Fermentative hydrogen production has been carried out both in batch and continuous system using r... more Fermentative hydrogen production has been carried out both in batch and continuous system using recombinant Escherichia coli BL 21. Effect of various process parameters, viz. size of inoculum, initial medium pH, initial substrate concentration, temperature and dilution rate, was examined with respect to maximum hydrogen productivity. Maximum hydrogen production rate obtained in this study was 66 mmol/(l h) using glucose as substrate at a dilution rate of 0.55 h À1 in the immobilized whole cell bioreactor. Black strap molasses, a by-product of sugar industry, was found suitable as a feedstock for fermentation using which maximum rate of hydrogen production was 97.4 mmol/(l h). Energy analysis reveals that the percentage of gaseous energy recovery obtained in this study using recombinant E. coli BL 21 and considering glucose as a substrate was 26.68%. A comparison of hydrogen production characteristics between the wild strain Enterobacter cloacae IIT-BT-08 and that of the recombinant E. coli BL21 indicates that optimum initial pH, initial glucose concentration and reaction temperature are almost comparable and/or marginally same for both the strains. However, the yield of hydrogen (mol H 2 /(mol glucose)) with the recombinant strain was 3.12 mol H 2 / (mol glucose) which was much higher than that reported for the wild strain. #
Combined dark and photo-fermentation was carried out to study the feasibility of biological hydro... more Combined dark and photo-fermentation was carried out to study the feasibility of biological hydrogen production. In dark fermentation, hydrogen was produced by Enterobacter cloacae strain DM11 using glucose as substrate. This was followed by a photo-fermentation process. Here, the spent medium from the dark process (containing unconverted metabolites, mainly acetic acid etc.) underwent photo-fermentation by Rhodobacter sphaeroides strain O.U.001 in a column photo-bioreactor. This combination could achieve higher yields of hydrogen by complete utilization of the chemical energy stored in the substrate. Dark fermentation was studied in terms of several process parameters, such as initial substrate concentration, initial pH of the medium and temperature, to establish favorable conditions for maximum hydrogen production. Also, the effects of the threshold concentration of acetic acid, light intensity and the presence of additional nitrogen sources in the spent effluent on the amount of hydrogen produced during photo-fermentation were investigated. The light conversion efficiency of hydrogen was found to be inversely proportional to the incident light intensity. In a batch system, the yield of hydrogen in the dark fermentation was about 1.86 mol H2 mol−1 glucose; and the yield in the photo-fermentation was about 1.5–1.72 mol H2 mol−1 acetic acid. The overall yield of hydrogen in the combined process, considering glucose as the preliminary substrate, was found to be higher than that in a single process.
When the partial pressure of H2 was decreased by lowering the total pressure in the headspace of ... more When the partial pressure of H2 was decreased by lowering the total pressure in the headspace of the reactor in a batch fermentation process from 760 mm Hg to 380 mm Hg containing Enterobacter cloacae, the molar yield of H2 increased from 1.9 mol to 3.9 mol H2/mol glucose. The maximum production rate was 0.017 mmol H2/h l at 380 mm Hg. The lag period as well as total batch time of H2 production decreased using a decreased partial pressure.
Hydrogen is the fuel of the future mainly due to its high conversion e ciency, recyclability and ... more Hydrogen is the fuel of the future mainly due to its high conversion e ciency, recyclability and nonpolluting nature. Biological hydrogen production processes are found to be more environment friendly and less energy intensive as compared to thermochemical and electrochemical processes. They are mostly controlled by either photosynthetic or fermentative organisms. Till today, more emphasis has been given on the former processes. Nitrogenase and hydrogenase play very important role. Genetic manipulation of cyanobacteria (hydrogenase negative gene) improves the hydrogen generation. The paper presents a survey of biological hydrogen production processes. The microorganisms and biochemical pathways involved in hydrogen generation processes are presented in some detail. Several developmental works are discussed. Immobilized system is found suitable for the continuous hydrogen production. About 28% of energy can be recovered in the form of hydrogen using sucrose as substrate. Fermentative hydrogen production processes have some edge over the other biological processes.
