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A lactose utilizing yeast strain, Kluyveromyces marxianus DSMZ-7239 was used for ethanol formation from cheese-whey powder (CWP) solution in batch experiments. Effects of initial substrate (CWP) and yeast concentrations on the rate and extent of ethanol formation were investigated. The initial pH and oxidation-reduction potential (ORP) was kept at 5 and -250 mV, respectively. The rate and extent of ethanol formation increased with increasing CWP concentration up to 156 g l(-1) (75 g l(-1) sugar) and then decreased for larger CWP concentrations due to substrate inhibition at high sugar concentrations. The ethanol yield coefficient was also maximum (0.54 g EtOH/g sugar) and equal to the theoretical yield at CWP concentration of 156 g l(-1). The growth yield coefficient was found to be Y(x/s)=1.2+/-0.1g biomass g sugar(-1). The rate of sugar utilization and ethanol formation also increased linearly with increasing initial biomass concentrations. A kinetic model describing the rate of sugar utilization and substrate inhibition as function of the initial substrate and the biomass concentrations was developed. The kinetic constants were determined using the experimental data. Model predictions of sugar utilization rates were in good agreement with the experimental data. The results indicated that the initial sugar concentration should be below 75 g l(-1) (CWP<156 g l(-1)) and the initial biomass should be above 850 mg l(-1) to obtain high rates and yields of ethanol formation and to avoid substrate inhibition.

Vinegar fermentation wastewater with an initial chemical oxygen demand (COD) content of was subjected to electrohydrolysis using aluminium, copper, and stainless-steel electrodes for hydrogen gas production. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (2,098 ml), hydrogen yield (), hydrogen formation rate (), percent hydrogen (99.5%) in the gas phase, percent COD removal (12%), and energy efficiency (21.3%) was obtained with the aluminium electrode. Hydrogen gas production by water electrolysis was 260 ml with the Al electrode, and wastewater control resulted in nearly in 96 h. Hydrogen gas was produced by reaction of () ions released from acetic acid and electrons provided by DC current. Aluminium electrode was the most suitable one among the others tested. [ABSTRACT FROM AUTHOR]

Abstract: Scrap aluminum particles and salt (NaCl) were added to the vinegar fermentation wastewater to improve hydrogen gas formation by electrohydrolysis of the wastewater organics. The applied DC voltage and initial COD of the wastewater were constant at 4 V and 33.16 g L−1, respectively. The highest cumulative hydrogen gas formation (2877 mL) was obtained with scrap Al (1 g L−1) and NaCl (1 g L−1) additions within 72 h as compared to 1925 mL H2 gas formation from raw wastewater. Hydrogen gas formation from Al and NaCl added water was 302 ml as compared to 260 ml from raw water. The highest H2 gas formation rate (952 mL d−1), the yield (1660 mL H2 g−1 COD) and the highest current intensity (163 mA) were also obtained with combined effects of scrap Al and NaCl additions. Almost pure hydrogen gas (99%) was produced using the raw wastewater. Initial conductivity of the raw wastewater increased from 1.80 mS cm−1 to 5.01 mS cm−1 with the addition of scrap Al and salt for which the final conductivities were 4.0 mS cm−1 and 6.91 mS cm−1, respectively. The highest energy conversion efficiency was obtained with only scrap Al addition (37.8%) as compared to 30.5% efficiency obtained with Al and salt additions. Additions of NaCl and scrap Al particles was found to be very beneficial for H2 gas formation by electrohydrolysis of vinegar fermentation wastewater. [Copyright &y& Elsevier]

Abstract: Vinegar fermentation wastewater with different initial COD contents (9.66–48.6 g L−1) were used for hydrogen gas production with simultaneous COD removal by electro-hydrolysis. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (3197 ml), hydrogen yield (2766 ml H2 g−1 COD), hydrogen formation rate (799 ml d−1), and percent hydrogen (99.5%) in the gas phase were obtained with the highest initial COD of 48.6 g COD L−1. The highest energy efficiency (48%) was obtained with the lowest COD content of 9.66 g L−1. Hydrogen gas production by water electrolysis was less than 250 ml and wastewater control resulted in less than 25 ml H2 in 96 h. The highest (12%) percent COD removal was obtained with the lowest COD content. Hydrogen gas was produced by reaction of (H+) ions present in raw WW ( pH = 3.0) and protons released from acetic acid with electrons provided by electrical current. Electro-hydrolysis of vinegar wastewater was proven to be an effective method of H2 gas production with some COD removal. [Copyright &y& Elsevier]

