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

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

EFFECT OF THE SUPPORT ON THE IMMOBILIZATION OF PSEUDOMONAS DENITRIFICANS CELLS

Abstract Biological means for biodegradation of pollutants in wastewater hav

BIODEGRADATION OF 1,2-DIBROMOETHANE BY BRADYRHIZOBIUM JAPONICUM 273 STRAIN BY FREE AND IMMOBILIZED CELLS STIMULATED BY CONSTANT ELECTRIC FIELD

Halogenated compounds are ubiquitous in the environment. This work examines the potential of Bradyrhizobium japonicum 273 strain for degrading 1,2-dibromoethane. This study compares biodegradation with free and immobilized cells onto a granular polymeric support. Processes of dehalogenation were carried out with different initial substrate concentrations in shaken flasks and in a laboratory bioreactor in presence and absence of constant electric field. There was significant positive effect of electric field on the biodegradation rate. Complete mineralization was verified by measuring stoichiometric release of the biodegradation products

THE BRADYRHIZOBIUM JAPONICUM 273 STRAIN’S ABILITY TO DEGRADE PHENOL. PART 1

Phenol and its derivatives are hazardous pollutants being highly toxic even at low concentrations. Biotechnology has been very effective in dealing with major environmental challenges through utilizing different types of bacteria and biocatalysts to develop innovative processes for the biodegradation, biotreatment and biosorption of various contaminants. Many aerobic phenol-degrading microorganisms have been isolated and the pathways for the aerobic degradation of phenol are now firmly established. In many studies the results showed that Bradyrhizobium japonicum produces the most stable enzymes for biodegradation of organic pollutants. In this study we investigate biodegradation of phenol by Bradyrhizobium japonicum 273 cells. We made experiments with poor and rich (with two organic carbon sources) mineral medium. We compare an aerobic biodegradation in shaking flasks of 250 ml in a rotary shaker with various initial concentration of substrate: 0,02; 0,04; 0,06 and 0,08 g dm-3 phenol. The phenol degradation time was 10 days. We investigated the impact of glucose as an additional carbon source on the phenol biodegradation process. The maximum amount of degraded phenol was 1.08 g. It was obtained in an experiment with 0.02 g dm-3 initial phenol concentration when working in poor medium. When using a poor nutrient medium, the amount of degraded phenol is bigger than that in the rich nutrient medium. In experiments with a rich medium, Bradyrhizobium japonicum 273 cells grow and, thanks to the second carbon source, glucose, which causes a smaller amount of phenol to be treated

1,2-DIBROMOETHANE BIODEGRADATION CAPACITY OF BRADYRHIZOBIUM JAPONICUM STRAIN 273

1,2-Dibromoethane is an extremely toxic chemical owing to its cancer-causing potential. Many years after its last known application as a soil fumigant, residual 1,2-DBE is still found at remarkably high concentrations in soil because it strongly interacts with the soil matrix. Its biodegradation passes through very toxic intermediates e.g. bromoethanol and bromo-acetaldehyde and that is why the complete biodegradation is not observed at higher substrate concentrations. This work examines potentials of Bradyrhizobium japonicum 273 strain for degrading 1,2-DBE.. The experiments were carried out in shaking flasks with various initial concentration of substrate: 0,05 g/l; 0,1 g/l; 0,2 g/l and 0,3 g\l 1,2-DBE. In order to verify biodegradation, formation of biodegradation products like bromoethanol and bromide ions were measured. The concentration of biomass, generated bromoethanol and the quantity of bromide ions were determined spectrophotometrically, and were calculated from the optical density, using a calibration curve. Complete mineralization was verified by measuring stoichiometric release of the biodegradation products

