Hydrogen gas production from acid hydrolyzed wheat starch by combined dark and photo-fermentation with periodic feeding

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 30 min 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 (41 ml d⁻¹), hydrogen yield (470 ml g⁻¹ total sugar = 3.4 mol 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 0.625 g L⁻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.     

Photo-fermentative hydrogen gas production from dark fermentation effluent of acid hydrolyzed wheat starch with periodic feeding

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.     

Effects of starch loading rate on performance of combined fed-batch fermentation of ground wheat for bio-hydrogen production

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.     

Dark fermentation of acid hydrolyzed ground wheat starch for bio-hydrogen production by periodic feeding and effluent removal

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.     

Bio-hydrogen production by photo-fermentation of dark fermentation effluent with intermittent feeding and effluent removal

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 ± 50 mg L⁻¹ total VFA with some nutrient supplementation. Hydraulic residence time (HRT) was varied between 24 and 120 hours. The highest steady-state daily hydrogen production (55 ml d⁻¹) and hydrogen yield (185 ml H₂ g⁻¹ VFA) were obtained at HRT = 72 hours (3 days). Biomass concentration increased with increasing HRT. Volumetric and specific hydrogen formation rates were also maximum at HRT = 72 h. High extent of TVFA fermentation at HRT = 72 h resulted in high hydrogen gas production.     

Effects of light source,intensity and lighting regime on bio-hydrogen production from ground wheat starch by combined dark and photo-fermentations

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.     

Bio-hydrogen production from acid hydrolyzed wheat starch by photo-fermentation using different Rhodobacter sp

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 15 min. 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 (178 ml), hydrogen yield (1.23 mol H₂ mol⁻¹ glucose) and specific hydrogen production rate (46 ml H₂ g⁻¹ biomass h⁻¹) at 5 g l⁻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 13 g l⁻¹ using the pure culture of R. sphaeroides RV. Cumulative hydrogen volume increased from 30 to 232 ml when total sugar concentration was increased from 2.2 to 8.5 g l⁻¹. Further increases in initial sugar concentration resulted in decreases in cumulative hydrogen formation. The highest hydrogen formation rate (3.69 ml h⁻¹) and yield (1.23 mol H₂ mol⁻¹ glucose) were obtained at a sugar concentration of 5 g l⁻¹.     

Dark fermentative bio-hydrogen production from waste wheat starch using co-culture with periodic feeding: Effects of substrate loading rate

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.     

Microbial culture selection for bio-hydrogen production from waste ground wheat by dark fermentation

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.     

Effects of dark/light bacteria ratio on bio-hydrogen production by combined fed-batch fermentation of ground wheat starch

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 20 g dm^?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 (1548 cm³), yield (65.2 cm³ g^?1 starch), and specific hydrogen production rate (5.18 cm³ 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.     

Bio-hydrogen production from acid hydrolyzed waste ground wheat by dark fermentation

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 X_o/S_o ratio, maximizing the yield and specific rate of hydrogen gas formation was X_o/S_o = 0.037. Dark fermentation of acid hydrolyzed ground wheat was found to be more beneficial as compared to simultaneous bacterial hydrolysis and fermentation.     

Biohydrogen from molasses with ethanol-type fermentation: Effect of hydraulic retention time

Though ethanol-type fermentation has many advantages for improving hydrogen production rate (HPR) in continuously mode hydrogen producing system, information on this fermentation is very deficient. The effect of hydraulic retention time (HRT) on biohydrogen production and operational stability of ethanol-type fermentation was investigated in a continuous stirred tank reactor (CSTR) using molasses as substrate. Five HRTs were examined, ranging from 4 to 10 h. At HRT 5 h, the highest HPR of 12.27 mmol L⁻¹ h⁻¹ was obtained from ethanol-type fermentation in the pH range of 4.3–4.4. During the whole operation process, ethanol, butyrate and acetate were the predominant metabolites. A total COD concentration of ethanol and acetate accounted for above 73.3% of total soluble microbial products. Linear regression showed that HPR and ethanol production rate were proportionately correlated at all HRTs which could be expressed as y = 0.9821x − 3.5151 (r² = 0.9498). It is meaningful that the proposed recovery of both hydrogen and ethanol from fermentation process can improve energy production rate and economic profit. Results demonstrated that the best energy production rate was 15.50 kJ L⁻¹ h⁻¹, occurred at HRT = 5 h.     