Dark fermentative hydrogen gas production from cheese whey powder solution was realized at 55°C. Experiments were performed at different initial biomass concentrations varying between 0.48 and 2.86 g L−1 with a constant initial substrate concentration of 26 ± 2 g total sugar (TS) per liter. The highest cumulative hydrogen evolution (633 mL, 30°C), hydrogen yield (1.56 mol H2 mol−1 glucose), and H2 formation rate (3.45 mL h−1) were obtained with 1.92 g L−1 biomass concentration. The specific H2 production rate decreased with increasing biomasss concentration from the highest value (47.7 mL g−1 h−1) at 0.48 g L−1 biomass concentration. Total volatile fatty acid concentration varied beetween 10 and 14 g L−1 with the highest level of 14.2 g L−1 at biomass concentration of 0.48 g L−1 and initial TS content of 28.4 g L−1. The experimental data were correlated with the Gompertz equation and the constants were determined. The most suitable initial biomass to substrate ratio yielding the highest H2 yield and formation rate was 0.082 g biomass per gram of TS. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 28: 931-936, 2012 [ABSTRACT FROM AUTHOR]

Abstract: Cheese whey powder (CWP) solution was used as the raw material for hydrogen gas production by mesophilic (35 °C) and thermophilic (55 °C) dark fermentations at constant initial total sugar and bacteria concentrations. Thermophilic fermentation yielded higher cumulative hydrogen formation (CHF = 171 mL), higher hydrogen yield (111 mL H2 g−1 total sugar), and higher hydrogen formation rate (3.46 mL H2 L−1 h−1) as compared to mesophilic fermentation. CHF in both cases were correlated with the Gompertz equation and the constants were determined. Despite the longer lag phase, thermophilic fermentation yielded higher specific H2 formation rate (2.10 mL H2 g−1cells h−1). Favorable results obtained in thermophilic fermentation were probably due to elimination of H2 consuming bacteria at high temperatures and selection of fast hydrogen gas producers. [Copyright &y& Elsevier]

Abstract: Hydrogen gas production from cheese whey powder (CWP) solution by thermophilic dark fermentation was investigated at 55 °C. Experiments were performed at different initial total sugar concentrations varying between 5.2 and 28.5 g L−1 with a constant initial bacteria concentration of 1 g L−1. The highest cumulative hydrogen evolution (257 mL) was obtained with 20 g L−1 total sugar (substrate) concentration within 360 h while the highest H2 formation rate (2.55 mL h−1) and yield (1.03 mol H2 mol−1 glucose) were obtained at 5.2 and 9.5 g L−1 substrate concentrations, respectively. The specific H2 production rate (SHPR = 4.5 mL h−1 g−1cells) reached the highest level at 20 g L−1 total sugar concentration. Total volatile fatty acid (TVFA) concentration increased with increasing initial total sugar content and reached the highest level (14.15 g L−1) at 28.5 g L−1 initial substrate concentration. The experimental data was correlated with the Gompertz equation and the constants were determined. The optimum initial total sugar concentration was 20 g L−1 above which substrate and product (VFA) inhibitions were observed. [Copyright &y& Elsevier]

Abstract: Waste ground wheat was subjected to acid hydrolysis (pH = 3.0) at 90 °C for 15 min using an autoclave. The sugar solution obtained from acid hydrolysis was subjected to dark fermentation for hydrogen gas production after neutralization. In the first set of experiments, initial total sugar concentration was varied between 3.9 and 27.5 g L−1 at constant biomass (cell) concentration of 1.3 g L−1. Biomass concentration was varied between 0.28 g L−1 and 1.38 g L−1 at initial total sugar concentration of 7.2 ± 0.2 g L−1 in the second set of experiments. The highest hydrogen yield (1.46 mol H2 mol−1 glucose) and the specific formation rate (83.6 ml H2 g−1 cell h−1) were obtained with 10 g L−1 initial total sugar concentration. Biomass (cell) concentration affected the specific hydrogen production rate yielding the highest rate (1221 ml H2 g−1 cell h−1) and the yield at the lowest (0.28 g L−1) initial biomass concentration. The most suitable Xo /So ratio, maximizing the yield and specific rate of hydrogen gas formation was Xo /So  = 0.037. Dark fermentation of acid hydrolyzed ground wheat was found to be more beneficial as compared to simultaneous bacterial hydrolysis and fermentation. [Copyright &y& Elsevier]

