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。     

Biological hydrogen production by dark fermentation: challenges and prospects towards scaled-up production

Among different technologies of hydrogen production, bio-hydrogen production exhibits perhaps the greatest potential to replace fossil fuels. Based on recent research on dark fermentative hydrogen production, this article reviews the following aspects towards scaled-up application of this technology: bioreactor development and parameter optimization, process modeling and simulation, exploitation of cheaper raw materials and combining dark-fermentation with photo-fermentation. Bioreactors are necessary for dark-fermentation hydrogen production, so the design of reactor type and optimization of parameters are essential. Process modeling and simulation can help engineers design and optimize large-scale systems and operations. Use of cheaper raw materials will surely accelerate the pace of scaled-up production of biological hydrogen. And finally, combining dark-fermentation with photo-fermentation holds considerable promise, and has successfully achieved maximum overall hydrogen yield from a single substrate. Future development of bio-hydrogen production will also be discussed.     

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.     

Microbiological and engineering aspects of biohydrogen production

Dramatically rising oil prices and increasing awareness of the dire environmental consequences of fossil fuel use, including startling effects of climate change, are refocusing attention worldwide on the search for alternative fuels. Hydrogen is poised to become an important future energy carrier. Renewable hydrogen production is pivotal in making it a truly sustainable replacement for fossil fuels, and for realizing its full potential in reducing greenhouse gas emissions. One attractive option is to produce hydrogen through microbial fermentation. This process would use readily available wastes as well as presently unutilized bioresources, including enormous supplies of agricultural and forestry wastes. These potential energy sources are currently not well exploited, and in addition, pose environmental problems. However, fuels are relatively low value products, placing severe constraints on any production process. Therefore, means must be sought to maximize yields and rates of hydrogen production while at the same time minimizing energy and capital inputs to the bioprocess. Here we review the various attributes of the characterized hydrogen producing bacteria as well as the preparation and properties of mixed microflora that have been shown to convert various substrates to hydrogen. Factors affecting yields and rates are highlighted and some avenues for increasing these parameters are explored. On the engineering side, we review the potential waste pre-treatment technologies and discuss the relevant bioprocess parameters, possible reactor configurations, including emerging technologies, and how engineering design-directed research might provide insight into the exploitation of the significant energy potential of biomass resources.     

Biohydrogen production from microalgae—Major bottlenecks and future research perspectives

The imprudent use of fossil fuels has resulted in high greenhouse gas (GHG) emissions, leading to climate change and global warming. Reduction in GHG emissions and energy insecurity imposed by the depleting fossil fuel reserves led to the search for alternative sustainable fuels. Hydrogen is a potential alternative energy carrier and is of particular interest because hydrogen combustion releases only water. Hydrogen is also an important industrial feedstock. As an alternative energy carrier, hydrogen can be used in fuel cells for power generation. Current hydrogen production mainly relies on fossil fuels and is usually energy and CO₂-emission intensive, thus the use of fossil fuel-derived hydrogen as a carbon-free fuel source is fallacious. Biohydrogen production can be achieved via microbial methods, and the use of microalgae for hydrogen production is outstanding due to the carbon mitigating effects and the utilization of solar energy as an energy source by microalgae. This review provides comprehensive information on the mechanisms of hydrogen production by microalgae and the enzymes involved. The major challenges in the commercialization of microalgae-based photobiological hydrogen production are critically analyzed and future research perspectives are discussed. Life cycle analysis and economic assessment of hydrogen production by microalgae are also presented.     

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.     

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.     

