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Results for “Bioremediation Journal”

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At least 19 recordsLinked to original sources
USGS2000

Controlled field study on the use of nitrate and oxygen for bioremediation of a gasoline source zone

Controlled releases of unleaded gasoline were utilized to evaluate the biotransformation of the soluble aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylene isomers, trimethylbenzene isomers, and naphthalene) within a source zone using nitrate and oxygen as electron acceptors. Experiments were conducted within two 2 m ?? 2 m ?? 3.5 m deep sheet-piling cells. In each treatment cell, a gasoline-contaminated zone was created below the water table. Groundwater amended with electron acceptors was then flushed continuously through the cells for 174 day. Electron-acceptor utilization and hydrocarbon-metabolite formation were noted in both cells, indicating that some microbial activity had been induced in response to flushing. Relative to the cell residence time, nitrate utilization was slow and aromatic-hydrocarbon mass losses in response to microaerophilic dissolved oxygen addition were not obvious under these in situ conditions. There was relatively little biotransformation of the aromatic hydrocarbons over the 2-m flow path monitored in this experiment. A large denitrifying population capable of aromatic hydrocarbon biotransformation failed to develop within the gasoline source zone over a 14-mo period of nitrate exposure.

Bioremediation Journal↗
USGS2002

Microbial mineralization of ethene under sulfate-reducing conditions

Previous investigations demonstrated that respiratoly reductive dechlorination of vinyl chloride (VC) can be efficient even at H 2 concentrations (≤2 n M ) that are characteristic of SO 4 -reducing conditions. In the study reported here, microorganisms indigenous to a lake-bed sediment completely mineralized [1,2- 14 C] ethene to 14 14CO 2 when incubated under SO 4 -reducing conditions. Together, these observations argue for a novel mechanism for the net anaerobic oxidation of VC to CO 2 : reductive dechlorination of VC to ethene followed by anaerobic oxidation of ethene to CO 2 . Moreover, the results of this study suggest that reliance on ethene and/or ethane accumulation as a quantitative indicator of complete reductive dechlorination of chioroethene contaminants may not be warranted.

Bioremediation Journal↗
USGS2002

Long-term evolution of biodegradation and volatilization rates in a crude oil-contaminated aquifer

Volatilization and subsequent biodegradation near the water Table make up a coupled natural attenuation pathway that results in significant mass loss of hydrocarbons. Rates of biodegradation and volatilization were documented twice 12 years apart at a crude-oil spill site near Bemidji, Minnesota. Biodegradation rates were determined by calibrating a gas transport model to O 2 , CO 2 , and CH 4 gas-concentration data in the unsaturated zone. Reaction stoichiometry was assumed in converting O 2 and CO 2 gas-flux estimates to rates of aerobic biodegradation and CH 4 gas-flux estimates to rates of methanogenesis. Model results indicate that the coupled pathway has resulted in significant hydrocarbon mass loss at the site, and it was estimated that approximately 10.52 kg/day were lost in 1985 and 1.99 kg/day in 1997. In 1985 3% of total volatile hydrocarbons diffusing from the floating oil were biodegraded in the lower 1 m of the unsaturated zone and increased to 52% by 1997. Rates of hydrocarbon biodegradation above the center of the floating oil were relatively stable from 1985 to 1997, as the primary metabolic pathway shifted from aerobic to methanogenic biodegradation. Model results indicate that in 1997 biodegradation under methanogenenic conditions represented approximately one-half of total hydrocarbon biodegradation in the lower 1 m of the unsaturated zone. Further downgradient, where substrate concentrations have greatly increased, total biodegradation rates increased by greater than an order of magnitude from 0.04 to 0.43 g/m 2 -day. It appears that volatilization is the primary mechanism for attenuation in early stages of plume evolution, while biodegradation dominates in later stages.

