Large quantity of wastewater is generated as a result of industrial, agricultural and domestic ac... more Large quantity of wastewater is generated as a result of industrial, agricultural and domestic activity of the human society. Final receivers of this water are artificial and natural water pools like reservoirs, rivers, lakes and seas. Nowadays, the accumulation and purification of wastewater is among the most serious ecological problems. Intensive research activity has been carried out on this problem, and wide variety of efficient purification technologies have been developed based on mechanical, physical, chemical and biological processes for separation, isolation, elimination, deactivation and degradation of harmful substances n the wastewater.
Biodegradation is the main process by which xenobiotics disappear from the environment. 1,2-dibro... more Biodegradation is the main process by which xenobiotics disappear from the environment. 1,2-dibromoethane released to the environment into the rivers, lakes soil and underground water. It breaks down very slowly in the water and most of him evaporates to the air. Dehalogenating activity and microbial cells growth were tested toward various of concentrations of 1,2-dibromoethane, used as main substrate. Experiments were carried out under aerobic and anaerobic conditions and in batch mode processes.
Hydrogen is a prospective energy carrier because there are practically no gaseous emissions of gr... more Hydrogen is a prospective energy carrier because there are practically no gaseous emissions of greenhouse gases in the atmosphere during its use as a fuel. The great benefit of hydrogen being a practically inexhaustible carbon-free fuel makes it an attractive alternative to fossil fuels. I.e., there is a circular process of energy recovery and use. Another big advantage of hydrogen as a fuel is its high energy content per unit mass compared to fossil fuels. Nowadays, hydrogen is broadly used as fuel in transport, including fuel cell applications, as a raw material in industry, and as an energy carrier for energy storage. The mass exploitation of hydrogen in energy production and industry poses some important challenges. First, there is a high price for its production compared to the price of most fossil fuels. Next, the adopted traditional methods for hydrogen production, like water splitting by electrolysis and methane reforming, lead to the additional charging of the atmosphere wi...
Nowadays pollution of natural waters, rivers and lakes by nitrate is one of the main problems rel... more Nowadays pollution of natural waters, rivers and lakes by nitrate is one of the main problems related to the environment. Nitrate originated from agriculture is increasingly growing all over the world due to the extreme use of fertilizers. Nitrate salts reach the underground water as they percolate through the soil. There are various methods for treatment of water for nitrates, but the majority of them yield 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. The potential of this method is high. The process of nitrate reduction is inhibited by nitrite accumulation being intermediate of microbial denitrification. In the present work the influence of nitrite ions on the process of microbial denitrification was investigated. Both free and immobilized microbial cells were tested. Granulated activated carbon was chosen as support for microbial cell immobilization. ...
Kinetic results on the glucomylase-catalysed hydrolysis of maltose and maltotriose, and glucose p... more Kinetic results on the glucomylase-catalysed hydrolysis of maltose and maltotriose, and glucose polymerization into maltose and isomaltose up to 450 g/L total sugar concentration are presented. Whereas the enzyme has a faster hydrolytic and synthetic activity on alpha-(1-->4) than on alpha-(1-->6) linkages, at equilibrium, on the contrary, the isomaltose level which represents 15% (w/w) of the total sugar concentration at the highest investigated concentrations is much higher than the corresponding maltose level. Under a wide range of initial conditions, experimental results are adequately described by a new kinetic model with simple first- and second-order, or Michaelian-type, rate expressions for the reversible hydrolysis of maltotriose, maltose, and isomaltose. The model also accounts for the inhibition of hydrolysis by glucose, but does not consider the concentration of water which, under the present conditions, was not found kinetically limiting.
Glucose, alcohol stillage and glycerol were used as substrates for bio-hydrogen production by the... more Glucose, alcohol stillage and glycerol were used as substrates for bio-hydrogen production by the newly isolated strain Clostridium beijerinckii 6A1 under batch conditions. High molar yields of hydrogen from the studied organic substrates were observed. There was a neat difference in the metabolic pathways of substrate digestion when hexose-based substrate or glycerol were used. The products of glycerol digestion showed that a pathway with no formic acid formation as intermediate was probable. In this case, considerable concentrations of acetic and propionic acid (up to 6 g dm−3) and small amounts of butanol were observed after 48 h. When glucose or hexose-based substrates were used, considerable amounts of formic acid (up to 6 g dm−3), i.e., the pathway proposed for Clostridia mixed cultures, were appropriate for the observed process of hydrogen release. For these substrates, considerable amounts of propionic acid in concentrations up to 1 g dm−3 were observed. That is why the path...
