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•H2 production by co-culture of R. sphaeroides and C. acetobutylicum was studied.•Photo and dark fermentation at different pH were compared with combined process.•H2 production rate ...by dark fermentation was controlled by varying operational pH.•Control of pH increased H2 production by photofermentation and co-culture process.•Control of pH at 7.0 was found optimum for bacteria cooperation in the co-culture.
The role of pH control on biohydrogen production by co-culture of dark-fermentative Clostridium acetobutylicum and photofermentative Rhodobacter sphaeroides was studied. Single stage dark fermentation, photofermentation and hybrid co-culture systems were studied at different values of controlled and uncontrolled pH. Increasing pH during dark fermentation resulted in lower hydrogen production rate (HPR) and longer lag time for both controlled and uncontrolled conditions. However, it only slightly affected cumulative H2 volume. Results have shown that pH control at pH 7.5 increased photofermentative hydrogen production from 0.966 to 2.502L H2/Lmedium when compared to uncontrolled process. Fixed pH value has proven to be an important control strategy also for the hybrid process and resulted in obtaining balanced co-culture of dark and photofermentative bacteria. Control of pH at 7.0 was found optimum for bacteria cooperation in the co-culture what resulted in obtaining 2.533L H2/Lmedium and H2 yield of 6.22mol H2/mol glucose.
Dark fermentative bacteria – Clostridium beijerinckii Display omitted
•Effect of light intensity on H2 production by dark fermentation.•The applied source of light had spectrum similar to the solar ...radiation.•C. beijerinckii showed 83% decrease of H2 production at high light intensities.•Light caused redirection of metabolic pathways to lactic acid production.
The role of light intensity on biohydrogen production from glucose by Clostridium beijerinckii, Clostridium acetobutylicum, and Rhodobacter sphaeroides was studied to evaluate the performance and possible application in co-culture fermentation system. The applied source of light had spectrum similar to the solar radiation. The influence of light intensity on hydrogen production in dark process by C. acetobutylicum was negligible. In contrast, dark fermentation by C. beijerinckii bacteria showed a significant decrease (83%) in produced hydrogen at light intensity of 540W/m2. Here, the redirection of metabolism from acetic and butyric acid formation towards lactic acid was observed. This not yet reported effect was probably caused by irradiation of these bacteria by light within UVA range, which is an important component of the solar radiation. The excessive illumination with light of intensity higher than 200W/m2 resulted in decrease in hydrogen production with photofermentative bacteria as well.
Dairy wastewater was applied as the source of organic carbon in photobiological generation of hydrogen in the presence of
Rhodobacter sphaeroides O.U. 001. Experiments were performed as batch tests ...with concentration of the waste varying from 5 to 40 v/v %, and concentration of inoculum of 0.36 g dry wt/l under illumination of 9 klx. The highest volumes of photogenerated hydrogen were obtained at concentration of 40 v/v %, but the maximal substrate yield was reached for lower concentrations of the waste (5–10 v/v %). Changes in concentrations of substrates and products were used for determination of kinetic model. An application of constant pH close to 7 allows for use the non-treated waste in photobiological hydrogen generation with good yield.
The influence of concentration of glycerol, inoculum and total nitrogen on hydrogen generation, in batch dark fermentation process in the presence of digested sludge (at 37
°C and at initial pH
=
6) ...was studied. Changes in substrate and products concentrations were modeled with modified Gompertz equations (correlation coefficient
R
2
=
0.9015). The 1,3-propandiol, butyric acid, acetic acid, lactic acid and ethanol were found as the main liquid metabolites. Maximal substrate yield for hydrogen was 0.41
mol
H
2/mol glycerol and was obtained for medium containing 10
g/l of glycerol with the lowest amount of inoculum – 1.16
g volatile suspended solid (VSS)/l. Increase of glycerol concentration from 5 to 30
g/l resulted in much better hydrogen generation, namely from 0.345 to 0.715
l
H
2/l. Further increase of glycerol concentration did not cause any changes. The H
2:CO
2 ratio in biogas in system with the highest substrate yield was always 1. The initial concentration of glycerol does not influence the rate of hydrogen generation. The increase of initial concentration of inoculum from 1.2 to 11.6
g
VSS/l results in the decrease of specific hydrogen yield. Nitrogen concentration in medium does not influence the hydrogen production.
Rhodobacter sphaeroides O.U. 001 (concentration of inoculum-0.36 g dry wt/l) and brewery wastewaters were applied in photobiogeneration of hydrogen under illumination of 116 W/m
2. The best results ...were obtained with filtered wastewaters sterilized at 120 °C for 20 min and maximal concentration of waste in medium equal 10% v/v. The main product in generated biogas was hydrogen (90%). After sterilization the amount of generated hydrogen was tripled (from 0.76 to 2.2 l H
2/l medium), whereas waste concentration of 10% v/v resulted in the best substrate yield (0.22 l H
2/l of waste). Under these conditions the amount of generated hydrogen was 2.24 l H
2/l medium and light conversion efficiency reached value of 1.7%. The modified Gompertz equations served in modeling of the kinetics of the studied process.