Nitrogenase a b s t r a c t Biological hydrogen production processes offer a technique through wh... more Nitrogenase a b s t r a c t Biological hydrogen production processes offer a technique through which renewable energy sources like biomass can be utilized for the generation of the cleanest energy carrier for the use of mankind. Hydrogen intensive research work has already been carried out on the advancement of these processes, such as the development of genetically modified microorganism, metabolic engineering, improvement of the reactor designs, use of different solid matrices for the immobilization of whole cells, biochemical assisted bioreactor, development of two-stage processes, etc. for higher H 2 -production rates. Maximum H 2 yield is found to be 7.1 mol H 2 /mol glucose. However, major bottlenecks for the commercialization of these processes are lower H 2 yield and rate of H 2 production. Suitable microbial cultures are required to handle waste materials efficiently, which are usually complex in nature. This will serve dual purposes: clean energy generation and bioremediation. Scale-up studies on fermentative H 2 -production processes have been done successfully. Pilot plant trials of the photo-fermentation processes require more attention.
Improvement in H2 production was achieved through redirection of metabolic pathways by blocking f... more Improvement in H2 production was achieved through redirection of metabolic pathways by blocking formation of alcohol and some organic acids in Enterobacter cloacae IIT-BT 08. The wild type strain was more susceptible to allyl alcohol (7 mM) and to the combined effect of NaBr and NaBrO3 (40 mM each at pH 5.5) than were double mutants, with defects in both alcohol and organic acid formation pathways, which had higher H2 yields (3.4 mol mol−1 glucose) than the wild type strain (2.1 mol mol−1 glucose).
This communication reports on the continuous biohydrogen production by Thermotoga neapolitana cel... more This communication reports on the continuous biohydrogen production by Thermotoga neapolitana cells immobilized on a stable cationic hydrogel bearing amine groups. This hydrogel was designed to perform two functional activities: to promote adhesion of T. neapolitana cells, and to buffer pH changes in the bacterial cultures. Repeated fed-batch cultures showed an average hydrogen production rate and yield of 50.6 mL L 21 h 21 and 3.3 mol H 2 /mol glucose, respectively. To the best of our knowledge, this is the first report detailing the immobilization of this bacterial strain on a polymeric support.
Fermentative hydrogen production was carried out by Enterobacter cloacae DM11, using glucose as t... more Fermentative hydrogen production was carried out by Enterobacter cloacae DM11, using glucose as the substrate. The effects of initial substrate concentration, initial medium pH, and temperature were investigated. Results showed that at an initial glucose concentration of 1.0% (m/v), the molar yield of hydrogen was 3.31 mol (mol glucose)(-1). However, at higher initial glucose concentration, both the rate and cumulative volume of hydrogen production decreased. The pH of 6.5 +/- 0.2 at a temperature of 37 degrees C was found most suitable with respect to maximum rate of production of hydrogen in batch fermentation. Activation enthalpies of fermentation and that of thermal deactivation of the present process were estimated following a modified Arrhenius equation. The values were 47.34 and 118.67 kJ mol(-1) K(-1), respectively. The effect of the addition of Fe(2+) on hydrogen production was also studied. It revealed that the presence of iron (Fe(2+)) in the media up to a concentration of 20 mg L(-1) had a marginal enhancing effect on total hydrogen production. A simple model developed from the modified Gompertz equation was applied to estimate the hydrogen production potential, production rate, and lag-phase time in a batch process, based on the cumulative hydrogen production curves, using the software program Curve Expert 1.3.
Two-stage process described in the present work is a combination of dark and photofermentation in... more Two-stage process described in the present work is a combination of dark and photofermentation in a sequential batch mode. In the first stage glucose is fermented to acetate, CO 2 and H 2 in an anaerobic dark fermentation by Enterobacter cloacae DM11. This is followed by a successive second stage where acetate is converted to H 2 and CO 2 in a photobioreactor by photosynthetic bacteria, Rhodobacter sphaeroides O.U. 001. The yield of hydrogen in the first stage was about 3:31 mol H 2 ðmol glucoseÞ À1 (approximately 82% of theoretical) and that in the second stage was about 1:521:72 mol H 2 ðmol acetic acidÞ À1 (approximately 37-43% of theoretical). The overall yield of hydrogen in two-stage process considering glucose as preliminary substrate was found to be higher compared to a single stage process. Monod model, with incorporation of substrate inhibition term, has been used to determine the growth kinetic parameters for the first stage. The values of maximum specific growth rate (m max Þ and K s (saturation constant) were 0:398 h À1 and 5:509 g l À1 , respectively, using glucose as substrate. The experimental substrate and biomass concentration profiles have good resemblance with those obtained by kinetic model predictions. A model based on logistic equation has been developed to describe the growth of R. sphaeroides O.U 001 in the second stage. Modified Gompertz equation was applied to estimate the hydrogen production potential, rate and lag phase time in a batch process for various initial concentration of glucose, based on the cumulative hydrogen production curves. Both the curve fitting and statistical analysis showed that the equation was suitable to describe the progress of cumulative hydrogen production.
Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological... more Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological hydrogen production compared with photosynthetic or chemical routes. Pure substrates, including glucose, starch and cellulose, as well as different organic waste materials can be used for hydrogen fermentation. Among a large number of microbial species, strict anaerobes and facultative anaerobic chemoheterotrophs, such as clostridia and enteric bacteria, are efficient producers of hydrogen. Despite having a higher evolution rate of hydrogen, the yield of hydrogen [mol H2 (mol substrate−1)] from fermentative processes is lower than that achieved using other methods; thus, the process is not economically viable in its present form. The pathways and experimental evidence cited in the literature reveal that a maximum of four mol of hydrogen can be obtained from substrates such as glucose. Modifications of the fermentation process, by redirection of metabolic pathways, gas sparging and maintaining a low partial pressure of hydrogen to make the reaction thermodynamically favorable, efficient product removal, optimum bioreactor design and integrating fermentative process with that of photosynthesis, are some of the ways that have been attempted to improve hydrogen productivity. This review briefly describes recent advances in these approaches towards improvement of hydrogen yield by fermentation.
Chemical Industry & Chemical Engineering Quarterly, 2008
Page 1. Available on line at Association of the Chemical Engineers AChE www.ache.org.yu/ CICEQ Ch... more Page 1. Available on line at Association of the Chemical Engineers AChE www.ache.org.yu/ CICEQ Chemical Industry & Chemical Engineering Quarterly 14 (2) (2008) 5767 CI&CEQ 57 DEBABRATA DAS1,2 NAMITA KHANNA1 T. NEJAT VEZIROĞLU2 ...
Fermentative hydrogen production has been carried out both in batch and continuous system using r... more Fermentative hydrogen production has been carried out both in batch and continuous system using recombinant Escherichia coli BL 21. Effect of various process parameters, viz. size of inoculum, initial medium pH, initial substrate concentration, temperature and dilution rate, was examined with respect to maximum hydrogen productivity. Maximum hydrogen production rate obtained in this study was 66 mmol/(l h) using glucose as substrate at a dilution rate of 0.55 h À1 in the immobilized whole cell bioreactor. Black strap molasses, a by-product of sugar industry, was found suitable as a feedstock for fermentation using which maximum rate of hydrogen production was 97.4 mmol/(l h). Energy analysis reveals that the percentage of gaseous energy recovery obtained in this study using recombinant E. coli BL 21 and considering glucose as a substrate was 26.68%. A comparison of hydrogen production characteristics between the wild strain Enterobacter cloacae IIT-BT-08 and that of the recombinant E. coli BL21 indicates that optimum initial pH, initial glucose concentration and reaction temperature are almost comparable and/or marginally same for both the strains. However, the yield of hydrogen (mol H 2 /(mol glucose)) with the recombinant strain was 3.12 mol H 2 / (mol glucose) which was much higher than that reported for the wild strain. #
Combined dark and photo-fermentation was carried out to study the feasibility of biological hydro... more Combined dark and photo-fermentation was carried out to study the feasibility of biological hydrogen production. In dark fermentation, hydrogen was produced by Enterobacter cloacae strain DM11 using glucose as substrate. This was followed by a photo-fermentation process. Here, the spent medium from the dark process (containing unconverted metabolites, mainly acetic acid etc.) underwent photo-fermentation by Rhodobacter sphaeroides strain O.U.001 in a column photo-bioreactor. This combination could achieve higher yields of hydrogen by complete utilization of the chemical energy stored in the substrate. Dark fermentation was studied in terms of several process parameters, such as initial substrate concentration, initial pH of the medium and temperature, to establish favorable conditions for maximum hydrogen production. Also, the effects of the threshold concentration of acetic acid, light intensity and the presence of additional nitrogen sources in the spent effluent on the amount of hydrogen produced during photo-fermentation were investigated. The light conversion efficiency of hydrogen was found to be inversely proportional to the incident light intensity. In a batch system, the yield of hydrogen in the dark fermentation was about 1.86 mol H2 mol−1 glucose; and the yield in the photo-fermentation was about 1.5–1.72 mol H2 mol−1 acetic acid. The overall yield of hydrogen in the combined process, considering glucose as the preliminary substrate, was found to be higher than that in a single process.