The possibility for catalytic oxidation of sulfide ions in model solutions of seawater is studied... more The possibility for catalytic oxidation of sulfide ions in model solutions of seawater is studied. The catalysts - synthe sized metal oxides incorporated in a matrix of activated carbon, are characterized by iodine adsorption. The possibility for using activated carbon as a catalyst is also considered. The influence of the amount of the catalyst is investigated. The experiments are performed at room temperature, with a constant mixing rate and initial concentrations. The oxidation of sulfide ions in the anode compartment of a laboratory scale fuel cell is described. A comparison is made of the oxidation rate into a fuel cell with the catalytical oxidation without electrodes and electrical connections at the same conditions.
The dehalogenation capacity of Klebsiella oxytoca is demonstrated on 1,2-dichloroethane and 1,2di... more The dehalogenation capacity of Klebsiella oxytoca is demonstrated on 1,2-dichloroethane and 1,2dibromoethane as substrates and sole carbon sources. Full degradation was observed at low and moderate initial concentrations. The chlorine is released in two steps of substrate biodegradation. It is observed that the cells retain chloride ions during their exponential phase of growth. About biodegradation of 1,2-dibromoethane, bromide ion release and reach their stoichiometric value when the concentration of microbial cells in the broth is the highest.
The possibility of catalytic oxidation of sulfide ions from model solutions of seawater in a lab-... more The possibility of catalytic oxidation of sulfide ions from model solutions of seawater in a lab-scale model of fuel cell is studied. Two types of metal-containing catalysts (Mn и Co) incorporated in a matrix of activated carbon are synthesized. The metals are in the form of spinel-type oxides containing about 35 % vol. of the activated carbon. The processes of oxidation occurring in the anode space are considered. Experiments with different initial concentrations of sulfide ions (25-125 mg/dm -3 ) are carried out. The quantity of catalyst added into the solution volume is varied. The experiments are performed at room temperature and with constant mixing rate. The sulfide ions are oxidized above 90 % in about 3 hours for all initial concentrations by the use of both types of catalysts whereas the process is much slower without a catalyst (40 % in about 3 hours).
Immobilized microbial cells can grow and detach from their carrier and grow independently as free... more Immobilized microbial cells can grow and detach from their carrier and grow independently as free ones in the liquid media. The present work proposes a numerical approach for evaluation the contribution for certain microbial conversions of immobilized cells and the free ones separately. For this purpose experimental data are required. This approach consists in mathematical models considering the microbial growth both of the free and immobilized cells, the cell detachment from the carrier and the kinetics of substrate consumption and product formation. The mathematical models are based on ordinary differential equations for cells attached to solid supports and of partial ones for entrapped cells. The cell release into the broth is taken into account introducing a cell detachment rate factor. Four different processes are considered: biodegradation of 1,2-dichloroethane by bacteria ( Klebsiella oxytoca ), fixed on activated carbon; the same substrate by Xanhobacter autotrophicus , entr...
Biological means for biodegradation of pollutants in wastewater have relatively low cost compared... more Biological means for biodegradation of pollutants in wastewater have relatively low cost compared to conventional physical and chemical processes. The use of immobilized cells is considered as more effective than for free cells. Reason for this is easier operation of solid-liquid separation, better operation stability, higher biodegradation rates, protection from toxic substances, increased plasmid stability. Many cells have the ability to adhere to other organisms (aggregate) or to solid surfaces. In this article different carriers for immobilization of cell of the strain Pseudomonas denitrificans are compared. They are granulated activated carbon, pyrolytic graphite fabric, graphite and polymer particles. The granulated activated carbon was the most suitable one.
With the development of technologies and the rise of the standard of living worldwide, the genera... more 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): 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. It is higher by 80% than for free cell degradation rate. In our opinion, the reason is that the activated ...
Sulfides and sulfites are toxic pollutants from different industrial, domestic and natural source... more Sulfides and sulfites are toxic pollutants from different industrial, domestic and natural sources. A way for their disposal and transformation to harmless products, even with a market value is their oxidation. Different type of catalysts for sulfide and sulfite oxidation to sulfates are studied and compared. The aim is to make a screening for the most appropriate catalyst for the process that can be used separately or that can be incorporated into electrodes in a fuel cell driven by the oxidation process. The technology for manufacturing of electrodes on the base of the obtained catalyst is given.
