Light fermentation of dark fermentation effluent for bio-hydrogen production by different Rhodobacter species at different initial volatile fatty acid (VFA) concentrations

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 48 ml H₂ in 180 h. However, RS–RV resulted in the highest hydrogen yield of 250 ml H₂ g⁻¹ TVFA. Specific hydrogen production rate (SHPR) with the RS–NRRL was also better in comparison to the others (13.8 ml H₂ g⁻¹ biomass h⁻¹). When combinations of those three strains were used, RS–RV + RS–DSMZ resulted in the highest cumulative hydrogen formation (90 ml H₂ in 330 h). However, hydrogen yield (693 ml H₂ g⁻¹ TVFA) and SHPR (12.1 ml H₂ g⁻¹ biomass h⁻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 47 mg L⁻¹, respectively.     

Chemical kinetics of Ru-catalyzed ammonia borane hydrolysis

Ammonia borane (AB) is a candidate material for on-board hydrogen storage, and hydrolysis is one of the potential processes by which the hydrogen may be released. This paper presents hydrogen generation measurements from the hydrolysis of dilute AB aqueous solutions catalyzed by ruthenium supported on carbon. Reaction kinetics necessary for the design of hydrolysis reactors were derived from the measurements. The hydrolysis had reaction orders greater than zero but less than unity in the temperature range from 16 °C to 55 °C. A Langmuir–Hinshelwood kinetic model was adopted to interpret the data with parameters determined by a non-linear conjugate-gradient minimization algorithm. The ruthenium-catalyzed AB hydrolysis was found to have activation energy of 76 ± 0.1 kJ mol⁻¹ and adsorption energy of −42.3 ± 0.33 kJ mol⁻¹. The observed hydrogen release rates were 843 ml H₂ min⁻¹ (g catalyst)⁻¹ and 8327 ml H₂ min⁻¹ (g catalyst)⁻¹ at 25 °C and 55 °C, respectively. The hydrogen release from AB catalyzed by ruthenium supported on carbon is significantly faster than that catalyzed by cobalt supported on alumina. Finally, the kinetic rate of hydrogen release by AB hydrolysis is much faster than that of hydrogen release by base-stabilized sodium borohydride hydrolysis.     

Bioaugmented cellulosic hydrogen production from cornstalk by integrating dilute acid-enzyme hydrolysis and dark fermentation

The cellulosic hydrogen production from cornstalk based on the integrating dilute acid with enzymatic hydrolysis was investigated using response surface methodology (RSM). The dilute acid pretreatment of cornstalk with the concentration of 1.5% H₂SO₄, 121 °C and 60 min was found to be most effective in the first prehydrolysis stage. Thereafter, the process parameters of enzymatic hydrolysis of the solid residue, which derived from acid-pretreated cornstalk, were further optimized by a three factor-five level central composite design (CCD) with temperature (X₁), pH (X₂), and enzyme loading (X₃) as the independent variables. The optimal parameters of enzymatic hydrolysis of substrate were observed to be 52 °C of temperature, pH 4.8 and 9.4 IU/g of enzyme loading. In this case, the total soluble sugar obtained in the hydrolysis stages was 562.1 ± 6.9 mg/g-TVS, and the maximum hydrogen yield from cornstalk by anaerobic mixed microflora was 209.8 ml/g-TVS. Biodegradation mechanism of cornstalk for hydrogen production was further discussed based on analyzing changes in the physical structure and chemical composition of cornstalk during the hydrolysis and fermentation processes.     

Bio-hydrogen production from cornstalk wastes by orthogonal design method

One-factor-at-a-time design and orthogonal design were used in the experimental design methods to optimize bio-hydrogen (bio-H₂) production from cornstalk wastes by anaerobic fermentation. Three series of experiments were designed to investigate the effects of substrate concentration, initial pH and orthogonal design on the bio-H₂ production by using the natural sludge as inoculant. Experimental results indicate that substrate concentration was the most significant condition for optimal hydrogen production. The optimum orthogonal design method was proposed to be at an enzymatic temperature of 50 °C, an enzymatic time of 72 h, an initial pH of 7.0 and a substrate concentration of 10 g/L. The proposed method facilitated the optimization of optimum design parameters, only with a few well-defined experimental sets. Under the proposed condition, the maximum cumulative H₂ yield was 141.29 ml g^?1-CS (cornstalk, or 164.48 ml g^?1-TS, total solid, TS = 0.859 W_{dried cornstalk}), with an average H₂ production rate of 12.31 ml g^?1-CS h^?1. The hydrogen content reached 57.85% and methane was not detected in the biogas.     

