微生物在生物能源生产中的应用(英文)

生物可再生能源是最有前景的石油替代品之一.生物能源的生产原料包括:植物、有机废弃物和微生物.微生物在生物能源生产上有着广泛的应用,利用微生物制备的主要生物能源包括:生物柴油、生物乙醇、生物甲烷等.某些微生物如微藻和真菌可以生产大量油脂,这些油脂可以转化为生物柴油;有些微生物如酵母可以将糖类、淀粉以及纤维素转化为燃料乙醇,添加乙醇的汽油或柴油燃烧排放明显降低;还有些厌氧微生物可以将有机废弃物转化为甲烷,可用做家用燃气、车用燃气或发电.除此之外微生物还具有在生产能源的同时治理环境污染的优势.总之研究开发微生物在生物能源生产中的应用有利于世界可持续发展.     

Renewable energy from Cyanobacteria: energy production optimization by metabolic pathway engineering

The need to develop and improve sustainable energy resources is of eminent importance due to the finite nature of our fossil fuels. This review paper deals with a third generation renewable energy resource which does not compete with our food resources, cyanobacteria. We discuss the current state of the art in developing different types of bioenergy (ethanol, biodiesel, hydrogen, etc.) from cyanobacteria. The major important biochemical pathways in cyanobacteria are highlighted, and the possibility to influence these pathways to improve the production of specific types of energy forms the major part of this review.     

生物柴油原料资源高油脂微藻的开发利用

生物柴油作为化石能源的替代燃料已在国际上得到广泛应用。至今生物柴油的原料主要来自油料植物, 但与农作物争地的情况以及较高的原料成本限制了生物柴油的进一步推广。微藻作为高光合生物有其特殊的原料成本优势, 微藻的脂类含量最高可达细胞干重的80%。利用生物技术改良微藻, 获得的高油脂基因工程微藻经规模养殖, 可大大降低生物柴油原料成本。介绍了国内外生物柴油的应用现状, 阐述了微藻作为生物柴油原料的优势, 对基因工程技术调控微藻脂类代谢途径的研究进展, 以及在构建工程微藻中面临的问题和应采取的对策进行了综述和展望。     

A new dawn for industrial photosynthesis

Several emerging technologies are aiming to meet renewable fuel standards, mitigate greenhouse gas emissions, and provide viable alternatives to fossil fuels. Direct conversion of solar energy into fungible liquid fuel is a particularly attractive option, though conversion of that energy on an industrial scale depends on the efficiency of its capture and conversion. Large-scale programs have been undertaken in the recent past that used solar energy to grow innately oil-producing algae for biomass processing to biodiesel fuel. These efforts were ultimately deemed to be uneconomical because the costs of culturing, harvesting, and processing of algal biomass were not balanced by the process efficiencies for solar photon capture and conversion. This analysis addresses solar capture and conversion efficiencies and introduces a unique systems approach, enabled by advances in strain engineering, photobioreactor design, and a process that contradicts prejudicial opinions about the viability of industrial photosynthesis. We calculate efficiencies for this direct, continuous solar process based on common boundary conditions, empirical measurements and validated assumptions wherein genetically engineered cyanobacteria convert industrially sourced, high-concentration CO₂ into secreted, fungible hydrocarbon products in a continuous process. These innovations are projected to operate at areal productivities far exceeding those based on accumulation and refining of plant or algal biomass or on prior assumptions of photosynthetic productivity. This concept, currently enabled for production of ethanol and alkane diesel fuel molecules, and operating at pilot scale, establishes a new paradigm for high productivity manufacturing of nonfossil-derived fuels and chemicals.     

Bioenergy production from waste: examples of biomethane and biohydrogen

This new century addresses several environmental challenges among which distribution of drinking water, global warming and availability of novel renewable energy sources to substitute for fossil fuels are of utmost importance. The last two concerns are closely related because the major part of carbon dioxide (CO(2)), considered as the main cause of the greenhouse effect, is widely produced from fossil fuel combustion. Renewable energy sources fully balanced in CO(2) are therefore of special interest, especially the issue of biological production from organic wastes. Among the possibilities of bioenergy production from wastes, two approaches are particularly interesting: The first one is relatively old and related to the production of biomethane by anaerobic digestion while the second one, more recent and innovative, relies on biohydrogen production by microbial ecosystems.     

