Utilization of Drilling Fluid Base Oil Hydrocarbons by Microorganisms Isolated from Diesel-Polluted Soil

Hydrocarbon-degrading microorganisms identified as Pseudomonas luteola, Pseudomonas alcaligenes, Pseudomonas aeruginosa, and Actinomyces sp. were isolated from diesel oil-polluted soils using an enrichment culture technique. The isolates grew luxuriantly on hydrocarbons, including crude oil, diesel, kerosene, engine oil, cyclohexane, and dodecanol. Naphthalene and pyrene were poorly utilized, while there was no growth on benzene. The organisms utilized drilling fluid base oil as the sole source of carbon and energy, with rapid exponential growth at a rate ranging from 0.015 to 0.094 h^?1. The concomitant doubling time was between 7.4 and 45.5 h. Gas chromatographic analyses of the culture revealed reduction in the height of the n-alkane peaks, confirming biodegradation of the compounds. Among the isolates, P. alcaligenes had the highest (99.4%) percentage hydrocarbon degradation. Remarkable (99.2% and 98.7%) hydrocarbon removal was also noted for P. luteola and P. aeruginosa, while the lowest (92.3%) value was recorded in Actinomyces sp. These bacteria with high degradative capacity for hydrocarbons in oil-based drilling fluids would be useful in bioremediation of a tropical environment, polluted with spent drilling mud and drill cuttings.     

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.     

Assessment of hydrocarbon biodegradability in clayed and weathered polluted soils

Hydrocarbon biodegradation in clayed and weathered polluted soils is a challenge; thus the aim of the present study was to determine the best experimental conditions that improve the hydrocarbon biodegradability in clayed and weathered polluted soils, modifying the nitrogen and phosphorous content considering the C:N:P ratio and the water content as a percentage of the water-holding capacity of the soil. Biodegradation tests were performed in microcosms containing 20 g of dry soil at 30 °C. A uniform-precision central composite design of second order with three levels was used to assess the effect of nutrient and water content adjustment on the hydrocarbon degradation rate, total carbon consumption, and microbial activity. The results showed that the water-holding capacity corresponding to 350% and a C:N:P ratio of 100:7.5:0.66 were the best experimental conditions for obtaining the highest hydrocarbon degradation rate (1145 mg TPH kg^?1 dry soil day^?1), whereas the hydrocarbon degradation rate in a non-stimulated control was only 129 mg TPH kg^?1 dry soil day^?1. Water content was the factor that showed the highest significant effect (p ≤ 0.05) on the hydrocarbon degradation rate. The results of the present study allowed the achievement of the best experimental conditions that enhance hydrocarbon biodegradability in clayed and weathered polluted soils. Also, these conditions are proposed for use as a biodegradability assay.     

Immobilisation, remineralisation and residual effects in subsequent crops of dairy cattle slurry nitrogen compared to mineral fertiliser nitrogen

