Hydrogen production from glucose by co-culture of Clostridium Butyricum and immobilized Rhodopseudomonas faecalis RLD-53

In this work, the effects of different parameters on co-culture hydrogen production using Clostridium Butyricum and immobilized Rhodopseudomonas faecalis RLD-53 were investigated. The maximum hydrogen yield of 4.134 mol H₂/mol glucose was obtained using 6 g/l glucose, 50 mmol/l phosphate buffer, initial pH of 7.5, the ratio of dark to photo bacteria of 1:10 and light intensity of 8000 lux. The maximum hydrogen production rate was 33.85 ml H₂/l/h. Phosphate buffer concentration was the most important parameter influencing hydrogen production in this co-culture. The ratio of acetate to butyrate increased from 0.74 to 1.82 in the soluble metabolites from C. butyricum with phosphate buffer concentration of 10–50 mmol/l. Experimental results could be of great significance for further pilot studies of co-culture hydrogen production.     

Biohydrogen using leachate from an industrial waste landfill as inoculum

Since hydrogen is a renewable energy source, biohydrogen has been researched in recent years. However, there is little data on hydrogen fermentation by a leachate from a waste landfill as inoculum. We investigated hydrogen production using a leachate from an industrial waste landfill in Kanagawa prefecture. The results showed no methane gas production and the leachate was a suitable inoculum for hydrogen fermentation. The maximum H₂ yield was 2.67 mol of H₂ per mol of carbohydrate added, obtained at 30 °C and initial pH 7. The acetate and butyrate production was significant when the H₂ yield was higher. The oxidation–reduction potential analysis of the culture suggested that hydrogen-producing bacteria in the leachate were facultatively anaerobic. Scanning electron microscope observations revealed hydrogen-producing bacteria comprised bacilli of about 2 μm in length.     

Renewable hydrogen generation by steam reforming of glycerol over zirconia promoted ceria supported catalyst

The study focuses on hydrogen production from steam reforming of glycerol over nickel based catalyst promoted by zirconia and supported over ceria. Catalyst was prepared by the wet-impregnation method and characterized by BET surface area analysis, X-ray diffraction technique and scanning electron microscopy (SEM) analysis. The performance of the catalyst was evaluated in terms of hydrogen yield, selectivity and glycerol conversion at 700 °C in a tubular fixed bed reactor. The effect of glycerol concentration in feed, space time (W/F_AO), temperature and time on stream (TOS) was analyzed for the catalyst Ni–ZrO₂/CeO₂ which showed the complete conversion of glycerol and high H₂ yield that corresponds to 3.95 mol of H₂ out of 7 mol. Thermodynamic analysis was also carried out using Aspen HYSYS for system having glycerol concentration 10 wt% and 20 wt% and experimental results were compared with thermodynamics. Kinetic study was carried out for the steam reforming of glycerol over Ni–ZrO₂/CeO₂ catalyst using the power law model. The values of activation energy and order of reaction were found to be 43.4 kJ/mol and 0.3 respectively.     

Effects of process factors on biological activity of granular sludge grown in an UASFF bioreactor

Control and operation of a hybrid granular sludge reactor are mainly related to biological behavior of the granules under different process conditions. In this study, a 1-l digester was used to examine biological activity of the granules grown in a hybrid anaerobic reactor (AHR). The biogas production process was modeled and analyzed with three-process variables viz., influent COD (3000, 6500 and 10,000 mg COD/l), biomass concentration (2000, 4000 and 6000 mg VSS/l) and initial alkalinity (200, 1100 and 2000 mg CaCO₃/l). Experiments were conducted based on a central composite face-centered design (CCFD) and analyzed using response surface methodology (RSM). In order to carry out a comprehensive analysis of the biogas production process, the indicative parameters viz., specific methanogenic activity (SMA), bicarbonate alkalinity produced-to-COD removed ratio, and COD removal were studied as the response. The maximum SMA was modeled to be 0.99 g CH₄-COD/g VSS d under COD_in, initial bicarbonate alkalinity (BA) and biomass concentrations of 10,000 mg COD/l, 2000 mg CaCO₃/l and 2000 mg VSS/l, respectively, while the observed value was 1.039 g CH₄-COD/g VSS d. The maximum COD removal was achieved at the condition when the influent COD was within the range of 4250–5250 mg/l and initial BA was more than 1100 mg CaCO₃/l. Initial BA and COD_in played an important role in the production of bicarbonate alkalinity during the digestion process.     

Photofermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study

For meeting the increasing demand of energy, biohydrogen production is to be considered in higher yield. Biohydrogen can be produced both by dark and photofermentative process. In this study, the photofermentative pathway is followed by using dl malic acid (IUPAC name: 2-hydroxybutanedioic acid, molecular weight: 134.08744 g mol^?1, molecular formula: C₄H₆O₅) as carbon source. Pure strain of purple non-sulfur (PNS) bacteria: Rhodobacter sphaeroides strain O.U.001 was studied to produce biohydrogen using the photobioreactor. The photobioreactor was constructed aiming the uniform light distribution. The objective of this study was to investigate the performance of 1 L annular photobioreactor operating in indoor conditions. The highest rate of hydrogen production was obtained at 92 h. In the designed photobioreactor, using Rhodobacter sphaeroides strain O.U.001 (initial dl malic acid concentration of 2.01 g L^?1) at an initial pH of 6.8 ± 0.2, temperature 32 ± 2 °C, inoculum volume 10% (v/v), inoculum age of 48 h, 250 rpm (rotation per minute) stirring and light intensity of 15 ± 1.1 W m^?2, the average H₂ production rate was about 6.5 ± 0.1 mL H₂ h^?1 L^?1 media and yield 4.5 ± 0.05 mol of H₂ mol^?1 of dl malic acid. Luedeking–Piret model was applied for the data fitting to determine the relationship between the cell growth and photofermentative hydrogen production. The photofermentative hydrogen production by this PNS bacterium was found to be microbial mixed growth associated function.     

Alkalinity and high total solids affecting H2 production from organic solid waste by anaerobic consortia

The optimization of total solids in the feed (%TS) and alkalinity ratio (γ) for H₂ production from organic solid wastes under thermophilic regime was carried out using response surface methodology based on a central composite design. The total solids levels were 20.9, 23.0, 28.0, 33.0 and 35.1% whereas the levels of alkalinity ratio (defined as g phosphate alkalinity/g dry substrate) were 0.15, 0.20, 0.30, 0.41 and 0.45. High levels of TS and γ affected in a negative way the H₂ productivity and yield; both response variables significantly increased upon decreasing the TS content and alkalinity ratio. The highest H₂ productivity and yield were 463.7 N mL/kg-d and 54.8 N mL/g VS_rem, respectively, predicted at 20.9% TS and alkalinity ratio 0.25 (0.11 g CaCO₃/g dry substrate). The alkalinity requirements for hydrogenogenic processes were lower than those reported for methanogenic processes (0.11 vs. 0.30 g CaCO₃/g COD). Adequate alkalinity ratio was necessary to maintain optimal biological activity for hydrogen production; however, excessive alkalinity negatively affected process performance probably due to an increase of osmotic pressure. Interestingly, reactor pH depended only on the alkalinity ratio, thus the buffer capacity was able to maintain a constant pH independently of TS levels. At γ = 0.15–0.30 the pHs were in the range 5.56–5.95, which corresponded to the highest hydrogen productivities and yields. Finally, the highest metabolite accumulation corresponded with the highest removal efficiencies but not with high H₂ productivities and yields. Therefore, it seems that organic matter removal was channeled toward solvent generation instead of hydrogen production at high TS and γ levels. This is the first study that shows the requirements of alkalinity in solid substrate fermentation conditions for H₂ production processes and their interaction with the content of total solids in the feed.     

Enhanced biohydrogen production from cornstalk wastes with acidification pretreatment by mixed anaerobic cultures

Biohydrogen production from the cornstalk wastes with acidification pretreatment was reported in this paper. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from cornstalk wastes. Two predominant bacterial morphologies, namely spore-forming rod shape bacteria and micrococcus were screened, purified, and identified after enriched from a hydrogen-producing fermentor with cow dung composts. The maximum cumulative H₂ yield of 149.69 ml H₂ g⁻¹ TVS was obtained at initial pH 7.0 and substrate concentration 15 g l⁻¹, the value is about 46-fold as compared with that of raw cornstalk wastes. The maximum hydrogen production rate was 7.6 ml H2 h⁻¹. The hydrogen concentration in biogas was 45–56% (v/v) and there was no significant methane observed in the biogas throughout this study. In addition, biodegradation characteristics of the substrate by microorganisms were also discussed. During the conversion of cornstalk wastes into hydrogen, the acetate, propionate, butyrate, and the ethanol were main by-products in the metabolism of hydrogen fermentation. The test results showed that the acidification pretreatment of the substrate plays a crucial role in conversion of the cornstalk wastes into biohydrogen gas by the cow dung composts generating hydrogen.     