This study proposes a mathematical modeling approach for evaluating the effect of applying a perm... more This study proposes a mathematical modeling approach for evaluating the effect of applying a permanent electric field on the biodegradation of 1,2-dibromoethane by bacterial cells of Bradyrhizobium japonicum 273. Two models for inhibited microbial growth including product inhibition were composed—one using the Monod–Yerusalimsky approach and another one—the Levenspiel kinetic equation. The models were used to process own experimental data obtained without an electric field and ones obtained at the application of an electric field. The experiments were carried out at an optimum anode potential of 0.8 V vs. the standard hydrogen electrode (SHE). Three initial concentrations of substrate were tested: 0.05, 0.1, and 0.15 g dm−3. The modeling takes into account the product inhibition on microbial growth assuming 2-bromoethanol as the first biodegradation product. It was found that the positive effect of the electric field is the enhancement of microbial growth, expressed by the increase ...
The successful ethanol fermentation from lignocellulosic substrates is impeded by the fact, that ... more The successful ethanol fermentation from lignocellulosic substrates is impeded by the fact, that cellulose and hemicellulose must be digested by different strains, hence full substrate utilization is not possible in one process. That is why these two polysaccharides should be treated separately by different microbial strains. The simplest way to accomplish these processes is to use bioreactor with separated compartments where cellulose and hemicellulose are fermented by different strains: S.cerevisae for cellulose and P. pastoris for hemicellulose. In the present work such a two-step process is modelled for a continuous operation. As substrates glucose (a hexose) and xylose (a pentose) resulting of the raw material acid pre-treatment are used. The addition of the produced ethanol in the first compartment to the second one as starting substrate and its inhibition impact are taken into account. The dilution rate, the initial substrate concentration and the inhibition effects are considered too. Acknowledgement. This work was supported by the Fund for Scientific Research, Republic of Bulgaria, by grant E02/16.
Biogas is an excellent example of renewable feedstock for energy production enabling closure of t... more Biogas is an excellent example of renewable feedstock for energy production enabling closure of the carbon cycle by photosynthesis of the existing vegetation, without charging the atmosphere with excessive carbon dioxide. The present review contains traditional as well as new methods for the preparation of raw materials for biogas production. These methods are compared by the biogas yield and biogas content with the possible applications. Various fields of biogas utilization are discussed. They are listed from simple heating, electricity production by co-generation, fuel cell applications to catalytic conversions for light fuel production by the Fischer-Tropsch process. The aspects of carbon dioxide recycling reaching methane production are considered too.
Large quantity of wastewater is generated as a result of industrial, agricultural and domestic ac... more Large quantity of wastewater is generated as a result of industrial, agricultural and domestic activity of the human society. Final receivers of this water are artificial and natural water pools like reservoirs, rivers, lakes and seas. Nowadays, the accumulation and purification of wastewater is among the most serious ecological problems. Intensive research activity has been carried out on this problem, and wide variety of efficient purification technologies have been developed based on mechanical, physical, chemical and biological processes for separation, isolation, elimination, deactivation and degradation of harmful substances n the wastewater.
Biodegradation is the main process by which xenobiotics disappear from the environment. 1,2-dibro... more Biodegradation is the main process by which xenobiotics disappear from the environment. 1,2-dibromoethane released to the environment into the rivers, lakes soil and underground water. It breaks down very slowly in the water and most of him evaporates to the air. Dehalogenating activity and microbial cells growth were tested toward various of concentrations of 1,2-dibromoethane, used as main substrate. Experiments were carried out under aerobic and anaerobic conditions and in batch mode processes.
Hydrogen is a prospective energy carrier because there are practically no gaseous emissions of gr... more Hydrogen is a prospective energy carrier because there are practically no gaseous emissions of greenhouse gases in the atmosphere during its use as a fuel. The great benefit of hydrogen being a practically inexhaustible carbon-free fuel makes it an attractive alternative to fossil fuels. I.e., there is a circular process of energy recovery and use. Another big advantage of hydrogen as a fuel is its high energy content per unit mass compared to fossil fuels. Nowadays, hydrogen is broadly used as fuel in transport, including fuel cell applications, as a raw material in industry, and as an energy carrier for energy storage. The mass exploitation of hydrogen in energy production and industry poses some important challenges. First, there is a high price for its production compared to the price of most fossil fuels. Next, the adopted traditional methods for hydrogen production, like water splitting by electrolysis and methane reforming, lead to the additional charging of the atmosphere wi...