When the partial pressure of H2 was decreased by lowering the total pressure in the headspace of ... more When the partial pressure of H2 was decreased by lowering the total pressure in the headspace of the reactor in a batch fermentation process from 760 mm Hg to 380 mm Hg containing Enterobacter cloacae, the molar yield of H2 increased from 1.9 mol to 3.9 mol H2/mol glucose. The maximum production rate was 0.017 mmol H2/h l at 380 mm Hg. The lag period as well as total batch time of H2 production decreased using a decreased partial pressure.
Hydrogen is the fuel of the future mainly due to its high conversion e ciency, recyclability and ... more Hydrogen is the fuel of the future mainly due to its high conversion e ciency, recyclability and nonpolluting nature. Biological hydrogen production processes are found to be more environment friendly and less energy intensive as compared to thermochemical and electrochemical processes. They are mostly controlled by either photosynthetic or fermentative organisms. Till today, more emphasis has been given on the former processes. Nitrogenase and hydrogenase play very important role. Genetic manipulation of cyanobacteria (hydrogenase negative gene) improves the hydrogen generation. The paper presents a survey of biological hydrogen production processes. The microorganisms and biochemical pathways involved in hydrogen generation processes are presented in some detail. Several developmental works are discussed. Immobilized system is found suitable for the continuous hydrogen production. About 28% of energy can be recovered in the form of hydrogen using sucrose as substrate. Fermentative hydrogen production processes have some edge over the other biological processes.
Nitrogenase a b s t r a c t Biological hydrogen production processes offer a technique through wh... more Nitrogenase a b s t r a c t Biological hydrogen production processes offer a technique through which renewable energy sources like biomass can be utilized for the generation of the cleanest energy carrier for the use of mankind. Hydrogen intensive research work has already been carried out on the advancement of these processes, such as the development of genetically modified microorganism, metabolic engineering, improvement of the reactor designs, use of different solid matrices for the immobilization of whole cells, biochemical assisted bioreactor, development of two-stage processes, etc. for higher H 2 -production rates. Maximum H 2 yield is found to be 7.1 mol H 2 /mol glucose. However, major bottlenecks for the commercialization of these processes are lower H 2 yield and rate of H 2 production. Suitable microbial cultures are required to handle waste materials efficiently, which are usually complex in nature. This will serve dual purposes: clean energy generation and bioremediation. Scale-up studies on fermentative H 2 -production processes have been done successfully. Pilot plant trials of the photo-fermentation processes require more attention.
Improvement in H2 production was achieved through redirection of metabolic pathways by blocking f... more Improvement in H2 production was achieved through redirection of metabolic pathways by blocking formation of alcohol and some organic acids in Enterobacter cloacae IIT-BT 08. The wild type strain was more susceptible to allyl alcohol (7 mM) and to the combined effect of NaBr and NaBrO3 (40 mM each at pH 5.5) than were double mutants, with defects in both alcohol and organic acid formation pathways, which had higher H2 yields (3.4 mol mol−1 glucose) than the wild type strain (2.1 mol mol−1 glucose).
This communication reports on the continuous biohydrogen production by Thermotoga neapolitana cel... more This communication reports on the continuous biohydrogen production by Thermotoga neapolitana cells immobilized on a stable cationic hydrogel bearing amine groups. This hydrogel was designed to perform two functional activities: to promote adhesion of T. neapolitana cells, and to buffer pH changes in the bacterial cultures. Repeated fed-batch cultures showed an average hydrogen production rate and yield of 50.6 mL L 21 h 21 and 3.3 mol H 2 /mol glucose, respectively. To the best of our knowledge, this is the first report detailing the immobilization of this bacterial strain on a polymeric support.