Effect of hydraulic retention time on biohydrogen and volatile fatty acids production during acidogenic digestion of dephenolized olive mill wastewaters

The influence of Hydraulic Retention Time (HRT) on the performances of a recently developed biotechnological anaerobic acidogenic process fed with dephenolized Olive Mill Wastewater (OMW) was investigated. The study was carried out under mesophilic conditions in Packed Bed Biofilm Reactors (PBBRs), filled with ceramic cubes and inoculated with a characterized and acclimated acidogenic microbial consortium. The PBBRs were fed with a HRT of 7, 5, 3 or 1 day, which corresponded to Organic Loading Rates (OLRs) of about 5.5, 7.8, 12.9 and 38.8 g L⁻¹ d⁻¹, respectively. A significant production of a H₂-rich biogas was observed when shorter HRTs were applied: in particular, H₂ relative amount and productivity increased from 3% to 32% and from 0.20 to 6.10 dm³ m⁻³ h⁻¹, respectively, by decreasing the HRT from 7 to 1 day. On the contrary, shorter HRTs turned into a lower accumulation of Volatile Fatty Acids (VFAs), whose highest amounts were found with HRTs of 7 and 5 days (about 18.4 and 19.7 g L⁻¹ COD equivalents, respectively). The highest conversion yield of COD into VFAs (36%) was obtained with a HRT of 5 days, when VFAs represented about 78% of the effluent COD. HRT also influenced the composition of the VFA mixture: acetic, propionic and butyric acid were the most prominent VFAs, being their relative amounts higher when PBBRs were operated with shorter HRTs (up to 19, 12 and 42% of the whole mixture, respectively, when HRT was 1 day).     

Bio-hydrogen production during acidogenic fermentation in a multistage stirred tank reactor

The objective of this study was to evaluate the production of hydrogen in a two-stage CSTR system – both reactors having the same volume – and compare its performance with a conventional one-stage process. The lab-scale two-stage and one-stage systems were operated at five pHs and five hydraulic retention time (HRTs). The maximum volumetric hydrogen productivity and yield obtained with the two-stage system were 5.8 mmol L⁻¹ h⁻¹ and 2.7 mol H₂ mol glucose⁻¹, respectively, at an HRT of 12 h and pH 5.5. Overall, the two-stage system showed, at steady state, a better performance that the one-stage system for all the evaluated pHs. However, a comparison between the one-stage system, operating at 6 h of HRT, and the first reactor of the two-stage system at the same HRT did not show any significant difference, highlighting the positive impact of having a two-stage process. The determination of the ratio between the experimental measured H₂ in the gas phase and the theoretical H₂ generated in the liquid phase (discrepancy factor) indicated that an important part of the hydrogen produced in the first reactor was transferred into the second reactor instead of being desorbed in the headspace. Therefore, the improving of hydrogen production in the two-stage system is rather attributed to the increased transfer of hydrogen from liquid to gas than an actual total hydrogen production increase.     

Dark fermentation of ground wheat starch for bio-hydrogen production by fed-batch operation

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 8.33 mL h⁻¹ (200 mL d⁻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 30 g L⁻¹. The residual starch (substrate) concentration in the fermenter decreased with operation time while starch consumption was increasing. The highest cumulative hydrogen production (3600 mL), hydrogen yield (465 mL H₂ g⁻¹ starch or 3.1 mol H₂ mol⁻¹ glucose) and hydrogen production rate (864 mL H₂ d⁻¹) were obtained after 4 days of fed-batch operation with the 20 g L⁻¹ feed WP concentration corresponding to a WP loading rate of 4 g WP d⁻¹. Low feed WP concentrations (10 g L⁻¹) resulted in low hydrogen yields and rates due to substrate limitations. High feed WP concentrations (30 g L⁻¹) resulted in the formation of volatile fatty acids (VFAs) in high concentrations causing inhibition on the rate and yield of hydrogen production.     

