259 Matching Results

Search Results

Advanced search parameters have been applied.

Induced biochemical interactions in immature and biodegraded heavy crude oils

Description: Studies in which selective chemical markers have been used to explore the mechanisms by which biocatalysts interact with heavy crude oils have shown that the biochemical reactions follow distinct trends. The term biocatalyst refers to a group of extremophilic microorganisms which, under the experimental conditions used, interact with heavy crude oils to (1) cause a redistribution of hydrocarbons, (2) cause chemical changes in oil fractions containing sulfur compounds and lower the sulfur content, (3) decrease organic nitrogen content, and (4) decrease the concentration of trace metals. Current data indicate that the overall effect is due to simultaneous reactions yielding products with relatively higher concentration of saturates and lower concentrations of aromatics and resins. The compositional changes depend on the microbial species and the chemistry of the crudes. Economic analysis of a potential technology based on the available data indicate that such a technology, used in a pre-refinery mode, may be cost efficient and promising. In the present paper, the background of oil biocatalysis and some recent results will be discussed.
Date: November 1, 1998
Creator: Premuzic, E.T.; Lin, M.S.; Bohenek, M.; Joshi-Tope, G.; Shelenkova, L. & Zhou, W.M.
Partner: UNT Libraries Government Documents Department

Molecular Approaches to Understanding C & N Dynamics in Marine Sediments

Description: Continental margin sediments constitute only about 10% of the total sediment surface area in the world’s oceans, nevertheless they are the dominant sites of nitrogen (N) cycling. Recent studies suggest that the oceanic nitrogen budget is unbalanced, primarily due to a higher nitrogen removal rate in contrast to the fixation rate, and it has been suggested that denitrification activity contributes significantly to this imbalance. Although denitrification in marine environments has been studied intensively at the process level, little is known about the species abundance, composition, distribution, and functional differences of the denitrifying population. Understanding the diversity of microbial populations in marine environments, their responses to various environmental factors such as NO3-, and how this impact the rate of denitrification is critical to predict global N dynamics. Environmental Microbiology has the prompt to study the influence of each microbial population on a biogeochemical process within a given ecosystem. Culture-dependent and –independent techniques using nucleic acid probes can access the identity and activity of cultured and uncultured microorganisms. Nucleic acid probes can target distintict genes which set phylogenetic relationships, such as rDNA 16S, DNA gyrase (gyrB) and RNA polymerase sigma 70 factor (rpoD). In the other hand, the genetic capabilities and their expression could be tracked using probes that target several functional genes, such as nirS, nirK, nosZ, and nifH, which are genes involved in denitrification. Selective detection of cells actively expressing functional genes within a community using In Situ Reverse Transcription-PCR (ISRT-PCR) could become a powerful culture-independent technique in microbial ecology. Here we describe an approach to study the expression of nirS genes in denitrifying bacteria. Pure cultures of Pseudomonas stutzeri and Paracoccus denitrificans, as well as co-cultures with non-denitrifying populations were used to optimize the ISRT-PCR protocol. Cells grown on nitrate broth were harvested and fixed at both logarithmic (24-48 ...
Date: May 16, 2007
Creator: Massol, Arturo; Tiedje, James; Zhou, Jizhong & Devol, Allan
Partner: UNT Libraries Government Documents Department

Final technical report for award NO. DE-FG02-95ER20206

Description: ABSTRACT Initial work focused on the regulation of nitrite reductase, the defining reaction of denitrification as well as nitric oxide (NO) reductase. Expression of the genes encoding both proteins was controlled by NnrR. This regulator was shown to be responsive to NO. More recent work has shown NnrR function is also likely inhibited by oxygen. Therefore, it is this protein that sets the oxygen level at which nitrate respiration takes over from aerobic respiration. The gene encoding NO reductase appears to only require NnrR for expression. Expression of the gene encoding nitrite reductase is more complex. In addition to NnrR, a two component sensor regulator complex termed PrrA and PrrB is also required for expression. These proteins are global regulators and serve to link denitrification with other bioenergetic processes in the cell. They also provide an additional layer of oxygen dependent regulation. The sequencing of the R. sphaeroides 2.4.3 genome allowed us to identify several other genes regulated by NnrR. Surprisingly, most of the genes were not essential for denitrification. Their high level of conservation in related denitrifiers suggests they do provide a selectable benefit to the bacterium, however. We also examined the role of nitrate reductase in contributing to denitrification in R. sphaeroides. Strain 2.4.3 is unusual in having two distinct, but related clusters of genes encoding nitrate reductase. One of these genes clusters is expressed under high oxygen conditions but is repressed, likely by PrrB-PrrA, under low oxygen conditions. The other cluster is expressed only under low oxygen conditions. This cluster expresses the nitrate reductase used during denitrification. The high oxygen expressed cluster encodes a protein used for redox homeostasis. Surprisingly, both clusters are fully expressed even in the absence of nitrate. During the course of this work we found that the type strain of R. sphaeroides, 2.4.1, ...
Date: February 23, 2010
Creator: Shapleigh, James P.
Partner: UNT Libraries Government Documents Department

