Biotransformation of Phytosterols to Androstenedione in Two Phase Water-oil Systems

The microbial transformation of phytosterols to androstenedione (androst-4-ene-3,17-dione, AD) and androstadienedione (androsta-1,4-diene-3,17-dione, ADD) in two-phase water-oil systems by means of the strain Mycobacterium sp. MB3683 has been studied. The effect of some process conditions, like the agitation speed, the age and amount of inoculum, the temperature and some additional carbon sources have been investigated. The highest conversion rates were attained with 10–15 % of inolucum of age t = 16–20 h at T = 34–35 "C and n = 400 min–1. Media containing high concentrations of carbohydrates have a negative impact on the process, while the natural nitrogen sources influence beneficially the bioconversion. The use of silicon oil and polypropylene-glycol as solubilizing agents was found suitable for the above-mentioned biotransformation and permitted to increase considerably the amount of the substrate in the system. On the other hand, the biotransformation rate depended on the amount of the oils, because they inhibited the microbial cells growth

Modeling of Biochemical Nitrate Reduction in Constant Electric Field

Experiments on the bioelectrochemical stimulation of enzyme reduction of nitrate to nitrite in a potentiostatic regime at different catode potentials were carried out. It was established that the stimulation effect of the constant electric field on nitrate reduction is also relevant for cell-free enzyme preparation, i.e. the effect is related to the constitutive enzymes nitrate-reductase and nitrite-reductase, contained in the cell membranes. Mathematical modeling of these experimental data as well as data for the same process accomplished by living immobilized cells was carried out. The purpose of the modeling was to select the most suitable kinetic model and then estimate the kinetic parameters and their dependence on the cathode potential. The mathematical models were based on the Michaelis-Menten kinetics taking into account inhibition by nitrate and nitrite. This modeling helped to conclude that the stimulation consists of two effects: enhanced maximum rate of nitrate enzyme reduction and faster nitrite reduction to eliminate nitrite inhibition on the overall process. It was found that the maximum reaction rates of nitrate and nitrite reduction depend on the cathode potential with maxima at + 0.01 V vs. the saturated hydrogen electrode

Mathematical Modeling for Studying Microbial Processes – Some Examples

Mathematical modeling may have different purposes in chemical and biochemical engineering sciences. One of them is to confirm or to reject kinetic models for certain processes, or to evaluate the importance of some transport phenomena on the net chemical or biochemical reaction rate. In the present paper different microbial processes are considered and modeled for evaluation of kinetic constants for batch and continuous processes accomplished by free and immobilized microbial cells. The practical examples are from the field of wastewater treatment and biosynthesis of products, like enzymes, lactic acid, gluconic acid, etc. By the aid of mathematical modeling the kinetics and the type of inhibition are specified for microbial wastewater denitrification and biodegradation of halogenated hydrocarbons. The importance of free and immobilized cells and their separate contribution to the overall microbial process is also evaluated for some fermentation processes: gluconic acid production, dichloroethane biodegradation, lactic acid fermentation and monochloroacetic acid biodegradation

Direct Energy Production From Hydrogen Sulfide in Black Sea Water - Electrochemical Study

A sulfide driven fuel cell is proposed to clean the Black Sea with the simultaneous A sulfide driven fuel cell is proposed to clean the Black Sea with the simultaneous production of energy. The process is hopeful even at low sulfide concentrations, i.e.10 to 25 mg/l being close to the ones in the Black Sea water. The main problem for the practical application of this type of fuel cell are the low current and power densities. The measurement of the generated electric current compared to the sulfide depletion show that the most probable anode reaction is oxidation of sulfide to sulfate. It is evident that parasite competitive reactions oxidation of sulfide occurs in the anode compartment of the fuel cell. The pH measurements shows that the transfer of hydroxylic anions from the cathodic compartment to the anodic one across the separating membrane is not fast enough to compensate its drop in the anode compartment

Modeling of 1,2-Dichloroethane Biodegradation by Xanthobacter autotrophicus GJ10 under Shock Loading of Other Halogenated Compounds in Continuous Stirred Tank Bioreactor

A mathematical model describing the behavior of a continuous culture that degrades 1,2-dichloroethane and receives a shock loading of another compound was developed. The model takes into account possible cell death due to toxicity, growth inhibition and additional growth of cells on the second carbon source. Biodegradation is coupled to cell growth on the additional carbon source or by incomplete and unproductive degradation. The model was tested with Xanthobacter autotrophicus strain GJ10 growing on 1,2-dichloroethane in a continuous stirred tank bioreactor. Dichloromethane, dibromomethane, 1,2-dibromoethane, monofluoroacetate, monochloroacetate and monochloroacetic acid were added separately in the form of a pulse. The effects that were observed varied from low toxicity in case of dihalomethanes and chloroacetate up to severe cell death followed by culture washout in the case of monofluoroacetate and 1,2-dibromoethane. The experimental profiles were in most cases satisfactorily described with the proposed model

Acceleration and increase of hydrogen production by simultaneous fermentation of Clostridium butyricum and Rhodobacter sphaeroides on wine-vinasse substrate

A fermentation process for hydrogen production as a result of the simultaneous effect of Rhodobacter sphaeroides and Clostridium butyricum on a wine-vinasse substrate was realized in a single illuminated bioreactor. The kinetics of the cooperative process indicates rapid and enhanced production of hydrogen showing yield of 65.41 mmol/l vinasse with a mixed culture as compared to processes using the two bacteria separately that have yields of 27.41 and 25.49 mmol/l vinasse for Rhodobacter and Clostridium, respectively. The experiment with a mixture of the two bacteria revealed co-operative assimilation of almost all components studied in the following sequence: malic acid > lactic acid > residual sugars> tartaric acid > citric acid. The use of vinasse substrate for hydrogen production would be a significant ecological energy resource for enterprises producing wine brandies together with waste utilization

Bacterial denitrification of waste water stimulated by constant electric field

The present paper considers the effect of constant electric field on the denitrification performance of the bacterium Pseudomonas denitrificans. It is shown that when constant electric field is applied on a denitrifying culture, the reduction of nitrate to elemental nitrogen runs faster than at a traditional microbial process due to the lack of a long lag-phase as it is in the case of traditional microbial dentrification. The process rate and the microbial specific activity are sensitive to the constant cathode potential if the latter is close to the one of an electro-chemical reduction process. However, evidence from the current yield in the experiments described here and from a comparison with data for electrochemical reduction without bacteria shows that a simple electrochemical process cannot explain the observed effect. (C) 2003 Elsevier B.V. All rights reserved