About 50–60% of dairy cattle slurry nitrogen is ammonium N. Part of the ammonium N in cattle slurry is immobilised due to microbial decomposition of organic matter in the slurry after application to soil. The immobilisation and the remineralisation influence the fertiliser value of slurry N and the amount of organic N that is retained in soil. The immobilisation and the remineralisation of 15 N-labelled dairy cattle slurry NH₄-N were studied through three growing seasons after spring application under temperate conditions. Effects of slurry distribution (mixing, layer incorporation, injection, surface-banding) and extra litter straw in the slurry on the plant utilisation of labelled NH₄-N from slurry were studied and compared to the utilisation of ¹⁵N-labelled mineral fertiliser. The initial immobilisation of slurry N was influenced by the slurry distribution in soil. More N was immobilised when the slurry was mixed with soil. Surface-banding of slurry resulted in significant volatilisation losses and less residual ¹⁵N in soil. Much more N was immobilised after slurry incorporation than after mineral fertiliser application. After 2.5 years the recovery of labelled N in soil (0–25 cm) was 46% for slurry mixed with soil, 42% for injected slurry, 22% for surface-banded slurry and 24% for mineral fertiliser N. The total N uptake in a ryegrass cover crop was 5–10 kg N/ha higher in the autumn after spring-application of cattle slurry (100–120 kg NH₄-N/ha) compared to the mineral fertiliser N reference, but the immobilised slurry N (labelled N) only contributed little to the extra N uptake in the autumn. Even in the second autumn after slurry application there was an extra N uptake in the cover crop (0–10 kg N/ha). The residual effect of the cattle slurry on spring barley N uptake was insignificant in the year after slurry application (equivalent to 3% of total slurry N). Eighteen months after application, 13% of the residual ¹⁵N in soil was found in microbial biomass whether it derived from slurry or mineral fertiliser, but the remineralisation rate (% crop removal of residual ¹⁵N) was higher for fertiliser- than for slurry-derived N, except after surface-banding. Extra litter straw in the slurry had a negligible influence on the residual N effects in the year after application. It is concluded that a significant part of the organic N retained in soil after cattle slurry application is derived from immobilised ammonium N, but already a few months after application immobilised N is stabilised and only slowly released. The immobilised N has negligible influence on the residual N effect of cattle slurry in the first years after slurry application, and mainly contributes to the long-term accumulation of organic N in soil together with part of the organic slurry N. Under humid temperate conditions the residual N effects of the manure can only be optimally utilised when soil is also covered by plants in the autumn, because a significant part of the residual N is released in the autumn, and there is a higher risk of N leaching losses on soils that receive cattle slurry regularly compared to soils receiving only mineral N fertilisers.     

Bioremediation of diesel-oil-contaminated alpine soils at low temperatures

Bioremediation of two diesel-oil-contaminated alpine subsoils, differing in soil type and bedrock, was investigated in laboratory experiments at 10 °C after supplementation with an inorganic fertilizer. Initial diesel oil contamination of 4000 mg kg⁻¹ soil dry matter (dm) was reduced to 380–400 mg kg⁻¹ dm after 155 days of incubation. In both soils, about 30 % of the diesel oil contamination (1200 mg kg⁻¹ dm) was eliminated by abiotic processes. The residual decontamination (60 %–65 %) could be attributed to microbial degradation activities. In both soils, the addition of a cold-adapted diesel-oil-degrading inoculum enhanced biodegradation rates only slightly and temporarily. From C/N and N/P ratios (determined by measuring the contents of total hydrocarbons, NH₄ ⁺ N, NO₃ ⁻ N and PO₄ ³⁻ P) of soils␣it could be deduced that there was no nutrient deficiency during the whole incubation period. Soil biological activities (basal respiration and dehydrogenase activity) corresponded to the course of biodegradation activities in the soils. Received: 9 September 1996 / Accepted: 7 December 1996     

Stimulation of Diesel Fuel Biodegradation by Indigenous Nitrogen Fixing Bacterial Consortia

Abstract Successful stimulation of N₂ fixation and petroleum hydrocarbon degradation in indigenous microbial consortia may decrease exogenous N requirements and reduce environmental impacts of bioremediation following petroleum pollution. This study explored the biodegradation of petroleum pollution by indigenous N₂ fixing marine microbial consortia. Particulate organic carbon (POC) in the form of ground, sterile corn-slash (post-harvest leaves and stems) was added to diesel fuel amended coastal water samples to stimulate biodegradation of petroleum hydrocarbons by native microorganisms capable of supplying a portion of their own N. It was hypothesized that addition of POC to petroleum amended water samples from N-limited coastal waters would promote the growth of N₂ fixing consortia and enhance biodegradation of petroleum. Manipulative experiments were conducted using samples from coastal waters (marinas and less polluted control site) to determine the effects of POC amendment on biodegradation of petroleum pollution by native microbial consortia. Structure and function of the microbial consortia were determined by measurement of N₂ fixation (acetylene reduction), hydrocarbon biodegradation (¹⁴C hexadecane mineralization), bacterial biomass (AODC), number of hydrocarbon degrading bacteria (MPN), and bacterial productivity (³H-thymidine incorporation). Throughout this study there was a consistent enhancement of petroleum hydrocarbon degradation in response to the addition of POC. Stimulation of diesel fuel biodegradation following the addition of POC was likely attributable to increases in bacterial N₂ fixation, diesel fuel bioavailability, bacterial biomass, and metabolic activity. Toxicity of the bulk phase water did not appear to be a factor affecting biodegradation of diesel fuel following POC addition. These results indicate that the addition of POC to diesel-fuel-polluted systems stimulated indigenous N₂ fixing microbial consortia to degrade petroleum hydrocarbons. Received: 29 December 1998; Accepted: 6 April 1999     

