Fermentative bio-hydrogen production from cellulose by cow dung compost enriched cultures

The performance of hydrogen production from cellulose by the cow dung compost enriched continuously in defined medium containing cellulose was investigated. In the initial experiments, batch-fermentation was carried out to observe the effects of different substrate concentration conditions on the rate of cellulose-degrading, growth of bacteria and the capability of hydrogen-producing from cellulose. The result showed that the cellulose degradation decreased from 55% at 5 g/l to 22% at 30 g/l. The maximum cumulative hydrogen production and the rate of hydrogen production first increased from 828 ml/l at 5 g/l to 1251 ml/l at 10 g/l then remained constant beyond 10 g/l. The maximum hydrogen production potential, the rate of hydrogen production and the yield of hydrogen was 1525 ml/l, 33 ml/l.h, and 272 ml/g-cellulose (2.09 mol/mol-hexose) was obtained at substrate concentration 10 g/l, the hydrogen concentration in biogas was 47–50%(v/v) and there was no methane observed. During the conversion of cellulose into hydrogen, acetate and butyrate were main liquid end-products in the metabolism of hydrogen fermentation. These results proposed that cow dung compost enriched cultures were ideal microflora for hydrogen production from cellulose.     

Effects of pretreatment method of natural bacteria source on microbial community and bio-hydrogen production by dark fermentation

The effects of pretreatment method of cow dung compost, which was employed as natural hydrogen bacteria source, on the microbial community, population distribution of microbes and hydrogen production potential were investigated in the batch tests. The maximum hydrogen yield of 290.8 mL/L-culture appeared in the pretreated method A (infrared drying) by dark fermentation. The pretreated method of compost significantly affected microbial succession, population distribution of microbes. Both Clostridium sp. and Enterobacter sp. were found to be two species of preponderant hydrogen-producing bacteria, the next best was Bacteroides sp. and Veillonella sp., the last was Lactobacillus sp. and Streptococcus sp., which were also essential. The results showed that the mutualism and symbiosis relations of the mixed bacteria played a critical role in hydrogen fermentation process.     

Simultaneous saccharification and fermentation of cellulose for bio-hydrogen production by anaerobic mixed cultures in elephant dung

The objective of this study was to optimize the culture conditions for simultaneous saccharification and fermentation (SSF) of cellulose for bio-hydrogen production by anaerobic mixed cultures in elephant dung under thermophilic temperature. Carboxymethyl cellulose (CMC) was used as the model substrate. The investigated parameters included initial pH, temperature and substrate concentration. The experimental results showed that maximum hydrogen yield (HY) and hydrogen production rate (HPR) of 7.22 ± 0.62 mmol H₂/g CMC_added and 73.4 ± 3.8 mL H₂/L h, respectively, were achieved at an initial pH of 7.0, temperature of 55 °C and CMC concentration of 0.25 g/L. The optimum conditions were then used to produce hydrogen from the cellulose fraction of sugarcane bagasse (SCB) at a concentration of 0.40 g/L (equivalent to 0.25 g/L cellulose) in which an HY of 7.10 ± 3.22 mmol H₂/g cellulose_added. The pre-dominant hydrogen producers analyzed by polymerase chain reaction-denaturing gel gradient electrophoresis (PCR-DGGE) were Thermoanaerobacterium thermosaccharolyticum and Clostridium sp. The lower HY obtained when the cellulose fraction of SCB was used as the substrate might be due to the presence of lignin in the SCB as well as the presence of Lactobacillus parabuchneri and Lactobacillus rhamnosus in the hydrogen fermentation broth.     

Enhanced bio-hydrogen production from corn stalk by anaerobic fermentation using response surface methodology

The key process parameters of solid state enzymolysis for the generation of soluble sugar (SS) and bio-hydrogen production from corn stalk were optimized by the response surface methodology (RSM) based on a three factor-five level central composite design (CCD), respectively. The result showed that the optimal solid state enzymolysis condition from corn stalk was 47.7 °C, SCED of 0.054 g/g and 10.3 days for the maximum SS yield of 526 mg/g-TVS. Correspondingly, the optimal enzymolysis conditions from corn stalk appeared at 46.3 °C, SCED of 0.049 g/g and 7.5 days for the maximum hydrogen yield of 205.5 mL/g-TVS from the hydrolyzed substrate by the next dark fermentation. In addition, the bio-hydrogen production mechanism from corn stalk was preliminary investigated by XRD and SEM analyses. The results suggested that the solid state enzymolysis of substrate played a vital role in the effective conversion of corn stalk into bio-hydrogen by dark fermentation.     