Bioremediation Journal↗
USGS2004

Effect of Fe(III) on 1,1,2,2-Tetrachloroethane degradation and vinyl chloride accumulation in wetland sediments of the Aberdeen Proving Ground

1,1,2,2-Tetrachloroethane (TeCA) contaminated groundwater at the Aberdeen Proving Ground discharges through an anaerobic wetland in West Branch Canal Creek (MD), where dechlorination occurs. Two microbially mediated pathways, dichloroelimination and hydrogenolysis, account for most of the TeCA degradation at this site. The dichloroelimination pathways lead to the formation of vinyl chloride (VC), a recalcitrant carcinogen of great concern. The goal of this investigation was to determine whether microbially-available Fe(III) in the wetland surface sediment influenced the fate of TeCA and its daughter products. Differences were identified in the TeCA degradation pathway between microcosms treated with amorphous ferric oxyhydroxide (AFO-treated) and untreated (no AFO) microcosms. TeCA degradation was accompanied by a lower accumulation of VC in AFO-treated microcosms than untreated microcosms. The microcosm incubations and subsequent experiments with the microcosm materials showed that AFO treatment resulted in lower production of VC by (1) shifting TeCA degradation from dichloroelimination pathways to production of a greater proportion of chlorinated ethane products, and (2) decreasing the microbial capability to produce VC from 1,2-dichloroethene (DCE). VC degradation was not stimulated in the presence of Fe(III). Rather, VC degradation occurred readily under methanogenic conditions and was inhibited under Fe(III)-reducing conditions.

Bioremediation Journal↗
USGS2004

Inhibition of acetoclastic methanogenesis in crude oil- and creosote-contaminated groundwater

Results from a series of studies of methanogenic processes in crude oil- and creosote-contaminated aquifers indicate that acetoclastic methanogenesis is inhibited near non-aqueous sources. At a crude oil-contaminated site, numbers of acetoclastic methanogens found close to crude oil were one hundred times fewer than those of hydrogen- and formate-utilizing methanogens. In laboratory toxicity assays, crude oil collected from the site inhibited methane production from acetate but not from formate or hydrogen. Toxicity assays with aqueous creosote extract completely inhibited acetate utilization over the range of tested dilutions but only mildly affected formate and hydrogen utilization. The combined results from the laboratory and field studies suggest that in methanogenic contaminated aquifers, inhibition of acetoclastic methanogenesis may lead to a buildup of acetate relative to dissolved organic carbon.

Florida, Minnesota↗
USGS2005

Biodegradation of N-nitrosodimethylamine in soil from a water reclamation facility

The potential introduction of N -nitrosodimethylamine (NDMA) into groundwater during water reclamation activities poses a significant risk to groundwater drinking supplies. Greater than 54% biodegradation of N -[methyl- 14 C]NDMA to 14 CO 2 or to 14 CO 2 and 14 CH 4 was observed in soil from a water reclamation facility under oxic or anoxic conditions, respectively. Likewise, biodegradation was significant in microcosms containing soil with no history of NDMA contamination. These results indicate that aerobic and anaerobic biodegradation of NDMA may be an effective component of NDMA attenuation in water reclamation facility soils.

Bioremediation Journal↗
USGS2005

RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) biodegradation in aquifer sediments under manganese-reducing conditions

A shallow, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)–contaminated aquifer at Naval Submarine Base Bangor has been characterized as predominantly manganese-reducing, anoxic with local pockets of oxic conditions. The potential contribution of microbial RDX degradation to localized decreases observed in aquifer RDX concentrations was assessed in sediment microcosms amended with [U- 14 C] RDX. Greater than 85% mineralization of 14 C-RDX to 14 CO 2 was observed in aquifer sediment microcosms under native, manganese-reducing, anoxic conditions. Significant increases in the mineralization of 14 C-RDX to 14 CO 2 were observed in anoxic microcosms under NO 3 -amended or Mn(IV)-amended conditions. No evidence of 14 C-RDX biodegradation was observed under oxic conditions. These results indicate that microbial degradation of RDX may contribute to natural attenuation of RDX in manganese-reducing aquifer systems.