Microbial proteases in peptide synthesis: approaches and applications

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the environment is often limited due to unfavorable nutrient conditions for the bacteria that use these PAHs as sole source of carbon and energy. Mycobacterium and Sphingomonas are 2 PAH-degrading specialists commonly present in PAH-polluted soil, but not much is known about their specific nutrient requirements. By adding different inorganic supplements of nitrogen (N) and phosphorus (P), affecting the overall carbon/nitrogen/phosphorus ratio of soil in soil slurry degradation tests, we investigated the impact of soil inorganic N and P nutrient conditions on PAH degradation by PAH-degrading Sphingomonas and Mycobacterium strains. The general theoretically calculated C/N/P ratio of 100/10/1 (expressed in moles) allowed rapid PAH metabolization by Sphingomonas and Mycobacterium strains without limitation. In addition, PAH-degradation rate and extent was not affected when ca. ten times lower concentrations of N and P were provided, indicating that Sphingomonas and Mycobacterium strains are capable of metabolizing PAHs under low nutrient conditions. Nor does PAH-degradation seem to be affected by excesses of N and P creating an imbalanced C/N/P ratio. However, supplements of N and P salts increased the salinity of soil slurry solutions and seriously limited or even completely blocked biodegradation.     

Degradation of oil sludge by landfarming — a case-study at the Ghent harbour

Large-scale landfarming experiments have been performed on a loamy sand soil. An amount of 1,350 m³/ha oil sludge together with nutrients (N,P,K) and a bacterial inoculum were applied at two different times over a five-year period. At both test periods, biodegradation of the hydrocarbons (HC) was best fitted with first order reaction kinetics with degradation rates ranging from about 4 g HC/kg dry soil per year to about 15 g HC/kg dry soil per year. Toxicity tests on the aqueous soil extracts as well as plant growth and worm tests on the landfarm soil showed no striking negative effects of residual hydrocarbons. Migration of oil, nitrate and phosphate to the groundwater was minimal. In view of the diversity of solvents recommended in the literature, twenty extractants were tested for their capacity to remove HC from the loamy sand soil. Chlorinated solvents, such as dichloromethane and chloroform, were the most effective. Yet, in view of its effectiveness and low toxicity, acetone appears a suitable solvent for the extraction of soils and sediments polluted with hydrocarbons. This case-study revealed that oil sludge can effectively be treated by landfarming, if appropriate technical measures are taken and a sufficient time (minimum 15 years) for bioremediation is provided.     

Comparison of the effects of poultry manure and its biochar on barley growth in petroleum-contaminated soils

This study was conducted to evaluate and compare the effectiveness of two organic amendments [poultry manure (PM) and poultry manure biochar (PMB)] for the degradation of petroleum hydrocarbons in contaminated soils by barley plant at three levels of total petroleum hydrocarbons (TPHs) during 5 months under greenhouse conditions. TPHs removal efficiency and microbial respiration were shown to be higher at soil-cultivated plant than at uncultivated soil and in lowest level of contamination rather than other levels of contamination and at organic amendment treatment than unamended soil. Soil microbial respiration and TPHs degradation in the rhizosphere of barley increased by 15.64 and 12.74% for PM-amended treatment and 28.07 and 26.83% for PMB-amended treatment, respectively, in the 4% TPHs level compared with unamended treatment. Comparison of two amendments showed that in PMB treatment soil, highest dry weight, microbial respiration, and TPHs degradation potential were observed.     

