Degradation Rates for Petroleum Hydrocarbons Undergoing Bioventing at the Meso-Scale

ABSTRACT

Bioventing can be effective for the remediation of soil contaminated with petroleum hydrocarbons. However, implementing laboratory results in field scenarios is difficult due to the lack of scale-up factors. Accordingly, laboratory bioventing experiments were undertaken at the meso-scale and then compared with previously completed micro-scale tests to evaluate the important scale-up factor. The developed meso-scale system holds 4 kg of soil, with bioventing conditions controlled from a nutrient, airflow, and water content perspective. Three soils were tested, and categorized as loamy sand, silt loam, and a mixture. Results over a 30-day period showed a two-stage degradation pattern that encompassed first-order degradation rates as compared with the single-stage first-order degradation rate determined in the micro-scale study. For the first stage (0–8 days), the degradation rate for loamy soil was 0.598 day^?1, with the silty soil at 0.460 day^?1, and mixed soil at 0.477 day^?1. After 8 days, the degradation rate constant for the loamy soil dropped to 0.123 day^?1, with the silty soil dropping to 0.075 day^?1, and the degradation rate for the mixed soil dropping to 0.093 day^?1. Comparison of the measured degradation rate values with the results from the micro-scale experiments gave scale-up factors varying from 1.9 to 2.7 for the types of soil considered in the current study. These differences in degradation rates between the two scales show the importance of scale-up factors when transferring feasibility study results to the field.     

Assessing mineralization rates of petroleum hydrocarbons in soils in relation to environmental factors and experimental scale

Mineralization rates of non-volatile petroleum hydrocarbons (HCs) in five different oil-contaminated soils with initial HC contents ranging from 0.1 to 13 g kg^-1 are estimated as a function of environmental factors. The aim of the study is threefold, (i) to study the relevance of environmental factors that may influence the mineralization rate, (ii) to compare mineralization rates estimated in two experiments at different scales, after standardizing them to environmental reference conditions, (iii) to evaluate the CO₂ production rate as a measure for the mineralization rate of HCs. Experiments were performed at laboratory scale (30–50 cm³ soil volume) in closed-jars under constant environmental conditions and in lysimeters (0.81 m³ soil volume) under dynamic climatic and hydrological conditions. A biodegradation model, coupled to transport models for soil heat, water, and gas dynamics is employed for data interpretation. The transport models are used to simulate the environmental conditions that influence the mineralization rate in the non-steady lysimeter experiments. The results show that temperature, O₂ concentration and HC content have an effect on the mineralization rates. Water content could not be identified as a direct governing environmental factor. However, an indirect effect of water content is that it influences the effective gas diffusion coefficient in soils. The CO₂ production rate seems to be a good quantity to express the mineralization rate of HCs for HC contents>1 g kg^-1. Measured CO₂ production rates standardized to reference conditions are similar for the two different experimental scales. This demonstrates that the usage of biodegradation rates obtained in the laboratory to predict the biodegradation rates under field conditions is sound, as long as the differences in environmental conditions have been taken into account.     

Bioremediation and phytoremediation of total petroleum hydrocarbons (TPH) under various conditions

Remediation of contaminated soils is often studied using fine-textured soils rather than low-fertility sandy soils, and few studies focus on recontamination events. This study compared aerobic and anaerobic treatments for remediation of freshly introduced used motor oil on a sandy soil previously phytoremediated and bioacclimated (microorganisms already adapted in the soil environment) with some residual total petroleum hydrocarbon (TPH) contamination. Vegetated and unvegetated conditions to remediate anthropogenic fill containing residual TPH that was spiked with nonaqueous phase liquids (NAPLs) were evaluated in a 90-day greenhouse pot study. Vegetated treatments used switchgrass (Panicum virgatum). The concentration of aerobic bacteria were orders of magnitude higher in vegetated treatments compared to unvegetated. Nevertheless, final TPH concentrations were low in all saturated soil treatments, and high in the presence of switchgrass. Concentrations were also low in unvegetated pots with fertilizer. Acclimated indigenous microbial communities were shown to be more effective in breaking down hydrocarbons than introducing microbes from the addition of plant treatments in sandy soils. Remediation of fresh introduced NAPLs on pre-phytoremediated and bioacclimated soil was most efficient in saturated, anaerobic environments, probably due to the already pre-established microbial associations, easily bioavailable contaminants, and optimized soil conditions for microbial establishment and survival.     