Isolation and evaluation of a high H2-producing lab isolate from cow dung

Hydrogen producing bacterial strain was isolated from Indian cow dung and identified of the bacterial family Enterobacteriaceae. This lab isolate was differentiated from Citrobacter Y-19 at molecular level by using RAPD, PCR based technique, and OPO-03₄₆₀ and OPO-17₈₀₀ RAPD marker for this specific strain (lab isolate) was identified. Fermentative studies were investigated for important parameters, starting with pH of the culture, temperature, inoculum age and inoculum volume, initial substrate concentration and different substrates. Among different substrates, dextrose and sucrose were the preferred substrates for hydrogen production. The optimal starting pH of the culture was found to be 5.0. The H₂ production increased with increase in temperature up to 30 °C. The maximum value of H₂ production was recorded when inoculum volume was 12.5% of the culture broth and inoculum age was 14 h. Under batch fermentation conditions, the maximum hydrogen production rate and yield were 355.2 ml l⁻¹ h⁻¹ and 2.1 mol/mol glucose (conversion 35%), respectively. These results indicate that this lab isolate is an ideal hydrogen producer.     

A sequential process of anaerobic solid-state fermentation followed by dark fermentation for bio-hydrogen production from Chlorella sp.

Microalgal biomass has recently been one of the most widely studied feedstocks for bio-hydrogen production, owing to its richness in fermentable components, e.g. polysaccharides and proteins, and high biomass productivity. In this study, biomass of microalga Chlorella sp. TISTR 8411 was converted to hydrogen through a sequential process consisting of an anaerobic solid-state fermentation (ASSF) followed by a dark fermentation. The microalga was grown photoautothrophically in 80-L rectangular glass tanks and then scaled-up to a 240-L open pond for the production of biomass. The highest biomass concentration attained was 4.45 g L⁻¹. The biomass was harvested with over 90% flocculation efficiency at pH 11.5 and a biomass concentration of 2.6 g/L. The sequential process gave a total hydrogen yield (HY) of 16.2 mL/g-volatile-solid (VS), of which 11.6 mL/g-VS was from ASSF. The high HY obtained from the ASSF indicated that it was effective and could be integrated with a conventional hydrogen production process to improve energy recovery from biomass.     

Effect of ultrasonic treatment of digestion sludge on bio-hydrogen production from sucrose by anaerobic fermentation

The utilization of ultrasonic treatment on digestion sludge to enhance microbial activity for bio-hydrogen production was investigated. The optimal conditions of ultrasonic time and density on digestion sludge were detected using Central Composite Experimental Design. The regression analysis showed that a significant increase of 1.34 fold in bio-hydrogen production rate could be obtained when ultrasonic time was 10 s and ultrasonic density around 130 W/l at digester sludge concentration of 15 g VSS/l. The analyses of biodegradation characteristics in bio-hydrogen producing process implied that ultrasound did not denature the digestion sludge but just improved its biodegradation efficiency. In order to find out the mechanism of ultrasonic treatment on digestion sludge, a control experiment was designed and COD values of digestion sludge in different treatment conditions was measured.     

Effect of organic loading rate and solids retention time on microbial population during bio-hydrogen production by dark fermentation in large lab-scale

The experimental investigation aimed at the study of the microbial population during the continuous operation of a complete mixed reactor in large lab-scale (30 L) by variation of the Organic Loading Rate (OLR) and Sludge Retention Time (SRT) ranging from 10 g sucrose/(L?d) to 30 g/(L?d) and from 12 h to 48 h respectively. H₂ yield reached to 1.72 mol H₂/mol hexose for HRT = 1.6 d and OLR = 20 g sucrose/(L?d). In each phase the dominant microbial genera were identified by sequencing after a Polymerase Chain Reaction (PCR) with universal primers for the domains of Archaea and Eubacteria and specific for Clostridium species and genetic material isolation by Denaturing Gradient Gel Electrophoresis (PCR-DGGE). The phylogenetic analyses showed that hydrogen producing Clostridium species could be affiliated in all experimental phases. Other dominant genera were affiliated mainly to Ethanoligenes harbinense and uncultured Prevotella and Selonomonas species. Bio-hydrogen production was associated to a mixed butyric/ethanol type fermentation facilitated mainly by Clostridium tyrobutyricum and E. harbinense in the presence of lactate as intermediate metabolic product.     