Denitrification by the sessile microbial community of a polluted river

Denitrification by the sessile microbial community of the River Tamagawa was studied in laboratory experiments. Inorganic nitrogen loss was observed when river water was incubated with sessile microbial community of the river in a continuously circulating system. It was confirmed by the ¹⁵N tracer technique that both sessile microbial communities of unpolluted and polluted areas had denitrifying activity, even though they were incubated in oxygenated river water. The denitrification rate of the sessile microbial community taken from a polluted area, measured by the ¹⁵N tracer technique, was 8–16 mg N/m²/day in October and December, 1977, and it was enhanced 10-fold by raising the water temperature from 14 to 30° C. Denitrification in the river was also suggested by determining the N₂: Ar ratio of gases evolved from the river bed.     

Phytoremediation of Total Petroleum Hydrocarbons From Highly Saline and Clay Soil Using Sorghum halepense (L.) Pers. and Aeluropus littoralis (Guna) Parl

This study evaluated the effects of native plants (Sorghum halepense and Aeluropus littoralis), total petroleum hydrocarbons (TPH) concentrations, and nutrients on the removal of TPHs from a highly saline clay soil. For a period of 180 days, rhizosphere microbial number, plant biomass, and residual TPHs were determined monthly. Results showed that TPH removal from soil in the rhizosphere was 13% higher than that in the control (unplanted soil). In addition, the number of heterotrophic bacteria in the rhizosphere and non-rhizosphere soil was 7.407 and 6.629 log₁₀CFU/g, respectively. The maximum TPH removal, microbial numbers, and plant biomass were measured in the treated soil, polluted with 0.86% (w/w) of TPH. The high clay and salinity of the experimental soil had a negative effect on the phytoremediation efficiency. Hence, it was necessary to improve the physicochemical properties of the soil to provide a good condition for plants and microbes, thereby increasing the phytoremediation efficiency.     

沼液还田对旱地红壤微生物群落代谢与多样性的影响

通过沼液还田定位实验,按照不同沼液全氮还田比例设6个等氮量(N-P_2O_5-K_2O量均为120-90-135 kg/hm~2(对照除外))处理:对照(不施肥,CK)、100%化学氮(NPK)、15%沼液氮+85%化学氮(BS15)、30%沼液氮+70%化学氮(BS30)、45%沼液氮+55%化学氮(BS45)和100%沼液氮(BS100),运用Biolog-ECO技术分析0—20cm花生收获期土壤微生物群落代谢功能多样性,阐明微生物群落代谢与沼液还田量的相关关系。结果表明:①BS45、BS30处理土壤微生物群落碳源代谢强度(AWCD)显著高于CK和NPK处理;而BS15、BS100处理土壤微生物群落碳源代谢强度(AWCD)与CK和NPK处理则无显著差异;②土壤微生物群落碳源代谢强度(AWCD)、丰富度指数、Shannon指数、Simpson优势度指数均表现为BS45BS30NPKCKBS100BS15;③结合主成分分析和聚类分析,表明各处理土壤微生物群落功能多样性分为4组:BS45、BS30处理为一组,微生物群落代谢活性最强,特别是碳水化合物、氨基酸、聚合物和胺类等碳源的代谢能力;NPK、CK、BS100处理为一组,微生物群落代谢活性次之;BS15处理为一组,微生物群落代谢能力最低,其碳水化合物、羧酸、氨基酸、聚合物、酚类和胺类等碳源的代谢能力均为最低。结合主成分分析综合得分,土壤微生物群落代谢和多样性的顺序为BS45BS30NPKCKBS100BS15。可见,沼液还田显著影响旱地红壤微生物群落的代谢活性和多样性,沼液不能完全替代化肥,当沼液全氮还田比例在30%—45%时,微生物群落代谢活性最强,有利于土壤质量提高,适于在我国旱地红壤地区推广。     