A Correlation to Estimate the Bioventing Degradation Rate Constant

Estimating the biodegradation rate is essential when designing a bioremediation strategy for petroleum-contaminated sites, and when evaluating assessment guidelines. However, estimating the biodegradation rate is difficult as the rate constant varies from site to site due to changing site conditions, which include soil type, biological activity, and type of contaminant. Accordingly, bench-scale biodegradation studies were completed using respirometers to measure first-order biodegradation rate constants for gasoline in several soils over 30 days of incubation. A total of seven soils were tested at various gasoline concentrations with constant nutrient ratios and water content. No microbial inhibition was observed for the range of gasoline concentrations studied. Analysis showed that the statistically significant parameters were the initial population of petroleum-degrading microorganisms and the organic matter content. The developed empirical correlation is a simple tool that practioners can use to estimate the biodegradation rate without conducting lengthy and expensive experiments.     

Enhancing the biodegradation of total petroleum hydrocarbons in oily sludge by a modified bioaugmentation strategy

The effect of successive inoculation with hydrocarbon-degrading bacteria on the dynamics of petroleum hydrocarbons degradation in soil was investigated in this study. Oily sludge was used as a source of mixed hydrocarbons pollutant. Two bacterial consortia composed of alkanes and polycyclic aromatic hydrocarbon degraders were constructed from bacteria isolated from soil and oily sludge. These consortia were applied to incubated microcosms either in one dose at the onset of the incubation or in two doses at the beginning and at day 62 of the incubation period, which lasted for 198 days. During this period, carbon mineralization was evaluated by respirometry while total petroleum hydrocarbons and its fractions were gravimetrically evaluated by extraction from soil and fractionation. Dosing the bacterial consortia resulted in more than 30% increase in the overall removal of total petroleum hydrocarbons from soil. While alkane removal was only slightly improved, aromatic and asphaltic hydrocarbon fraction removal was significantly enhanced by the addition of the second consortium. Polar compounds (resins) were enriched only as a result of aromatics and asphaltene utilization. Nonetheless, their concentration declined back to the original level by the end of the incubation period.     

Degradation of straight-chain aliphatic and high-molecular-weight polycyclic aromatic hydrocarbons by a strain of Mycobacterium austroafricanum

AIMS: Our goal was to characterize a newly isolated strain of Mycobacterium austroafricanum, obtained from manufactured gas plant (MGP) site soil and designated GTI-23, with respect to its ability to degrade polycyclic aromatic hydrocarbons (PAHs). METHODS AND RESULTS: GTI-23 is capable of growth on phenanthrene, fluoranthene, or pyrene as a sole source of carbon and energy; it also extensively mineralizes the latter two in liquid culture and is capable of extensive degradation of fluorene and benzo[a]pyrene, although this does not lead in either of these cases to mineralization. Supplementation of benzo[a]pyrene-containing cultures with phenanthrene had no significant effect on benzo[a]pyrene degradation; however, this process was substantially inhibited by the addition of pyrene. Extensive and rapid mineralization of pyrene by GTI-23 was also observed in pyrene-amended soil. CONCLUSIONS: Strain GTI-23 shows considerable ability to mineralize a range of polycyclic aromatic hydrocarbons, both in liquid and soil environments. In this regard, GTI-23 differs markedly from the type strain of Myco. austroafricanum (ATCC 33464); the latter isolate displayed no (or very limited) mineralization of any tested PAH (phenanthrene, fluoranthene or pyrene). When grown in liquid culture, GTI-23 was also found to be capable of growing on and mineralizing two aliphatic hydrocarbons (dodecane and hexadecane). SIGNIFICANCE AND IMPACT OF THE STUDY: These findings indicate that this isolate of Myco. austroafricanum may be useful for bioremediation of soils contaminated with complex mixtures of aromatic and aliphatic hydrocarbons.     

Establishing Correlations and Scale-Up Factor for Estimating the Petroleum Biodegradation Rate in Soil

The proper design of a bioremediation strategy for petroleum-contaminated sites requires a reasonable estimate of the biodegradation rate constant, which is not easy due to spatial heterogeneity. Accordingly, predictive models were developed by completing a bioventing study at the meso-scale. Reactors holding 4 kg of disturbed soil were tested using five different types of soils. Using statistical analysis, a two-stage process was observed, with a fast rate of hydrocarbon degradation in the first 8 days and a slower rate in the remaining 22 days. Review of the correlations showed that the initial population of petroleum-degrading bacteria and increasing silt content had a positive effect on the degradation. A negative impact on the degradation rate was seen by increasing the fraction of organic matter and clay content. Comparison of previously completed micro-scale and meso-scale degradation rates gave a scale-up factor (SF) of 1.8 ± 0.5. Soils with an increased sand fraction had slightly higher SF values, whereas soils high in organic matter content had lower SF values. The measured SF values and developed correlations will help practitioners with site closure decisions, indicating the need for additional SF work to allow better transfer of meso-scale data to the field.     