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.     

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.     

Biological hydrogen production from corn stover by moderately thermophile Thermoanaerobacterium thermosaccharolyticum W16

This study addressed the utilization of an agro-waste, corn stover, as a renewable lignocellulosic feedstock for the fermentative H₂ production by the moderate thermophile Thermoanaerobacterium thermosaccharolyticum W16. The corn stover was first hydrolyzed by cellulase with supplementation of xylanase after delignification with 2% NaOH. It produced reducing sugar at a yield of 11.2 g L⁻¹ glucose, 3.4 g L⁻¹ xylose and 0.5 g L⁻¹ arabinose under the optimum condition of cellulase dosage 25 U g⁻¹ substrate with supplement xylanase 30 U g⁻¹ substrate. The hydrolyzed corn stover was sequentially introduced to fermentation by strain W16, where, the cell density and the maximum H₂ production rate was comparable to that on simulated medium, which has the same concentration of reducing sugars with hydrolysate. The present results suggest a promising combined hydrogen production process from corn stover with enzymatic hydrolysis stage and fermentation stage using W16.     

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.     

Effects of electroless deposition conditions on microstructures of cobalt–phosphorous catalysts and their hydrogen generation properties in alkaline sodium borohydride solution

Cobalt–phosphorous (Co–P) catalysts with a high hydrogen generation rate in alkaline sodium borohydride (NaBH₄) solution are developed by electroless deposition. The microstructures of the Co–P catalysts and their catalytic activities for hydrolysis of NaBH₄ are analyzed as a function of the electroless deposition conditions such as the pH and temperature of the Co–P bath. The electroless-deposited Co–P catalysts are composed of nano-crystalline Co and amorphous Co–P. The size of the nano-crystalline Co particles dispersed in amorphous Co–P matrix depends largely on the electroless deposition conditions. Moreover, Co–P catalysts with finer crystalline Co exhibit a higher hydrogen generation rate. In particular, the Co–P catalysts formed in a pH 12.5 bath at 60–70 °C exhibit the best hydrogen generation rate of 3300 ml min⁻¹ g⁻¹-catalyst in 1 wt.% NaOH + 10 wt.% NaBH₄ solution at 30 °C, which is 60 times faster than that obtained with a Co catalyst.     

Low temperature behaviour of TiO2 rutile as negative electrode material for lithium-ion batteries

High surface nanosized rutile TiO₂ is prepared via a sol-gel method from an ethylene glycol-based titanium-precursor in the presence of a non-ionic surfactant, at pH 0. Its electrochemical behaviour has been investigated at low temperature using two different potential windows. Typically, the potential window of the rutile system is 1-3 V but the use of an enlarged potential window (0.1-3 V), leads to an excellent reversible capacity of 341 mAh g⁻¹ which is comparable to graphite anodes. The electrochemical performance was investigated by cyclic voltammetry and galvanostatic techniques at temperatures ranging from −40 to 20 °C. Nanosized TiO₂ exhibits excellent rate capability (341 mAh g⁻¹ at 20 °C, 197 mAh g⁻¹ at −10 °C, 138 mAh g⁻¹ at −20 °C, and 77 mAh g⁻¹ at −40 °C at a C/5 rate) and good cycling stability. The superior low-temperature electrochemical performance of nanosized rutile TiO₂ may make it a promising candidate as lithium-ion battery material.     

Determining optimum conditions for hydrogen production from glucose by an anaerobic culture using response surface methodology (RSM)

Hydrogen fermentation is a very complex process and is greatly influenced by many factors. Previous studies have demonstrated that temperature, pH and substrate are important factors controlling biological H₂ production. Response surface methodology with central composite design was used in this study to optimize H₂ production from glucose by an anaerobic culture. The individual and interactive effects of pH, temperature and glucose concentration on H₂ production were also evaluated. The optimum conditions for maximum H₂ yield of 1.75 mol-H₂ mol-glucose⁻¹ were found as temperature 38.8 °C, pH 5.7 and glucose concentration 9.7 g L⁻¹. The linear effects of temperature and pH as well as their quadratic effects on H₂ yield were significant, while the interactive effects of three parameters were minor.     