驯化复合微生物菌群处理废弃钻井泥浆活性研究

【背景】油田废弃钻井泥浆含油量高,污染物复杂,环境危害严重,现有技术无法满足日益发展的石油开采行业在废弃钻井泥浆处理方面的需求。生物法处理废弃钻井泥浆,工艺简单,成本低,但也存在局限,包括广谱性差、处理周期长、原油降解率低、泥浆性质波动冲击工艺稳定性等。【目的】构建一种高活性和高环境耐受能力的微生物菌群,分析遗传稳定性和综合性能,提高废弃钻井泥浆处理技术水平。【方法】通过定向富集、诱导驯化的方法,提高活性群落对石油烃乳化降解效率,降低共代谢底物反馈抑制和群体感应系统敏感度,分析群落结构和活性成员的种群类别,分析乳化降解石油烃的活性对应关系。【结果】从含油量超过12g/kg、芳烃-胶质沥青含量超过80%、含盐量超过8g/kg的钻井废弃泥浆中富集得到1个活性微生物菌群,主要成员包括假单胞菌属(Pseudomonas)、根瘤菌属(Rhizobium)、红细菌属(Rhodobacter)和嗜碱还原硫素杆菌(Dethiobacter alkaliphilus),比例分别达27.44%、20.73%、8.54%和7.93%。在超过22代的连续驯化过程中,假单胞菌(Pseudomonas)、类希瓦氏菌(Alishewanella)和盐单胞菌(Halomonas)数量达92.72%,菌群结构和活性趋于稳定。处理钻井废弃泥浆5 d,土壤含油率由处理前的12403 mg/kg降低到处理后的42 mg/kg,综合脱油效率99.67%,石油烃降解率68.9%。分析微生物群落作用前后石油饱和土壤中的石油含量变化,原始含油量261 g/kg,处理后含油量305 mg/kg,脱油率99.88%。【结论】菌群驯化后活性稳定,耐受高盐环境能力强,在钻井废弃泥浆、含油土壤及油泥污染物处理方面具有很强的工业应用潜力。     

Organic matter turnover in a sagebrush steppe landscape

Laboratory incubations of¹⁵N-amended soils from a sagebrush steppe in south-central Wyoming indicate that nutrient turnover and availability have complex patterns across the landscape and between microsites. Total and available N and P and microbial C and N were highest in topographic depressions characterized by tall shrub communities. Net and gross N mineralization rates and respiration were also highest in these areas, but microbial efficiencies expressing growth relative to respiration cost were highest in soils of exposed ridgetop sites (prostrate shrub communities). Similar patterns occurred between shrub and intershrub soils, with greater nutrient availability under shrubs, but lower microbial efficiencies under shrubs than between. Surface soils had higher soil nutrient pools and N mineralization rates than subsurface soils, but N and C turnover and microbial efficiencies were lower in those surface soils. All soils decreased in respiration, mineralization, and immobilization rates during the 30-day incubation period, apparently approaching a steady-state substrate use. Soil microbial activity of the high organic matter accumulation areas was apparently more limited by labile substrate.     

Comparison of bioremediation strategies for soil impacted with petrochemical oily sludge

Different bioremediation techniques (natural attenuation, biostimulation and bioaugmentation) in contaminated soils with two oily sludge concentrations (1.5% and 6.0%) in open and closed microcosms systems were assessed during 90 days. The results showed that the highest biodegradation rates were obtained in contaminated soils with 6% in closed microcosms. Addition of microbial consortium and nutrients in different concentrations demonstrated higher biodegradation rate of total petroleum hydrocarbons (TPH) than those of the natural attenuation treatment. Soils treated in closed microcosms showed highest removal rate (84.1 ± 0.9%) when contaminated at 6% and bacterial consortium and nutrients in low amounts were added. In open microcosms, the soil contaminated at 6% using biostimulation with the highest amounts of nutrients (C:N:P of 100:10:1) presented the highest degradation rate (78.7 ± 1.3%). These results demonstrate that the application of microbial consortium and nutrients favored biodegradation of TPH present in oily sludge, indicating their potential applications for treatment of the soils impacted with this important hazardous waste.     