中国如何突破生物柴油产业的原料瓶颈

因应我国日益严峻的能源资源、能源环境和能源安全形势,国家大力倡导发展可再生能源。生物柴油是最重要的液体可再生燃料之一,在能源性质方面可以完全替代化石柴油,而且还具有安全环保等其它优良特性。当前利用动植物油脂生产生物柴油,原料成本偏高,而且稳定、充足的油脂原料供应体系尚未形成。我国是油脂资源短缺国家,近年来植物油进口量逐年增加。同时,我国耕地资源匮乏,粮食供应形势不容乐观,扩大油料作物种植的潜力非常有限。但是,我国宜林地丰富,农林废弃生物质资源量巨大。综合以上因素,我国应重点发展木本油料植物规模化种植和推广,加快微生物油脂发酵技术创新和产业化进程;同时,利用植物遗传育种技术提高油料作物产量以及选择性发展不与粮争地的油料作物。依靠各方面的进步,发展创新的油脂生产技术,保障我国生物柴油产业和油脂化工行业健康发展。     

Addressing the energy crisis: using microbes to make biofuels

Much of the energy being used to power our lives comes from fossil fuels such as coal, natural gas and petroleum. These energy sources are non-renewable, are being exhausted and also pollute the air, water and soil with toxic chemicals. Their mining, transportation, refining and use are associated with a large carbon footprint that contributes significantly to global warming. In addition, the geopolitical complexities surrounding the main fossil fuel producers create risks and uncertainties around the world. Replacing fossil fuels with clean, renewable forms of energy is paramount to creating a sustainable and healthy future, and for laying the foundations for global political stability and prosperity. Using biomass from plants, microbes can produce biofuels that are identical to or perform as well as fossil fuels. In addition of creating sustainable energy, advancing the biofuel industry will create new, high-quality rural jobs whilst improving energy security.     

Second Generation Biofuels: High-Efficiency Microalgae for Biodiesel Production

The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the “dangerously high” threshold of 450 ppm CO₂-e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO₂. Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (～66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO₂-neutral fuel production with CO₂ sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO₂ for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae.     

Microbial fuel cells: novel microbial physiologies and engineering approaches

The possibility of generating electricity with microbial fuel cells has been recognized for some time, but practical applications have been slow to develop. The recent development of a microbial fuel cell that can harvest electricity from the organic matter stored in marine sediments has demonstrated the feasibility of producing useful amounts of electricity in remote environments. Further study of these systems has led to the discovery of microorganisms that conserve energy to support their growth by completely oxidizing organic compounds to carbon dioxide with direct electron transfer to electrodes. This suggests that self-sustaining microbial fuel cells that can effectively convert a diverse range of waste organic matter or renewable biomass to electricity are feasible. Significant progress has recently been made to increase the power output of systems designed to convert organic wastes to electricity, but substantial additional optimization will be required for large-scale electricity production.     

Natural climate solutions versus bioenergy: Can carbon benefits of natural succession compete with bioenergy from short rotation coppice?

Short rotation plantations are often considered as holding vast potentials for future global bioenergy supply. In contrast to raising biomass harvests in forests, purpose‐grown biomass does not interfere with forest carbon (C) stocks. Provided that agricultural land can be diverted from food and feed production without impairing food security, energy plantations on current agricultural land appear as a beneficial option in terms of renewable, climate‐friendly energy supply. However, instead of supporting energy plantations, land could also be devoted to natural succession. It then acts as a long‐term C sink which also results in C benefits. We here compare the sink strength of natural succession on arable land with the C saving effects of bioenergy from plantations. Using geographically explicit data on global cropland distribution among climate and ecological zones, regionally specific C accumulation rates are calculated with IPCC default methods and values. C savings from bioenergy are given for a range of displacement factors (DFs), acknowledging the varying efficiency of bioenergy routes and technologies in fossil fuel displacement. A uniform spatial pattern is assumed for succession and bioenergy plantations, and the considered timeframes range from 20 to 100 years. For many parameter settings—in particular, longer timeframes and high DFs—bioenergy yields higher cumulative C savings than natural succession. Still, if woody biomass displaces liquid transport fuels or natural gas‐based electricity generation, natural succession is competitive or even superior for timeframes of 20–50 years. This finding has strong implications with climate and environmental policies: Freeing land for natural succession is a worthwhile low‐cost natural climate solution that has many co‐benefits for biodiversity and other ecosystem services. A considerable risk, however, is C stock losses (i.e., emissions) due to disturbances or land conversion at a later time.     

