Hydrogen production by Rhodobacter sphaeroides strain O.U.001 using spent media of Enterobacter cloacae strain DM11

Combined dark and photo-fermentation was carried out to study the feasibility of biological hydrogen production. In dark fermentation, hydrogen was produced by Enterobacter cloacae strain DM11 using glucose as substrate. This was followed by a photo-fermentation process. Here, the spent medium from the dark process (containing unconverted metabolites, mainly acetic acid etc.) underwent photo-fermentation by Rhodobacter sphaeroides strain O.U.001 in a column photo-bioreactor. This combination could achieve higher yields of hydrogen by complete utilization of the chemical energy stored in the substrate. Dark fermentation was studied in terms of several process parameters, such as initial substrate concentration, initial pH of the medium and temperature, to establish favorable conditions for maximum hydrogen production. Also, the effects of the threshold concentration of acetic acid, light intensity and the presence of additional nitrogen sources in the spent effluent on the amount of hydrogen produced during photo-fermentation were investigated. The light conversion efficiency of hydrogen was found to be inversely proportional to the incident light intensity. In a batch system, the yield of hydrogen in the dark fermentation was about 1.86 mol H₂ mol⁻¹ glucose; and the yield in the photo-fermentation was about 1.5–1.72 mol H₂ mol⁻¹ acetic acid. The overall yield of hydrogen in the combined process, considering glucose as the preliminary substrate, was found to be higher than that in a single process.     

Improvement of corn stover bioconversion efficiency by using plant glycoside hydrolase

Plant cell wall is the most abundant substrate for bioethanol production, and plants also represent a key resource for glycoside hydrolase (GH). To exploit efficient way for bioethanol production with lower cellulase loading, the potential of plant GH for lignocellulose bioconversion was evaluated. The GH activity for cell wall proteins (CWPs) was detected from fresh corn stover (FCS), and the synergism of which with Trichoderma reesei cellulase was also observed. The properties for the GH of FCS make it a promising enzyme additive for lignocellulose biodegradation. To make use of the plant GH, novel technology for hydrolysis and ethanol fermentation was developed with corn stover as substrate. Taking steam-exploded corn stover as substrate for hydrolysis and ethanol fermentation, compared with T. reesei cellulase loaded alone, the final glucose and ethanol accumulation increased by 60% and 63% respectively with GH of FCS as an addition.     

Fermentative hydrogen production from low-value substrates

Hydrogen is a promising energy source that is believed to replace the conventional energy sources e.g. fossil fuels over years. Hydrogen production methods can be divided into conventional production methods which depend mainly on fossil fuels and alternative production methods including electrolysis of water, biophotolysis and fermentation hydrogen production from organic waste materials. Compared to the conventional methods, the alternative hydrogen production methods are less energy intensive and negative-value substrates i.e. waste materials can be used to produce hydrogen. Among the alternative methods, fermentation process including dark and photo-fermentation has gained more attention because these processes are simple, waste materials can be utilized, and high hydrogen yields can be achieved. The fermentation process is affected by several parameters such as type of inoculum, pH, temperature, substrate type and concentration, hydraulic retention time, etc. In order to achieve optimum hydrogen yields and maximum substrate degradation, the operating conditions of the fermentation process must be optimized. In this review, two routes for biohydrogen production as dark and photo-fermentation are discussed. Dark/photo-fermentation technology is a new approach that can be used to increase the hydrogen yield and improve the energy recovery from organic wastes.     

暗发酵-光发酵两阶段联合生物制氢技术研究进展

随着能源紧缺的日益加剧,以及化石燃料燃烧引起的环境问题逐渐突显,氢能作为一种清洁可再生能源越来越受到青睐。生物制氢与热化学及电化学制氢相比其反应条件温和、低耗、绿色,是一项非常有应用前景的技术。生物制氢从广义上可以分为暗发酵和光发酵产氢两种,其中暗发酵微生物可以利用有机废弃物产生氢气以及有机酸等副产物,光合细菌在光照和固氮酶的作用下可以将暗发酵产生的有机酸继续用于产氢,因此两种发酵产氢方式相结合可以提高有机废物的资源化效率。将近年来暗发酵-光发酵两阶段生物制氢技术进行整理分析,从其产氢机理、主要影响因素、暗发酵-光发酵产氢结合方式(两步法、混合培养产氢)几个方面进行阐述,最后指出该技术面临的挑战。     

Perspectives on cultivation strategies and photobioreactor designs for photo-fermentative hydrogen production