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•Repeated fed-batch co-culture dark and photofermentation from starch was studied.•pH above 6.5 strongly disfavored H2 formation by dark fermentative bacteria.•Photo bacteria prefer ...high acetate/butyrate ratio after dark fermentation process.•Cooperation between dark and photobacteria at pH 7.0 was suppressed after few days.•Redirection of dark fermentative metabolism led to low H2 yields in the co-culture.
Hydrogen production from starch by a co-culture hybrid dark and photofermentation under repeated fed-batch conditions at different organic loading rates (OLR) was studied. Effective cooperation between bacteria in co-culture during initial days was observed at controlled pH 7.0. However, at pH above 6.5 dark fermentation phase was redirected from H2 formation towards production of formic acid, lactic acid and ethanol (which are not coupled with hydrogen production) with simultaneous lower starch removal efficiency. This resulted in decrease in the hydrogen production rate. The highest H2 production in co-culture process (3.23LH2/Lmedium – after 11days) was achieved at OLR of 1.5gstarch/L/day, and it was twofold higher than for dark fermentation process (1.59LH2/Lmedium). The highest H2 yield in the co-culture (2.62molH2/molhexose) was obtained at the OLR of 0.375gstarch/L/day. Different pH requirements of bacteria were proven to be a key limitation in co-culture system.
The influence of concentration of distillery wastewaters, concentration of inoculum and pH value on hydrogen generation in batch dark fermentation process was studied. Anaerobic digested sludge from ...municipal purification unit was applied as the source of bacteria mixture. The best specific yield was obtained in system containing 10% v/v of inoculum and 20% v/v of the waste (S0/X0 = 2.8), whereas the maximum amount of hydrogen and the highest rate of reaction was achieved in system containing 25% v/v inoculum and 40% v/v of waste (S0/X0 = 2.2). The content of generated hydrogen in biogas was always higher than 62%. Maximum amount of generated hydrogen was 1 l H2/l medium and the rate was 0.12 l/l/h. Liquid metabolites of hydrogen generation process were mainly acetic and butyric acids. Ethanol and propionic acid were in traces. The ratio of HBu/HAc in medium influenced the yield of generated hydrogen.
•Application of distillery wastewater in microbiological hydrogen generation.•Optimization of the reaction conditions.•Determination of major non-gaseous metabolites (for future use in hybrid systems).
The effect of pH control in biohydrogen production from starch by co-culture of dark fermentative Clostridium acetobutylicum and photofermentative Rhodobacter sphaeroides bacteria was studied. It was ...compared with hydrogen production rate and H2 yield obtained for single culture photo and dark fermentation. Development of stable bacteria co-culture resulted in complete decomposition of starch without accumulation of volatile fatty acids. Moreover, the amount of produced hydrogen was 2.5 fold higher than for single dark fermentation process, where maximum H2 production reached 0.939 L H2/Lmedium at pH 5.5. Acclimatization of C. acetobutylicum to starch and control of pH at 7.0 was found optimum for bacteria cooperation in the co-culture, resulting in simultaneous H2 production by both bacteria species. Cumulative H2 production and H2 yield in this process reached 2.29 L H2/Lmedium and 5.11 mol H2/molglucose, respectively. Higher amounts of hydrogen (2.67 L H2/Lmedium) were obtained in a co-culture process in which pH was raised from 6.0 to 7.5 after dark fermentation stage. However, under these conditions dark and photofermentation stages were separated in time.
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•H2 production by co-culture of R. sphaeroides and C. acetobutylicum was studied.•Starch from corn was applied as a complex carbon source.•Activation of C. acetobutylicum on starch was crucial for the process at higher pH.•Control of pH at 7.0 was the key issue for bacteria cooperation in the co-culture.•No VFAs accumulation was observed at the end of the co-culture process.
Two-step hybrid system of microbiological hydrogen production with the diluted solid wastes from chewing gum production as a substrate was studied. As the first step, dark fermentation with the ...digested sludge at different concentrations of waste was performed. The effluent originating from the dark process was subsequently applied in photofermentation with Rhodobacter sphaeroides bacteria. In the first step, the degradation of sweetening substances as well as Talha gum remaining in waste was observed. Hydrogen, carbon dioxide and liquid metabolites (Volatile Fatty Acids - VFAs) were the main products. The maximum hydrogen production in dark fermentation (0.36 L/Lmedium) was observed at concentration of 67 g waste/L. Effluents from the first step, containing mainly xylitol, butyric, acetic, lactic and propionic acids, served as the source of organic carbon for photofermentation. The maximum amount of hydrogen at this step reached 0.80 L H2/L of diluted (1:8) effluent. The presence of significant concentration of ammonium ions (∼480 mg/L) in non-diluted effluent completely ceased the hydrogen formation by nitrogenase, therefore reduction in the amount of NH4+ ions in the medium was necessary. This was realized by the dilution of effluent from dark fermentation. The total amount of hydrogen produced in sequential dark and photo-fermentation process under the optimized reaction conditions reached the volume of ∼6.7 L H2/L of non-diluted waste.
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•Microbiological hydrogen generation - hybrid system.•H2 production in dark- and photofermentation from chewing gum production wastes.•Decomposition of Talha gum during dark fermentation with anaerobic digested sludge.•Rhodobacter sphaeroides utilized xylitol and VFAs from dark fermentation effluents.•80% COD reduction in a two-step process.
