摘要:

Protocols were developed to determine whether microbial metabolism limits the ultimate removal of contaminants from soil. Two soils were used: a creosote contaminated soil and a soil contaminated with crude oil. A laboratory-scale slurry-phase bioreactor was used to maximize the rate of desorption of components from the soil to the aqueous phase. The protocols to enhance the ultimate removal of hydrocarbons were as follows: stimulation of the bacterial cultures with either naphthalene or a mixture of anthracene and phenanthrene, the use of static conditions to enhance bacterial attachment to the nonaqueous phase liquids in the soil, and increased incubation temperature. Addition of the polycyclic aromatic hydrocarbon (PAH) compounds did not stimulate removal of individual target compounds, classes of compounds or total thermally extractable organics. A comparison of well-mixed and static culture conditions showed equivalent removal, except for the lightest PAH and petroleum fractions that were removed more under well-mixed conditions. Increasing the temperature to 30°C from 21°C gave more rapid initial removal of petroleum components, but the ultimate removal was unaffected. Removal of components from the creosote-contaminated soil was unaffected by temperature. These results suggest that desorption of contaminants from the soils limited the ultimate removal of contaminants, not the biological activity.

ISSN:1088-9868    

DOI:10.1080/10889860091114220

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Controlled releases of unleaded gasoline were used 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 performed within two 2 m×2 m×3.5 m deep sheet-piling cells. A gasoline-contaminated zone was created below the water table in each treatment cell. Groundwater amended with electron acceptors was then flushed continuously through the cells for 174 d. One cell received approximately 100 mg/L nitrate and “microaerophilic” (i.e., 2 mg/L or less) dissolved oxygen (DO), a second cell received micro aerophilic DO only. Electron-acceptor utilization and hydrocarbon-metabolite formation were observed in both cells, suggesting that some microbial activity had been induced in response to flushing. However, nitrate utilization was slow relative to the cell residence time, and aromatic-hydrocarbon mass losses in response to microaerophilic DO addition were not apparent under these in situ conditions. Concentration trends in both cells suggested that there was relatively little biotransformation of the aromatic hydrocarbons over the 2-m flow path monitored in this experiment. Extraction-well concentration trends, for example, were consistent with abiotic gasoline dissolution. The results from the nitrate-amended cell suggest that a large denitrifying population capable of aromatic hydrocarbon biotransformation failed to develop within the gasoline source zone over a 14-month period of nitrate exposure. This study reinforces the need for detailed aquifer-specific testing prior to selecting bioremediation for full-scale cleanup, particularly for recent hydrocarbon spills.

ISSN:1088-9868    

DOI:10.1080/10889860091114239

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil was investigated using a mixed bacterial culture (community five) isolated from an abandoned industrial site. Community five was inoculated into contaminated soil containing a total PAH (two- to five-ring compounds) concentration of approximately 820 mg/kg soil. PAH degradation by the indigenous microbial population was restricted to the lower molecular weight compounds (naphthalene, acenaphthene, fluorene and phenanthrene) even with yeast extract addition: these compounds decreased by 14 to 37%, in soil hydrated to 50% water capacity, following 91 days of incubation at 24°C. Inoculation of community five into this PAH-contaminated soil resulted in significant decreases in the concentration of all PAHs over the incubation period: greater than 86% of naphthalene, acenaphthene, fluorene, and phenanthrene were degraded after 91 days, while anthracene, fluoranthene, and pyrene were degraded to lesser extents (51.7 to 57.6%). A lag period of 48 to 63 days was observed before the onset of benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene removal. However, significant decreases in the concentration of these compounds (32.6, 25.2, and 18.5%, respectively) were observed after 91 days. No significant decrease in the mutagenic potential of organic soil extracts (as measured by the Ames Test) was observed after incubation of the soil with the indigenous microflora; however, the Microtox toxicity of aqueous soil extracts was reduced sevenfold. In contrast, extracts from contaminated soil inoculated with community five underwent a 43% decrease in mutagenic potential and the toxicity was reduced 170-fold after 91 days incubation. These observations suggest that community five could be utilised for the detoxification of PAH-contaminated soil.

ISSN:1088-9868    

DOI:10.1080/10889860091114248

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Dechlorination studies were conducted using microbial cultures developed in a fluidized-bed reactor (FBR) that dechlorinates pentachlorophenol (PCP) to 3,4-dichlorophenol (3,4-DCP) and 4-monochlorophenol (4-MCP). Electron donor experiments demonstrated that lactate, propionate, and H2can serve as electron donors for chlorophenol (CP) dechlorination in mixed, anaerobic, PCP-enriched cultures. Dechlorination did not proceed in the absence of an electron donor. Acetate, which resulted in little H2production, was a poor electron donor. The results of inhibition studies using vancomycin and 2-bromoethanesulfonic acid implicate members of the domain bacteria in the dechlorination of CPs, whereas methanogens do not appear to be involved in dechlorination. Brief heat treatment (80°C for 90 min) of the FBR enrichment cultures implicated endospore formers in the dechlorination of CPs, primarily at theorthoposition, where PCP was dechlorinated to 3,4,5-trichlorophenol (3,4,5-TCP) (the sole TCP detected) and subsequently to 3,4-DCP. Both lactate and H2served as electron donors in the heat-and oxygen-treated cultures. In contrast, a lactate-fed anaerobic spread-plate enrichment culture exhibited solelymeta-dechlorination, where PCP dechlorinated solely to 2,4,6-TCP. The separation ofortho- andmeta-specific dechlorination reactions provides evidence that PCP dechlorination in the FBR enrichment culture was catalyzed by at least the following two separate groups of CP-dechlorinating bacteria: onemeta-dechlorinating group and one primarilyortho-dechlorinating group.