Nowadays pollution of natural waters, rivers and lakes by nitrate is one of the main problems rel... more Nowadays pollution of natural waters, rivers and lakes by nitrate is one of the main problems related to the environment. Nitrate originated from agriculture is increasingly growing all over the world due to the extreme use of fertilizers. Nitrate salts reach the underground water as they percolate through the soil. There are various methods for treatment of water for nitrates, but the majority of them yield 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. The potential of this method is high. The process of nitrate reduction is inhibited by nitrite accumulation being intermediate of microbial denitrification. In the present work the influence of nitrite ions on the process of microbial denitrification was investigated. Both free and immobilized microbial cells were tested. Granulated activated carbon was chosen as support for microbial cell immobilization. ...
Kinetic results on the glucomylase-catalysed hydrolysis of maltose and maltotriose, and glucose p... more Kinetic results on the glucomylase-catalysed hydrolysis of maltose and maltotriose, and glucose polymerization into maltose and isomaltose up to 450 g/L total sugar concentration are presented. Whereas the enzyme has a faster hydrolytic and synthetic activity on alpha-(1-->4) than on alpha-(1-->6) linkages, at equilibrium, on the contrary, the isomaltose level which represents 15% (w/w) of the total sugar concentration at the highest investigated concentrations is much higher than the corresponding maltose level. Under a wide range of initial conditions, experimental results are adequately described by a new kinetic model with simple first- and second-order, or Michaelian-type, rate expressions for the reversible hydrolysis of maltotriose, maltose, and isomaltose. The model also accounts for the inhibition of hydrolysis by glucose, but does not consider the concentration of water which, under the present conditions, was not found kinetically limiting.
Glucose, alcohol stillage and glycerol were used as substrates for bio-hydrogen production by the... more Glucose, alcohol stillage and glycerol were used as substrates for bio-hydrogen production by the newly isolated strain Clostridium beijerinckii 6A1 under batch conditions. High molar yields of hydrogen from the studied organic substrates were observed. There was a neat difference in the metabolic pathways of substrate digestion when hexose-based substrate or glycerol were used. The products of glycerol digestion showed that a pathway with no formic acid formation as intermediate was probable. In this case, considerable concentrations of acetic and propionic acid (up to 6 g dm−3) and small amounts of butanol were observed after 48 h. When glucose or hexose-based substrates were used, considerable amounts of formic acid (up to 6 g dm−3), i.e., the pathway proposed for Clostridia mixed cultures, were appropriate for the observed process of hydrogen release. For these substrates, considerable amounts of propionic acid in concentrations up to 1 g dm−3 were observed. That is why the path...
The possibility for catalytic oxidation of sulfide ions in model solutions of seawater is studied... more The possibility for catalytic oxidation of sulfide ions in model solutions of seawater is studied. The catalysts - synthe sized metal oxides incorporated in a matrix of activated carbon, are characterized by iodine adsorption. The possibility for using activated carbon as a catalyst is also considered. The influence of the amount of the catalyst is investigated. The experiments are performed at room temperature, with a constant mixing rate and initial concentrations. The oxidation of sulfide ions in the anode compartment of a laboratory scale fuel cell is described. A comparison is made of the oxidation rate into a fuel cell with the catalytical oxidation without electrodes and electrical connections at the same conditions.
The dehalogenation capacity of Klebsiella oxytoca is demonstrated on 1,2-dichloroethane and 1,2di... more The dehalogenation capacity of Klebsiella oxytoca is demonstrated on 1,2-dichloroethane and 1,2dibromoethane as substrates and sole carbon sources. Full degradation was observed at low and moderate initial concentrations. The chlorine is released in two steps of substrate biodegradation. It is observed that the cells retain chloride ions during their exponential phase of growth. About biodegradation of 1,2-dibromoethane, bromide ion release and reach their stoichiometric value when the concentration of microbial cells in the broth is the highest.
The possibility of catalytic oxidation of sulfide ions from model solutions of seawater in a lab-... more The possibility of catalytic oxidation of sulfide ions from model solutions of seawater in a lab-scale model of fuel cell is studied. Two types of metal-containing catalysts (Mn и Co) incorporated in a matrix of activated carbon are synthesized. The metals are in the form of spinel-type oxides containing about 35 % vol. of the activated carbon. The processes of oxidation occurring in the anode space are considered. Experiments with different initial concentrations of sulfide ions (25-125 mg/dm -3 ) are carried out. The quantity of catalyst added into the solution volume is varied. The experiments are performed at room temperature and with constant mixing rate. The sulfide ions are oxidized above 90 % in about 3 hours for all initial concentrations by the use of both types of catalysts whereas the process is much slower without a catalyst (40 % in about 3 hours).
