, for others, the fraction ranged from 36 to 85%. The first-order rate constant (k2) of PAH released during the slow phase of chemical release ranged from 0.0001 to 0.01 per hour.     

Germination and development of Mimosa pilulifera in petroleum-contaminated soil and bioremediated soil

In 2000 there was an oil spill at the Getúlio Vargas Refinery (REPAR/PETROBRÁS) in Paraná, Brazil. Nearly five years after contamination and the use of bioremediation, a study was carried out to identify the effects of the contaminated soil and the bioremediated soil on the germination and initial growth of Mimosa pilulifera seedlings. The experiment consisted of three treatments: petroleum-contaminated soil, bioremediated soil and uncontaminated soil, with five repetitions each. The following measurements were taken after 30, 60 and 90 days of planting: the percentage of germination, biomass and leaf area of the eophylls, biomass and length of the shoot and the roots in addition to the shoot/root ratio. The percentage of germination and the root biomass were not affected by the contaminated soil or by the bioremediated soil. On both the contaminated soil and the bioremediated soil biomass and leaf area of the eophyll were reduced. Plant length and shoot biomass were lower in the contaminated soil. Furthermore, the effect of the contaminated soil and the bioremediated soil was greater in the shoot than in the root system, since the bioremediation reduced the toxicity of the petroleum-contaminated soil.     

Effects of diurnal temperature variation on microbial community and petroleum hydrocarbon biodegradation in contaminated soils from a sub‐Arctic site

Contaminated soils are subject to diurnal and seasonal temperature variations during on‐site ex‐situ bioremediation processes. We assessed how diurnal temperature variations similar to that in summer at the site from which petroleum hydrocarbon‐contaminated soil was collected affect the soil microbial community and the extent of biodegradation of petroleum hydrocarbons compared with constant temperature regimes. Microbial community analyses for 16S rRNA and alkB genes by pyrosequencing indicated that the microbial community for soils incubated under diurnal temperature variation from 5°C to 15°C (VART5‐15) evolved similarly to that for soils incubated at constant temperature of 15°C (CST15). In contrast, under a constant temperature of 5°C (CST5), the community evolved significantly different. The extent of biodegradation of C10–C16 hydrocarbons in the VART5‐15 systems was 48%, comparable with the 41% biodegradation in CST15 systems, but significantly higher than CST5 systems at 11%. The enrichment of Gammaproteobacteria was observed in the alkB gene‐harbouring communities in VART5‐15 and CST15 but not in CST5 systems. However, the Actinobacteria was abundant at all temperature regimes. The results suggest that changes in microbial community composition as a result of diurnal temperature variations can significantly influence petroleum hydrocarbon bioremediation performance in cold regions.