ISSN:1088-9868    

DOI:10.1080/10889860091114257

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Successful remediation of soils co-contaminated with organics and metals may require a combination of technologies. This research addresses the organic component within co-contaminated sites. It is well known that metal contaminants in soil can partially or completely inhibit normal heterotrophic microbial activity and hence prevent in situ biodegradation of organics. Previous work has shown that a rhamnolipid biosurfactant can complex metals such as lead and cadmium. It has also been demonstrated, in pure culture, that rhamnolipid can mitigate metal inhibition during the degradation of naphthalene. The goal of this study was to investigate whether rhamnolipid could reduce the toxicity of a model metal, cadmium, to indigenous soil populations in two different soils, Brazito and Gila, during the mineralization of phenanthrene. Results show that cadmium inhibited phenanthrene mineralization in both soils at bioavailable cadmium concentrations as low as 27 µM. This inhibition was reduced by the addition of rhamnolipid. Since rhamnolipid is degraded by soil populations, a rhamnolipid pulsing strategy was used to maintain a constant level of rhamnolipid in the system. Using this strategy, phenanthrene mineralization levels comparable to the control (0 mM Cd/0 mM rhamnolipid) were achieved in the presence of toxic cadmium concentrations. This research demonstrates that pulsed application of rhamnolipid may allow bioremediation of organic contaminants in sites that are co-contaminated with organics and metals.

ISSN:1088-9868    

DOI:10.1080/10889860091114266

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

ISSN:1088-9868    

DOI:10.1080/10889860091114275

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

A nationwide survey of chlorinated volatile organic compound (CVOC) plumes was conducted across a spectrum of sites from diverse hydrogeologic environments and contaminant release scenarios. The goal was to evaluate significant trends in the data that relate plume behavior to site variables (e.g., source strength, mean groundwater velocity, reductive dehalogenation regime) through correlation and population analyses. Data from 65 sites (government facilities, dry cleaners, landfills) were analyzed, yielding 247 individual CVOC plumes by compound. Data analyses revealed several trends, notably correlations between plume length and maximum observed concentration (presumably reflecting the source term) and mean groundwater velocities. Reductive dehalogenation, indicated by daughter products and groundwater geochemistry, appears to exert a relatively subtle effect on plume length, apparent only after the contributions of source strength and groundwater velocity are factored out. CVOC properties (Koc, Henry's Law constant) exert significant effects on variability in maximum observed concentrations between sites but hold little influence on plume length. Probabilistic plume modeling, entailing Monte Carlo simulation of an analytical solution for average plume behavior with parameter distributions derived from site data, was used to produce a synthetic plume set for comparison with field data. Modeling results exhibited good agreement with field data in terms of parameter sensitivity.

ISSN:1088-9868    

DOI:10.1080/10889860091114284

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Natural attenuation of trichloroethene (TCE) was evaluated for a groundwater plume at the Idaho National Engineering and Environmental Laboratory. Significant evidence demonstrated that reductive dechlori-nation is occurring, but is limited to a small area around the contamination source. In spite of this, the plume is relatively stable. Three first-order rate estimation methods were used to help understand transport processes affecting TCE in the large, aerobic portion of the plume. Two of the methods gave attenuation half-life estimates for TCE of approximately 8 years; however, these methods do not adequately distinguish between degradation and dispersion. The third method showed TCE attenuation relative to the co-contaminants, tritium and tetrachloroethene (PCE), and used these “tracers” to distinguish between dispersion and degradation. The estimated aerobic degradation half-life for TCE was between 13 and 21 years. Aerobic cometabolism of TCE has been identified as a potential mechanism for the apparent degradation. The importance of distinguishing between dispersion and degradation was shown using an analytical model. The model demonstrated that, in general, the rate of contaminant concentration decrease due to dispersion is not constant with time after the source is removed. This has important implications for predicting the long-term effectiveness of natural attenuation for groundwater restoration.

ISSN:1088-9868    

DOI:10.1080/10889860091114293

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Chemical, isotopic, and biological parameters were evaluated over a 1-year period to characterize microbial processes associated with intrinsic bioremediation in a petroleum hydrocarbon-contaminated aquifer located in Studen, Switzerland. Chemical parameters measured included oxidants such as O2, NO3−, and SO42−, reduced species such as Fe2+and CH4, and dissolved inorganic carbon (DIC). Stable carbon isotope analyses of DIC were used to differentiate between different processes that contribute to DIC production. Microbial populations were identified by sequence analysis of archaeal 16S rDNA and in situ hybridization using a general DNA binding dye (DAPI) and specific probes targeting the domain Archaea (Arch915) and Bacteria (Eub338), as well as the speciesMethanosaeta concilii(Rotcl1) andMethanospirillumsp. (Rotcl2). Groundwater exhibited reduced conditions and elevated concentrations of DIC within the contaminated zone. Spatially distinct values of δ13C ranging from −16.5l%c to −4.44%o were found, indicating the presence of different ongoing microbial processes. Detected microbial populations (% of DAPI-stained cells) within the contaminated zone belonged to Archaea (9±2% to 31±13%) and Bacteria (13±3% to 32±13%). In wells with methanogenic activity, Methanosaeta concilii accounted for up to 26% of all DAPI-detected microorganisms. These results demonstrate that this novel combination of chemical, isotopic, and biological analysis provides valuable insights that can be used for the characterization of microbial processes in contaminated aquifers.

ISSN:1088-9868    

DOI:10.1080/10889860091114301

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor