situ assessment of microbial sulfate reduction in a petroleum-contaminated aquifer using push-pull tests and stable sulfur isotope analyses

Abstract Anaerobic microbial activities such as sulfate reduction are important for the degradation of Ž . petroleum hydrocarbons PHC in contaminated aquifers. The objective of this study was to evaluate the feasibility of single-well push-pull tests in combination with stable sulfur isotope analyses for the in situ quantification of microbial sulfate reduction. A series of push-pull tests Ž was performed in an existing monitoring well of a PHC-contaminated aquifer in Studen Switzer-. land . Sulfate transport behavior was evaluated in a first test. In three subsequent tests, we injected Ž . Ž y . anoxic test solutions up to 1000 l , which contained 0.5 mM bromide Br as conservative tracer Ž 2y . and 1 mM sulfate SO as reactant. Ž . PII: S 0 1 6 9 -7 7 2 2 0 1 0 0 1 2 8 -0 Schroth et al.r Journal of Contaminant Hydrology 51 2001 179-195 180 analyses proved useful for the in situ quantification of microbial sulfate reduction in a PHC-contaminated aquifer.

Impact of oil on bacterial community structure in bioturbated sediments

Oil spills threaten coastlines where biological processes supply essential ecosystem services. Therefore, it is crucial to understand how oil influences the microbial communities in sediments that play key roles in ecosystem functioning. Ecosystems such as sediments are characterized by intensive bioturbation due to burrowing macrofauna that may modify the microbial metabolisms. It is thus essential to consider the bioturbation when determining the impact of oil on microbial communities. In this study, an experimental laboratory device maintaining pristine collected mudflat sediments in microcosms closer to true environmental conditions - with tidal cycles and natural seawater - was used to simulate an oil spill under bioturbation conditions. Different conditions were applied to the microcosms including an addition of: standardized oil (Blend Arabian Light crude oil, 25.6 mg.g21 wet sediment), the common burrowing organism Hediste (Nereis) diversicolor and both the oil and H. diversicolor. The addition of H. diversicolor and its associated bioturbation did not affect the removal of petroleum hydrocarbons. After 270 days, 60% of hydrocarbons had been removed in all microcosms irrespective of the H. diversicolor addition. However, 16S-rRNA gene and 16S-cDNA T-RFLP and RT-PCR-amplicon libraries analysis showed an effect of the condition on the bacterial community structure, composition, and dynamics, supported by PerMANOVA analysis. The 16S-cDNA libraries from microcosms where H. diversicolor was added (oiled and un-oiled) showed a marked dominance of sequences related to Gammaproteobacteria. However, in the oiled-library sequences associated to Deltaproteobacteria and Bacteroidetes were also highly represented. The 16S-cDNA libraries from oiled-microcosms (with and without H. diversicolor addition) revealed two distinct microbial communities characterized by different phylotypes associated to known hydrocarbonoclastic bacteria and dominated by Gammaproteobacteria and Deltaproteobacteria. In the oiled-microcosms, the addition of H. diversicolor reduced the phylotype-richness, sequences associated to Actinobacteria, Firmicutes and Plantomycetes were not detected. These observations highlight the influence of the bioturbation on the bacterial community structure without affecting the biodegradation capacities

Monitoring of microbial hydrocarbon remediation in the soil

Bioremediation of hydrocarbon pollutants is advantageous owing to the cost-effectiveness of the technology and the ubiquity of hydrocarbon-degrading microorganisms in the soil. Soil microbial diversity is affected by hydrocarbon perturbation, thus selective enrichment of hydrocarbon utilizers occurs. Hydrocarbons interact with the soil matrix and soil microorganisms determining the fate of the contaminants relative to their chemical nature and microbial degradative capabilities, respectively. Provided the polluted soil has requisite values for environmental factors that influence microbial activities and there are no inhibitors of microbial metabolism, there is a good chance that there will be a viable and active population of hydrocarbon-utilizing microorganisms in the soil. Microbial methods for monitoring bioremediation of hydrocarbons include chemical, biochemical and microbiological molecular indices that measure rates of microbial activities to show that in the end the target goal of pollutant reduction to a safe and permissible level has been achieved. Enumeration and characterization of hydrocarbon degraders, use of micro titer plate-based most probable number technique, community level physiological profiling, phospholipid fatty acid analysis, 16S rRNA- and other nucleic acid-based molecular fingerprinting techniques, metagenomics, microarray analysis, respirometry and gas chromatography are some of the methods employed in bio-monitoring of hydrocarbon remediation as presented in this review

A comparative study of different mesh types for transport processes near gas bubbles regarding accuracy, stability, and run time

Mass transfer at a single gas bubble rising in incompressible liquid is studied. Only the liquid phase is simulated. A fixed bubble model is used and non-deformable spheroidal gas bubbles with aspect ratio χ = 3 are considered. The Reynolds number is varied between 50 and 500 and two Schmidt numbers, 10 and 100 , are taken into account. Four meshing strategies are compared with respect to accuracy, stability and run-time. The main focus is on mesh sensitivity of the target quantities close to the interface and in the bubble wake. The results are compiled in a Best Practice Guide