Nitrogen‐rich microbial products provide new organo‐mineral associations for the stabilization of soil organic matter

Understanding the cycling of C and N in soils is important for maintaining soil fertility while also decreasing greenhouse gas emissions, but much remains unknown about how organic matter (OM) is stabilized in soils. We used nano‐scale secondary ion mass spectrometry (NanoSIMS) to investigate the changes in C and N in a Vertisol and an Alfisol incubated for 365 days with ¹³C and ¹⁵N pulse labeled lucerne (Medicago sativa L.) to discriminate new inputs of OM from the existing soil OM. We found that almost all OM within the free stable microaggregates of the soil was associated with mineral particles, emphasizing the importance of organo‐mineral interactions for the stabilization of C. Of particular importance, it was also found that ¹⁵N‐rich microbial products originating from decomposition often sorbed directly to mineral surfaces not previously associated with OM. Thus, we have shown that N‐rich microbial products preferentially attach to distinct areas of mineral surfaces compared to C‐dominated moieties, demonstrating the ability of soils to store additional OM in newly formed organo‐mineral associations on previously OM‐free mineral surfaces. Furthermore, differences in ¹⁵N enrichment were observed between the Vertisol and Alfisol presumably due to differences in mineralogy (smectite‐dominated compared to kaolinite‐dominated), demonstrating the importance of mineralogy in regulating the sorption of microbial products. Overall, our findings have important implications for the fundamental understanding of OM cycling in soils, including the immobilization and storage of N‐rich compounds derived from microbial decomposition and subsequent N mineralization to sustain plant growth.     

Microbial Factors Rather Than Bioavailability Limit the Rate and Extent of PAH Biodegradation in Aged Crude Oil Contaminated Model Soils

The rate and extent of polynuclear aromatic hydrocarbons (PAH) biodegradation in a set of aged model soils that had been contaminated with crude oil at the high concentrations (i.e.,>20,000?mg/kg) normally found in the environment were measured in 90-week slurry bioremediation experiments. Soil properties such as organic matter content, mineral type, particle diameter, surface area, and porosity did not significantly influence the PAH biodegradation kinetics among the 10 different model soils. A comparison of aged and freshly spiked soils indicates that aging affects the biodegradation rate and extent only for higher-molecular-weight PAHs, while the effects of aging are insignificant for 4-ring PAHs and total PAHs. In all model soils with the exception of kaolinite clay, the rate of abiotic desorption was faster than the rate of biodegradation during the initial phase of bioremediation treatment, indicating that PAH biodegradation was limited by microbial factors. Similarly, any of the higher-molecular-weight PAHs that were still present after 90 weeks of treatment were released rapidly during abiotic desorption tests, which demonstrates that bioavailability limitations were not responsible for the recalcitrance of these hydrocarbons. Indeed, an analysis of microbial counts indicates that a severe reduction in hydrocarbon degrader populations may be responsible for the observed incomplete PAH biodegradation. Therefore, it can be concluded that the recalcitrance of PAHs during bioremediation is not necessarily due to bioavailability limitations and that these residual contaminants therefore might pose a greater risk to environmental receptors than previously thought.     