Development of 10 kW-scale hydrogen generator using chemical hydride

We have developed a hydrogen generator that generates high purity hydrogen gas from the aqueous solution of sodium borohydride, NaBH₄. This paper discussed the performance testing of the hydrogen generator using a Pt-LiCoO₂-coated honeycomb monolith. The NaBH₄ solution hydrolyzed to generate H₂ and sodium metaborate when it contacted the monolith. The gravimetric and the volumetric H₂ densities of the system were 2 wt.% and 1.5 kg H₂/100 l, respectively. The volumetric density was similar to that of the compressed H₂ at 25 MPa. The hydrogen generator successfully provided a maximum H₂ generation rate of 120 nl/min. Assuming a standard PEM (polymer electrolyte fuel cell, PEFC) fuel cell operated at 0.7 V, generating 120 nl/min was equivalent to12 kW.     

Phototrophic hydrogen production from acetate and butyrate in wastewater

Phototrophic hydrogen production was conducted using individual substrates, acetate and butyrate, which are the main products of dark fermentation. Effects of initial pH (ranging 5.0–10.0) and individual substrate concentrations (acetate ranging from 800 to 4100 mg/l, and butyrate ranging from 1000 to 5100 mg/l) on phototrophic hydrogen production were evaluated. The maximum hydrogen yields were 2.5 mol-H₂/mol-acetate at an initial pH of 8.0 treating 800 mg/l of acetate, 3.7 mol-H₂/mol-butyrate at an initial pH of 9.0 treating 1000 mg/l of butyrate. Analyses of DGGE (denaturing gradient gel electrophoresis) profiles of 16S rDNA fragments and FISH (fluorescent in situ hybridization) images show that both phototrophic hydrogen-producing sludges comprised only one predominant species resembling Rhodobacter capsulatus with over 80% relative abundance.     

Biohydrogen-production from beer lees biomass by cow dung compost

Efficient conversion of beer lees wastes into biohydrogen gas by microorganisms was reported for the first time. Batch tests were carried out to analyze influences of several environmental factors on yield of H₂ from beer lees wastes. The maximum yield of H₂ 68.6 ml H₂/g TVS was observed, the value is about 10-fold as compared with that of raw beer lees wastes. The hydrogen content in the biogas was more than 45% and there was no significant methane observed in this study. In addition, biodegradation characteristics of the substrate were also discussed. The results indicated that the HCl pretreatment of the substrate plays a key role in the conversion of the beer lees wastes into biohydrogen by the cow dung composts.     

Effects of biomass,COD and bicarbonate concentrations on fermentative hydrogen production from POME by granulated sludge in a batch culture

Effects of three selected variables viz. biomass concentration, initial chemical oxygen demand (COD) concentration and initial bicarbonate alkalinity (BA) on biological hydrogen production from palm oil mill effluent (POME) using the granulated sludge in batch culture were investigated. The experimental results were analyzed and modeled using a central composite design (CCD) of response surface methodology (RSM). In order to carry out a comprehensive analysis of the biohydrogen production process, indicative parameters namely hydrogen yield (Y_H), specific hydrogen production rate (SHPR), and COD removal efficiency were studied as the process responses. Maximum hydrogen yield (124.5 mmol H₂/g COD_removed) and specific hydrogen production rate (55.42 mmol H₂/g VSS.d) were achieved at COD_in 3000 and 6500 mg/l, MLVSS 4000 and 2000 mg/l, and initial BA 1100 mg CaCO₃/l, respectively.     