Plant and microbial controls on nitrogen retention and loss in a Humid Tropical Forest

Description: Humid tropical forests are generally characterized by the lack of nitrogen (N) limitation to net primary productivity, yet paradoxically have high potential for N loss. We conducted an intensive field experiment with {sup 15}NH{sub 4} and {sup 15}NO{sub 3} additions to highly weathered tropical forest soils to determine the relative importance of N retention and loss mechanisms. Over half of all the NH{sub 4}{sup +} produced from gross mineralization was rapidly converted to NO{sub 3}{sup -} during the process of gross nitrification. During the first 24 h plant roots took up 28 % of the N mineralized, dominantly as NH{sub 4}{sup +}, and were a greater sink for N than soil microbial biomass. Soil microbes were not a significant sink for added {sup 15}NH{sub 4}{sup +} or {sup 15}NO{sub 3}{sup -} during the first 24 hr, and only for {sup 15}NH{sub 4}{sup +} after 7 d. Patterns of microbial community composition, as determined by Terminal Restriction Fragment Length Polymorphism analysis, were weakly, but significantly correlated with nitrification and denitrification to N{sub 2}O. Rates of dissimilatory NO{sub 3}{sup -} reduction to NH{sub 4}{sup +} (DNRA) were high in this forest, accounting for up to 25 % of gross mineralization and 35 % of gross nitrification. DNRA was a major sink for NO{sub 3}{sup -} which may have contributed to the lower rates of N{sub 2}O and leaching losses. Despite considerable N conservation via DNRA and plant NH{sub 4}{sup +} uptake, the fate of approximately 45% of the NO{sub 3}{sup -} produced and 22% of the NH{sub 4}{sup +} produced were not measured in our fluxes, suggesting that other important pathways for N retention and loss (e.g., denitrification to N{sub 2}) are important in this system. The high proportion of mineralized N that was rapidly nitrified and the fates of that NO{sub ...
Date: September 15, 2009
Creator: Templer, P.; Silver, W.; Pett-Ridge, J.; DeAngelis, K.M. & Firestone, M.K.
Partner: UNT Libraries Government Documents Department

Process/economic strategy for upgrading shale oil

Description: A prime difficulty with the production of transportation fuels from Western US shale oil is the high heteroatom content, especially nitrogen. Nitrogen containing molecules are known to have high market value for non-fuel uses. Selective extraction of nitrogen-containing molecules from shale oil recovers these potentially valuable components while upgrading the remaining shale oil for refining to transportation fuels. A thermodynamically logical separation process sequence consisting of primarily distillation and liquid-liquid extraction has been shown effective in selective isolation of polar heteroatom-containing molecules. The polar fraction may be processed for the production of chemical intermediates and specialty chemicals of high value. Projected material balances show an overall product split of 80% refinery feed and 20% polar products. Based on product values and composition, a preliminary economic analysis yields 30% internal rate of return. A summary of the economic strategy, process results and promising products will be presented.
Date: December 31, 1994
Creator: Bunger, J.W.; Russell, C.P.; Devineni, P.A.V.; Cogswell, D.E. & Wiser, J.W.
Partner: UNT Libraries Government Documents Department