多环芳烃污染土壤生物修复研究进展

多环芳烃 (Polycyclic aromatic hydrocarbons,PAHs) 是一类广泛分布于环境中的持久性污染物,结构稳定、难以降解,对生态环境和生物具有“三致”毒害性,其环境去除和修复备受关注。绿色、安全、经济的生物修复技术被广泛应用于PAHs污染土壤的修复。本文从土壤中PAHs的来源、迁移、归趋和污染水平总结了目前我国土壤多环芳烃污染的基本状况;归纳了具有PAHs降解作用的微生物、植物种类及机理;比较了微生物修复、植物修复和联合修复3类主要的生物修复技术。指出植物与微生物的互作机理的解析,抗逆菌株、植株的筛选与培育,实际应用的安全和效能评估应成为多环芳烃污染土壤修复领域未来的研究方向。     

Effect of salinity on the bioremediation of petroleum hydrocarbons in a saline-alkaline soil

Aims: The aim of this paper is to check the effect of salinity on the bioremediation process of petroleum hydrocarbons in the saline‐alkaline soil. Methods and Results: In this study, soil salinity was adjusted to different levels by water leaching method and the bioremediation process was conducted for 28 days. Soil pH increased after leaching and decreased during bioremediation process. At initial time, moderate salinity enhanced the biodegradation and addition of microbial consortium was not effective in enhancing degradation rate of petroleum hydrocarbons. At day of 28 days, higher degradation rate was found in treatments with more leaching times with a maximum value of 42·36%. Dehydrogenase activity increased with the progress of bioremediation and positive correlation was found between dehydrogenase activity and degradation rate of petroleum hydrocarbons. Denaturing gradient gel electrophoresis analysis result showed decreased microbial community diversity with increased salt content. Conclusions: The result suggested that salinity had great impact on bioremediation, and leaching and addition of inoculated consortium were effective in enhancing biodegradation of petroleum hydrocarbons in the saline‐alkaline soil. Significance and Impact of the Study: The result of this study is important for understanding the bioremediation process of petroleum in contaminated soil. New remediation method of petroleum contaminated soil can be developed based on this study.     

Effect of scale-up and seasonal variation on biokinetics in the enhanced bioremediation of petroleum hydrocarbon-contaminated soil

The biodegradation rate of petroleum hydrocarbon-contaminated soil was evaluated by the effect of temperature variation through bioaugmentation and biostimulation. In this study, biokinetics of batch-, pilot-, and field-scale biodegradation were performed by the optimization of enhanced biodegradation, minimizing the inhibitory effects of seasonal variations such as the rainy and cold winter seasons. From the relationship between remedial timescale and initial concentration, the biokinetic isolines of the biodegradation were smaller in the winter than those in the other seasons. The scale-up of biodegradation process led to enhance its activation energy, and then the field-scale remedial action should be performed in the way to lower the activation energy from the chemical diffusion and microbial activation. Therefore, a remedial or field worker can obtain the remedial timescale from the given apparent data of biokinetics with respect to initial TPH concentration only after the simple remedial investigation.     

In situ bioremediation of hydrocarbon in soil

Laboratory and field experiments were carried out for bioremediation of soils contaminated by fuel oil and motor oil. Bioventing was combined with the application of selected bacteria and dissolved nutrients. In the field experiments, soil gas was evacuated by air pumps from the permeable boreholes. The process was followed by both soil and gas analysis. Biodegradation of oil contamination and the microbial activity was measured by the oil and cell concentration in the soil. In 2 months, the oil content decreased considerably, and the cell number increased by one order of magnitude or more. The evacuated gas was tested for CO₂, O₂ and volatilized hydrocarbon content. The CO₂ level proves the presence of biodegradation: a permanent high value about ten times higher than normal, could be measured for 2 months, followed by a slow decrease in the third month. Volatilized hydrocarbon content was the highest in the first 2 d. After a continuous decrease, it dropped under the threshold of measurability for the third month. Selective biodegradation of hydrocarbon mixtures (oily wastes) was investigated as well: gas Chromatographic oil analysis showed the changes in the oil composition. The appropriate microflora was working in an ideal commensalism, and as a result, all of the hydrocarbon components were degraded nearly to the same extent.     