Comparative study on bio-hydrogen production from corn stover: Photo-fermentation,dark-fermentation and dark-photo co-fermentation

In this study, three different fermentation methods, such as photo-fermentation (PF), dark-fermentation (DF) and dark-photo co-fermentation (DPCF) for bio-hydrogen production from corn stover were compared in terms of hydrogen production, substrate consumption, by-products formation and energy conversion efficiency. A modified Gompertz model was applied to perform the kinetic analysis of hydrogen production. The maximum cumulative hydrogen yield of 141.42 mL·(g TS)⁻¹ was achieved by PF, DF with the minimum cumulative hydrogen yield of 36.08 mL· (g TS)⁻¹ had the shortest lag time of 4.33 h, and DPCF had the maximum initial hydrogen production rate of 1.88 mL· (g TS)⁻¹·h⁻¹ and maximum initial hydrogen content of 44.40%. The results also indicated PF was an acid-consuming process with a low total VFAs concentration level of 2.90–4.19 g·L⁻¹, DF was a process of VFAs accumulation with a maximum total VFAs concentration of 12.66 g·L⁻¹, and DPCF was a synergistic process in which the total VFAs concentration was significantly reduced and the hydrogen production efficiency was effectively improved compared with DF. The energy conversion efficiency of PF, DF and DPCF were 10.12%, 2.58% and 6.45%, respectively.     

Hydrogen production by combined dark and light fermentation of ground wheat solution

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 = 76 ml), hydrogen yield (176 ml H₂ g⁻¹ starch) and formation rate (12.2 ml H₂ g⁻¹ biomass h⁻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.     

Production of hydrogen and methane by one and two stage fermentation of food waste

Anaerobic digestion is an attractive process for generation of hydrogen and methane, which involves complex microbial processes on decomposition of organic wastes and subsequent conversion of metabolic intermediates to hydrogen and methane. Comparative performance of a sequential hydrogen and methane fermentation in two stage process and methane fermentation in one stage process were tested in batch reactor at varying ratios of feedstock to microbial inoculum (F/M) under mesophilic incubation. F/M ratios influence biogas yield, production rate, and potential. The highest H₂ and CH₄ yields of 55 and 94 mL g⁻¹ VS were achieved at F/M of 7.5 in two stage process, while the highest CH₄ yield of 82 mL g⁻¹ VS in one stage process was observed at the same F/M. Acetic and butyric acids are the main volatile fatty acids (VFAs) produced in the hydrogen fermentation stage with the concentration range 10–25 mmol L⁻¹. Little concentrations of VFAs were accumulated in methane fermentation in both stage processes. Total energy recovery in two stage process is higher than that in one stage by 18%. This work demonstrated two stage fermentation achieved a better performance than one stage process.     

Influence of linoleic acid,pH and HRT on anaerobic microbial populations and metabolic shifts in ASBRs during dark hydrogen fermentation of lignocellulosic sugars

In this study, controlling an anaerobic microbial community to increase the hydrogen (H₂) yield during the degradation of lignocelluosic sugars was accomplished by adding linoleic acid (LA) at low pH and reducing the hydraulic retention time (HRT) of an anaerobic sequencing batch reactor (ASBR). At pH 5.5 and a 1.7 d HRT, the maximum H₂ yield for LA treated cultures fed glucose or xylose reached 2.89 ± 0.18 mol mol⁻¹ and 1.94 ± 0.17 mol mol⁻¹, respectively. The major soluble metabolites at pH 5.5 with a 1.7 day HRT differed between the control and LA treated cultures. A metabolic shift toward H₂ production resulted in increased hydrogenase activity in both the xylose (13%) and glucose (34%) fed LA treated cultures relative to the controls. In addition, the Clostridia population and the H₂ yield were elevated in cultures treated with LA. A flux balance analysis for the LA treated cultures showed a reduction in homoacetogenic activity which was associated with reducing the Bacteriodes levels from 12% to 5% in the glucose fed cultures and 16% to 10% in the xylose fed cultures. Strategies for controlling the homoacetogens and optimal hydrogen production from glucose and xylose are proposed.     

Bio-hydrogen production from cheese whey powder (CWP) solution: Comparison of thermophilic and mesophilic dark fermentations

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.