Abstract: Hydrogen gas production from acid hydrolyzed waste wheat starch by combined dark and photo-fermentation was investigated in continuous mode with periodic feeding and effluent removal. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides (NRRL-B 1727) were used as the seed culture for dark and light fermentations, respectively with biomass ratio of Rhodobacter/sludge=3. Hydraulic residence time (HRT) was changed between 1 and 8 days by adjusting the feeding periods. Ground waste wheat was acid hydrolyzed at pH=3 and 121°C for 30min using an autoclave and the resulting sugar solution was used as the substrate for combined fermentation after pH adjustment and nutrient addition. The highest daily hydrogen gas production (41mld−1), hydrogen yield (470mlg−1 total sugar=3.4mol H2 mol−1glucose), volumetric and specific hydrogen production rates were obtained at the HRT of 8 days. The highest biomass and the lowest total volatile fatty acids (TVFA) concentrations were also realized at HRT=8 days indicating VFA fermentation by Rhodobacter sp. at high HRTs. The lowest total sugar loading rate of 0.625gL−1 d−1 resulted in the highest hydrogen yield and formation rate. Hydrogen gas production by combined fermentation with periodic feeding was proven to be an effective method resulting in high hydrogen yields at long HRTs. [Copyright &y& Elsevier]

Abstract: This article overviews reported studies on bio-hydrogen production from different raw materials by dark and photo-fermentations operated with different modes. Sequential and combined dark and photo-fermentations operated in batch, continuous and fed-batch modes were compared. Operating conditions and modes resulting in the highest hydrogen yield and formation rate were revealed. Relative advantages of sequential and combined dark and photo-fermentations were discussed. Sequential fermentation was found to be preferable due to high H2 yields and productivities. High cell density fed-batch culture with controlled feeding and simultaneous product removal was concluded to be the most suitable operation mode at the optimum environmental conditions. [Copyright &y& Elsevier]

Abstract: Dark fermentation experiments were performed for bio-hydrogen production from ground wheat starch solution (10 ± 1 g l−1) using periodic feeding and effluent removal. A mixed culture of Clostridium butyricum-NRRL 1024 and Clostridium pasteurianum-NRRL B-598 were used with an initial biomass ratio of 1/1.Effects of wheat starch loading rate on the rate and yield of bio-hydrogen formation were investigated. Substrate loading rate was varied between 0.54 and 5.52 g d−1 (HRT = 6–60 h). The highest hydrogen formation rate (280 ml d−1), volumetric hydrogen formation rate (1857 ml H2 l−1 d−1) and volatile fatty acids (VFAs) concentration were obtained with a substrate loading rate of 5.52 g d−1 (HRT = 6 h). The highest hydrogen yield (109 ml H2 g TS −1) was obtained with a substrate loading rate of 1.38 g d−1. [Copyright &y& Elsevier]

Abstract: Hydrogen gas production by photo-fermentation of dark fermentation effluent of acid hydrolyzed wheat starch was investigated at different hydraulic residence times (HRT = 1–10 days). Pure Rhodobacter sphaeroides (NRRL B-1727) culture was used in continuous photo-fermentation by periodic feeding and effluent removal. The highest daily hydrogen gas production (85 ml d−1) was obtained at HRT = 4 days (96 h) while the highest hydrogen yield (1200 ml H2 g−1 TVFA) was realized at HRT = 196 h. Specific and volumetric hydrogen formation rates were also the highest at HRT = 96 h. Steady-state biomass concentrations and biomass yields increased with increasing HRT. TVFA loading rates of 0.32 g L−1 d−1 and 0.51 g L−1 d−1 resulted in the highest hydrogen yield and formation rate, respectively. Hydrogen gas yield obtained in this study compares favorably with the relevant literature reports probably due to operation by periodic feeding and effluent removal. [Copyright &y& Elsevier]

Abstract: Batch dark fermentation experiments were performed to investigate the effects of biomass and substrate concentration on bio-hydrogen production from acid hydrolyzed ground wheat at 55 °C. In the first set of experiments, the substrate concentration was constant at 20 g total sugar L−1 and biomass concentration was varied between 0.52 and 2.58 g L−1. Total sugar concentration was varied between 4.2 and 23.7 g L−1 in the second set of experiments with a 1.5 g L−1 constant biomass concentration. The highest cumulative hydrogen formation (582 mL, 30 °C, 1 atm), formation rate (5.43 mL h−1) and final total volatile fatty acid (TVFA) concentration (6.54 g L−1) were obtained with 1.32 g L−1 biomass concentration. In variable substrate concentration experiments, the highest cumulative hydrogen (365 mL) and TVFA concentration (4.8 g L−1) were obtained with 19.25 g L−1 initial total sugar concentration while hydrogen gas formation rate (12.95 mL h−1) and the yield (200 mL H2 g−1 total sugar) were the highest with 4.2 g L−1 total sugar concentration. [Copyright &y& Elsevier]