Photosynthetic bacteria have considerable biotechnological potential for biological hydrogen production due to higher substrate conversion efficiency and hydrogen yield. Phototrophic fermentation using photosynthetic bacteria has a major advantage of being able to further convert the byproducts originating from dark fermentation (e.g., volatile fatty acids) to hydrogen. Through the combination of dark and photo-fermentation processes, organic feedstock is fully converted into gaseous product (H₂) at the highest possible H₂ yield, with significant reduction of chemical oxygen demand (COD). The performance of photo-fermentation is highly dependent on the medium composition, culture conditions, and photobioreactor design. Therefore, this article provides a critical review of the effects of key factors affecting the photo-hydrogen production efficiency of photosynthetic bacteria, and also summarizes the strategies being applied in promoting the performance of photo-fermentation.     

Effects of light/dark cycle, mixing pattern and partial pressure of H2 on biohydrogen production by Rhodobacter sphaeroides ZX-5

The effects of light/dark cycle, mixing pattern and partial pressure of H₂ on the growth and hydrogen production of Rhodobacter sphaeroides ZX-5 were investigated. The results from light/dark cycle culture showed that little or no hydrogen production was observed during the dark periods, and the hydrogen production immediately recovered once illumination was resumed. Also, it was found that the optimum condition of shaking velocity was 120 rpm for hydrogen photo-fermentation. Meanwhile, shaking during H₂ production phase (i.e., cell growth stationary phase) of photo-fermentation played a crucial role on effectively enhancing the phototrophic hydrogen production, rather than that during cell exponential growth phase. The other factor evaluated was hydrogen partial pressure in the culture system. The substrate conversion efficiency increased from 86.07% to 95.56% along with the decrease of the total pressure in the photobioreactor from 1.082 × 10⁵ to 0.944 × 10⁵ Pa, which indicated that reduction of H₂ partial pressure by lowering the operating pressure substantially improved H₂ production in an anaerobic, photo-fermentation process.     

Acidogenic fermentation of corn stover

Corn stover was fermented by anaerobic acidogenic bacteria to produce volatile (C₂–C₆) organic acids. Mild pretreatment with dilute alkali solutions produced a two-fold increase in fermentability. A mixture of lime and sodium carbonate was found to be a better pretreatment agent than sodium hydroxide. Methane generation was inhibited by low temperature (? 25°C) and high solids [≥ 2.5% (w/v)] fermentation. Volatile acid yields of 0.5–0.55 g acetic acid equiv/g dry ash-free (DAF) stover could be obtained in batch fermentations. Several extractants and extraction solvents for organic acids were found to be nontoxic to acidogenic fermentation. The data show that acidogenic fermentation can produce useful volatile fatty acids in high yields from a complex lignocellulosic feedstock. These fermentations are nonsterile, need no stirring, and are easy to run. Moreover, cellulose, pentosans, and other carbohydrates are directly utilized by acidogenic bacteria. Hence, acidogenic fermentation could be useful in converting biomass to chemical feedstocks and fuel.     

Simultaneous saccharification and fermentation of ground corn stover for the production of fuel ethanol using Phanerochaete chrysosporium, Gloeophyllum trabeum, Saccharomyces cerevisiae, and Escherichia coli K011

Enzymatic saccharification of corn stover using Phanerochaete chrysosporium and Gloeophyllum trabeum and subsequent fermentation of the saccharification products to ethanol by Saccharomyces cerevisiae and Escherichia coli K011 were achieved. Prior to simultaneous saccharification and fermentation (SSF) for ethanol production, solid-state fermentation was performed for four days on ground corn stover using either P. chrysosporium or G. trabeum to induce in situ cellulase production. During SSF with S. cerevisiae or E. coli, ethanol production was the highest on day 4 for all samples. For corn stover treated with P. chrysosporium, the conversion to ethanol was 2.29 g/100 g corn stover with S. cerevisiae as the fermenting organism, whereas for the sample inoculated with E. coli K011, the ethanol production was 4.14 g/100 g corn stover. Corn stover treated with G. trabeum showed a conversion 1.90 and 4.79 g/100 g corn stover with S. cerevisiae and E. coli K011 as the fermenting organisms, respectively. Other fermentation co-products, such as acetic acid and lactic acid, were also monitored. Acetic acid production ranged between 0.45 and 0.78 g/100 g corn stover, while no lactic acid production was detected throughout the 5 days of SSF. The results of our experiment suggest that it is possible to perform SSF of corn stover using P. chrysosporium, G. trabeum, S. cerevisiae and E. coli K011 for the production of fuel ethanol.     