Induced biochemical interactions in crude oils

Description: In the evolution of oil from sedimentary to reservoir conditions, the hydrogen to carbon ratios decrease while the oxygen, nitrogen, and sulfur to carbon ratios increase. During this process, the oils become heavier and richer in asphaltenes. In terms of chemical composition, the oils become enriched in resins, asphaltenes, and polar compounds containing the heteroatoms and metals. Over the geological periods of time, the chemical and physical changes have been brought about by chemical, biological (biochemical) and physical (temperature and pressure) means as well as by the catalytic effects of the sedimentary matrices, migration, flooding, and other physical processes. Therefore, different types of oils are the end products of a given set of such interactions which were brought about by multiple and simultaneous physicochemical processes involving electron transfer, free radical, and chemical reactions. A biocatalyst introduced into a reaction mixture of the type produced by such reactions will seek available chemical reaction sites and react at the most favorable ones. The rates and the chemical pathways by which the biocatalytic reactions will proceed will depend on the oil type and the biocatalyst(s). Some of the possible reaction pathways that may occur in such complex mixtures are discussed.
Date: August 1, 1996
Creator: Premuzic, E.T. & Lin, M.S.
Partner: UNT Libraries Government Documents Department

Economic feasibility of biochemical processes for the upgrading of crudes and the removal of sulfur, nitrogen, and trace metals from crude oil -- Benchmark cost establishment of biochemical processes on the basis of conventional downstream technologies. Final report FY95

Description: During the past several years, a considerable amount of work has been carried out showing that microbially enhanced oil recovery (MEOR) is promising and the resulting biotechnology may be deliverable. At Brookhaven National Laboratory (BNL), systematic studies have been conducted which dealt with the effects of thermophilic and thermoadapted bacteria on the chemical and physical properties of selected types of crude oils at elevated temperatures and pressures. Current studies indicate that during the biotreatment several chemical and physical properties of crude oils are affected. The oils are (1) emulsified; (2) acidified; (3) there is a qualitative and quantitative change in light and heavy fractions of the crudes; (4) there are chemical changes in fractions containing sulfur compounds; (5) there is an apparent reduction in the concentration of trace metals; and (6) the qualitative and quantitative changes appear to be microbial species dependent; and (7) there is a distinction between biodegraded and biotreated oils. The downstream biotechnological crude oil processing research performed thus far is of laboratory scale and has focused on demonstrating the technical feasibility of downstream processing with different types of biocatalysts under a variety of processing conditions. Quantitative economic analysis is the topic of the present project which investigates the economic feasibility of the various biochemical downstream processes which hold promise in upgrading of heavy crudes, such as those found in California, e.g., Monterey-type, Midway Sunset, Honda crudes, and others.
Date: August 1, 1996
Creator: Premuzic, E.T.
Partner: UNT Libraries Government Documents Department


Description: Studies in which selective chemical markers have been used to explore the mechanisms by which biocatalysts interact with heavy crude oils have shown that the biochemical reactions follow distinct trends. The term biocatalyst refers to a group of extremophilic microorganisms which, under the experimental conditions used, interact with heavy crude oils to (1) cause a redistribution of hydrocarbons, (2) cause chemical changes in oil fractions containing sulfur compounds and lower the sulfur content, (3) decrease organic nitrogen content, and (4) decrease the concentration of trace metals. Current data indicate that the overall effect is due to simultaneous reactions yielding products with relatively higher concentration of saturates and lower concentrations of aromatics and resins. The compositional changes depend on the microbial species and the chemistry of the crudes. Economic analysis of a potential technology based on the available data indicate that such a technology, used in a pre-refinery mode, may be cost efficient and promising. In the present paper, the background of oil biocatalysis and some recent results will be discussed.
Date: October 27, 1998
Partner: UNT Libraries Government Documents Department

Biological upgrading of coal liquids. Final report

Description: A large number of bacterial enrichments have been developed for their ability to utilize nitrogen and sulfur in coal liquids and the model compound naphtha. These bacteria include the original aerobic bacteria isolated from natural sources which utilize heteroatom compounds in the presence of rich media, aerobic nitrogen-utilizing bacteria and denitrifying bacteria. The most promising isolates include Mix M, a mixture of aerobic bacteria; ER15, a pyridine-utilizing isolate; ERI6, an aniline-utilizing isolate and a sewage sludge isolate. Culture optimization experiments have led to these bacteria being able to remove up to 40 percent of the sulfur and nitrogen in naphtha and coal liquids in batch culture. Continuous culture experiments showed that the coal liquid is too toxic to the bacteria to be fed without dilution or extraction. Thus either semi-batch operation must be employed with continuous gas sparging into a batch of liquid, or acid extracted coal liquid must be employed in continuous reactor studies with continuous liquid flow. Isolate EN-1, a chemical waste isolate, removed 27 percent of the sulfur and 19 percent of the nitrogen in fed batch experiments. Isolate ERI5 removed 28 percent of the nitrogen in coal liquid in 10 days in fed batch culture. The sewage sludge isolate removed 22.5 percent of the sulfur and 6.5 percent of the nitrogen from extracted coal liquid in continuous culture, and Mix M removed 17.5 percent of the nitrogen from medium containing extracted coal liquid. An economic evaluation has been prepared for the removal of nitrogen heteroatom compounds from Wilsonville coal liquid using acid extraction followed by fermentation. Similar technology can be developed for sulfur removal. The evaluation indicates that the nitrogen heteroatom compounds can be removed for $0.09/lb of coal liquid treated.
Date: February 1, 1995
Partner: UNT Libraries Government Documents Department