Is woody bioenergy carbon neutral? A comparative assessment of emissions from consumption of woody bioenergy and fossil fuel

Under the current accounting systems, emissions produced when biomass is burnt for energy are accounted as zero, resulting in what is referred to as the ‘carbon neutrality’ assumption. However, if current harvest levels are increased to produce more bioenergy, carbon that would have been stored in the biosphere might be instead released in the atmosphere. This study utilizes a comparative approach that considers emissions under alternative energy supply options. This approach shows that the emission benefits of bioenergy compared to use of fossil fuel are time‐dependent. It emerges that the assumption that bioenergy always results in zero greenhouse gas (GHG) emissions compared to use of fossil fuels can be misleading, particularly in the context of short‐to‐medium term goals. While it is clear that all sources of woody bioenergy from sustainably managed forests will produce emission reductions in the long term, different woody biomass sources have various impacts in the short‐medium term. The study shows that the use of forest residues that are easily decomposable can produce GHG benefits compared to use of fossil fuels from the beginning of their use and that biomass from dedicated plantations established on marginal land can be carbon neutral from the beginning of its use. However, the risk of short‐to‐medium term negative impacts is high when additional fellings are extracted to produce bioenergy and the proportion of felled biomass used for bioenergy is low, or when land with high C stocks is converted to low productivity bioenergy plantations. The method used in the study provides an instrument to identify the time‐dependent pattern of emission reductions for alternative bioenergy sources. In this way, decision makers can evaluate which bioenergy options are most beneficial for meeting short‐term GHG emission reduction goals and which ones are more appropriate for medium to longer term objectives.     

微藻与其他微生物共培养的研究进展及应用

化石燃料的挖掘和燃烧导致环境污染以及气候变化.与化石燃料相比,微藻被认为是一种更有前途的生物柴油生产原料,它具有生长速度快、含油量高、不占用耕地的特点.尽管微藻被认为是生产第三代生物燃料的最佳生产者之一,但单独培养微藻容易污染且采收成本高,与化石燃料和传统可再生能源相比缺乏竞争力.利用微藻与其他微生物共培养能够实现自絮...     

Bioethanol Potentials and Life-Cycle Assessments of Biofuel Feedstocks

A wide range of bioenergy crops has been proposed as feedstocks that can serve as renewable and ecologically sound substitutes to fossil fuels. In the United States, corn grain (Zea mays) ethanol is the primary biofuel, with over 49 billion liters produced in 2010. Along with the Energy Independence and Security Act (EISA) of 2007 mandate, concerns about competition for food, land availability, nutrient and water requirements, energy balances, and greenhouse gas (GHG) emissions have prompted researchers to investigate other potential feedstocks. These include second-generation lignocellulosic feedstock and third-generation biodiesel from microalgae and cyanobacteria. However, each feedstock option has associated benefits and consequences for its use. One technique used to evaluate the energy efficiency of bioenergy production systems is the life-cycle assessment (LCA), where system inputs and outputs are computed in terms of either C or energy equivalents to assess the net gains in energy or C offsets. This article collates and synthesizes information about feedstock production options. Results show a wide range of calculated energy and GHG balances, even for the same feedstock species. Discrepancies in LCA and uncertainty thus make direct comparisons difficult and prevent a consensus in determining feedstock suitability. Recommendations must be based upon LCA model assumptions, crop species, cultivation methods, management practices, and energy conversion choices. Currently lignocellulosic feedstock, while a better alternative than corn grain, is not a long-term viable energy source. New feedstocks and technologies are necessary if bioenergy is to be C-neutral and efficient in energy production and land use. Although C fluxes are considered in LCA, one important ecosystem C stock that has previously been left out of many LCA models is changes to soil organic carbon (SOC). Future research, developments, and priorities are discussed for options to produce low C fuel sources and stabilize the climate.     

