Biorefinery: Toward an industrial metabolism

Fossil fuel reserves are running out, global warming is becoming a reality, waste recycling is becoming ever more costly and problematic, and unrelenting population growth will require more and more energy and consumer products. There is now an alternative to the 100% oil economy; it is a renewable resource based on agroresources by using the whole plant. Production and development of these new products are based on biorefinery concept. Each constituent of the plant can be extracted and functionalized in order to produce non-food and food fractions, intermediate agro-industrial products and synthons. Three major industrial domains can be concerned: molecules, materials and energy. Molecules can be used as solvent surfactants or chemical intermediates in substitution of petrol derivatives. Fibers can be valorized in materials like composites. Sugars and oils are currently used to produce biofuels like bioethanol or biodiesel, but second-generation biofuels will use lignocellulosic biomass as raw material. Lipids can be used to produce a large diversity of products like solvent, lubricants, pastes or surfactants. Industrial biorefinery will be linked to the creation of new processes based on the twelve principles of green chemistry (clean processes, atom economy, renewable feedstocks…). Biotechnology, especially white biotechnology, will take a major part into these new processes with biotransformations (enzymology, micro-organisms…) and fermentation. The substitution of oil products by biobased products will develop a new bioeconomy and new industrial processes respecting the sustainable development concept. Industrial biorefinery can be developed on the principle that any residues of one can then be exploited as raw material by others in an industrial metabolism.     

Cradle-to-gate assessment of environmental impacts for a broad set of biomass-to-product process chains

Purpose

This study advocates a modular approach combining unit processes as building blocks to formulate biomass process chains. This approach facilitates a transparent environmental life cycle impact assessment for bio-based products. It also enhances the ability to develop and assess more complex biorefinery systems, identifies critical parameters and offers useful material to support environmental impact assessment in early design stages.

Methods

Twenty-three different products were assessed with regard to the environmental burden associated with their production paths. Life cycle inventories (LCIs) for 32 unit processes were compiled (using information from pilot plants, simulation and literature data) and organized in biomass process chains. Then, 58 study systems were formed based on various combinations of the unit processes, each study system referring to the production of a selected product. Three indicators were used for quantification of the impacts: non-renewable fossil cumulative energy demand (CED), global warming potential (GWP) and water depletion as defined in the ReCiPe method.

Results and discussion

Factors influencing the variation of results even for similar products are discussed (e.g. production path and allocation method lead to a range of GWP values for ethylene production from 0.43 to 3.37 kg CO₂ eq/kg ethylene). For the majority of bio-products, CED has lower values than fossil-based equivalents (average difference 39–70 MJ eq/kg product depending on the allocation method), while mixed trends are obtained for the GWP and water depletion indicators. Assessments also highlight attributes that have a significant effect in the environmental profile of a production path such as the synthesis path, the process chemistry (water intensity) and process-related factors (energy intensity, degree of energy integration/heat recovery).

Conclusions

The analysis of impacts per unit process is able to demonstrate the particular production stages featuring high environmental intensities along a path further hinting to suggestions for amendments and improvements from an overall performance perspective. The study makes a useful source for biorefinery design studies especially in adopting a modular approach to represent and to analyse biomass process chains; it also provides a reference point for comparison (benchmarking) between different process technologies for biomass utilization. Finally, the analysis is compatible with the standards of the LCA methodology, and it is based on the use of the most common LCA databases, which facilitates the comparison of the results with other relevant studies.

     

Ethanol Tolerance in Bacteria

Abstract

One promising application of biotechnology is in making the production of energy and chemical products from plants (“biomass”) practical. Applications include new markets for crops and reduction of wastes by using field residues or “wastelands” as feedstocks in biomass energy production. In addition, engineered crops could synthesize complex compounds. However, conversion to widespread use of biomass could have undesirable impacts. For example, changes in cropping practices may reduce wildlife populations or disrupt food chains. Other negative impacts of an environmentally insensitive development might include increased release of CO₂ (worsening global warming), and production of wastes, either water, chemical or biological, that present disposal problems. Biotechnology applied to biomass and chemical production has the potential for aiding economic development while greatly improving environmental quality. Environmental concerns are expressed in this paper, in the belief that consideration of potential problems at the inception of a technology increases the likelihood that environmentally sound courses will be pursued.     