一株高浓度多环芳烃降解菌的鉴定和降解特性

采用选择性富集培养方法,从沈抚灌区土壤中分离得到多环芳烃(PAHs)高效降解菌NI2,应用此降解菌制备固定化菌剂,修复焦化厂内高浓度PAHs污染土壤,并通过生理生化和16S rDNA测序进行微生物鉴定.经过30 d的降解实验,菌N12对污染土壤中各PAH的去除率＞66％,总去除率为80％.生理生化和16S rDNA测序分析表明,分离得到的菌株N12为分支杆菌属(Mycobacterium sp.),该菌具有与其他分枝杆菌同源的双加氧酶基因nidA和pdoA2.结果表明,从土壤中筛选获得的分枝杆菌可以修复高浓度PAHs污染工业土壤.     

Evaluation of Soil Vapor Extraction and Bioventing for a Petroleum-Contaminated Shallow Aquifer in Korea

The feasibility of soil vapor extraction and bioventing technologies was examined for a petroleum hydrocarbon-contaminated site. The test site was highly contaminated with toluene, ethylbenzene, and xylene, due to leakage from petroleum storage tanks. Three respiration tests demonstrated that the test site conditions were appropriate for application of air-based remediation technologies. The oxygen consumption rates ranged from 4.32 to 7.68 %-O₂/day and biodegradation rates ranged from 2.72 to 4.84?mg/kg-day in respiration tests. In a 120-day soil vapor extraction pilot test, high initial mass removals (with tailing effects) were observed. As expected for the soil vapor extraction, the volatilization rate was much higher than the biodegradation rate. In a bioventing trial, the biodegradation effect was predominant, but a tailing effect was not observed. From this study, the suggested sequence of remediation is to construct an integrated system of soil vapor extraction and bioventing and initially operate the soil vapor extraction system until the volatilization rate becomes smaller than the biodegradation rate. After that, the system needs to be changed over to a bioventing mode. Field demonstration supports the feasibility of the proposed integrated system.     

Degradation of hydrocarbons and alcohols by Rhodococcus erythropolis DCL14: A comparison in scale performance

The degradation of alkanes and alcohols by Rhodococcus erythropolis DCL14 growing cells was tested at different reactor scales, ranging from a 2-L fermenter to 300 µL 96-well plates. The highest growth rates were attained in the fermenter, where pH, temperature and aeration rate, in particular, are monitored and controlled. However, the results acquired in reactors smaller than 100 mL indicate that these reactors may be successfully used in testing carbon sources, since the normalized results obtained with the different carbons sources were maintained in the 100-0.3 mL range. This study also shows the great potential of R. erythropolis DCL14 cells to degrade a wide range of alcohols and alkanes, which may be used in bioremediation of contaminated sites.     

Degradation of hydrocarbons and alcohols by Rhodococcus erythropolis DCL14: A comparison in scale performance

The degradation of alkanes and alcohols by Rhodococcus erythropolis DCL14 growing cells was tested at different reactor scales, ranging from a 2-L fermenter to 300 µL 96-well plates. The highest growth rates were attained in the fermenter, where pH, temperature and aeration rate, in particular, are monitored and controlled. However, the results acquired in reactors smaller than 100 mL indicate that these reactors may be successfully used in testing carbon sources, since the normalized results obtained with the different carbons sources were maintained in the 100–0.3 mL range. This study also shows the great potential of R. erythropolis DCL14 cells to degrade a wide range of alcohols and alkanes, which may be used in bioremediation of contaminated sites.     

专一营养与兼性甲烷氧化菌降解氯代烃的研究现状、动力学分析及展望

生物修复技术被认为是氯代烃类污染物处理处置的最有效途径之一,而甲烷氧化菌在该领域表现出较大的应用潜力。近期研究发现,突破了仅能利用单碳化合物的局限,兼性甲烷氧化菌能够利用多种底物降解氯代烃,这一独特的新陈代谢特性,使其在污染物生物处置领域逐渐受到关注。结合本课题组研究成果,对甲烷氧化菌降解氯代烃进行了全面总结,主要包括:分析了不同菌株(纯菌株和混合菌株)对不同氯代烃的降解效果;比较了不同类型甲烷单加氧酶在不同底物体系中的活性表达和催化特性;总结了模型菌株甲基弯菌Methylosinus trichosporium OB3b降解氯代烃的动力学特性;概述了兼性甲烷氧化菌株降解氯代烃的特性及其应用潜力;最后讨论了甲烷氧化菌降解氯代烃存在的问题及未来发展方向。     