Hydrotreating studies involving NiMo/silica-doped hydrous titanium oxide (HTO:Si)-coated alumina catalysts

Description: For hydrotreating a petroleum-derived liquid feed at 400 C, LHSV = 2. 5 g/g{sub cat}/h, and 1500 psig hydrogen (H) pressure, both HDS and HDN activities were roughly equivalent for a name/TO:Si-coated Amocat catalyst and a commercial alumina-supported name catalyst (Amocat 1C). Superior HDN performance was exhibited by the name/TO: Si-coated Amocat catalyst at low H pressure (500 psig) and after H pressure cycling (1500-500-1500 psig) relative to Amocat 1C. Consistent with previous results obtained on a coal-derived liquid feed, the HDS/HDN results with the petroleum-derived liquid showed that the performance of the name/TO:Si-coated Amocat catalyst on an active metals weight basis exceeded the performance of Amocat 1C at all test conditions. The name/TO:Si-coated Amocat catalyst also showed potentially increased hydrogenation activity, increased resistance to deactivation, and increased yields of lower boiling point distillate fractions, although further work is needed.
Date: July 1, 1996
Creator: Gardner, T.J.; Miller, J.E.; McLaughlin, L.I. & Trudell, D.E.
Partner: UNT Libraries Government Documents Department

Environmental significance of biocatalytic conversion of low grade oils

Description: Studies dealing with the interactions between extremophilic microorganisms and crude oils have led to the identification of biocatalysts which through multiple biochemical reactions catalyze desulfurization, denitrogenation, and demetalation reactions in oils. Concurrently, the oils are also converted to lighter oils. These complex biochemical reactions have served as models in the development of the crude oil bioconversion technology to be applied prior to the treatment of oils by conventional chemical processes. In practical terms, this means that the efficiency of the existing technology is being enhanced. For example, the recently introduced additional regulation for the emission of nitrogen oxides in some states restricts further the kinds of oils that may be used in burners. The biocatalysts being developed in this laboratory selectively interact with nitrogen compounds, i.e. basic and neutral types present in the oil and, hence, affect the fuel NOx production. This, in turn, has a cost-efficient influence on the processed oils and their consumption. In this paper, these cost-efficient and beneficial effects will be discussed in terms of produced oils, the lowering of sulfur and nitrogen contents, and the effect on products, as well as the longevity of catalysts due to the removal of heteroatoms and metal containing compounds found in crudes.
Date: September 1, 1996
Creator: Lin, M.S.; Premuzic, E.T.; Lian, H.; Zhou, W.M. & Yablon, J.
Partner: UNT Libraries Government Documents Department

The use of chemical markers in the evaluation of crude oil bioconversion products, technology, and economic analysis

Description: Experimental data gathered over the past several years show that the interactions of microorganisms with crude oils are variable and depend on the microbial species and the chemical composition of crude oils. Systematic studies of chemical mechanisms by which selected microorganisms react with crude oils have led to the identification of biochemical markers characteristic of the interactions of microbes with oils. These biomarkers belong to several groups of natural products ranging from saturate and polyaromatic hydrocarbons containing heterocyclics to organometallic compounds. Chemical marker analyses indicate that the interaction of microbes with crude oils involves multiple chemical reactions resulting from the biochemical interactions between microbes and oils. Different interactions may influence the efficiency of processes in which single or mixed microbial species are used for the oil treatment and may also suggest possible combinations of biological and chemical technologies. Further, the biochemical conversions of oils can be monitored by these chemical markers, which is particularly useful in the optimization of biochemical processing, cost efficiency, and engineering studies. Recent results from these studies are discussed.
Date: March 1, 1996
Creator: Premusic, E.T.; Lin, M.S.; Lian, H.; Zhou, W.M. & Yablon, J.
Partner: UNT Libraries Government Documents Department