Microbial diversity and genomics in aid of bioenergy

In view of the realization that fossil fuels reserves are limited, various options of generating energy are being explored. Biological methods for producing fuels such as ethanol, diesel, hydrogen (H₂), methane, etc. have the potential to provide a sustainable energy system for the society. Biological H₂ production appears to be the most promising as it is non-polluting and can be produced from water and biological wastes. The major limiting factors are low yields, lack of industrially robust organisms, and high cost of feed. Actually, H₂ yields are lower than theoretically possible yields of 4 mol/mol of glucose because of the associated fermentation products such as lactic acid, propionic acid and ethanol. The efficiency of energy production can be improved by screening microbial diversity and easily fermentable feed materials. Biowastes can serve as feed for H₂ production through a set of microbial consortia: (1) hydrolytic bacteria, (2) H₂ producers (dark fermentative and photosynthetic). The efficiency of the bioconversion process may be enhanced further by the production of value added chemicals such as polydroxyalkanoate and anaerobic digestion. Discovery of enormous microbial diversity and sequencing of a wide range of organisms may enable us to realize genetic variability, identify organisms with natural ability to acquire and transmit genes. Such organisms can be exploited through genome shuffling for transgenic expression and efficient generation of clean fuel and other diverse biotechnological applications. JIMB 2008: BioEnergy-Special issue     

Biohydrogen production and bioprocess enhancement: a review

This paper provides an overview of the recent advances and trends in research in the biological production of hydrogen (biohydrogen). Hydrogen from both fossil and renewable biomass resources is a sustainable source of energy that is not limited and of different applications. The most commonly used techniques of biohydrogen production, including direct biophotolysis, indirect biophotolysis, photo-fermentation and dark-fermentation, conventional or "modern" techniques are examined in this review. The main limitations inherent to biochemical reactions for hydrogen production and design are the constraints in reactor configuration which influence biohydrogen production, and these have been identified. Thereafter, physical pretreatments, modifications in the design of reactors, and biochemical and genetic manipulation techniques that are being developed to enhance the overall rates and yields of biohydrogen generation are revisited.     

Physiological characteristics of the extreme thermophile <Emphasis Type="Italic">Caldicellulosiruptor saccharolyticus</Emphasis>: an efficient hydrogen cell factory

Global concerns about climate changes and their association with the use of fossil fuels have accelerated research on biological fuel production. Biological hydrogen production from hemicellulose-containing waste is considered one of the promising avenues. A major economical issue for such a process, however, is the low substrate conversion efficiency. Interestingly, the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus can produce hydrogen from carbohydrate-rich substrates at yields close to the theoretical maximum of the dark fermentation process (i.e., 4 mol H₂/mol hexose). The organism is able to ferment an array of mono-, di- and polysaccharides, and is relatively tolerant to high partial hydrogen pressures, making it a promising candidate for exploitation in a biohydrogen process. The behaviour of this Gram-positive bacterium bears all hallmarks of being adapted to an environment sparse in free sugars, which is further reflected in its low volumetric hydrogen productivity and low osmotolerance. These two properties need to be improved by at least a factor of 10 and 5, respectively, for a cost-effective industrial process. In this review, the physiological characteristics of C. saccharolyticus are analyzed in view of the requirements for an efficient hydrogen cell factory. A special emphasis is put on the tight regulation of hydrogen production in C. saccharolyticus by both redox and energy metabolism. Suggestions for strategies to overcome the current challenges facing the potential use of the organism in hydrogen production are also discussed.     

Biohydrogen production and bioprocess enhancement: A review

This paper provides an overview of the recent advances and trends in research in the biological production of hydrogen (biohydrogen). Hydrogen from both fossil and renewable biomass resources is a sustainable source of energy that is not limited and of different applications. The most commonly used techniques of biohydrogen production, including direct biophotolysis, indirect biophotolysis, photo-fermentation and dark-fermentation, conventional or “modern” techniques are examined in this review. The main limitations inherent to biochemical reactions for hydrogen production and design are the constraints in reactor configuration which influence biohydrogen production, and these have been identified. Thereafter, physical pretreatments, modifications in the design of reactors, and biochemical and genetic manipulation techniques that are being developed to enhance the overall rates and yields of biohydrogen generation are revisited.     