Industrial‐strength ecology: trade‐offs and opportunities in algal biofuel production

Microalgae represent one of the most promising groups of candidate organisms for replacing fossil fuels with contemporary primary production as a renewable source of energy. Algae can produce many times more biomass per unit area than terrestrial crop plants, easing the competing demands for land with food crops and native ecosystems. However, several aspects of algal biology present unique challenges to the industrial‐scale aquaculture of photosynthetic microorganisms. These include high susceptibility to invading aquatic consumers and weeds, as well as prodigious requirements for nutrients that may compete with the fertiliser demands of other crops. Most research on algal biofuel technologies approaches these problems from a cellular or genetic perspective, attempting either to engineer or select algal strains with particular traits. However, inherent functional trade‐offs may limit the capacity of genetic selection or synthetic biology to simultaneously optimise multiple functional traits for biofuel productivity and resilience. We argue that a community engineering approach that manages microalgal diversity, species composition and environmental conditions may lead to more robust and productive biofuel ecosystems. We review evidence for trade‐offs, challenges and opportunities in algal biofuel cultivation with a goal of guiding research towards intensifying bioenergy production using established principles of community and ecosystem ecology.     

Sustainable Cultivation Concepts for Domestic Energy Production from Biomass

Referee: Dr. J. Grant McLeod, Semiarid Prairie Agricultural Research Centre, Research Branch, Agriculture and Agri-Food Canada, P.O. Box 1030 Swift Current, Saskatchewan S9H 3X2, Canada According to the European Union, biomass will play a major role in the substitution of fossil fuels with renewable resources. Biomass will contribute 83% to the increased use of renewable resources by the year 2010. In contrast to other solar energy sources, plant biomass is always available and can be converted into energy continuously. An important objective in the production of energy crops on arable farm land should be to realize a high net energy yield and fulfill obligations in the field of environmental protection. The “double cropping system” was developed to meet these obligations. Silaging as a conservation method for wet biomass makes this sustainable cultivation system possible. It includes a diverse array of crops and provides the opportunity to integrate rural organic wastes into this energy concept. The model presented, “the energy self supplying farm”, shows that it is possible to meet the energy consumption requirements of a livestock farming operation with energy crop production on 10 to 18% of the arable farm land. According to a new rape energy concept, a land resource requirement of roughly 10% is feasible if biomass residues from rape oil production for liquid fuels are also utilized for energy production. For a farm with livestock, anaerobic digestion technology is an appropriate technique to deliver heat and electricity for the farmstead. Digestion residues, used as fertilizer in energy crop production, results in an almost complete nutrient recycling. Energy output can be increased above the demand of the farm via the biogas reactor, using the total biomass produced with double cropping. Surplus electricity is supplied to the grid at a guaranteed price. Biomass is a domestic energy resource, and farmers have the chance to extend their function from a supplier of raw material to managers of domestic energy resources. Under the currently established framework, monetary return per hectare could be more than double with biomass energy production via biogas. This will allow the agricultural economy to recover and promote a sustainable regional development. In addition to being a convenient method of waste management, sustainable energy crop production can make a significant contribution to environmental protection and the improvement of the social and economic cohesion within a community.     

微藻能源技术开发和产业化的发展思路与策略

随着石油资源的日益减少及实现低碳经济的迫切需要,微藻能源已成为世界各国重点研究与发展的战略方向。微藻能源关系国家能源重大战略储备,因此我国迫切需要自主开发微藻能源产业化技术。文中分析了我国发展微藻能源的优势,及目前微藻能源产业化中存在的瓶颈和亟待解决的问题,既包括基础科学研究内容,也包括产业化进程中亟需攻克的关键技术问题。在此基础上,提出微藻能源的发展思路和策略,指出了其产业化中的主要环节的技术发展方向,展望了产业化进程。     

生物能源专刊序言

生物能源作为可再生能源,有望减少能源供给中对石油的依赖程度。近年来,我国生物能源的发展非常迅速,已经成为继巴西和美国后的第三大燃料乙醇生产国和消费国。为促进生物能源相关技术研究的发展,本期“生物能源”专刊收录了我国生物能源专家学者在燃料乙醇、生物柴油、微生物油脂、生物燃料系统分析等领域的最新研究进展。     

Bioenergy crops,biodiversity and ecosystem services in temperate agricultural landscapes—A review of synergies and trade-offs