Immobilized microbial cells can grow and detach from their carrier and grow independently as free... more Immobilized microbial cells can grow and detach from their carrier and grow independently as free ones in the liquid media. The present work proposes a numerical approach for evaluation the contribution for certain microbial conversions of immobilized cells and the free ones separately. For this purpose experimental data are required. This approach consists in mathematical models considering the microbial growth both of the free and immobilized cells, the cell detachment from the carrier and the kinetics of substrate consumption and product formation. The mathematical models are based on ordinary differential equations for cells attached to solid supports and of partial ones for entrapped cells. The cell release into the broth is taken into account introducing a cell detachment rate factor. Four different processes are considered: biodegradation of 1,2-dichloroethane by bacteria ( Klebsiella oxytoca ), fixed on activated carbon; the same substrate by Xanhobacter autotrophicus , entr...
Biological means for biodegradation of pollutants in wastewater have relatively low cost compared... more Biological means for biodegradation of pollutants in wastewater have relatively low cost compared to conventional physical and chemical processes. The use of immobilized cells is considered as more effective than for free cells. Reason for this is easier operation of solid-liquid separation, better operation stability, higher biodegradation rates, protection from toxic substances, increased plasmid stability. Many cells have the ability to adhere to other organisms (aggregate) or to solid surfaces. In this article different carriers for immobilization of cell of the strain Pseudomonas denitrificans are compared. They are granulated activated carbon, pyrolytic graphite fabric, graphite and polymer particles. The granulated activated carbon was the most suitable one.
With the development of technologies and the rise of the standard of living worldwide, the genera... more 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): 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. It is higher by 80% than for free cell degradation rate. In our opinion, the reason is that the activated ...
Sulfides and sulfites are toxic pollutants from different industrial, domestic and natural source... more Sulfides and sulfites are toxic pollutants from different industrial, domestic and natural sources. A way for their disposal and transformation to harmless products, even with a market value is their oxidation. Different type of catalysts for sulfide and sulfite oxidation to sulfates are studied and compared. The aim is to make a screening for the most appropriate catalyst for the process that can be used separately or that can be incorporated into electrodes in a fuel cell driven by the oxidation process. The technology for manufacturing of electrodes on the base of the obtained catalyst is given.
This study proposes a mathematical modeling approach for evaluating the effect of applying a perm... more This study proposes a mathematical modeling approach for evaluating the effect of applying a permanent electric field on the biodegradation of 1,2-dibromoethane by bacterial cells of Bradyrhizobium japonicum 273. Two models for inhibited microbial growth including product inhibition were composed—one using the Monod–Yerusalimsky approach and another one—the Levenspiel kinetic equation. The models were used to process own experimental data obtained without an electric field and ones obtained at the application of an electric field. The experiments were carried out at an optimum anode potential of 0.8 V vs. the standard hydrogen electrode (SHE). Three initial concentrations of substrate were tested: 0.05, 0.1, and 0.15 g dm−3. The modeling takes into account the product inhibition on microbial growth assuming 2-bromoethanol as the first biodegradation product. It was found that the positive effect of the electric field is the enhancement of microbial growth, expressed by the increase ...
The successful ethanol fermentation from lignocellulosic substrates is impeded by the fact, that ... more The successful ethanol fermentation from lignocellulosic substrates is impeded by the fact, that cellulose and hemicellulose must be digested by different strains, hence full substrate utilization is not possible in one process. That is why these two polysaccharides should be treated separately by different microbial strains. The simplest way to accomplish these processes is to use bioreactor with separated compartments where cellulose and hemicellulose are fermented by different strains: S.cerevisae for cellulose and P. pastoris for hemicellulose. In the present work such a two-step process is modelled for a continuous operation. As substrates glucose (a hexose) and xylose (a pentose) resulting of the raw material acid pre-treatment are used. The addition of the produced ethanol in the first compartment to the second one as starting substrate and its inhibition impact are taken into account. The dilution rate, the initial substrate concentration and the inhibition effects are considered too. Acknowledgement. This work was supported by the Fund for Scientific Research, Republic of Bulgaria, by grant E02/16.
Biogas is an excellent example of renewable feedstock for energy production enabling closure of t... more Biogas is an excellent example of renewable feedstock for energy production enabling closure of the carbon cycle by photosynthesis of the existing vegetation, without charging the atmosphere with excessive carbon dioxide. The present review contains traditional as well as new methods for the preparation of raw materials for biogas production. These methods are compared by the biogas yield and biogas content with the possible applications. Various fields of biogas utilization are discussed. They are listed from simple heating, electricity production by co-generation, fuel cell applications to catalytic conversions for light fuel production by the Fischer-Tropsch process. The aspects of carbon dioxide recycling reaching methane production are considered too.
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Papers by Venko Beschkov