Methods for environmental monitoring of DOE waste disposal and storage sites: Proposal for optimizing a biological treatment system for denitrification of Y-12 waste streams. Semiannual progress report, November 1, 1987--March 31, 1988

Description: The denitrification process at Y-12 involves the use of sludge to denitrify aqueous plating waste containing relatively high levels of NO{sub 3}. The process from time to time does not denitrify. The factors associated with the failure of the process remains to be resolved. The authors propose to resolve those factors by taking the following research approaches: (1) isolation and identification of microorganisms originating from sewage sludge which are associated with denitrification; (2) define physiological factors required for denitrification in this process system; and (3) define toxic factors associated with the aqueous waste that may affect the process of denitrification.
Date: December 31, 1988
Creator: Hicks, G.M. & Revis, N.
Partner: UNT Libraries Government Documents Department

Simultaneous removal of H{sub 2}S and NH{sub 3} from coal gas. Final report

Description: Hydrogen sulfide (H{sub 2}S) and ammonia (NH{sub 3}) are the primary sulfur and nitrogen contaminants released when coal is gasified. Before coal gas can be utilized in an integrated gasification combined cycle (IGCC) plant to produce electricity, these contaminants need to be removed. The objective of this research was to develop sorbent-catalysts with the ability to simultaneously remove H{sub 2}S and NH{sub 3} from coal gas. Microreactor tests with HART-49, a zinc-based sorbent-catalyst with Ni, Co, and Mo as catalyst additives, showed that this material had the potential to remove 90% NH{sub 3} and reduce H{sub 2}S to <20 ppmv at 1 atm and 550 to 700 C. HART-49 was prepared in attrition-resistant fluidizable form (HART-56) using up to 75 wt% binder. Bench-scale fluidized-bed multicycle tests were conducted with the attrition-resistant sorbent-catalyst, HART-56, at 20 atm and 550 C. The H{sub 2}S and NH{sub 3} removal performance over the first two cycles was good in the presence of 5% steam but deteriorated thereafter when steam level was increased to 15%. The results point to a complex mechanism for simultaneous H{sub 2}S and NH{sub 3} removal, potentially involving both chemisorption and catalytic decomposition of NH{sub 3}. Further research and development is needed to develop a sorbent-catalyst for simultaneous H{sub 2}S and NH{sub 3} removal at IGCC hot-gas cleanup conditions.
Date: May 1, 1998
Creator: Gangwal, S.K. & Portzer, J.W.
Partner: UNT Libraries Government Documents Department

Simultaneous removal of H{sub 2}S and NH{sub 3} in coal gasification processes. [Quarterly report], January 1, 1996--March 31, 1996

Description: The objective of this study is to develop advanced high-temperature coal gas desulfurization mixed-metal oxide sorbents with stable ammonia decomposition materials at 550-800{degree} C (1022- 1472{degree} F). The specific objectives of the project are to: (1) develop a combined sorbent-catalyst materials shall be capable of removing hydrogen sulfide to less than 20 ppmv and ammonia by at least 90 percent (objective completed); (2) carry out comparative fixed-bed studies of absorption and regeneration with various formulations of sorbent-catalyst systems and select most promising sorbent-catalyst type (also completed); (3) conduct long-term (at least 30 cycles) durability and chemical reactivity in the fixed-bed with the superior sorbent-catalyst. Since HART-49 sorbent-catalysts showed a very promising catalyst activity for ammonia decomposition it was decided to run the multicycle runs using HART-49 sorbent-catalysts. Initially, up to 180 min the sorbent catalyst showed a very high activity ({gt}90{percent}). The decline in activity after 180 min is mainly due to the poisoning of the catalyst by H{sub 2}S. The pre-breakthrough H{sub 2}S level was below 20 ppm. Complete sorbent conversion was observed at breakthrough. The average conversion was increased from 54 to 70 {percent} as the temperature was increased from 500 to 770 {degree}C for HART-49 sorbent catalysts. Additional multicycle runs will be conducted using HART-51 sorbent-catalysts. 5 refs., 6 figs.
Date: August 1, 1996
Creator: Jothimurugesan, K.; Adeyiga, A.A. & Gangwal, S.K.
Partner: UNT Libraries Government Documents Department

Supercritical fluid reactions for coal processing. Quarterly progress report, January 1, 1995--March 31, 1995