Abstract: Pure culture of Rhodobacter sphaeroides (NRRL- B1727) was used for continuous photo-fermentation of volatile fatty acids (VFA) present in the dark fermentation effluent of ground wheat starch. The feed contained 1950±50mgL−1 total VFA with some nutrient supplementation. Hydraulic residence time (HRT) was varied between 24 and 120hours. The highest steady-state daily hydrogen production (55mld−1) and hydrogen yield (185ml H2 g−1 VFA) were obtained at HRT=72hours (3 days). Biomass concentration increased with increasing HRT. Volumetric and specific hydrogen formation rates were also maximum at HRT=72h. High extent of TVFA fermentation at HRT=72h resulted in high hydrogen gas production. [Copyright &y& Elsevier]

Abstract: Continuous combined fermentation of ground wheat starch was realized in an annular-hybrid bioreactor (AHB) for hydrogen gas production. A mixture of pure cultures of Clostridium beijerinkii (DSMZ-791) and Rhodobacter sphaeroides-RV were used as seed cultures in combined fermentation. The feed contained 5 g L−1 ground wheat with some nutrient supplementation. Effects of hydraulic residence time (HRT) on the rate and yield of hydrogen gas formation were investigated. Steady-state daily hydrogen production decreased but, hydrogen yield increased with increasing HRT. The highest hydrogen yield was 90 ml g−1 starch at HRT of 6 days. Hydrolysis of starch and fermentation of glucose to volatile fatty acids (VFA) were readily realized at all HRTs. However, slow conversion of VFAs to H2 and CO2 by photo-fermentation caused accumulation of VFAs in the medium. Specific and volumetric rates of hydrogen formation also decreased with increasing HRT. High hydrogen yields obtained at high HRTs are due to partial fermentation of VFAs by Rhodobacter sp. The system should be operated at HRTs longer than 5 days for effective hydrogen gas formation by the dark and photo-fermentation bacteria. [Copyright &y& Elsevier]

Abstract: Bio-hydrogen production by combined dark and light fermentation of ground wheat starch was investigated using fed-batch operation. Serum bottles containing heat-treated anaerobic sludge and a mixture of Rhodobacter sp. was fed with a medium containing 20gdm−3 wheat powder (WP) at a constant flow rate. The system was operated at different initial dark/light biomass ratios (D/L). The optimum D/L ratio was 1/2 yielding the highest cumulative hydrogen (1548cm3), yield (65.2cm3 g−1 starch), and specific hydrogen production rate (5.18cm3 g−1 h−1). Light fermentation alone yielded higher hydrogen production than dark fermentation due to fermentation of volatile fatty acids (VFAs) to H2 and CO2. The lowest hydrogen formation was obtained with D/L ratio of 1/1 due to accumulation of VFAs in the medium. [Copyright &y& Elsevier]

Composition of the mixed culture was varied in combined dark-light fermentation of wheat powder starch in order to improve hydrogen gas formation rate and yield. Heat-treated anaerobic sludge and pure culture of Clostridium beijerinckii ( DSMZ 791 T) were combined with two different light fermentation bacteria of Rhodobacter sphaeroides (RS-NRRL and RS-RV) in order to select a more suitable mixture resulting in high hydrogen yield and formation rate. A combination of the anaerobic sludge and RS-NRRL yielded the highest cumulative hydrogen (CHF = 140 ml), the highest yield (0.36 mol H2 mol−1 glucose) and specific hydrogen formation rate (2.5 ml H2 g−1 biomass h−1). During dark fermentation (70 h) hydrogen was produced simultaneously by the dark and light fermentation bacteria using glucose from hydrolyzed starch. However, only light fermentation bacteria produced hydrogen from VFA’s derived from dark fermentation after a long adaptation period. [ABSTRACT FROM AUTHOR]

Abstract: Combined dark and photo-fermentation of ground wheat starch was carried out by using different light sources, intensities and lighting regime. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides-RV with a certain light/dark bacteria ratio was used in batch experiments. Tungsten, fluorescent, infrared (IR), tungsten + infrared, halogen lamps were used as light sources with a light intensity of 270 Wm−2 along with sunlight. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (178 ml) and yield (218 ml g−1 starch). Combined fermentations were performed at different light intensities (1–10 klux) using the halogen lamp in the second set of experiments. The optimum light intensity was found to be 10 klux (approx. 352 Wm−2) resulting in the highest cumulative hydrogen (111 ml) and hydrogen yield (139 ml H2 g−1 starch). Hydrogen formation was limited by the availability of light at low light intensities below 10 klux. Durations of dark/light cycles were changed to determine the most suitable lighting regime. Hydrogen gas formation increased with increasing cycle time and continuous lighting resulted in the highest cumulative hydrogen formation and hydrogen yield. [Copyright &y& Elsevier]