Bioremediation Journal↗
USGS2006

Characterization of a microbial consortium capable of rapid and simultaneous dechlorination of 1,1,2,2-tetrachloroethane and chlorinated ethane and ethene intermediates:

Mixed cultures capable of dechlorinating chlorinated ethanes and ethenes were enriched from contaminated wetland sediment at Aberdeen Proving Ground (APG) Maryland. The “West Branch Consortium” (WBC-2) was capable of degrading 1,1,2,2-tetrachloroethane (TeCA), trichloroethene (TCE), cis and trans 1,2-dichloroethene (DCE), 1,1,2-trichloroethane (TCA), 1,2-dichloroethane, and vinyl chloride to nonchlorinated end products ethene and ethane. WBC-2 dechlorinated TeCA, TCA, and cis DCE rapidly and simultaneously. A Clostridium sp. phylogenetically closely related to an uncultured member of a TCE-degrading consortium was numerically dominant in the WBC-2 clone library after 11 months of enrichment in culture. Clostridiales, including Acetobacteria, comprised 65% of the bacterial clones in WBC-2, with Bacteroides (14%), and epsilon Proteobacteria (14%) also numerically important. Methanogens identified in the consortium were members of the class Methanomicrobia, which includes acetoclastic methanogens. Dehalococcoides did not become dominant in the culture, although it was present at about 1% in the microbial population. The WBC-2 consortium provides opportunities for the in situ bioremediation of sites contaminated with mixtures of chlorinated ethenes and ethanes.

Bioremediation Journal↗
USGS2007

Anaerobic biodegradation and hydrogeochemical controls on natural attenuation of trichloroethene in an inland forested wetland

Anaerobic biodegradation was conducted in a forested wetland where a plume of trichloroethylene discharges from a sand aquifer through organic-rich wetland and stream-bottom sediments. The rapid response of the wetland hydrology to precipitation events altered groundwater flow and geochemistry during wet conditions in the spring compared to the drier conditions in the summer and fall. During dry conditions, partial reductive dechlorination of trichloroethylene to cis-1,2-dichloroethylene occurred in methanogenic wetland porewater. Influx of oxygenated recharge during wet conditions led to a change from methanogenic to iron-reducing conditions and a lack of 1,2-dichloroethylene production in the wet spring conditions. During these wet conditions, dilution was the primary attenuation mechanism evident for trichloroethylene in the wetland porewater. Trichloroethylene degradation was insignificant in anaerobic microcosms constructed with the shallow wetland sediment. Natural attenuation of chlorinated solvents by anaerobic biodegradation may not be efficient at all wetland sites, despite organic-rich characteristics of the sediment.

Bioremediation Journal↗
USGS2008

Selecting remediation goals by assessing the natural attenuation capacity of groundwater systems

Remediation goals for the source areas of a chlorinated ethene‐contaminated groundwater plume were identified by assessing the natural attenuation capacity of the aquifer system. The redox chemistry of the site indicates that sulfate‐reducing (H 2 ∼ 2 nanomoles [nM]) per liter conditions near the contaminant source grade to Fe(III)‐reducing conditions (H 2 ∼ 0.5 nM) downgradient of the source. Sulfate‐reducing conditions facilitate the initial reduction of perchloroethene (PCE) to trichloroethene (TCE), cis ‐dichloroethene ( cis ‐DCE), and vinyl chloride (VC). Subsequently, the Fe(III)‐reducing conditions drive the oxidation of cis ‐DCE and VC to carbon dioxide and chloride. This sequence gives the aquifer a substantial capacity for biodegrading chlorinated ethenes. Natural attenuation capacity (the slope of the steady‐state contaminant concentration profile along a groundwater flowpath) is a function of biodegradation rates, aquifer dispersive characteristics, and groundwater flow velocity. The natural attenuation capacity at the Kings Bay, Georgia site was assessed by estimating groundwater flowrates (∼0.23 ± 0.12 m/d) and aquifer dispersivity (∼1 m) from hydrologic and scale considerations. Apparent biodegradation rate constants (PCE and TCE ∼ 0.01 d −1 ; cis ‐DCE and VC ∼ 0.025 d −1 ) were estimated from observed contaminant concentration changes along aquifer flowpaths. A boundary‐value problem approach was used to estimate levels to which contaminant concentrations in the source areas must be lowered (by engineered removal), or groundwater flow velocities lowered (by pumping) for the natural attenuation capacity to achieve maximum concentration limits (MCLs) prior to reaching a predetermined regulatory point of compliance.