ENVIRONMENTAL PROTECTION OF WATER RESOURCES FROM POLLUTANTS. A REVIEW

This paper is a review of environmental protection of water resources from pollutants and includes eight chapters: introduction, types of water resources, pollutants, biodegradation, environmental protection, effect of climate and environmental changes, conserving water resources and conclusion. Each chapter is separated. Water resources occupy a special place among other natural resources. Water is the most widely distributed on our planet: albeit in different amounts, it is available everywhere and plays a vital role in both the environment and human life. Of most importance is fresh water. Human life itself is impossible without it because it can be substituted by nothing else. Pollution of the environment has been one of the largest concerns to science and the general public in the last years. Biodegradation can be used to remove or to transform pollutants found in the environment, dissolved in natural bodies of water, into harmless compounds. To avoid further water problems and lessen projected harsh outcomes for the future we must conserve water and energy, and protect land and biological resources that are vital for a sustainable economy and environment

PHENOL BIODEGRADATION OF IMMOBILIZED BRADYRHIZOBIUM JAPONICUM CELLS. PART 2

With the development of technologies and the rise of the standard of living worldwide, the generation of wastewater is steadily increasing and at the same time the requirements for their purification are being increased before they are released into the environment. Wastewater treatment methods are diverse, chemical ones which have a significant drawback, are expensive and generate secondary pollutants. These disadvantages are avoided by the use of biological methods, which are very flexible and easy to manage. This article examines the ability of cells from the Bradyrhizobium japonicum 273 strain, successfully immobilized on activated carbon, to oxidize and degrade phenol. Initial pollutant concentrations are (in g dm-3): 0.02, 0.04, 0.06 and 0.08, but they do not have a significant effect on the rate and amount of phenol degradation, which in 240 hours is approximately 10 g dm-3. It is higher by 80% than for free cell degradation rate. In our opinion, the reason is that the activated carbon adsorbs the phenol and gradually releases it in cell-tolerant amounts, i.e. thus avoiding substrate inhibition

IMPACT OF NITRATE IONS CONCENTRATION ON THE DENITRIFICATION PROCESS

Underground and surface water are contaminated by nitrate in several ways. Nitrate originated from agriculture is increasingly growing all over the world due to the extreme use of fertilizers. Nitrate salts reach the groundwater as they percolate through the soil. Some other sources of nitrate in ground and surface water are from uncontrolled discharges of treated or un-treated wastewater from domestic and industrial sources, landfills and animal waste particularly from animal farms. Various methods for treatment of water from nitrates are known, but the majority of them generate secondary pollutants. An exception is the biological denitrification, at which nitrates are reduced to harmless nitrogen gas, and side waste products practically do not occur. In this paper the influence of nitrite ions on the process of denitrification was investigated. It is established that the denitrification process depends on the ratio between nitrate and nitrite concentration. The process is inhibited even at low nitrite concentration

BIODEGRADATION OF XENOBIOTICS

The compounds as 1, 2-dibromoethane, 1, 2-dichloroethane and phenol are ones of the most dangerous pollutants in the environment. 1, 2-Dibromoethane (DBE) is a synthetic organic chemical that is mainly used as a gasoline additive. It is also one of the widely used pesticide fumigants. 1,2-Dichloroethane is one of the most commonly used chlorinated industrial products and falls into the environment by using it as a chemical intermediate in the synthesis of a number of chlorinated hydrocarbons. Phenol is a waste product from the plastics, petroleum and pharmaceutical industries. There are different methods for treating wastewater containing the listed xenobiotics. Applied physicochemical methods are often economically ineffective and may cause other toxic products to occur. For this reason, microbiological treatment methods are preferred. We tested three different bacterial strains: Pseudomonas putida, Bradyrhizobium japonicum and Xanthobacter autotrophicus GJ10. In our studies for a period of 14 days with pre-adapted culture of Pseudomonas putida strain, we have achieved a degradation of 0.26 g/l of phenol in shaking flasks and a fed-batch process.. Over a period of 6 days, 1.2 g/l of 1,2 dibromethane was degraded using the Bradyrhizobium japonicum strain, and for 3 days Xanthobacter autotrophicus GJ10 degraded 0.9 g / l of 1,2-dichloroethane