Abstract: Dark fermentation effluent of wheat powder solution was subjected to light fermentation for bio-hydrogen production using different light sources and intensities. Tungsten, fluorescent, infrared (IR), halogen lamps were used as light sources with a light intensity of 270Wm−2 along with sunlight. Pure culture of Rhodobacter sphaeroides-RV was used in batch light fermentation experiments. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (CHF, 252ml) and yield (781ml H2 g−1 TVFA). In the second set of experiments, light fermentations were performed at different light intensities (1–10klux) using halogen lamp. The optimum light intensity was found to be 5klux (approx. 176Wm−2) resulting in the highest CHF (88ml) and hydrogen yield (1037ml H2 g−1TVFA). Hydrogen formation was limited by the availability of light at low light intensities below 5klux and was inhibited by the excess light above 5klux. [Copyright &y& Elsevier]

Abstract: Ground wheat powder solution (10 g L−1) was subjected to combined dark and light fermentations for bio-hydrogen production by fed-batch operation. A mixture of heat treated anaerobic sludge (AN) and Rhodobacter sphaeroides-NRRL (RS-NRRL) were used as the mixed culture of dark and light fermentation bacteria with an initial dark/light biomass ratio of 1/2. Effects of wheat starch loading rate on the rate and yield of bio-hydrogen formation were investigated. The highest cumulative hydrogen formation (CHF = 3460 ml), hydrogen yield (201 ml H2 g−1 starch) and formation rate (18.1 ml h−1) were obtained with a starch loading rate of 80.4 mg S h−1. Complete starch hydrolysis and glucose fermentation were achieved within 96 h of fed-batch operation producing volatile fatty acids (VFA) and H2. Fermentation of VFAs by photo-fermentation for bio-hydrogen production was most effective at starch loading rate of 80.4 mg S h−1. Hydrogen formation by combined fermentation took place by a fast dark fermentation followed by a rather slow light fermentation after a lag period. [Copyright &y& Elsevier]

Abstract: Three different pre-treatment methods were applied on two different anaerobic sludge cultures and their mixtures in order to investigate the effects of pre-treatment methods on bio-hydrogen production from dark fermentation of waste ground wheat solution. Repeated heat, chloroform and combinations of heat and chloroform pre-treatment methods were applied to anaerobic sludges from different sources. Repeated heat treatment (2×5h) was found to be more effective in selecting hydrogen producing bacteria compared to the other treatment methods tested on the basis of cumulative hydrogen production. The highest hydrogen formation (652ml) and specific hydrogen production rate (SHPR=25.7mlH2 g−1 cellsh−1) were obtained with the anaerobic sludge pre-treated by repeated boiling. Both the type of anaerobic sludge and the pre-treatment method had considerable effects on bio-hydrogen production from wheat powder solution (WPS) by dark fermentation. [Copyright &y& Elsevier]

Abstract: Effects of the substrate and cell concentration on bio-hydrogen production from ground wheat solution were investigated in combined dark-light fermentations. The ratio of the dark to light bacteria concentration (D/L) was kept constant at 1/10 while the wheat powder (WP) concentration was changed between 2.5 and 20gL−1 with a total cell concentration of 0.41gL−1 in the first set of experiments. Cell concentration was changed between 0.5 and 5gL−1 in the second set of experiments while the wheat powder concentration was constant at 5gL−1 with a D/L ratio of 1/7. The highest cumulative hydrogen (135ml) and formation rate (3.44mlH2 h−1) were obtained with the 20gL−1 wheat powder concentration. However, the highest yield (63.9mlg−1 starch) was obtained with the 2.5gL−1 wheat powder. In variable cell concentration experiments, the highest cumulative hydrogen (118ml) and yield (156.8mlH2 g−1 starch) were obtained with 1.1gL−1 cell concentration yielding an optimal biomass/substrate ratio of 0.22gcells/gWP. [Copyright &y& Elsevier]

Abstract: Ground waste wheat was subjected to combined dark and light batch fermentation for hydrogen production. The dark to light biomass ratio (D/L) was changed between 1/2 and 1/10 in order to determine the optimum D/L ratio yielding the highest hydrogen formation rate and the yield. Hydrogen production by only dark and light fermentation bacteria was also realized along with the combined fermentations. The highest cumulative hydrogen formation (CHF=76ml), hydrogen yield (176mlH2 g−1 starch) and formation rate (12.2mlH2 g−1 biomassh−1) were obtained with the D/L ratio of 1/7 while the lowest CHF was obtained with the D/L ratio of 1/2. Dark–light combined fermentation with D/L ratio of 1/7 was faster as compared to the dark and light fermentations alone yielding high hydrogen productivity and reduced fermentation time. Dark and light fermentations alone also yielded considerable cumulative hydrogen, but slower than the combined fermentation. [Copyright &y& Elsevier]