Enhanced H2 production from corn stalk by integrating dark fermentation and single chamber microbial electrolysis cells with double anode arrangement

The low conversion efficiency of substrate is one of the main bottlenecks in dark fermentation for bio-H₂ production. Herein, an enhanced H₂ yield from corn stalk was achieved by integrating dark fermentation and single chamber microbial electrolysis cells (MECs). In the dark fermentation stage, a H₂ yield of 129.8 mL H₂/g-corn stalk and an average H₂ production rate of 1.73 m³/m³ d were recorded at 20 g/L of corn stalk and initial pH 7.0. The effluent from dark fermentation was diluted and further employed as feedstock to generate H₂ by MECs. A H₂ yield of 257.3 mL H₂/g-corn stalk, an HPR of 3.43 ± 0.12 m³/m³ d and an energy efficiency of 166 ± 10% were obtained with the effluent COD of 3995.5 mg/L under 0.8 V applied voltage. During MECs operation stage, about 90 ± 2% of acetate was converted to H₂ and the corresponding COD removal reached 44 ± 2% in MECs. Overall, the H₂ yield can reach 387.1 mL H₂/g-corn stalk by integrating dark fermentation and MECs, which had nearly tripled as against that of dark fermentation.     

Co-producing hydrogen and methane from higher-concentration of corn stalk by combining hydrogen fermentation and anaerobic digestion

In this paper, the high concentration of corn stalk (60 g/L) was employed as feedstock to produce bio-hydrogen and methane by combining hydrogen fermentation and anaerobic digestion. In the first stage of hydrogen fermentation, the effects of several key parameters, such as strain enhancement technique, cetyl trimethyl ammonium bromide (CTAB), NH₄HCO₃ on hydrogen production from cornstalk were investigated and optimized. The maximum hydrogen yield of 79.8 ± 1.5 ml H₂/g-TS and hydrogen production rate of 3.78 ml/g-cornstalk h was observed at fixed acidizing cornstalk of 60 g/L, strains Bacillus sp. FS2011 dosage of 10%(v/v), CTAB of 30 mg/L, NH₄HCO₃ of 1.2 g/L and initial pH of 7.5 ± 0.5 at 36 ± 1 °C, respectively. In the second stage of anaerobic digestion, the effluent from hydrogen production bio-reactor was further employed as the feedstock to produce methane by methanogenic bacteria, the maximum methane yield of 227 ± 2.5 ml CH₄/g-COD and COD removal rate of 95  ± 1% was recorded. The interesting observations were that the total amount of the organic wastewater produced in a higher substrate concentration (60 g/l) by hydrogen fermentation was reduced by about two-thirds compared with that of traditional low substrate concentration (≤20 g/l).     

Comparison of bio-hydrogen production from hydrolyzed wheat starch by mesophilic and thermophilic dark fermentation

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.     

Effect of microbiological inocula on chemical and physical properties and microbial community of cow manure compost

The effect of the microbiological inocula to efficiently decompose animal manures into mature compost was studied. In general, TOC, water contents and C/N ratio decreased during decomposition in two composts and those properties dropped faster in the microbiological inocula compost than the natural compost. The total nitrogen content and NO₃⁻-N behaved in the opposite manner and those properties increased faster in the microbiological inocula compost than the natural compost. The pH and NH₄⁺-N increased first, and then decreased in two composts. The microbiological inocula showed a more rapid rate of temperature elevation at the start of composting and prolonged the time of high-temperature process. The microbiological inocula were able to facilitate the microbial diversity of the compost. Based on germination assays, the microbiological inocula seems to be advantageous in reducing the maturation time of cow manure compost.     

Effects of sludge pre-treatment method on bio-hydrogen production by dark fermentation of waste ground wheat

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 × 5 h) 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 (652 ml) and specific hydrogen production rate (SHPR = 25.7 ml H₂ g⁻¹ cells h⁻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.     