Description: Exciting opportunities exist for the application of supercritical fluid (SCF) reactions for the pre-treatment of coal. Utilizing reactants which closely resemble the organic sulfur and nitrogen containing components of coal, we propose to develop a method to tailor chemical reactions in supercritical fluid solvents for the specific application of coal desulfurization and denitrogenation. Diels-Alder reactions involving such compounds have been extensively studied and characterized in liquids. However, there is very little understanding of such reactions in SCF`S. We are developing an approach which will allow optimum design of coal desulfurization and denitrogenation processes.
Date: August 1, 1995
Creator: Eckert, C.A.
Partner: UNT Libraries Government Documents Department

Hydrotreating of coal-derived liquids

Description: The objective of Sandia`s refining of coal-derived liquids project is to determine the relationship between hydrotreating conditions and Product characteristics. The coal-derived liquids used in this work were produced In HTI`s first proof-of-concept run using Illinois No. 8 coal. Samples of the whole coal liquid product, distillate fractions of this liquid, and Criterion HDN-60 catalyst were obtained from Southwest Research Inc. Hydrotreating experiments were performed using a continuous operation, unattended, microflow reactor system. A factorial experimental design with three variables (temperature, (310{degrees}C to 388{degrees}C), liquid hourly space velocity (1 to 3 g/h/cm{sup 3}(cat)), pressure (500 to 1000 psig H{sub 2}) is being used in this project. Sulfur and nitrogen contents of the hydrotreated products were monitored during the hydrotreating experiments to ensure that activity was lined out at each set of reaction conditions. Results of hydrotreating the whole coal liquid showed that nitrogen values in the products ranged from 549 ppM at 320{degrees}C, 3 g/h/cm{sup 3}(cat), 500 psig H{sub 2} to <15 ppM at 400{degrees}C, 1 g/h/ cm{sup 3}(cat), 1000 psig H{sub 2}.
Date: June 1, 1995
Creator: Stohl, F.V.; Lott, S.E.; Diegert, K.V.; Goodnow, D.C. & Oelfke, J.B.
Partner: UNT Libraries Government Documents Department

Simultaneous removal of H{sub 2}S and NH{sub 3} in coal gasification processes. Final report

Description: Nitrogen (N{sub 2}) occurs in coal in the form of tightly bound organic ring compounds, typically at levels of 1 to 2 wt.% on a dry-ash-free basis. During gasification, this fuel-bound nitrogen is released principally as ammonia. The formation of NH{sub 3} in coal gasification processes is a function of the coal N{sub 2} content and the gasifier operating conditions.During the use of coal gas to generate electricity in gas-fired turbines or molten carbonate fuel cells, fuel bound N{sub 2} is converted to nitrogen oxides (NO{sub x}), which are difficult to remove and are highly undesirable as atmospheric pollutants. Thus it is desirable to remove NH{sub 3} from coal gas in addition to other major contaminants such as hydrogen sulfide (H{sub 2}S) and particulates. The objective of this study was to develop a successful sorbent-catalyst combination of an NH{sub 3} decomposition catalyst with a zinc-based mixed-metal oxide H{sub 2}S sorbent with stable NH{sub 3} decomposition and H{sub 2}S removal efficiency under cyclic sulfidation-regeneration conditions in the temperature range of 500 to 700 C. Combining the NH{sub 3} and H{sub 2}S removal steps is expected to reduce capital and operating costs in an integrated gasification combined cycle (IGCC) power plant.
Date: November 1, 1996
Creator: Jothimurugesan, K.; Adeyiga, A. A. & Gangwal, S. K.
Partner: UNT Libraries Government Documents Department

Incorporation of aqueous reaction kinetics and biodegradation intoTOUGHREACT: Application of a multi-region model to hydrobiogeoChemicaltransport of denitrification and sulfate reduction