Effects of pH and carbon sources on biohydrogen production by co-culture of Clostridium butyricum and Rhodobacter sphaeroides

To improve the hydrogen yield from biological fermentation of organic wastewater, a co-culture system of dark- and photo-fermentation bacteria was investigated. In a pureculture system of the dark-fermentation bacterium Clostridium butyricum, a pH of 6.25 was found to be optimal, resulting in a hydrogen production rate of 18.7 ml-H?/l/h. On the other hand, the photosynthetic bacterium Rhodobacter sphaeroides could produce the most hydrogen at 1.81 mol-H?/mol-glucose at pH 7.0. The maximum specific growth rate of R. sphaeroides was determined to be 2.93 h?1 when acetic acid was used as the carbon source, a result that was significantly higher than that obtained using either glucose or a mixture of volatile fatty acids (VFAs). Acetic acid best supported R. sphaeroides cell growth but not hydrogen production. In the co-culture system with glucose, hydrogen could be steadily produced without any lag phase. There were distinguishable inflection points in a plot of accumulated hydrogen over time, resulting from the dynamic production or consumption of VFAs by the interaction between the dark- and photofermentation bacteria. Lastly, the hydrogen production rate of a repeated fed-batch run was 15.9 ml-H?/l/h, which was achievable in a sustainable manner.     

Hydrogen production by immobilized R. faecalis RLD-53 using soluble metabolites from ethanol fermentation bacteria E. harbinense B49

In order to increase the hydrogen yield from glucose, hydrogen production by immobilized Rhodopseudomonas faecalis RLD-53 using soluble metabolites from ethanol fermentation bacteria Ethanoligenens harbinense B49 was investigated. The soluble metabolites from dark-fermentation mainly were ethanol and acetate, which could be further utilized for photo-hydrogen production. Hydrogen production by B49 was noticeably affected by the glucose and phosphate buffer concentration. The maximum hydrogen yield (1.83 mol H₂/mol glucose) was obtained at 9 g/l glucose. In addition, we found that the ratio of acetate/ethanol (A/E) increased with increasing phosphate buffer concentration, which is favorable to further photo-hydrogen production. The total hydrogen yield during dark- and photo-fermentation reached its maximum value (6.32 mol H₂/mol glucose) using 9 g/l glucose, 30 mmol/l phosphate buffers and immobilized R. faecalis RLD-53. Results demonstrated that the combination of dark- and photo- fermentation was an effective and efficient process to improve hydrogen yield from a single substrate.     

Evaluation of Simultaneous Saccharification and Ethanol Fermentation of Undetoxified Steam-Exploded Corn Stover by Saccharomyces cerevisiae Y5

Toxin-tolerant yeast strains that produce high ethanol yield are inevitably requited for cost-effective ethanol production from undetoxified steam-exploded corn stover. To verify the ethanol-producing capability of the strain Saccharomyces cerevisiae Y5 developed in our laboratory, simultaneous saccharification and fermentation of undetoxified steam-exploded corn stover with solids loading of 30 % (w/v) was carried out in different-sized flasks and an automatic fermenter. After 96 h, the ethanol concentrations had reached 50, 47.8, and 47.5 g/L in the 100-mL flask, 3,000-mL flask, and 5-L automatic fermenter, respectively. The experiment demonstrates that ethanol production from undetoxified steam-exploded corn stover using S. cerevisiae Y5 simplifies the production process, reduces equipment investment and water consumption, and generates highly concentrated ethanol. S. cerevisiae Y5 is a promising strain that could reduce the cost of producing ethanol from steam-exploded corn stover.     

Enhanced phenolic antioxidants production in submerged cultures of Inonotus obliquus in a ground corn stover medium

The medicinal mushroom Inonotus obliquus has been a folk remedy for a long time in East-European and Asian countries. It is currently ascribed to a number of phenolic compounds as well as triterpenoids and polysaccharides responsible for significant biological and pharmacological properties. A study was conducted to determine the effects of inclusion of lignocellulosic material, in this case corn stover on production and antioxidant activity of extracellular (EPC) and intracellular phenolic compounds (IPC) by Inonotus obliquus in submerged fermentation. The corn stover medium contained 3% ground corn stover and 3.5% corn flour but the control medium contained 5% corn flour without corn stover. All of the other components were same in the two media. Decomposition rates of cellulose, hemicellulose, and lignin in the corn stover substrate were 20.9%, 17.9%, and 19.8% through 288 h of submerged cultivation. Lignocellulose decomposition in the corn stover-containing medium yielded significantly higher EPC (118.9/135.7 mg GAE (gallic acid equivalents)) and IPC (21.2/23.7 mg GAE) than in the control medium (34.7/42.5 mg GAE of EPC and 12.5/13.5 mg GAE of IPC) per liter of culture broth (EPC) and per gram of mycelia (IPC) in shake flask cultures/10 L fermenter runs. Both EPC and IPC from the corn stover medium showed a higher scavenging activity against hydroxyl radicals and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals than those from the control medium during the later fermentation period. In dose-dependent experiments, EPC from the corn stover medium at 216 h demonstrated a significantly stronger free radical scavenger activity against DPPH and hydroxyl radicals, shown as much lower IC50 values, than that from the control medium and IPC from the two media.     

Co-generation of ethanol and <Emphasis Type="SmallCaps">l</Emphasis>-lactic acid from corn stalk under a hybrid process

Background

Corn stover, as one important lignocellulosic material, has characteristics of low price, abundant output and easy availability. Using corn stover as carbon source in the fermentation of valuable organic chemicals contributes to reducing the negative environmental problems and the cost of production. In ethanol fermentation based on the hydrolysate of corn stover, the conversion rate of fermentable sugars is at a low level because the native S. cerevisiae does not utilize xylose. In order to increase the conversion rate of fermentable sugars deriving from corn stover, an effective and energy saving biochemical process was developed in this study and the residual xylose after ethanol fermentation was further converted to l-lactic acid.

Results

In the hybrid process based on the hydrolysate of corn stover, the ethanol concentration and productivity reached 50.50 g L^?1 and 1.84 g L^?1 h^?1, respectively, and the yield of ethanol was 0.46 g g^?1. The following fermentation of l-lactic acid provided a product titer of 21.50 g L^?1 with a productivity of 2.08 g L^?1 h^?1, and the yield of l-lactic acid was 0.76 g g^?1. By adopting a blank aeration before the inoculation of B. coagulans LA1507 and reducing the final cell density, the l-lactic acid titer and yield reached 24.25 g L^?1 and 0.86 g g^?1, respectively, with a productivity of 1.96 g L^?1 h^?1.

Conclusions

In this work, the air pumped into the fermentor was used as both the carrier gas for single-pass gas stripping of ethanol and the oxygen provider for the aerobic growth of B. coagulans LA1507. Ethanol was effectively separated from the fermentation broth, while the residual medium containing xylose was reused for l-lactic acid production. As an energy-saving and environmental-friendly process, it introduced a potential way to produce bioproducts under the concept of biorefinery, while making full use of the hydrolysate of corn stover.

     

Comparison of three Pediococcus strains for lactic acid production from glucose in the presence of inhibitors generated by acid hydrolysis of lignocellulosic biomass

Pediococcus acidilactici DQ2, an isolate from corn stover hydrolysate, has been reported to produce more than 100 g/L lactic acid from corn stover hydrolysate. To determine if the outstanding performance is strain-specific or species-specific, three Pediococcus strains, two strains of P. acidilactici (DQ2 and DSM 20284) and one strain of P. pentosaceus (ATCC 25745), were compared for lactic acid production from glucose in the presence of inhibitors often found in lignocellulosic hydrolysates. P. acidilactici DQ2 showed the best results among the three strains tested, suggesting that the excellent performance of DQ2 is a unique feature of this specific strain.     

Study of the acidogenic phase of the anaerobic fermentation of stillage from ethanol distilleries

Summary A bench scale continuously stirred reactor was used to study the acidogenic phase of the anaerobic fermentation of stillage. The residence time of the effluent in the reactor ranged from 15.7 to 8.2 hours, pH was around 5.0 and temperature was maintained at 35°C. The results indicate that the residence time had no appreciable effect on the production or composition of the organic acids. The main acid products found in the reactor effluent were acetic, propionic and butiric acids.     