Anaerobic biotechnological approaches for production of liquid energy carriers from biomass

In recent years, increasing attention has been paid to the use of renewable biomass for energy production. Anaerobic biotechnological approaches for production of liquid energy carriers (ethanol and a mixture of acetone, butanol and ethanol) from biomass can be employed to decrease environmental pollution and reduce dependency on fossil fuels. There are two major biological processes that can convert biomass to liquid energy carriers via anaerobic biological breakdown of organic matter: ethanol fermentation and mixed acetone, butanol, ethanol (ABE) fermentation. The specific product formation is determined by substrates and microbial communities available as well as the operating conditions applied. In this review, we evaluate the recent biotechnological approaches employed in ethanol and ABE fermentation. Practical applicability of different technologies is discussed taking into account the microbiology and biochemistry of the processes.     

Metabolic engineering for the utilization of carbohydrate portions of lignocellulosic biomass

The petrochemical industry has grown to meet the need for massive production of energy and commodities along with an explosive population growth; however, serious side effects such as greenhouse gas emissions and global warming have negatively impacted the environment. Lignocellulosic biomass with myriad quantities on Earth is an attractive resource for the production of carbon-neutral fuels and chemicals through environmentally friendly processes of microbial fermentation. This review discusses metabolic engineering efforts to achieve economically feasible industrial production of fuels and chemicals from microbial cell factories using the carbohydrate portion of lignocellulosic biomass as substrates. The combined knowledge of systems biology and metabolic engineering has been applied to construct robust platform microorganisms with maximum conversion of monomeric sugars, such as glucose and xylose, derived from lignocellulosic biomass. By comprehensively revisiting carbon conversion pathways, we provide a rationale for engineering strategies, as well as their features, feasibility, and recent representative studies. In addition, we briefly discuss how tools in systems biology can be applied in the field of metabolic engineering to accelerate the development of microbial cell factories that convert lignocellulosic biomass into carbon-neutral fuels and chemicals with economic feasibility.     

碳一气体生物转化中的产乙酸菌改造与发酵工艺优化

当前的线性经济发展模式依赖化石能源且增加二氧化碳的排放,加剧全球变暖和环境污染。因此,亟需开发碳捕获和利用的技术,建立循环经济。利用产乙酸菌进行碳一气体(一氧化碳和二氧化碳)转化是一项前景广阔的技术,具有较高的碳源灵活性和产物选择性,能够合成多种化学品和燃料。本文聚焦产乙酸菌在碳一气体转化过程中的生理代谢机制、遗传和代谢工程改造、发酵工艺优化以及提升碳原子经济性等方面的研究进展,以期为产乙酸菌气体发酵的工业规模放大及“负碳”生产提供参考。     

Fermentation for future food systems: Precision fermentation can complement the scope and applications of traditional fermentation

Modern biotechnology holds great potential for expanding the scope of fermentation to create novel foods and improve the sustainability of food production.

The growing human population and global warming pose an impending threat for global food security (Linder, 2019). This has prompted a critical re‐examination of the food supply chain from producers to consumers in order to increase the overall efficiency of food production, storage and transport. Much research in plant science consequently aims to increase production with new, high‐yield crop, fruit and vegetable varieties better adapted to changing climatic conditions. Yet, there is also much room for improving food safety by minimising food losses and recycling waste, valorising by‐products, improving nutritional value and increasing storage time. This is where fermentation comes in as a cost‐efficient, versatile and proven technology that extends the shelf life of food products and enhances their nutritional content. Moreover, there is enormous potential in fermentation to further increase efficiency and product range and even create new food products from non‐food biomass.

… there is enormous potential in fermentation to further increase efficiency and product range and even create new food products from non‐food biomass.