Effect of organic loading rate on fermentative hydrogen production from continuous stirred tank and membrane bioreactors

The influence of organic loading rates (OLRs) on the performance of fermentative hydrogen-producing bioreactors operating in continuous stirred tank reactor (CSTR) and membrane bioreactor (MBR) modes was examined. Five OLRs were examined, ranging from 4.0 to 30 g COD L^?1 d^?1, with influent glucose concentrations ranging from 1.3 to 10 g COD L^?1. At OLRs up to 13 g COD L^?1 d^?1, all influent glucose was utilized and the H₂ yield was not significantly influenced by OLR, although the yield in the CSTR mode was significantly higher than that in the MBR mode, 1.25 versus 0.97 mol H₂ (mol Gluc. Conv.)^?1, respectively. At an OLR of 30 g COD L^?1 d^?1, both reactor modes were overloaded with respect to glucose utilization and also had significantly higher H₂ yields of 1.77 and 1.49 mol H₂ (mol Gluc. Conv.)^?1 for the CSTR and MBR modes, respectively, versus the underloaded operation. At the intermediate OLR of 22 g COD L^?1 d^?1, the H₂ yield was maximized at 1.78 mol H₂ (mol Gluc. Conv.)^?1 for both the CSTR and MBR operation. Overall H₂ production was 50% higher in the MBR mode, 0.78 versus 0.51 moles d^?1, because the CSTR mode was overloaded with respect to glucose utilization at this OLR. These results suggest that an optimum OLR that maximizes H₂ yield and H₂ production may be near the OLR that causes overload with respect to substrate utilization. Additionally, while the CSTR mode is easier to operate and provides higher H₂ yields at underloaded and overloaded OLRs, the MBR mode may be preferable when operating near the optimum OLR.     

Optimization of conditions for hydrogen production from brewery wastewater by anaerobic sludge using desirability function approach

Brewery wastewater was converted H₂ by anaerobic sludge in batch experiments. A three-factor three-level experimental design of Box-Behnken method was adopted to find the optimum H₂ production conditions. The effects of three major influence factors, temperature, pH and brewery wastewater concentration (BWC), on H₂ yield and H₂ maximum production rate (R_max) were evaluated by applying response surface methodology (RSM) integrating a desirability function approach. Desirable H₂ yield and R_max simultaneously were achieved under temperature 35.9 °C, pH 5.95 and BWC 6.05 g/l by a desirability function approach which produced the maximum overall desirability 0.894. Correspondingly, the H₂ yield and R_max were 149.6 ml H₂/g COD and 53.6 ml/h, respectively. The verification test confirms that the optimum H₂ yield and R_max measured were in good agreement with the predicted values, suggesting that the desirability function approach with RSM was a useful technique to get the maximum H₂ yield and R_max simultaneously.     

Screening of microorganisms for xylitol production and fermentation behavior in high concentrations of xylose

Microorganisms with the ability to produce xylitol from high concentrations of xylose were screened from soils by enrichment culture using xylose as a sole carbon source. The selected strain was classified and determined as Candida sp. according to a taxonomic identification. In this strain, various conditions for xylitol production were investigated. Organic nutrients such as peptone and yeast extract were essential for xylitol production, and the optimal initial pH and k_La were between 4.0 and 6.0, and 5.2/h, respectively. Under the optimal condition, xylitol production from 200 g/l of xylose was 173 g/l after 5 days incubation, a 99.3% yield of the theoretical value. In order to produce a higher concentration of xylitol, a fed-batch culture of xylose was carried out by feeding 2.0 g of xylose per 10 ml of culture medium. The production from 4.0 g of xylose was 2.9 g of xylitol (concentration of 256 g/l) after 11.5 days which is a yield of 85.0%.     

Biohydrogen production from ricebran using Clostridium saccharoperbutylacetonicum N1-4

Treated ricebran hydrolysate was fermented anaerobically using Clostridium saccharoperbutylacetonicum N1-4 at an initial pH of 6 ± 0.2 and an operating temperature of 30 °C for production of hydrogen. The effects of different pretreatment methods on the liberation of sugar from 100 g of ricebran per litre of medium (distilled water) were investigated. In addition, the effects of the pretreatment method on ricebran hydrolysates of different initial ricebran concentrations on liberated sugar as well as the effects of the initial inoculum concentration, ricebran (substrate) concentration, and FeSO₄·7H₂O concentration on the yield as well as the productivity of hydrogen were investigated. The combination of enzymatic hydrolysis and a boiling pretreatment method produced the most fermentable sugar, 29.03 ± 0.0 g/L from 100 g of ricebran per litre of medium (distilled water), while the amount of sugar liberated by ricebran hydrolysates of different initial ricebran concentrations upon pretreatment monotonically increased with the initial ricebran concentration. The increment in substrate, inoculum, and FeSO₄·7H₂O concentrations had a significantly positive effect (p < 0.05) on both the yield and productivity of hydrogen. The maximum hydrogen gas yield (Y_P/S) and productivity of 3.37 mol-H₂ per mol-sugar consumed and 7.58 mmol/(L h), respectively, were obtained from ricebran hydrolysate with a 100 g/L ricebran concentration (equivalent to 28.59 ± 1.27 g sugar/L). In other experiments, 0.03 g/L FeSO₄·7H₂O and 1.5 g/L inoculum resulted in the best hydrogen gas yield and productivity from ricebran hydrolysates.     