Lactic acid production from corn stover using mixed cultures of Lactobacillus rhamnosus and Lactobacillus brevis

Mixed cultures of Lactobacillus rhamnosus and Lactobacillus brevis was studied for improving utilization of both cellulose- and hemicellulose-derived sugars from corn stover for lactic acid production. During simultaneous saccharification and fermentation (SSF) of NaOH-treated corn stover by the mixed cultures, a lactic acid yield of 0.70 g/g was obtained, which was about 18.6% and 29.6% higher than that by single cultures of L. rhamnosus and L. brevis, respectively. Our results indicated that lactic acid yield from NaOH-pretreated corn stover by mixed cultures of L. rhamnosus and L. brevis was comparable to that from pure sugar mixtures (0.73 g/g of glucose/xylose mixture at 3:1 w/w).     

Oxytetracycline Formation by Streptomyces rimosus in Chemically Defined Media

Details in the fermentation of oxytetracycline in a synthetic medium with Streptomyces rimosus have been presented. In these studies, an organic nitrogen source was shown to be essential for the production of significant amounts of antibiotic activity. Of the amino acids tested, aspartic acid, proline, threonine, valine, and beta-alanine were utilized well for both growth and antibiotic production. Markedly different fermentation patterns were observed with aspartic acid and beta-alanine. Glycerol and glucose supported antibiotic yields superior to those found with other carbohydrates tested. Short chain organic acids were not effectively utilized for growth in the absence of a readily fermentable carbohydrate.     

Simultaneous Saccharification and Ethanol Fermentation of Corn Stover at High Temperature and High Solids Loading by a Thermotolerant Strain Saccharomyces cerevisiae DQ1

The thermotolerant strain Saccharomyces cerevisiae DQ1 was applied to the simultaneous saccharification and fermentation (SSF) at high temperature and high solids loading of the dilute acid-pretreated corn stover in the present study. The SSF using S. cerevisiae DQ1 was operated at 30?% solids loading of the pretreated corn stover with three-step SSF mode and achieved up to ethanol titer of 48?g/L and yield of 65.6?%. S. cerevisiae DQ1 showed strong thermotolerance in both the regular one-step SSF and the three-step SSF with changing temperature in each step. The three-step SSF at 40°C using S. cerevisiae DQ1 tolerated the greater cellulase dosage and solids loading of the pretreated corn stover and resulted in increased ethanol production. The present study provided a practical potential for the future SSF of lignocellulose feedstock at high temperature to reach high ethanol titer.     

Production of ethanol,organic acids and hydrogen: an opportunity for mixed culture biotechnology?

Anaerobic fermentation of biodegradable organic materials is usually carried out to obtain the final product, methane, a valuable energy source. However, it is also well known that various intermediates are produced in this process, e.g. ethanol, volatile organic acids and hydrogen. All these species have applications and value as fuels or chemicals. This paper shows a critical analysis of the potential of using anaerobic fermentation by mixed cultures to produce intermediates, e.g. ethanol, acetic, lactic and butyric acid and hydrogen, rather than methane. This paper discusses the current processes to produce these chemicals and compares them with the alternative approach of using open mixed cultures to produce them simultaneously via fermentation from renewable resources. None of these chemicals is currently produced via mixed culture fermentation: ethanol and lactic acid are usually produced in pure culture fermentation using food crops, e.g. corn or sugar cane, as starting materials; hydrogen, acetic and butyric acids are mainly produced via chemical synthesis from fossil fuel derived starting materials. A possible flow-sheet for the production of these chemicals from organic waste using mixed culture fermentation is proposed and the advantages and disadvantages of this process compared to current processes are critically discussed. The paper also discusses the research challenges which need to be addressed to make this process feasible.     

Production of Bakers' Yeast in Cheese Whey Ultrafiltrate

A process for the production of bakers' yeast in whey ultrafiltrate (WU) is described. Lactose in WU was converted to lactic acid and galactose by fermentation. Streptococcus thermophilus was selected for this purpose. Preculturing of S. thermophilus in skim milk considerably reduced its lag. Lactic fermentation in 2.3×-concentrated WU was delayed compared with that in unconcentrated whey, and fermentation could not be completed within 60 h. The growth rate of bakers' yeast in fermented WU differed among strains. The rate of galactose utilization was similar for all strains, but differences in lactic acid utilization occurred. Optimal pH ranges for galactose and lactic acid utilization were 5.5 to 6.0 and 5.0 to 5.5, respectively. The addition of 4 g of corn steep liquor per liter to fermented WU increased cell yields. Two sources of nitrogen were available for growth of Saccharomyces cerevisiae: amino acids (corn steep liquor) and ammonium (added during the lactic acid fermentation). Ammonium was mostly assimilated during growth on lactic acid. This process could permit the substitution of molasses by WU for the industrial production of bakers' yeast.