A comparative study of different mesh types for transport processes near gas bubbles regarding accuracy, stability, and run time

Mass transfer at a single gas bubble rising in incompressible liquid is studied. Only the liquid phase is simulated. A fixed bubble model is used and non-deformable spheroidal gas bubbles with aspect ratio χ = 3 are considered. The Reynolds number is varied between 50 and 500 and two Schmidt numbers, 10 and 100 , are taken into account. Four meshing strategies are compared with respect to accuracy, stability and run-time. The main focus is on mesh sensitivity of the target quantities close to the interface and in the bubble wake. The results are compiled in a Best Practice Guide

Multicomponent transport of sulfate in a goethite-silica sand system at variable pH and ionic strength

In this work, existing models for adsorption of protons and sulfate on goethite and silica were used in combination with a one-dimensional mass- transport model to predict the transport of sulfate at variable pH and ionic strength in a goethite-silica system. The predicted multicomponent transport phenomena are discussed, and an evaluation is made of the sensitivity of the results to different input parameters. This information was used to select optimal conditions for independent experimental testing of the model. Column experiments were carried out in which solutions of known pH, sulfate concentration, and salt concentration were infiltrated into a goethite-coated quartz sand column. The agreement between the experiments and the predictions is very good, especially considering the fact that no fitting of model parameters to the actual experimental system was involved. According to the model calculations, transport behavior of sulfate in a goethite system is very sensitive to relatively small amounts of adsorbed sulfate initially present. This could be an explanation for the remaining differences between the predicted and the measured curves. It also implies that, for the application of such mechanistic models to soils, accurate information on the initial composition of the soil is essential. | In this work, existing models for adsorption of protons and sulfate on goethite and silica were used in combination with a one-dimensional mass-transport model to predict the transport of sulfate at variable pH and ionic strength in a goethite-silica system. The predicted multicomponent transport phenomena are discussed, and an evaluation is made of the sensitivity of the results to different input parameters. This information was used to select optimal conditions for independent experimental testing of the model. Column experiments were carried out in which solutions of known pH, sulfate concentration, and salt concentration were infiltrated into a goethite-coated quartz sand column. The agreement between the experiments and the predictions is very good, especially considering the fact that no fitting of model parameters to the actual experimental system was involved. According to the model calculations, transport behavior of sulfate in a goethite system is very sensitive to relatively small amounts of adsorbed sulfate initially present. This could be an explanation for the remaining differences between the predicted and the measured curves. It also implies that, for the application of such mechanistic models to soils, accurate information on the initial composition of the soil is essential

Structure of sediment-associated bacterial communities along a hydrocarbon contamination gradient in coastal sediment

The bacterial diversity of a chronically oil-polluted retention basin sediment located in the Berre lagoon (Etang-de-Berre, France) was investigated. This study combines chemical and molecular approaches in order to define how the in situ petroleum hydrocarbon contamination level affects the bacterial community structure of a subsurface sediment. Hydrocarbon content analysis clearly revealed a gradient of hydrocarbon contamination in both the water and the sediment following the basin periphery from the pollution input to the lagoon water. The nC17 and pristane concentrations suggested alkane biodegradation in the sediments. These results, combined with those of terminal-restriction fragment length polymorphism analysis of the 16S rRNA genes, indicated that bacterial community structure was obviously associated with the gradient of oil contamination. The analysis of bacterial community composition revealed dominance of bacteria related to the Proteobacteria phylum (Gamma-, Delta-, Alpha-, Epsilon- and Betaproteobacteria), Bacteroidetes and Verrucomicrobium groups and Spirochaetes, Actinobacteria and Cyanobacteria phyla. The adaptation of the bacterial community to oil contamination was not characterized by dominance of known oildegrading bacteria, because a predominance of populations associated to the sulphur cycle was observed. The input station presented particular bacterial community composition associated with a low oil concentration in the sediment, indicating the adaptation of this community to the oil contamination

Genotypic distribution of an indigenous model microorganism along an estuarine gradient

Using the genus Desulfobulbus as an indigenous model, microbial distribution along an estuarine gradient was investigated. Denaturing gradient gel electrophoresis analysis indicated a sequential change in Desulfobulbus genotypes along the estuary with marine, brackish and freshwater genotypes detected. This differential distribution was significantly correlated with porewater concentrations of chloride, sulphate and nitrate. Temporal analysis indicated that there was a shift in the whole Desulfobulbus community towards to marine end of the estuary by the end of the winter compared with the late summer. This distribution pattern is similar to those seen with other estuarine organisms and, given the correlation with chloride and sulphate, is indicative of classic niche separation within this genus driven by gross environmental factors such as salinity. These results will help in developing a truly ecological description of microbial biodiversity