Bioremediation Journal↗
USGS2010

Biodegradation of aliphatic vs. aromatic hydrocarbons in fertilized arctic soils

A study was carried out to test a simple bioremediation treatment strategy in the Arctic and analyze the influence of fertilization the degradation of aliphatic and aromatic hydrocarbons, e.g., pristine, n-tetradecane, n-pentadecane, 2-methylnaphthalene, naphthalene, and acenaphthalene. The site was a coarse sand pad that once supported fuel storage tanks. Diesel-range organics concentrations were 250-860 mg/kg soil at the beginning of the study. Replicate field plots treated with fertilizer yielded final concentrations of 0, 50, 100, or 200 mg N/kg soil. Soil pH and soil-water potentials decreased due to fertilizer application. The addition of fertilizer considerably increased soil respiration potentials, but not the populations of microorganisms measured. Fertilizer addition also led to ??? 50% loss of measured aliphatic and aromatic hydrocarbons in surface and subsurface soils. For fertilized plots, hydrocarbon loss was not associated with the quantity of fertilizer added. Losses of aliphatic hydrocarbons were ascribed to biotic processes, while losses of aromatic hydrocarbons were due to biotic and abiotic processes.

Bioremediation Journal↗
USGS2001

Biodegradation of trichloroethylene and its anaerobic daughter products in freshwater wetland sediments

Laboratory microcosms were prepared under methanogenic, sulfate-reducing, and aerobic conditions using sediment and groundwater from a freshwater wetland that is a discharge area for a trichloroethylene (TCE) to evaluate potential biodegradation rates of TCE and its anaerobic daughter products (cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, and vinyl chloride (VC)). Anaerobic degradation of TCE was about an order of magnitude faster under methanogenic conditions than under sulfate-reducing conditions. Both 12DCE and VC were found under sulfate-reducing conditions in the microcosms containing the wetland sediment, but their production, especially for VC, was substantially slower than under methanogenic conditions. Methane concentrations remained approximately constant (when losses in the formalin-amended controls are considered) in the microcosms amended with TCE and increased in the microcosms amended with the 12DCE isomers and VC during the first 18-25 days of incubation. The most rapid decrease in concentrations of TCE, cis-12DCE, trans-12DCE, and VC was found after aerobic methane-oxidizing conditions were definitely established.

Bioremediation Journal↗
USGS2003

Effect of hydrologic and geochemical conditions on oxygen-enhanced bioremediation in a gasoline-contaminated aquifer

The effect of pre-existing factors, e.g., hydrologic, geochemical, and microbiological properties, on the results of oxygen addition to a reformulated gasoline-contaminated groundwater system was studied. Oxygen addition with an oxygen-release compound (a proprietary form of magnesium peroxide produced different results with respect to dissolved oxygen (DO) generation and contaminant decrease in the two locations. Oxygen-release compound injected at the former UST source area did not significantly change measured concentrations of DO, benzene, toluene, or MTBE. Conversely, oxygen-release compound injected 200 m downgradient of the former UST source area rapidly increased DO levels, and benzene, toluene, and MTBE concentrations decreased substantially. The different results could be related to differences in hydrologic and geochemical conditions that characterized the two locations prior to oxygen addition. The lack of recharge to ground water in the paved UST source area led to a much larger geochemical sink for DO compared to ground water in the unpaved area.

Bioremediation Journal↗
USGS2003

Inhibition of acetoclastic methanogenesis in crude oil- and creosote-contaminated groundwater

The inhibition of acetoclastic methanogenesis in crude oil- and creosote-contaminated groundwater was studied. The crude oil and water-soluble components of creosote contributed to the inhibition of acetoclastic methanogens. Acetoclastic methanogenesis was much more susceptible to the toxic inhibition of crude oil and creosote than either hydrogen- or formate-utilizing methanogenesis. The effect of this toxic inhibition was apparent in the population of the methanogenic trophic groups near nonaqueous crude oil at the Bemidji, MN, site. At a crude oil-contaminated site, numbers of acetoclastic methanogens found close to crude oil were 100 times fewer than those of hydrogen- and formate-utilizing methanogens. In laboratory toxicity assays, crude oil collected from the site inhibited methane production from acetate but not from formate or hydrogen. Toxicity assays with aqueous creosote extract completely inhibited acetate utilization over the range of tested dilutions but only mildly affected formate and hydrogen utilization. Wastewater reactor studies indicated that this toxicity would result in a decrease in the biodegradation rate of contaminants at sites where toxic compounds are present.

Florida, Minnesota↗
USGS2000

Influence of dissimilatory metal reduction on fate of organic and metal contaminants in the subsurface

Geobacter become dominant members of the microbial community when Fe(III)-reducing conditions develop as the result of organic contamination, or when Fe(III) reduction is artificially stimulated. These results suggest that further understanding of the ecophysiology of Geobacter species would aid in better prediction of the natural attenuation of organic contaminants under anaerobic conditions and in the design of strategies for the bioremediation of subsurface metal contamination.

Hydrogeology Journal↗
USGS1998

Field and laboratory evidence for intrinsic biodegradation of vinyl chloride contamination in a Fe(III)-reducing aquifer

Intrinsic bioremediation of chlorinated ethenes in anaerobic aquifers previously has not been considered feasible, due, in large part, to 1) the production of vinyl chloride during microbial reductive dechlorination of higher chlorinated contaminants and 2) the apparent poor biodegradability of vinyl chloride under anaerobic conditions. In this study, a combination of field geochemical analyses and laboratory radiotracer ([1,2-14C] vinyl chloride) experiments was utilized to assess the potential for intrinsic biodegradation of vinyl chloride contamination in an Fe(III)-reducing, anaerobic aquifer. Microcosm experiments conducted under Fe(III)-reducing conditions with material from the Fe(III)-reducing, chlorinated-ethene contaminated aquifer demonstrated significant oxidation of [1,2-14C] vinyl chloride to 14CO2 with no detectable production of ethene or other reductive dehalogenation products. Rates of degradation derived from the microcosm experiments (0.9-1.3% d-1) were consistent with field-estimated rates (0.03-0.2% d-1) of apparent vinyl chloride degradation. Field estimates of apparent vinyl chloride biodegradation were calculated using two distinct approaches; 1) a solute dispersion model and 2) a mass balance assessment. These findings demonstrate that degradation under Fe(III) reducing conditions can be an environmentally significant mechanism for intrinsic bioremediation of vinyl chloride in anaerobic ground-water systems.

Journal of Contaminant Hydrology↗
USGS2005

Geochemical controls on microbial nitrate-dependent U(IV) oxidation

After reductive immobilization of uranium, the element may be oxidized and remobilized in the presence of nitrate by the activity of dissimilatory nitrate-reducing bacteria. We examined controls on microbially mediated nitrate-dependent U(IV) oxidation in landfill leachate-impacted subsurface sediments. Nitrate-dependent U(IV)-oxidizing bacteria were at least two orders of magnitude less numerous in these sediments than glucose- or Fe(II)-oxidizing nitrate-reducing bacteria and grew more slowly than the latter organisms, suggesting that U(IV) is ultimately oxidized by Fe(III) produced by nitrate-dependent Fe(II)-oxidizing bacteria or by oxidation of Fe(II) by nitrite that accumulates during organotrophic dissimilatory nitrate reduction. We examined the effect of nitrate and reductant concentration on nitrate-dependent U(IV) oxidation in sediment incubations and used the initial reductive capacity (RDC = [reducing equivalents] - [oxidizing equivalents]) of the incubations as a unified measurement of the nitrate or reductant concentration. When we lowered the RDC with progressively higher nitrate concentrations, we observed a corresponding increase in the extent of U(IV) oxidation, but did not observe this relationship between RDC and U(IV) oxidation rate, especially when RDC > 0, suggesting that nitrate concentration strongly controls the extent, but not the rate of nitrate-dependent U(IV) oxidation. On the other hand, when we raised the RDC in sediment incubations with progressively higher reductant (acetate, sulfide, soluble Fe(II), or FeS) concentrations, we observed progressively lower extents and rates of nitrate-dependent U(IV) oxidation. Acetate was a relatively poor inhibitor of nitrate-dependent U(IV) oxidation, while Fe(II) was the most effective inhibitor. Based on these results, we propose that it may be possible to predict the stability of U(IV) in a bioremediated aquifer based on the geochemical characteristics of that aquifer.

Geomicrobiology Journal↗