In a broader sense, fermentation can be defined as the cultivation of microorganisms such as bacteria, yeasts and fungi to break down complex molecules into simpler ones, notably organic acids, alcohols or esters. In a practical sense, it is one of the oldest food processing technologies to increase storage life along with cooking, smoking or air‐drying: fermentation was already fully industrialised for producing beer and bread millennia ago in ancient Mesopotamia and Egypt. It is also an elegant and simple technology as these microorganisms do most of the work without much human involvement.Louis Pasteur’s discovery that microorganisms cause fermentation laid the basis for further improvement of the technology from traditional spontaneous fermentation to the use of defined starter cultures. Fermentation is now widely used to produce alcoholic beverages, bread and pastry, dairy products, pickled vegetables, soy sauce and so on. More recent advances based on genomics and synthetic biology include precision and biomass fermentation to produce specific compounds for the food and chemical industry or medicinal use. This is not the limit though: when combined with genomics, fermentation has even greater potential for creating novel foods and other products.     

Biomass energy: the scale of the potential resource

Increased production of biomass for energy has the potential to offset substantial use of fossil fuels, but it also has the potential to threaten conservation areas, pollute water resources and decrease food security. The net effect of biomass energy agriculture on climate could be either cooling or warming, depending on the crop, the technology for converting biomass into useable energy, and the difference in carbon stocks and reflectance of solar radiation between the biomass crop and the pre-existing vegetation. The area with the greatest potential for yielding biomass energy that reduces net warming and avoids competition with food production is land that was previously used for agriculture or pasture but that has been abandoned and not converted to forest or urban areas. At the global scale, potential above-ground plant growth on these abandoned lands has an energy content representing approximately 5% of world primary energy consumption in 2006. The global potential for biomass energy production is large in absolute terms, but it is not enough to replace more than a few percent of current fossil fuel usage. Increasing biomass energy production beyond this level would probably reduce food security and exacerbate forcing of climate change.     

生物质制氢技术研究进展

氢能以其清洁,来源广泛及用途广等优点成为最有希望的替代能源之一,用可再生能源制氢是氢能发展的必然趋势。由于生物质制氢具有一系列独特的优点,它已成为发展氢经济颇具前景的研究领域之一。生物质制氢技术可以分为两类,一类是以生物质为原料利用热物理化学方法制取氢气,如生物质气化制氢,超临界转化制氢,高温分解制氢等热化学发制氢,以及基于生物质的甲烷、甲醇、乙醇的化学重整转化制氢等;另一类是利用生物转化途径转换制氢,包括直接生物光解,间接生物光解,光发酵,光合异养细菌水气转移反应合成氢气,暗发酵和微生物燃料电池等技术。本文综述了目前主要的生物质制氢技术及其发展概况,并分析了各技术的发展趋势。     

Assessment of technological options and economical feasibility for cyanophycin biopolymer and high-value amino acid production

Major transitions can be expected within the next few decades aiming at the reduction of pollution and global warming and at energy saving measures. For these purposes, new sustainable biorefinery concepts will be needed that will replace the traditional mineral oil-based synthesis of specialty and bulk chemicals. An important group of these chemicals are those that comprise N-functionalities. Many plant components contained in biomass rest or waste stream fractions contain these N-functionalities in proteins and free amino acids that can be used as starting materials for the synthesis of biopolymers and chemicals. This paper describes the economic and technological feasibility for cyanophycin production by fermentation of the potato waste stream Protamylasse™ or directly in plants and its subsequent conversion to a number of N-containing bulk chemicals.     

Algal Photosynthesis as the Primary Driver for a Sustainable Development in Energy, Feed, and Food Production