Description: The need to consider aqueous and sorption kinetics andmicrobiological processes arises in many subsurface problems. Ageneral-rate expression has been implemented into the TOUGHREACTsimulator, which considers multiple mechanisms (pathways) and includesmultiple product, Monod, and inhibition terms. This paper presents aformulation for incorporating kinetic rates among primary species intomass-balance equations. The space discretization used is based on aflexible integral finite difference approach that uses irregular griddingto model bio-geologic structures. A general multi-region model forhydrological transport interacted with microbiological and geochemicalprocesses is proposed. A 1-D reactive transport problem with kineticbiodegradation and sorption was used to test the enhanced simulator,which involves the processes that occur when a pulse of water containingNTA (nitrylotriacetate) and cobalt is injected into a column. The currentsimulation results agree very well with those obtained with othersimulators. The applicability of this general multi-region model wasvalidated by results from a published column experiment ofdenitrification and sulfate reduction. The matches with measured nitrateand sulfate concentrations were adjusted with the interficial areabetween mobile hydrological and immobile biological regions. Resultssuggest that TOUGHREACT can not only be a useful interpretative tool forbiogeochemical experiments, but also can produce insight into processesand parameters of microscopic diffusion and their interplay withbiogeochemical reactions. The geometric- and process-based multi-regionmodel may provide a framework for understanding field-scalehydrobiogeochemical heterogeneities and upscaling parameters.
Date: July 13, 2006
Creator: Xu, Tianfu
Partner: UNT Libraries Government Documents Department

Factors Controlling In Situ Uranium and Technetium Bio-Reduction and Reoxidation at the NABIR Field Research Center

Description: Summary of Recent Field Testing: Extensive in situ (in ground) field testing using the push-pull method has demonstrated that indigenous microorganisms in the shallow (&lt; 8 m) aquifer in FRC Areas 1 and 2 are capable of coupling the oxidation/fermentation of injected ethanol, glucose, or acetate to the reduction of U(VI) and Tc(VII). Despite highly variable initial (prior to testing) contaminant concentrations (pH: 3.3-7.2; Nitrate: 0.1-140 mM; U(VI): 1-12 uM; Tc(VII): 200-15000 pM), sequential donor additions resulted in increased rates of microbial activity (Denitrification: 01.-4.0 mM/hr; sulfate reduction: 0- 0.03 mM/hr; U(VI) reduction: 10-4 to 10-3 uM/hr; Tc(VII) reduction: 4-150 pM/hr) in all wells tested. Tc(VII) reduction and denitrification proceeded concomitantly in all tests. U(VI) reduction was concomitant with Fe(II) production in Area 1 but little Fe(II) was detected under sulfate reducing conditions in Area 2. Reoxidation of U(IV) (precipitated in the vicinity of the wells during previous tests) but not Tc(IV) was observed when injected test solutions contained initial nitrate concentrations &gt; {approx} 20 mM. Field data and laboratory studies suggest that U(IV) is likely oxidized by Fe(III) minerals produced by enzymatic Fe(II) oxidation or by Fe(II) oxidation by nitrite. U(IV) reoxidation rates (10-3 to 10-2 uM/hr) were somewhat larger than U(VI) reduction rates indicating that sustained nitrate removal will be necessary to maintain the stability of U(IV) in this environment.
Date: May 5, 2004
Creator: Istok, Jonathan; Krumholz, L; McKinley, J. & Gu, B.
Partner: UNT Libraries Government Documents Department

Influence of Reactive Transport on the Reduction of U(VI) in the Presence of Fe(III) and Nitrate: Implications for U(VI) Immobilization by Bioremidation/Biobarriers

Description: The purposes of this report are to: (1) to determine how flow and transport influence the distribution of U(VI) under field-relevant conditions and the transfer of reductive equivalents to the aqueous and solid phases by DMRB; and (2) to examine the solid-phase stability of bioreduced uranium phases--effects of mass transfer on reoxidation of U(IV) by O{sub 2} and other oxidants (e.g., NO{sub 3}{sup -}, denitrification products).
Date: March 17, 2004
Creator: Wood, Brian; Liu, Chongxuan & Zachara, John
Partner: UNT Libraries Government Documents Department

Multi-scale Characterization and Prediction of Coupled Subsurface Biogeochemical-Hydrological Processes

Description: To advance solutions needed for remediation of DOE contaminated sites, approaches are needed that can elucidate and predict reactions associated with coupled biological, geochemical, and hydrological processes over a variety of spatial scales and in heterogeneous environments. Our previous laboratory experimental experiments, which were conducted under controlled and homogeneous conditions, suggest that geophysical methods have the potential for elucidating system transformations that often occur during remediation. Examples include tracking the onset and aggregation of precipitates associated with sulfate reduction using seismic and complex resistivity methods (Williams et al., 2005; Ntarlagiannis et al., 2005) as well as estimating the volume of evolved gas associated with denitrification using radar velocity. These exciting studies illustrated that geophysical responses correlated with biogeochemical changes, but also that multiple factors could impact the geophysical signature and thus a better understanding as well as integration tools were needed to advance the techniques to the point where they can be used to provide quantitative estimates of system transformations.
Date: June 1, 2006
Creator: Hubbard, Susan; Williams, Ken; Steefel, Carl; Banfield, Jill; Long, Phil; Slater, Lee et al.
Partner: UNT Libraries Government Documents Department