Integrated system approach to dark fermentative biohydrogen production for enhanced yield,energy efficiency and substrate recovery

The challenges of climate change, dwindling fossil reserves, and environmental pollution have fuelled the need to search for clean and sustainable energy resources. The process of biohydrogen has been highlighted as a propitious alternative energy of the future because it has many socio-economic benefits such as non-polluting features, the ability to use diverse feedstocks including waste materials, the process uses various microorganisms, and it is the simplest method of producing hydrogen. However, the establishment of a biohydrogen driven economy has been hindered by low process yields due to the accumulation of inhibitory products. Over the past few years, various optimization methods have been used in literature. Among these, integration of bioprocesses is gaining increasing prominence as an effective approach that could be used to achieve a theoretical yield of 4 mol H₂ mol^?1 glucose. In batch integrated systems, dark fermentation is used as a primary process for conversion of substrates into biohydrogen, carbon dioxide, and volatile fatty acids. This is followed by a secondary anaerobic process for further biohydrogen conversion efficiency. This review discusses the current challenges facing scale-up studies in dark fermentation process. It elucidates the potential of batch integrated systems in biohydrogen process development. Furthermore, it explores the various integrated fermentation techniques that are employed in biohydrogen process development. Finally, the review concludes with recommendations on improvement of these integrated processes for enhanced biohydrogen yields which could pave a way for the establishment of a large-scale biohydrogen production process.     

Microbial CO conversions with applications in synthesis gas purification and bio-desulfurization

Recent advances in the field of microbial physiology demonstrate that carbon monoxide is a readily used substrate by a wide variety of anaerobic micro-organisms, and may be employed in novel biotechnological processes for production of bulk and fine chemicals or in biological treatment of waste streams. Synthesis gas produced from fossil fuels or biomass is rich in hydrogen and carbon monoxide. Conversion of carbon monoxide to hydrogen allows use of synthesis gas in existing hydrogen utilizing processes and is interesting in view of a transition from hydrogen production from fossil fuels to sustainable (CO2-neutral) biomass. The conversion of CO with H2O to CO2 and H2 is catalyzed by a rapidly increasing group of micro-organisms. Hydrogen is a preferred electron donor in biotechnological desulfurization ofwastewaters and flue gases. Additionally, CO is a good alternative electron donor considering the recent isolation of a CO oxidizing, sulfate reducing bacterium. Here we review CO utilization by various anaerobic micro-organisms and their possible role in biotechnological processes, with a focus on hydrogen production and bio-desulfurization.     

Fermentative biohydrogen production systems integration

Acidogenic fermentation can be used to produce hydrogen from a range of biomass sources. The effluent from this process can be utilised in a number of biological processes enabling further recovery of energy from the biomass. In this review a number of candidate technologies are assessed including conventional methanogenic anaerobic digestion, dark fermentative hydrogen production, photo-fermentation, and bioelectrochemical systems. The principles, benefits and challenges associated with integrating these technologies are discussed, with particular emphasis on integration with fermentative hydrogen production, and the current state of integrative development is presented. The various system configurations for potential integrations presented here may simultaneously permit an increase in the conversion efficiency of biomass to energy, improved adaptability to varying operating conditions, and improved stability. Such integration, while increasing system complexity, may mean that these bioprocesses could be deployed in a wider range of scenarios and be used with a greater range of substrates.     

Microbial CO Conversions with Applications in Synthesis Gas Purification and Bio-Desulfurization

ABSTRACT

Recent advances in the field of microbial physiology demonstrate that carbon monoxide is a readily used substrate by a wide variety of anaerobic micro-organisms, and may be employed in novel biotechnological processes for production of bulk and fine chemicals or in biological treatment of waste streams. Synthesis gas produced from fossil fuels or biomass is rich in hydrogen and carbon monoxide. Conversion of carbon monoxide to hydrogen allows use of synthesis gas in existing hydrogen utilizing processes and is interesting in view of a transition from hydrogen production from fossil fuels to sustainable (CO₂-neutral) biomass. The conversion of CO with H₂O to CO₂ and H₂ is catalyzed by a rapidly increasing group of micro-organisms. Hydrogen is a preferred electron donor in biotechnological desulfurization of wastewaters and flue gases. Additionally, CO is a good alternative electron donor considering the recent isolation of a CO oxidizing, sulfate reducing bacterium. Here we review CO utilization by various anaerobic micro-organisms and their possible role in biotechnological processes, with a focus on hydrogen production and bio-desulfurization.     