Fermentative hydrogen production was carried out by Enterobacter cloacae DM11, using glucose as t... more Fermentative hydrogen production was carried out by Enterobacter cloacae DM11, using glucose as the substrate. The effects of initial substrate concentration, initial medium pH, and temperature were investigated. Results showed that at an initial glucose concentration of 1.0% (m/v), the molar yield of hydrogen was 3.31 mol (mol glucose)(-1). However, at higher initial glucose concentration, both the rate and cumulative volume of hydrogen production decreased. The pH of 6.5 +/- 0.2 at a temperature of 37 degrees C was found most suitable with respect to maximum rate of production of hydrogen in batch fermentation. Activation enthalpies of fermentation and that of thermal deactivation of the present process were estimated following a modified Arrhenius equation. The values were 47.34 and 118.67 kJ mol(-1) K(-1), respectively. The effect of the addition of Fe(2+) on hydrogen production was also studied. It revealed that the presence of iron (Fe(2+)) in the media up to a concentration of 20 mg L(-1) had a marginal enhancing effect on total hydrogen production. A simple model developed from the modified Gompertz equation was applied to estimate the hydrogen production potential, production rate, and lag-phase time in a batch process, based on the cumulative hydrogen production curves, using the software program Curve Expert 1.3.
Two-stage process described in the present work is a combination of dark and photofermentation in... more Two-stage process described in the present work is a combination of dark and photofermentation in a sequential batch mode. In the first stage glucose is fermented to acetate, CO 2 and H 2 in an anaerobic dark fermentation by Enterobacter cloacae DM11. This is followed by a successive second stage where acetate is converted to H 2 and CO 2 in a photobioreactor by photosynthetic bacteria, Rhodobacter sphaeroides O.U. 001. The yield of hydrogen in the first stage was about 3:31 mol H 2 ðmol glucoseÞ À1 (approximately 82% of theoretical) and that in the second stage was about 1:521:72 mol H 2 ðmol acetic acidÞ À1 (approximately 37-43% of theoretical). The overall yield of hydrogen in two-stage process considering glucose as preliminary substrate was found to be higher compared to a single stage process. Monod model, with incorporation of substrate inhibition term, has been used to determine the growth kinetic parameters for the first stage. The values of maximum specific growth rate (m max Þ and K s (saturation constant) were 0:398 h À1 and 5:509 g l À1 , respectively, using glucose as substrate. The experimental substrate and biomass concentration profiles have good resemblance with those obtained by kinetic model predictions. A model based on logistic equation has been developed to describe the growth of R. sphaeroides O.U 001 in the second stage. Modified Gompertz equation was applied to estimate the hydrogen production potential, rate and lag phase time in a batch process for various initial concentration of glucose, based on the cumulative hydrogen production curves. Both the curve fitting and statistical analysis showed that the equation was suitable to describe the progress of cumulative hydrogen production.
Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological... more Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological hydrogen production compared with photosynthetic or chemical routes. Pure substrates, including glucose, starch and cellulose, as well as different organic waste materials can be used for hydrogen fermentation. Among a large number of microbial species, strict anaerobes and facultative anaerobic chemoheterotrophs, such as clostridia and enteric bacteria, are efficient producers of hydrogen. Despite having a higher evolution rate of hydrogen, the yield of hydrogen [mol H2 (mol substrate−1)] from fermentative processes is lower than that achieved using other methods; thus, the process is not economically viable in its present form. The pathways and experimental evidence cited in the literature reveal that a maximum of four mol of hydrogen can be obtained from substrates such as glucose. Modifications of the fermentation process, by redirection of metabolic pathways, gas sparging and maintaining a low partial pressure of hydrogen to make the reaction thermodynamically favorable, efficient product removal, optimum bioreactor design and integrating fermentative process with that of photosynthesis, are some of the ways that have been attempted to improve hydrogen productivity. This review briefly describes recent advances in these approaches towards improvement of hydrogen yield by fermentation.
Chemical Industry & Chemical Engineering Quarterly, 2008
Page 1. Available on line at Association of the Chemical Engineers AChE www.ache.org.yu/ CICEQ Ch... more Page 1. Available on line at Association of the Chemical Engineers AChE www.ache.org.yu/ CICEQ Chemical Industry & Chemical Engineering Quarterly 14 (2) (2008) 5767 CI&CEQ 57 DEBABRATA DAS1,2 NAMITA KHANNA1 T. NEJAT VEZIROĞLU2 ...
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