Abstract: Ground wheat solution was used for bio-hydrogen production by dark fermentation using heat-treated anaerobic sludge in a completely mixed fermenter operating in fed-batch mode. The feed wheat powder (WP) solution was fed to the anaerobic fermenter with a constant flow rate of 8.33mLh−1 (200mLd−1). Cumulative hydrogen production, starch utilization and hydrogen yields were determined at three different WP loading rates corresponding to the feed WP concentrations of 10, 20 and 30gL−1. The residual starch (substrate) concentration in the fermenter decreased with operation time while starch consumption was increasing. The highest cumulative hydrogen production (3600mL), hydrogen yield (465mL H2 g−1 starch or 3.1mol H2 mol−1 glucose) and hydrogen production rate (864mL H2 d−1) were obtained after 4 days of fed-batch operation with the 20gL−1 feed WP concentration corresponding to a WP loading rate of 4g WPd−1. Low feed WP concentrations (10gL−1) resulted in low hydrogen yields and rates due to substrate limitations. High feed WP concentrations (30gL−1) resulted in the formation of volatile fatty acids (VFAs) in high concentrations causing inhibition on the rate and yield of hydrogen production. [Copyright &y& Elsevier]

Abstract: Hydrogen formation performances of different anaerobic bacteria were investigated in batch dark fermentation of waste wheat powder solution (WPS). Serum bottles containing wheat powder were inoculated with pure cultures of Clostridium acetobutylicum (CAB), Clostridium butyricum (CB), Enterobacter aerogenes (EA), heat-treated anaerobic sludge (ANS) and a mixture of those cultures (MIX). Cumulative hydrogen formation (CHF), hydrogen yield (HY) and specific hydrogen production rate (SHPR) were determined for every culture. The heat-treated anaerobic sludge was found to be the most effective culture with a cumulative hydrogen formation of 560 ml, hydrogen yield of 223 ml H2 g−1 starch and a specific hydrogen production rate of 32.1 ml H2 g−1 h−1. [Copyright &y& Elsevier]

Abstract: Hydrogen gas production from sugar solution derived from acid hydrolysis of ground wheat starch by photo-fermentation was investigated. Three different pure strains of Rhodobacter sphaeroides (RV, NRLL and DSZM) were used in batch experiments to select the most suitable strain. The ground wheat was hydrolyzed in acid solution at pH=3 and 90°C in an autoclave for 15min. The resulting sugar solution was used for hydrogen production by photo-fermentation after neutralization and nutrient addition. R. sphaeroides RV resulted in the highest cumulative hydrogen gas formation (178ml), hydrogen yield (1.23molH2 mol−1 glucose) and specific hydrogen production rate (46mlH2 g−1 biomassh−1) at 5gl−1 initial total sugar concentration among the other pure cultures. Effects of initial sugar concentration on photo-fermentation performance were investigated by varying sugar concentration between 2.2 and 13gl−1 using the pure culture of R. sphaeroides RV. Cumulative hydrogen volume increased from 30 to 232ml when total sugar concentration was increased from 2.2 to 8.5gl−1. Further increases in initial sugar concentration resulted in decreases in cumulative hydrogen formation. The highest hydrogen formation rate (3.69mlh−1) and yield (1.23molH2 mol−1 glucose) were obtained at a sugar concentration of 5gl−1. [Copyright &y& Elsevier]

Abstract: Dark fermentation effluents of wheat powder (WP) solution containing different concentrations of volatile fatty acids (VFAs) were subjected to low voltage (1–3V) DC current to produce hydrogen gas. Graphite and copper electrodes were tested and the copper electrode was found to be more effective due to higher electrical conductivity. The effects of solution pH (2–7), applied voltage (1–3V) and the total VFA (TVFA) concentration (1–5gL−1) on hydrogen gas production were investigated. Hydrogen production increased with decreasing pH and became maximum at pH=2. Increases in applied voltage and the TVFA concentration also increased the cumulative hydrogen formation. The most suitable conditions for the highest cumulative hydrogen production was pH=2, with 3V applied voltage and 5g TVFA L−1. Up to 110ml hydrogen gas was obtained with 5gL−1 TVFA at pH=5.8 and 2V applied voltage within 37.5h. The highest energy efficiency (56%) was obtained with the 2V applied voltage and 10.85gL−1 TVFA. Hydrogen production by electrolysis of water in control experiments was negligible for pH>4. Hydrogen production by electrohydrolysis of VFA containing anaerobic treatment effluents was found to be an effective method with high energy efficiency. [Copyright &y& Elsevier]