Association of Microbial Community Composition and Activity with Lead, Chromium, and Hydrocarbon Contamination

Microbial community composition and activity were characterized in soil contaminated with lead (Pb), chromium (Cr), and hydrocarbons. Contaminant levels were very heterogeneous and ranged from 50 to 16,700 mg of total petroleum hydrocarbons (TPH) kg of soil⁻¹, 3 to 3,300 mg of total Cr kg of soil⁻¹, and 1 to 17,100 mg of Pb kg of soil⁻¹. Microbial community compositions were estimated from the patterns of phospholipid fatty acids (PLFA); these were considerably different among the 14 soil samples. Statistical analyses suggested that the variation in PLFA was more correlated with soil hydrocarbons than with the levels of Cr and Pb. The metal sensitivity of the microbial community was determined by extracting bacteria from soil and measuring [³H]leucine incorporation as a function of metal concentration. Six soil samples collected in the spring of 1999 had IC₅₀ values (the heavy metal concentrations giving 50% reduction of microbial activity) of approximately 2.5 mM for CrO₄²⁻ and 0.01 mM for Pb²⁺. Much higher levels of Pb were required to inhibit [¹⁴C]glucose mineralization directly in soils. In microcosm experiments with these samples, microbial biomass and the ratio of microbial biomass to soil organic C were not correlated with the concentrations of hydrocarbons and heavy metals. However, microbial C respiration in samples with a higher level of hydrocarbons differed from the other soils no matter whether complex organic C (alfalfa) was added or not. The ratios of microbial C respiration to microbial biomass differed significantly among the soil samples (P < 0.05) and were relatively high in soils contaminated with hydrocarbons or heavy metals. Our results suggest that the soil microbial community was predominantly affected by hydrocarbons.     

Optimization of field scale biopiles for bioremediation of petroleum hydrocarbon contaminated soil at low temperature conditions by response surface methodology (RSM)

Ex-Situ Bioremediation has been increasingly viewed as an appropriate remediation technology for hydrocarbon contaminated soils under cold climates conditions in countries like Canada. A response surface methodology (RSM) based on a factorial design was performed to investigate and optimize the effects of the microbial consortia application rate and amount of mature compost amendment on the TPH removal (964 μg g⁻¹ initial concentration). 18 field-scale biopiles (16 m³ each) were constructed, maintained and subjected to different microbial consortium and mature compost application rates under cold climate conditions over a period of 94 days. TPHs removal rates in the range of 74–82% was observed in the treatments setups where mature compost and microbial consortia were used simultaneously, compared to an average 48% of TPHs removal in control setup.The interaction between these two factors were studied and modelled using a statistical regression model, which showed that the microbial consortia application rate, the mature compost amendment and their interactions had a significant effect on TPHs degradation with a coefficient of determination (R²) of 0.88. Furthermore, using a numerical optimization approach, the optimum rates predicted via RSM were estimated at 4.1 ml m⁻³ and 7% for microbial consortia and compost application rates to obtain a maximum TPH removal of 90.7%.     

Biodegradation process and the nature of metabolism of metalaxyl in soil

The enhanced biodegradation of metalaxyl was studied in tobacco, citrus, avocado and corn soils. The most rapid degradation of metalaxyl occurred in a tobacco soil in which the half-life (50% degradation) of metalaxyl was 6 days. The main breakdown product of metalaxyl in all soils was the acid metabolite. Ring labelled [¹⁴C]metalaxyl incubated for 4 wk in 6 soils demonstrated a low rate of ¹⁴CO₂ evolution ranging from 2.1% to 11.3% which was unrelated to the biodegradation properties of the soil. A relationship between the concentration of metalaxyl and the subsequent rate of biodegradation was found in the tobacco soils. Higher concentrations of metalaxyl resulted in faster biodegradation rates. A single exposure of tobacco and corn soils to metalaxyl (100 μg/ml or 200 μg/g dry weight of soil) significantly increased their subsequent capacity to degrade the fungicide. Addition of the fungicide thiram or the antibiotics streptomycin and chloramphenicol to an avocado soil resulted in 75% and 51% inhibition of metalaxyl degradation, respectively. A combination of the fungicide and antibiotics resulted in 89% inhibition. The results indicate that enhanced microbial degradation of metalaxyl can occur in a wide range of soils. Under experimental conditions using soil solutions or soil systems, a single application of the fungicide may trigger this event. A wide range of fungi and bacteria appear to take part in degrading metalaxyl.