Whole-Genome Transcriptional Analysis of Chemolithoautotrophic Thiosulfate Oxidation by Thiobacillus denitrificans Under Aerobic vs. Denitrifying Conditions

Description: Thiobacillus denitrificans is one of the few known obligate chemolithoautotrophic bacteria capable of energetically coupling thiosulfate oxidation to denitrification as well as aerobic respiration. As very little is known about the differential expression of genes associated with ke chemolithoautotrophic functions (such as sulfur-compound oxidation and CO2 fixation) under aerobic versus denitrifying conditions, we conducted whole-genome, cDNA microarray studies to explore this topic systematically. The microarrays identified 277 genes (approximately ten percent of the genome) as differentially expressed using Robust Multi-array Average statistical analysis and a 2-fold cutoff. Genes upregulated (ca. 6- to 150-fold) under aerobic conditions included a cluster of genes associated with iron acquisition (e.g., siderophore-related genes), a cluster of cytochrome cbb3 oxidase genes, cbbL and cbbS (encoding the large and small subunits of form I ribulose 1,5-bisphosphate carboxylase/oxygenase, or RubisCO), and multiple molecular chaperone genes. Genes upregulated (ca. 4- to 95-fold) under denitrifying conditions included nar, nir, and nor genes (associated respectively with nitrate reductase, nitrite reductase, and nitric oxide reductase, which catalyze successive steps of denitrification), cbbM (encoding form II RubisCO), and genes involved with sulfur-compound oxidation (including two physically separated but highly similar copies of sulfide:quinone oxidoreductase and of dsrC, associated with dissimilatory sulfite reductase). Among genes associated with denitrification, relative expression levels (i.e., degree of upregulation with nitrate) tended to decrease in the order nar &gt; nir &gt; nor &gt; nos. Reverse transcription, quantitative PCR analysis was used to validate these trends.
Date: April 22, 2006
Creator: Beller, H R; Letain, T E; Chakicherla, A; Kane, S R; Legler, T C & Coleman, M A
Partner: UNT Libraries Government Documents Department

Integrated Analysis of Protein Complexes and Regulatory Networks Involved in Anaerobic Energy Metabolism of Shewanella Oneidensis MR-1

Description: Anaerobic Nitrate Reduction. Nitrate is an extensive co-contaminant at some DOE sites making metal and radionuclide reduction problematic. Hence, we sought to better understand the nitrate reduction pathway and its control in S. oneidensis MR-1. It is not known whether the nitrate reduction is by denitrification or dissimilatory nitrate reduction into ammonium (DNRA). By both physiological and genetic evidence, we proved that DNRA is the nitrate reduction pathway in this organism. Using the complete genome sequence of S. oneidensis MR-1, we identified a gene encoding a periplasmic nitrate reductase based on its 72% sequence identity with the napA gene in E. coli. Anaerobic growth of MR-1 on nitrate was abolished in a site directed napA mutant, indicating that NapA is the only nitrate reductase present. The anaerobic expression of napA and nrfA, a homolog of the cytochrome b552 nitrite reductase in E. coli, increased with increasing nitrate concentration until a plateau was reached at 3 mM KNO3. This indicates that these genes are not repressed by increasing concentrations of nitrate. The reduction of nitrate can generate intermediates that can be toxic to the microorganism. To determine the genetic response of MR-1 to high concentrations of nitrate, DNA microarrays were used to obtain a complete gene expression profile of MR-1 at low (1 mM) versus high (40 mM) nitrate concentrations. Genes encoding transporters and efflux pumps were up-regulated, perhaps as a mechanism to export toxic compounds. In addition, the gene expression profile of MR-1, grown anaerobically with nitrate as the only electron acceptor, suggested that this dissimilatory pathway contributes to N assimilation. Hence the nitrate reduction pathway could serve a dual purpose. The role of EtrA, a homolog of Fnr (global anaerobic regulator in E. coli) was examined using an etrA deletion mutant we constructed, S. oneidensis EtrA7-1.
Date: June 1, 2005
Creator: Tiedje, James M.
Partner: UNT Libraries Government Documents Department