温度条件对猪粪厌氧发酵沼气产气特性的影响

以猪粪为发酵原料、以中温厌氧发酵瓶的底物为接种物,在自制的小型厌氧发酵装置上,研究了温度条件对猪粪厌氧发酵产气特性的影响。结果表明,在发酵初、中期,中温（37℃）试验组显现了明显的优势,日产气量和累积产气量都高于高温（52℃）和室温试验组。高温和室温试验组的微生物活性因受到环境温度改变的影响,甲烷化反应受到明显抑制。当发酵进行到后期时,高温试验组日产气量高于室温和中温试验组。中温、高温和室温3个试验组在发酵15d时,沼气中甲烷含量分别为59．8％,70％,62.3％。     

Effect of microwave pretreatment of mixed culture on biohydrogen production from waste of sweet produced from Benincasa hispida

To enhance the production of biohydrogen from biomass, various pretreatment methods play important role. In this study, effect of microwave irradiation on the culture was studied on biohydrogen production from Benincasa hispida (Petha) solid waste at different powers for a fixed interval of time. The highest power studied was 800 W with a frequency of 2450 MHz. The amount of soluble sugars found in the waste was 13.9 mg/L having the chemical oxygen demand (COD) of 3000 mg/L. Studies have been performed in batch reactors using mixed consortia and results were also compared with the reactor operated at the normal conditions i.e. without any inoculum pretreatment. Maximum hydrogen produced was 14 mmol H₂ per mol of soluble sugar consumed in the reactor in which the inoculum was exposed to 320 W of microwave for 5 min. SEM analysis of this microwave pretreated culture was done.     

Hydrogen production characteristics from dark fermentation of maltose by an isolated strain F.P 01

A hydrogen producing strain F.P 01 was newly isolated from cow dung sludge in an anaerobic bioreactor. The strain F.P 01 was a mesophilic and facultative anaerobic bacterium, which exhibited gram-negative staining in both the exponential and stationary growth phases, and a regular long rod-shaped bacteria with the size of 0.6–0.9 μm × 1.2–2.5 μm, and also could biodegrade a variety of carbohydrates such as glucose, xylose, maltose, etc. The effects of important process parameters on hydrogen producing of F.P 01 were further investigated from hydrogen fermentation of maltose by strain F.P 01, including substrate concentration, medium pH, etc. And the results showed that hydrogen production potential and hydrogen production rate from maltose of this strain F.P 01 was180 mLH₂/g-maltose and 4.0 mLH₂/h, respectively. The corresponding hydrogen concentration of 58–73% was also be observed. Both butyric acid and acetic acid as main by-product was left in the reactor.     

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.     

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.     

Bio-hydrogen production from tequila vinasses: Effect of detoxification with activated charcoal on dark fermentation performance

Hydrogen production from dark fermentation is a potential source of sustainable fuel when it is generated from waste. This study compared hydrogen production resulting from fermentation using raw and detoxified tequila vinasse. Vinasse was detoxified with granular activated charcoal, which was used to adsorb compounds that could inhibit the production of hydrogen by dark fermentation. In batch cultures detoxification of vinasse led to up to 20% higher maximum velocities of hydrogen production, a 5.4 h reduction in the lag phase and an 11% higher molar yield, compared to results obtained with raw vinasse. Losses of sugars after detoxification provoked that the specific hydrogen volumetric yields obtained with detoxified vinasse were 30–40% lower with 5 g COD/L and 15 g COD/L initial concentrations, compared to the ones obtained with raw vinasse. For an initial 30 g COD/L no differences in specific hydrogen yields were observed between raw or detoxified vinasse in batch fermentation. Continuous culture fermentation of vinasse showed hydrogen production rates between 1.32 ± 0.07 to 1.39 ± 0.14 NL H₂/L-d when extra nutrients were added, while a stable production of hydrogen through fermentation of detoxified vinasse could not be maintained despite nutrient addition. Production of hydrogen from vinasse diluted with water with no additional nutrients was assessed and rates close to 0.42 ± 0.02 NL H₂/L-d and hydrogen content close to 37% were obtained. Accumulation of lactic acid and a predominant production of butyric acid over acetic acid suggested that the fermentation dynamics of vinasse with no supplementary nutrients were especially susceptible to high substrate loading rates and prolonged hydraulic retention times.