High oil prices and global warming that accompany the use of fossil fuels are an incentive to find alternative forms of energy supply. Photosynthetic biofuel production represents one of these since for this, one uses renewable resources. Sunlight is used for the conversion of water and CO₂ into biomass. Two strategies are used in parallel: plant-based production via sugar fermentation into ethanol and biodiesel production through transesterification. Both, however, exacerbate other problems, including regional nutrient balancing and the world's food supply, and suffer from the modest efficiency of photosynthesis. Maximizing the efficiency of natural and engineered photosynthesis is therefore of utmost importance. Algal photosynthesis is the system of choice for this particularly for energy applications. Complete conversion of CO₂ into biomass is not necessary for this. Innovative methods of synthetic biology allow one to combine photosynthetic and fermentative metabolism via the so-called Photanol approach to form biofuel directly from Calvin cycle intermediates through use of the naturally transformable cyanobacterium Synechocystis sp. PCC 6803. Beyond providing transport energy and chemical feedstocks, photosynthesis will continue to be used for food and feed applications. Also for this application, arguments of efficiency will become more and more important as the size of the world population continues to increase. Photosynthetic cells can be used for food applications in various innovative forms, e.g., as a substitute for the fish proteins in the diet supplied to carnivorous fish or perhaps—after acid hydrolysis—as a complex, animal-free serum for growth of mammalian cells in vitro.     

The role of forest residues in the accounting for the global warming potential of bioenergy

Bioenergy makes up a significant portion of the global primary energy pie, and its production from modernized technology is foreseen to substantially increase. The climate neutrality of biogenic CO₂ emissions from bioenergy grown from sustainably managed biomass resource pools has recently been questioned. The temporary change caused in atmospheric CO₂ concentration from biogenic carbon fluxes was found to be largely dependent on the length of biomass rotation period. In this work, we also show the importance of accounting for the unutilized biomass that is left to decompose in the resource pool and how the characterization factor for the climate impact of biogenic CO₂ emissions changes whether residues are removed for bioenergy or not. With the case of Norwegian Spruce biomass grown in Norway, we found that significantly more biogenic CO₂ emissions should be accounted towards contributing to global warming potential when residues are left in the forest. For a 100‐year time horizon, the global warming potential bio factors suggest that between 44 and 62% of carbon‐flux, neutral biogenic CO₂ emissions at the energy conversion plant should be attributed to causing equivalent climate change potential as fossil‐based CO₂ emissions. For a given forest residue extraction scenario, the same factor should be applied to the combustion of any combination of stem and forest residues. Life cycle analysis practitioners should take these impacts into account and similar region/species specific factors should be developed.     

Terrestrial carbon‐cycle feedback to climate warming: experimental evidence on plant regulation and impacts of biofuel feedstock harvest

Feedback between global carbon (C) cycles and climate change is one of the major uncertainties in projecting future global warming. Coupled carbon–climate models all demonstrated a positive feedback between terrestrial C cycle and climate warming. The positive feedback results from decreased net primary production (NPP) in most models and increased respiratory C release by all the models under climate warming. Those modeling results present interesting hypotheses of future states of ecosystems and climate, which are yet to be tested against experimental results. In this study, we examined ecosystem C balance and its major components in a warming and clipping experiment in a North America tallgrass prairie. Infrared heaters have been used to elevate soil temperature by approximately 2 °C continuously since November 1999. Clipping once a year was to mimic hay or biofuel feedstock harvest. On average of data over 6 years from 2000 to 2005, estimated NPP under warming increased by 14% without clipping (P<0.05) and 26% with clipping (P<0.05) in comparison with that under control. Warming did not result in instantaneous increases in soil respiration in 1999 and 2000 but significantly increased it by approximately 8% without clipping (P<0.05) from 2001 to 2005. Soil respiration under warming increased by 15% with clipping (P<0.05) from 2000 to 2005. Warming‐stimulated plant biomass production, due to enhanced C₄ dominance, extended growing seasons, and increased nitrogen uptake and use efficiency, offset increased soil respiration, leading to no change in soil C storage at our site. However, biofuel feedstock harvest by biomass removal resulted in significant soil C loss in the clipping and control plots but was carbon negative in the clipping and warming plots largely because of positive interactions of warming and clipping in stimulating root growth. Our results demonstrate that plant production processes play a critical role in regulation of ecosystem carbon‐cycle feedback to climate change in both the current ambient and future warmed world.     