A novel design for a flow field configuration, of a direct methanol fuel cell

We proposed and tested a new and novel arrangement for a direct methanol fuel cell consisting of one inlet for a methanol solution and four outlets for oxidant gas (air), in both the anode and cathode flow fields. It utilizes different operating temperatures of 40 °C and 60 °C, and different methanol solution flow rates of 5 ml min⁻¹, 10 ml min⁻¹, and 20 ml min⁻¹. Test results indicate a significant reduction in produced CO₂ gas in the anode flow channels and product water in the cathode flow channels; consequently, cell performance can be greatly improved. Furthermore, methanol crossover can also be avoided and reduced.     

Effects of the substrate and cell concentration on bio-hydrogen production from ground wheat by combined dark and photo-fermentation

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 20 g L⁻¹ with a total cell concentration of 0.41 g L⁻¹ in the first set of experiments. Cell concentration was changed between 0.5 and 5 g L⁻¹ in the second set of experiments while the wheat powder concentration was constant at 5 g L⁻¹ with a D/L ratio of 1/7. The highest cumulative hydrogen (135 ml) and formation rate (3.44 ml H₂ h⁻¹) were obtained with the 20 g L⁻¹ wheat powder concentration. However, the highest yield (63.9 ml g⁻¹ starch) was obtained with the 2.5 g L⁻¹ wheat powder. In variable cell concentration experiments, the highest cumulative hydrogen (118 ml) and yield (156.8 ml H₂ g⁻¹ starch) were obtained with 1.1 g L⁻¹ cell concentration yielding an optimal biomass/substrate ratio of 0.22 g cells/g WP.     

A highly active Co-B catalyst for hydrogen generation from sodium borohydride hydrolysis

Co-B catalysts were prepared by the chemical reduction of CoCl₂ with NaBH₄ for hydrogen generation from borohydride hydrolysis. The catalytic properties of the Co-B catalysts were found to be sensitive to the preparation conditions including pH of the NaBH₄ solution and mixing manner of the precursors. A Co-B catalyst with a very high catalytic activity was obtained through the formation of a colloidal Co(OH)₂ intermediate. The ultra-fine particle size of 10 nm accounted for its super activity for hydrogen generation with a maximum rate of 26 L min⁻¹ g⁻¹ at 30 °C. The catalyst also changed the hydrolysis kinetics from zero-order to first-order.     

Effects of magnesium doping on electronic conductivity and electrochemical properties of LiFePO4 prepared via hydrothermal route

Carbon free composites Li_1−xMg_xFePO₄ (x = 0.00, 0.02) were synthesized from LiOH, H₃PO₄, FeSO₄ and MgSO₄ through hydrothermal route at 180 °C for 6h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), flame atomic absorption spectroscopy and electronic conductivity measurement. To investigate their electrochemical properties, the samples were mixed with glucose as carbon precursors, and fired at 750 °C for 6 h. The charge–discharge curves and cycle life test were carried out at 23 ± 2 °C. The Rietveid refinement results of lattice parameters of the samples indicate that the magnesium ion has been successfully doped into the M1 (Li) site of the phospho-olivine structure. With the same order of magnitude, there is no material difference in terms of the electronic conductivities between the doped and undoped composites. Conductivities of the doped and undoped samples are 10⁻¹⁰ S cm⁻¹ before being fired, 10⁻⁹ S cm⁻¹ after being fired at 750 °C, and 10⁻¹ S cm⁻¹ after coated with carbon, respectively. Both the doped and undoped composites coated with carbon exhibit comparable specific capacities of 146 mAh g⁻¹ vs. 144 mAh g⁻¹ at 0.2 C, 140 mAh g⁻¹ vs. 138 mAh g⁻¹ at 1 C, and 124 mAh g⁻¹ vs. 123 mAh g⁻¹ at 5 C, respectively. The capacity retention rates of both doped and undoped samples over 50 cycles at 5 C are close to 100% (vs. the first-cycle corresponding C-rate capacity). Magnesium doping has little effects on electronic conductivity and electrochemical properties of LiFePO₄ composites prepared via hydrothermal route.     

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.     

