Mechanisms of intrinsic bioremediation of gas condensate hydrocarbons in saturated soil

Applied Biochemistry and Biotechnology - The addition of gas condensate hydrocarbons to saturated soil from a gas production site stimulated sulfate reduction under anaerobic and oxygen-limiting...     

Ultrasound promoted asymmetric transfer hydrogenation of ketones using Ru(II)arene/amino alcohol catalyst system

Asymmetric transfer hydrogenation of ketones using Ru(II)arene/amino alcohol catalyst system proceeds with significant rate enhancement by ultrasound promotion. Comparison of the silent reactions carried out at 25 degrees C with reactions under sonochemical activation at 25 degrees C clearly showed enhancement in catalytic activity by 5-10 times without significantly affecting the enantioselectivity.     

Mesophilic Digestion Kinetics of Manure Slurry

Anaerobic digestion kinetics study of cow manure was performed at 35°C in bench-scale gas-lift digesters (3.78 l working volume) at eight different volatile solids (VS) loading rates in the range of 1.11–5.87 g l⁻¹ day⁻¹. The digesters produced methane at the rates of 0.44–1.18 l l⁻¹ day⁻¹, and the methane content of the biogas was found to increase with longer hydraulic retention time (HRT). Based on the experimental observations, the ultimate methane yield and the specific methane productivity were estimated to be 0.42 l CH₄ (g VS loaded)^–1 and 0.45 l CH₄ (g VS consumed)^–1, respectively. Total and dissolved chemical oxygen demand (COD) consumptions were calculated to be 59–17% and 78–43% at 24.4–4.6 days HRTs, respectively. Maximum concentration of volatile fatty acids in the effluent was observed as 0.7 g l^–1 at 4.6 days HRT, while it was below detection limit at HRTs longer than 11 days. The observed methane production rate did not compare well with the predictions of Chen and Hashimoto’s [1] and Hill’s [2] models using their recommended kinetic parameters. However, under the studied experimental conditions, the predictions of Chen and Hashimoto’s [1] model compared better to the observed data than that of Hill’s [2] model. The nonlinear regression analysis of the experimental data was performed using a derived methane production rate model, for a completely mixed anaerobic digester, involving Contois kinetics [3] with endogenous decay. The best fit values for the maximum specific growth rate (μ _m) and dimensionless kinetic parameter (K) were estimated as 0.43 day^–1 and 0.89, respectively. The experimental data were found to be within 95% confidence interval of the prediction of the derived methane production rate model with the sum of residual squared error as 0.02.     

Biomodification of coal to remove mercury

A biological process for removal of mercury from coal is under investigation. Iron and sulfur oxidizing bacteria have previously been used for desulfurization of coal and for mineral mining. We have shown that removal of mercury from coal is also possible via the same principles. Two pure cultures, Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans and four environmental consortium samples obtained from an acid mine drainage site were studied for mercury removal from coal. Four different coal samples were included in the study and the preliminary results have shown that up to 20% of the mercury can be removed in batch cultures compared to control. Additional parameters such as media composition and inoculum size were also studied. This is the first report demonstrating successful leaching of mercury from coal using biological treatment.     

Comparison of batchstirred and electrospray reactors for biodesulfurization of dibenzothiophene in crude oil and hydrocarbon feedstocks

Biological removal of organic sulfur from petroleum feedstocks offers an attractive alternative to conventional thermochemical treatment, because of the mild operating conditions afforded by the biocatalyst. In order for biodesulfurization to realize commercial success, reactors must be designed that allow for sufficient liquid-liquid and gas-liquid mass transfer, while simultaneously reducing operating costs. Electro-spray bioreactors were investigated for use as desulfurization reactors because of their reported operational cost savings relative to mechanically agitated reactors. Unlike batch-stirred reactors, which mix the biocatalystcontaining aqueous phase with the organic feedstock by imparting momentum to the entire bulk solution, electro-spray reactors have the potential for tremendous cost savings, creating an emulsion <5 (μm in diameter, at a cost of only 3 W/L. Power law relationships indicate that mechanically stirred reactors would require 100-1000-fold more energy to create such a fine emulsion, but these relationships generally do not account for the effect of endogenously produced surfactant in the system. Here, the rates dibenzothiophene (DBT) oxidation to 2-hydroxybiphenyl (2-HBP) in hexadecane, byRhodococcus sp IGTS8 are compared in the two reactor systems. Desulfurization rates ranged from 1.0 to 5.0 mg 2-HBP/(dry g cells · h), independent of the reactor employed. The batch-stirred reactor was capable of forming a very fine emulsion in the presence of the biocatalyst IGTS8, similar to that formed in the emulsion phase contactor (EP^TM), presumably because the biocatalyst produces its own surfactant. Although EPC did not prove to be advantageous for the IGTS8 desulfurization system, it may prove advantageous for systems that do not produce surface-active bioagents, in addition to being mass-transport limited.     

The potential for intrinsic bioremediation of BTEX hydrocarbons in soil/ground water contaminated with gas condensate

Applied Biochemistry and Biotechnology - Gas condensate liquids contaminate soil and ground water at two gas production sites in the Denver Basin, CO. A detailed field study was carried out at...     

Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1-2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30-50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.     

Performance of chloroperoxidase stabilization in mesoporous sol-gel glass using In situ glucose oxidase peroxide generation

A unique mesoporous sol-gel glass possessing a highly ordered porous structure (with three pore sizes of about 50, 150, and 200 Å diameter) was used as a support material for immobilization of the enzyme chloroperoxidase (CPO). CPO was bound onto the glass via a bifunctional ligand, trimethoxysilylpropanal. In situ production of the cosubstrate, H₂O₂, was achieved using glucose oxidase. Solvent stability in acetonitrile mixtures was enhanced when a pore size larger than the size of CPO was used (i.e., 200) Å From these results, it appears that the glass-enzyme complex developed through the present work can be used as high-performance biocatalysts for various chemical-processing applications, particularly in harsh conditions.     

Improving Activity of Salt-Lyophilized Enzymes in Organic Media

Lyophilization with salts has been identified as an important method of activating enzymes in organic media. Using salt-activated enzymes to transform molecules tethered to solid surfaces in organic phase requires solubilization of enzymes in the solvents. Methods of improving performance of salt-lyophilized enzymes, further, via chemical modification, and use of surfactants and surfactants to create fine emulsions prior to lyophilization are investigated. The reaction system used is transesterification of N-acetyl phenylalanine ethyl ester with methanol or propanol. Initial rate of formation of amino acid esters by subtilisin Carlsberg (SC) was studied and found to increase two to sevenfold by either chemical modification or addition of surfactants in certain solvents, relative to the salt (only)-lyophilized enzyme. The method to prepare highly dispersed enzymes in a salt-surfactant milieu also improved activity by two to threefold. To test the effect of chemical modification on derivatization of drug molecules, acylation of bergenin was investigated using chemically modified SC.