Material and energy balances of an integrated biological hydrogen production and purification system and their implications for its potential to reduce greenhouse gas emissions

The materials and energy in an integrated biological hydrogen production and purification system involving hydrolysis, dark fermentation, photo fermentation, CO₂ fixation and anaerobic digestion are balanced by integrating the results from multiple experiments, simulations and the literature. The findings are two fold. First, using 1000 kg rice straw as a substrate, 19.8 kg H₂ and 138.0 kg CH₄ are obtained. The net energy balance (NEB) and net energy ratio (NER) are −738.4 kWh and 77.8%, respectively, both of which imply an unfavorable energy production system. Opportunities to improve the performance particularly lie in the photo fermentation process. Second, greenhouse gas emissions are evaluated for various options. The results were comparable with the emission inventory of electricity generated from fossil fuels. NEB and NER under a zero-carbon-emission constraint were discussed in detail to clarify completely the implications of the energy and material balances on greenhouse gas emissions.     

Acetate as a carbon source for hydrogen production by photosynthetic bacteria

Hydrogen is a clean energy alternative to fossil fuels. Photosynthetic bacteria produce hydrogen from organic compounds by an anaerobic light-dependent electron transfer process. In the present study hydrogen production by three photosynthetic bacterial strains (Rhodopseudomonas sp., Rhodopseudomonas palustris and a non-identified strain), from four different short-chain organic acids (lactate, malate, acetate and butyrate) was investigated. The effect of light intensity on hydrogen production was also studied by supplying two different light intensities, using acetate as the electron donor. Hydrogen production rates and light efficiencies were compared. Rhodopseudomonas sp. produced the highest volume of H2. This strain reached a maximum H2 production rate of 25 ml H2 l(-1) h(-1), under a light intensity of 680 micromol photons m(-2) s(-1), and a maximum light efficiency of 6.2% under a light intensity of 43 micromol photons m(-2) s(-1). Furthermore, a decrease in acetate concentration from 22 to 11 mM resulted in a decrease in the hydrogen evolved from 214 to 27 ml H2 per vessel.     

Photo-fermentation of Rhodobacter sphaeroides for hydrogen production using lignocellulose-derived organic acids

In this study, the corn stover was pretreated, enzymatically hydrolyzed, and then fermented in the lipid production fermentation. The corn stover fermentation effluent was utilized for the photo-fermentation of a Rhodobacter sphaeroides ZX-5 for hydrogen production. The hydrogen production was more than twofolds greater than that in the synthetic medium under the similar organic acid concentration range. The synergism among the pure organic acids was found to facilitate cell growth and hydrogen production, although some organic acid was not utilized for hydrogen production directly. The synergism among the components in the corn stover fermentation effluent was also found. The initial pH value was found to be an important parameter for the photo-fermentation of R. sphaeroide ZX-5 using the corn stover fermentation effluent. The results provided a possible way to utilize lignocellulose-derived organic acids for hydrogen production, and to treat fermentation wastewater in biofuel production using lignocellulose.     

Evaluation of dairy cattle manure as a supplement to improve net energy gain in fermentative hydrogen production from sucrose

This study evaluated fermentative biohydrogen production from sucrose supplemented with dairy cattle manure at different sucrose:manure ratios. Hydrogen yields found in this study (2.9-5.3 M hydrogen/M sucrose) at ambient temperature are higher than literature results obtained at mesophilic temperatures. This study demonstrated that dairy cattle manure could serve as a buffering agent to maintain recommended pH levels; as a nutrient source to provide the required nutrients for hydrogen production; as a seed to produce hydrogen from sucrose; and as a co-substrate to improve the hydrogen yield. Based on an analysis of the net energy gain, it is concluded that positive net energy gains can be realized with non-thermal pretreatment and/or by combining dark fermentation with anaerobic digestion or microbial fuel cells to extract additional energy from the aqueous products of dark fermentation.     

发酵生物制氢研究进展

综述了近年来发酵生物制氢领域的研究进展?在菌种方面,除了对现有产氢菌种的深入研究外,还采用生物学,分子生物学及生物信息学手段建立产氢菌种库;在氢酶的研究方面,已逐步从基因确定、功能研究拓展到基因工程构建高效产氢菌研究：而在与废弃生物质处理相结合的反应过程方面,研究主要集中在利用不同种类的废弃物的产氢和高效产氢反应器上。此外,还初步总结了目前对发酵制氢可行性和经济性的评价,并对其发展方向提出了新的看法。