Abstract: Three different Rhodobacter sphaeroides (RS) strains (RS–NRRL, RS–DSMZ and RS–RV) and their combinations were used for light fermentation of dark fermentation effluent of ground wheat containing volatile fatty acids (VFA). In terms of cumulative hydrogen formation, RS–NRRL performed better than the other two strains producing 48mlH2 in 180h. However, RS–RV resulted in the highest hydrogen yield of 250mlH2 g−1 TVFA. Specific hydrogen production rate (SHPR) with the RS–NRRL was also better in comparison to the others (13.8mlH2 g−1 biomassh−1). When combinations of those three strains were used, RS–RV+RS–DSMZ resulted in the highest cumulative hydrogen formation (90mlH2 in 330h). However, hydrogen yield (693mlH2 g−1 TVFA) and SHPR (12.1mlH2 g−1 biomassh−1) were higher with the combination of the three different strains. On the basis of Gompertz equation coefficients mixed culture of the three different strains gave the highest cumulative hydrogen and formation rate probably due to synergistic interaction among the strains. The effects of initial TVFA and NH4–N concentrations on hydrogen formation were investigated for the mixed culture of the three strains. The optimum TVFA and NH4–N concentrations maximizing the hydrogen formation were determined as 2350 and 47mgL−1, respectively. [Copyright &y& Elsevier]

Abstract: Powdered wheat solution was fermented batchwise for bio-hydrogen production using heat-treated anaerobic-acidogenic sludge as the inoculum at initial pH of 7.0 and temperature of 37°C. In order to determine the most suitable wheat powder (WP) and cell concentrations yielding the highest hydrogen formation, initial WP concentration was varied between 5 and 30gL−1 at a constant initial biomass concentration (2.6gL−1). The initial biomass concentration was varied between 0.5 and 5.0gL−1 at constant WP concentration of 20gL−1 in another set of experiments. Cumulative bio-hydrogen formation, hydrogen yield and the formation rate were maximum at the WP concentration of 20gL−1. Higher WP concentrations resulted in lower fermentation performance probably due to substrate and product (VFA) inhibition. Similarly, hydrogen formation rate and the yield were maximum with a biomass concentration of 2.5gL−1. Higher biomass concentrations resulted in lower hydrogen yield and formation rates due to product inhibition. The optimum initial biomass/substrate ratio maximizing the hydrogen yield and formation rate was found to be 0.125g biomassg−1 WP. A kinetic model was developed for bio-hydrogen formation from powdered wheat starch and the constants were determined by regression analysis. [Copyright &y& Elsevier]

Abstract: Cheese whey powder (CWP) solution containing 50gL−1 total sugar was fermented to ethanol in a continuously operated packed column bioreactor (PCBR) using olive pits as support particles for cell attachment. Pure culture of Kluyveromyces marxianus (DSMZ 7239) was used in the PCBR for ethanol formation from lactose content of CWP solution. Sugar utilization and ethanol formation were investigated as function of the hydraulic residence time (HRT) between 17.6 and 64.4h. Sugar concentration decreased with increasing ethanol concentration along the height of the column. Percent sugar utilization increased while effluent sugar concentration was decreasing with HRT between 17.6 and 50h. Similarly, effluent ethanol concentration increased while ethanol productivity was decreasing with increasing HRT up to 50h. Further increases in HRT above 50h resulted in decreases in effluent ethanol concentration. The ethanol yield coefficient also increased with increasing HRT and reached the highest level of 0.54gEg−1S at an HRT of 50h. Due to cell settling to the bottom of the column, high fermentation rates were obtained in the lower section of the system. Therefore, the system can be operated with a height of 36cm from the inlet to obtain high ethanol contents in the effluent with an HRT of 18h. [Copyright &y& Elsevier]

Abstract: The effects of C/N and C/P ratio on hydrogen yield and specific production rate were investigated in dark fermentation of wheat powder solution (WPS) by external addition of N and P since the wheat powder was N and P deficient. A Box–Wilson statistical experiment design approach was used. C/N ratio was varied between 20 and 200 while C/P ratio was between 50 and 1000. A quadratic response function was used to correlate the objective functions with the independent variables and the response function coefficients were determined by regression analysis. Hydrogen yield increased with increasing C/N and C/P ratios. Low nitrogen concentrations required low phosphorous contents for high hydrogen yields. A C/N ratio of 200 and C/P ratio of 1000 yielded the highest yield of at STP. SHPR also increased with increasing C/N and C/P ratios. Again the highest SHPR ( at STP) was obtained at C/N and C/P ratios of 200 and 1000, respectively. The C/N/P ratio maximizing the yield and formation rate of hydrogen was 100/0.5/0.1 . [Copyright &y& Elsevier]