Investigation of hydrogen production from boron compounds for pem fuel cells

This paper presents a comprehensive study of hydrogen production from sodium borohydride (NaBH₄), which is synthesized from sodium tetraborate (Na₂B₄O₇) decomposition, for proton exchange membrane (PEM) fuel cells. For this purpose, Na₂B₄O₇ decomposition reaction at 450–500 °C under hydrogen atmosphere and NaBH₄ decomposition reaction at 25–40 °C under atmospheric pressure are selected as a common temperature range in practice, and the inlet molar quantities of Na₂B₄O₇ are chosen from 1 to 6 mol with 0.5 mol interval as well. In order to form NaBH₄ solution with 7.5 wt.% NaBH₄, 1 wt.% NaOH, 91.5 wt.% H₂O, the molar quantities of NaBH₄ are determined. For a PEM fuel cell operation, the required hydrogen production rates are estimated depending on 60, 65, 70 and 75 g of catalyst used in the NaBH₄ solution at 25, 32.5 and 40 °C, respectively. It is concluded that the highest rate of hydrogen production per unit area from NaBH₄ solution at 40 °C is found to be 3.834 × 10⁻⁵ g H₂ s⁻¹ cm⁻² for 75 g catalyst. Utilizing 80% of this hydrogen production, the maximum amounts of power generation from a PEM fuel cell per unit area at 80 °C under 5 atm are estimated as 1.121 W cm⁻² for 0.016 cm by utilizing hydrogen from 75 g catalyst assisted NaBH₄ solution at 40 °C.     

Optimization of ethanol production from hot-water extracts of sugar maple chips

Hot-water extracts from sugar maple chips prior to papermaking was employed in this study to produce ethanol by Pichia stipitis 58784. The effects of several factors, seed culture age, fermentation time, inoculum quantity, agitation rate, percent extract, concentration of inorganic nitrogen source (NH₄)₂SO₄ and pH value, on ethanol production were investigated by orthogonal experiments. Orthogonal analysis shows that the optimal fermentation was obtained in the condition of 48-h seed culture, 120-h fermentation, 16% inoculum, 180 rpm, containing 30% extracts, 8% ammonium sulphate supplement and pH 5. This optimal condition was verified at 800-mL level in a 1.3 L fermentor. The ethanol yield reached 82.27% of the theoretical (20.57 g/L) after 120 h.     

Dark fermentative hydrogen production from sucrose and molasses

There are many factors affecting the dark fermentative hydrogen production. The interaction of these factors, that is, their combined effects, should be investigated for better design of the systems with stable and higher hydrogen yields. This study aimed to investigate the combined effects of initial substrate, pH, and biomass (or initial substrate to biomass) values on hydrogen production from sucrose and sugar‐beet molasses. Therefore, optimum initial chemical oxygen demand (COD), pH, and volatile suspended solids (VSS) or initial substrate to biomass (VSS) ratio (S/X_o) values leading to the highest dark fermentative hydrogen production were investigated in batch reactors. An experimental design approach (response surface methodology) was used. Results revealed that when sucrose was the substrate, maximum hydrogen production yield (HY) of 2.3 mol H₂/mol sucrose_added was obtained at initial pH of 7 and COD of 10 g/L. Initial S/X_o values studied (4–20 g COD/g VSS) had no effect on HY, while the initial pH was found as the parameter mostly affecting both HY and hydrogen production rate (HPR). When substrate was molasses, initial COD concentration was the only variable affecting HY and HPR. Maximum of both was achieved at 10 g/L initial COD. Initial VSS values studied (2.5–7.5 g/L) had no effect on HPR and HY. This study also indicated that molasses leads to homoacetogenesis for potentially containing intrinsic microorganism and/or natural constituents; thus, sucrose is more advantageous for hydrogen production via fermentation. Homoacetogenesis should be prevented for effective optimization via response surface methodology, if substrate is a natural carbon source potential to have intrinsic microorganisms. Copyright © 2017 John Wiley & Sons, Ltd.     

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.