Comparison of heavy metal accumulation and cadmium phytoextraction rates among ten leading tobacco (Nicotiana tabacum L.) cultivars in China

Abstract

Cadmium (Cd) contamination is one of the most serious global environmental problems, and phytoremediation, which uses Cd-accumulator plants, is potentially one of the sustainable solutions. Pot experiments with natural and Cd-amended soils were conducted to investigate the accumulation of heavy metals in 10 leading cultivars of tobacco in China. The extraction ability and profiles of Cd accumulation among plant organs were also analyzed. The tobacco roots accumulated cobalt, nickel, and Cd, while the leaf highly bioaccumulated Cd and lowly accumulated zinc, selenium and mercury. The transport from the tobacco stem to the leaf plays a critical role in the accumulation of these elements. The ratios of Cd concentration in the leaves at lower, middle and upper positions were comparatively stable. The high Cd-extracting cultivars were “Hongda”, “NC89” and “Zhongyan 100” when grown in normal soils, “CuiBi 1” and “Hongda” in moderately contaminated soils, and “YuYan 87”, “LongJiang 851” and “K326” in severely contaminated soils. Tobacco leaves could accumulate about 80% of the total Cd extracted from the soil by the plant. Considering the Cd-extraction limitations exhibited by leading tobacco cultivars, screening of germplasm resources for high or low levels of Cd-accumulation is still an important target for the future.     

石油烃和酚类物质在土中的生物降解与土壤酶活性

本文通过模拟实验,研究了不同条件下石油烃和酚类物质在土中的降解进程及其与土壤酶活性的关系,并在此基础上,对所述污染物的土地处理提出了若干建议。     

Characterization of polycyclic aromatic hydrocarbons degradation and arsenate reduction by a versatile Pseudomonas isolate

A Pseudomonas isolate, designated PAHAs-1, was found capable of reducing arsenate and degrading polycyclic aromatic hydrocarbons (PAHs) independently and simultaneously. This isolate completely reduced 1.5 mM arsenate within 48 h and removed approximately 100% and 50% of 60 mg l⁻¹ phenanthrene and 20 mg l⁻¹ pyrene within 60 h, respectively. Using PAHs as the sole carbon source, however, this isolate showed a slow arsenate reduction rate (4.62 μM h⁻¹). The presence of arsenic affected cell growth and concurrent PAHs removal, depending on PAH species and arsenic concentration. Adding sodium lactate to the medium greatly enhanced the arsenate reduction and pyrene metabolism. The presence of the alpha subunit of the aromatic ring-hydroxylating dioxygenase (ARHD) gene, arsenate reductase (arsC) and arsenite transporter (ACR3(2)) genes supported the dual function of the isolate. The finding of latter two genes indicated that PAHAs-1 possibly reduced arsenate via the known detoxification mechanism. Preliminary data from hydroponic experiment showed that PAHAs-1 degraded the majority of phenanthrene (>60%) and enhanced arsenic uptake by Pteris vittata L. (from 246.7 to 1187.4 mg kg⁻¹ As in the fronds). The versatile isolate PAHAs-1 may have potentials in improving the bioremediation of PAHs and arsenic co-contamination using the plant-microbe integrated strategy.     

Effects of community-accessible biochar and compost on diesel-contaminated soil

Petroleum pollution is a global problem that requires effective and accessible remediation strategies that takes ecosystem functioning into serious consideration. Bioremediation can be an effective tool to address the challenge. In this study, we used a mesocosm experiment to evaluate the effects of locally sourced and community produced biochar and compost amendments on diesel-contaminated soil. At the end of the 90-day experiment, we quantified the effects of the amendments on total petroleum hydrocarbons (C9-C40) (TPH) and soil pH, organic matter, aggregate stability, soil respiration, extractable phosphorus, extractable potassium, and micronutrients (Mg, Fe, Mn, and Zn). We observed significantly higher TPH degradation in compost-amended soils than in controls and soils amended with biochar. We propose that the addition of compost improved TPH biodegradation by augmenting soil nutrient content and microbial activity. Our results suggest that community-accessible compost can improve TPH biodegradation, and that implementation is possible at the community level.