High performance metal-supported intermediate temperature solid oxide fuel cells fabricated by atmospheric plasma spraying

The LSGM(La_0.8Sr_0.2Ga_0.8Mg_0.2O₃) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La_0.75Sr_0.25Cr_0.5Mn_0.5O₃) interlayer on the nickel substrate, a nano-structured LDC(Ce_0.55La_0.45O₂)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La_0.58Sr_0.4Co_0.2Fe_0.8O₃) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270 mW cm⁻² (800 °C), 978 mW cm⁻² (750 °C) and 702 mW cm⁻² (700 °C) at 0.6 V cell voltage under 335 ml min⁻¹ H₂ and 670 ml min⁻¹ air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3% kh⁻¹ at the test conditions of 400 mA cm⁻² constant current density and 700 °C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.     

Solid state synthesis of hydrous ruthenium oxide for supercapacitors

A novel solid state route has been successfully developed for the synthesis of nano-scale hydrous ruthenium oxide (denoted as RuO₂·xH₂O). The procedure involves directly mixing RuCl₂·xH₂O with alkali to form RuO₂·xH₂O in a mortar at room temperature. Transmission electron microscopy (TEM) and N₂ adsorption–desorption measurement indicate that the RuO₂·xH₂O particle is approximately 30–40 nm with mesoporous structure. The crystalline structure and the electrochemical properties of RuO₂·xH₂O have been systematically explored as a function of annealing temperature. At lower temperatures, the RuO₂·xH₂O powder was found in an amorphous phase and the maximum capacitance of 655 F g⁻¹ was obtained by annealing at 150 °C. Higher temperatures (exceeding 175 °C) presumably converted amorphous phase into crystalline one and the corresponding specific capacitance dropped rapidly from 547 F g⁻¹ at 175 °C to 87 F g⁻¹ at 400 °C. Also, the dependence of electrochemical performance on annealing conditions of RuO₂·xH₂O was investigated by electrical impedance spectroscopy (EIS) study.     

Optimization of dilute acid and enzymatic hydrolysis for dark fermentative hydrogen production from the empty fruit bunch of oil palm

Pretreatment of the empty fruit brunch (EFB) from oil palm was investigated for H₂ fermentation. The EFB was hydrolyzed at various temperatures, H₂SO₄ concentrations, and reaction times. Subsequently, the acid-hydrolysate underwent enzymatic saccharification under various temperature, pH, and enzymatic loading conditions. Response surface methodology derived the optimum sugar concentration (SC), hydrogen production rate (HPR), and hydrogen yield (HY) as 28.30 g L⁻¹, 2601.24 mL H₂ L⁻¹d⁻¹, and 275.75 mL H₂ g⁻¹ total sugar (TS), respectively, at 120 °C, 60 min of reaction, and 6 vol% H₂SO₄, with the combined severity factor of 1.75. Enzymatic hydrolysis enhanced the SC, HY, and HPR to 34.52 g L⁻¹, 283.91 mL H₂ g⁻¹ TS, and 3266.86 mL H₂ L⁻¹d⁻¹, respectively, at 45 °C, pH 5.0, and 1.17 mg enzyme mL⁻¹. Dilute acid hydrolysis would be a viable pretreatment for biohydrogen production from EFB. Subsequent enzymatic hydrolysis can be performed if enhanced HPR is required.     

Production of hydrogen via hydrolysis of hydrides in Mg–La system

Hydrogen generation via hydrolysis of 250 mg hydrogenated Mg₃La and La₂Mg₁₇ in 100 ml water has been investigated at 298 K. Hydrolysis reactions of hydrogenated Mg₃La and La₂Mg₁₇ obtained by induction melting and then hydrogenated at 298 K is found to be fast when they are immersed in water. The hydrolysis reaction of hydrogenated Mg₃La almost completes within 21 min with faster kinetics and higher yield than those obtained of hydrogenated La₂Mg₁₇. The hydrogen production rate is 43.8 ml min⁻¹ g⁻¹ of hydrogen in the first 20 min of reaction compared to a conversion yield of 88% for hydrogenated Mg₃La and 40.1 ml min⁻¹ g⁻¹ of hydrogen in the first 20 min of reaction for hydrogenated La2Mg17. It is related to the catalytic effect of LaH₃ formed during the hydriding process, accentuating corrosion of MgH₂ greatly. The experimental curves of hydrogen generation kinetics at room temperature are well fitted by the Avrami–Erofeev equation. The reaction mechanism of hydrogenated Mg₃La and La₂Mg₁₇ was also discussed.