Abstract: Cheese whey powder (CWP) solution was used for ethanol fermentation by Kluyveromyces marxianus NRRL-1195 in batch experiments. Effects of initial pH, CWP concentration and external nutrient (N, P) supplementation on ethanol formation rate and extent were investigated. The initial pH was varied between 3 and 7. The most suitable initial pH maximizing the final ethanol yield was found to be 5. Nutritional requirements of the organisms were investigated by supplementing the CWP solution with external nitrogen and phosphate sources. The rate and extent of ethanol formation did not increase with external nutrient addition indicating the fact that the nitrogen and phosphorous content of CWP was sufficient for ethanol fermentation. CWP concentration was varied between 50 and 300gl−1 with total sugar concentrations between 25 and 150gl−1. Final ethanol concentration and the rate of ethanol formation increased with increasing CWP concentration indicating no substrate or product inhibitions, but substrate limitations. The yield coefficient of ethanol varied between 0.35 and 0.54gethanolgsugar−1 and reached the theoretical level (0.54gEtOHgsugar−1) at 300gl−1 CWP concentration. [Copyright &y& Elsevier]

Abstract: Hydrogen gas production potentials of acid-hydrolyzed and boiled ground wheat were compared in batch dark fermentations under mesophilic (37 °C) and thermophilic (55 °C) conditions. Heat-treated anaerobic sludge was used as the inoculum and the hydrolyzed ground wheat was supplemented by other nutrients. The highest cumulative hydrogen gas production (752 ml) was obtained from the acid-hydrolyzed ground wheat starch at 55 °C and the lowest (112 ml) was with the boiled wheat starch within 10 days. The highest rate of hydrogen gas formation (7.42 ml H2 h−1) was obtained with the acid-hydrolyzed and the lowest (1.12 ml H2 h−1) with the boiled wheat at 55 °C. The highest hydrogen gas yield (333 ml H2 g−1 total sugar or 2.40 mol H2 mol−1 glucose) and final total volatile fatty acid (TVFA) concentration (10.08 g L−1) were also obtained with the acid-hydrolyzed wheat under thermophilic conditions (55 °C). Dark fermentation of acid-hydrolyzed ground wheat under thermophilic conditions (55 °C) was proven to be more beneficial as compared to mesophilic or thermophilic fermentation of boiled (partially hydrolyzed) wheat starch. [ABSTRACT FROM AUTHOR]

Abstract: Dark fermentation of acid hydrolyzed ground wheat starch for bio-hydrogen production by periodic feeding and effluent removal was investigated at different feeding intervals. Ground wheat was acid hydrolyzed at pH = 3 and T = 121 °C for 30 min using an autoclave. The resulting sugar solution was subjected to dark fermentation with periodic feeding and effluent removal. The feed solution contained 9 ± 0.5 g L−1 total sugar supplemented with some nutrients. Depending on the feeding intervals hydraulic residence time (HRT) was varied between 6 and 60 h. Steady-state daily hydrogen production increased with decreasing HRT. The highest daily hydrogen production (305 ml d−1) and volumetric hydrogen production rate (1220 ml H2 L−1 d−1) were obtained at HRT of 6 h. Hydrogen yield (130 ml H2 g−1 total sugar) reached the highest level at HRT = 24 h. Effluent total sugar concentration decreased, biomass concentration and yield increased with increasing HRT indicating more effective sugar fermentation at high HRTs. Dark fermentation end product profile shifted from acetic to butyric acid with increasing HRT. High acetic/butyric acid ratio obtained at low HRTs resulted in high hydrogen yields. [ABSTRACT FROM AUTHOR]

Abstract: Effects of N/C, P/C and Fe(II)/C ratios in fermentation medium on biohydrogen production by dark fermentation of acid-hydrolyzed wheat starch was investigated. The powdered wheat was autoclaved at pH=3 and 90°C for 15min and the resulting sugar solution was fermented after external addition of N, P and Fe(II) to overcome nutrient limitations. Box–Wilson statistical experiment design was used by considering the N/C (0–0.05, ww−1), P/C (0–0.02) and Fe(II)/C (0–0.03) ratios as the independent variables while the hydrogen yield and specific hydrogen production rate (SHPR) were the objective functions to be optimized. A quadratic response function was used to correlate the response functions with the independent variables. Low levels of the variables (N/C<0.02, P/C<0.01, Fe(II)/C<0.01) resulted in low hydrogen yield and SHPR due to nutrient limitations and high levels of nutrients caused inhibitions. The optimum conditions yielding the maximum hydrogen yield (Y =2.84mol H2 mol−1 glucose) were N/C=0.02, P/C=0.008 and Fe(II)/C=0.015. The maximum SHPR (96mL H2 g−1 biomassh−1) was obtained at N/C=0.025, P/C=0.008 and Fe(II)/C=0.015 (ww−1). [Copyright &y& Elsevier]