The Paris agreement on climate change requires rapid reductions in greenhouse gas emissions. One important mitigation strategy, at least in the intermediate future, is the substitution of fossil fuels with bioenergy. However, using agriculture- and forest-derived biomass for energy has sparked controversy regarding both the climate mitigation potential and conflicts with biodiversity conservation. The urgency of the climate crisis calls for using forests for carbon sequestration and storage rather than for bioenergy, making agricultural biomass an attractive alternative for fossil energy substitution. However, this calls for comprehensive assessments of its sustainability in terms of consequences for biodiversity and ecosystem services. In this review, we provide a first holistic overview of the impacts on ecosystems of land-use changes from bioenergy crop production in temperate climates, by synthesizing results on both biodiversity and ecosystem service impacts. We found that bioenergy-related land-use changes can have both positive and negative effects on ecosystems, with original land use, bioenergy crop type and scale of bioenergy production being important moderators of impacts. Despite the risk of opportunity cost for food production, perennial crop cultivation on arable land had the lowest occurrence of negative impacts on biodiversity and ecosystem services. Growing biomass for bioenergy on surplus land has been suggested as a way to alleviate competition with food production and biodiversity conservation, but our results demonstrate that utilizing marginal or abandoned land for bioenergy crop production cannot fully resolve these trade-offs. Furthermore, there is a lack of empirical studies of the biodiversity value of marginal and abandoned land, limiting our understanding of the sustainability implications of biomass cultivation on surplus land. We argue that future research and policies for bioenergy production must explicitly consider biodiversity and ecosystem services in combination to avoid potential trade-offs between the two and to ensure sustainable bioenergy production.     

Microbial utilization of crude glycerol for the production of value-added products

Energy fuels for transportation and electricity generation are mainly derived from finite and declining reserves of fossil hydrocarbons. Fossil hydrocarbons are also used to produce a wide range of organic carbon-based chemical products. The current global dependency on fossil hydrocarbons will not be environmentally or economically sustainable in the long term. Given the future pessimistic prospects regarding the complete dependency on fossil fuels, political and economic incentives to develop carbon neutral and sustainable alternatives to fossil fuels have been increasing throughout the world. For example, interest in biodiesel has undergone a revival in recent times. However, the disposal of crude glycerol contaminated with methanol, salts, and free fatty acids as a by-product of biodiesel production presents an environmental and economic challenge. Although pure glycerol can be utilized in the cosmetics, tobacco, pharmaceutical, and food industries (among others), the industrial purification of crude glycerol is not economically viable. However, crude glycerol could be used as an organic carbon substrate for the production of high-value chemicals such as 1,3-propanediol, organic acids, or polyols. Microorganisms have been employed to produce such high-value chemicals and the objective of this article is to provide an overview of studies on the utilization of crude glycerol by microorganisms for the production of economically valuable products. Glycerol as a by-product of biodiesel production could be used a feedstock for the manufacture of many products that are currently produced by the petroleum-based chemical industry.     

Biofuels and other approaches for decreasing fossil fuel emissions from agriculture

Biofuels offer one method for decreasing emissions of carbon dioxide (CO2) from fossil fuels, thus helping to meet UK and EU targets for mitigating climate change. They also provide a rational option for land use within the EU that could be economically viable, provided that an appropriate financial and policy environment is developed. If 80% of current set‐aside land in the UK were used for production of biomass crops for electricity generation, about 3% of current UK electricity demand could be met from this source. Considering possibilities for increasing yields and land area devoted to such crops over the coming decades, this could possibly rise to 12%. These estimates exclude consideration of developments in electricity generation which should increase the efficiency of conversion. Also, the use of combined heat and power units at local level (e.g. on farms or in rural communities) gives additional energy saving. Dedicated biomass crops such as willow, poplar, miscanthus, switchgrass or reed canary grass are perennials: in comparison with annual arable crops they would be expected to deliver additional environmental benefits. The elimination of annual cultivation should give a more stable environment, beneficial for farmland biodiversity. Some increase in soil organic matter content is likely, leading to some sequestration of carbon in soil and long‐term improvements in soil quality. The impact on water quality may be positive as nitrate losses are small and a similar trend is expected for phosphate and pesticides. However, these crops may well use more water than arable crops so their impact on water resources could be negative – an issue for further research. Agricultural land can also be used to produce liquid fuels for use in transport. At present biodiesel can be produced from oilseed rape and ethanol from either sucrose in sugar beet or cellulose from virtually any plant material. In the short‐term, liquid biofuels are an easy option as they require little change to either agriculture or transport infrastructure. However, their benefits for CO2 emissions are much less than for biomass used for generating electricity. It is therefore necessary to debate the priorities for land use in this context.