Recent advances in membrane technologies for biorefining and bioenergy production

The bioeconomy, and in particular, biorefining and bioenergy production, have received considerable attention in recent years as a shift to renewable bioresources to produce similar energy and chemicals derived from fossil energy sources, represents a more sustainable path. Membrane technologies have been shown to play a key role in process intensification and products recovery and purification in biorefining and bioenergy production processes. Among the various separation technologies used, membrane technologies provide excellent fractionation and separation capabilities, low chemical consumption, and reduced energy requirements. This article presents a state-of-the-art review on membrane technologies related to various processes of biorefining and bioenergy production, including: (i) separation and purification of individual molecules from biomass, (ii) removal of fermentation inhibitors, (iii) enzyme recovery from hydrolysis processes, (iv) membrane bioreactors for bioenergy and chemical production, such as bioethanol, biogas and acetic acid, (v) bioethanol dehydration, (vi) bio-oil and biodiesel production, and (vii) algae harvesting. The advantages and limitations of membrane technologies for these applications are discussed and new membrane-based integrated processes are proposed. Finally, challenges and opportunities of membrane technologies for biorefining and bioenergy production in the coming years are addressed.     

Perspectives and advances of biological H2 production in microorganisms

The rapid development of clean fuels for the future is a critically important global challenge for two main reasons. First, new fuels are needed to supplement and ultimately replace depleting oil reserves. Second, fuels capable of zero CO₂ emissions are needed to slow the impact of global warming. This review summarizes the development of solar powered bio-H₂ production processes based on the conversion of photosynthetic products by fermentative bacteria, as well as using photoheterotrophic and photoautrophic organisms. The use of advanced bioreactor systems and their potential and limitations in terms of process design, efficiency, and cost are also briefly reviewed.     

Lignocellulose Biotechnology: Current and Future Prospects

Abstract

Lignocellulose is the most abundant biomass available on Earth. It has attracted considerable attention as an alternate feed stock and energy resource because of the large quantities available and its renewable nature. The potential uses of lignocelluloses are in pulp and paper industries, production of fuel alcohol and chemicals, protein for food, and feed using biotechnological means. The current industrial activity of lignocellulosic biomass fermentation is limited mainly because of the difficulty in economic bioconversion of these materials to value-added products. Considerable improvement in many processes related to lignocellulose biotechnology appeared during the last decade. Current uses of lignocellulosic biomass, process constraints, and areas of future research are discussed here.     

Energy requirements and environmental impacts associated with the production of short rotation willow (Salix sp.) chip in Ireland

Willow Salix sp. is currently cultivated as a short rotation forestry crop in Ireland as a source of biomass to contribute to renewable energy goals. The aim of this study is to evaluate the energy requirements and environmental impacts associated with willow (Salix sp.) cultivation, harvest, and transport using life cycle assessment (LCA). In this study, only emissions from the production of the willow chip are included, end‐use emissions from combustion are not considered. In this LCA study, three impact categories are considered; acidification potential, eutrophication potential and global warming potential. In addition, the cumulative energy demand and energy ratio of the system are evaluated. The results identify three key processes in the production chain which contribute most to all impact categories considered; maintenance, harvest and transportation of the crop. Sensitivity analysis on the type of fertilizers used, harvesting technologies and transport distances highlights the effects of these management techniques on overall system performance. Replacement of synthetic fertilizer with biosolids results in a reduction in overall energy demand, but raises acidification potential, eutrophication potential and global warming potential. Rod harvesting compares unfavourably in comparison with direct chip harvesting in each of the impact categories considered due to the additional chipping step required. The results show that dedicated truck transport is preferable to tractor‐trailer transport in terms of energy demand and environmental impacts. Finally, willow chip production compares favourably with coal provision in terms of energy ratio and global warming potential, while achieving a higher energy ratio than peat provision but also a higher global warming potential.     

Belowground responses of <Emphasis Type="Italic">Picea asperata</Emphasis> seedlings to warming and nitrogen fertilization in the eastern Tibetan Plateau

The impacts of global climatic change on belowground ecological processes of terrestrial ecosystems are still not clear. We therefore conducted an experiment in the subalpine coniferous forest ecosystem of the eastern edges of the Tibetan Plateau to study roots of Picea asperata seedlings and rhizosphere soil responses to soil warming and nitrogen availability from April 2007 to December 2008. The seedlings were subjected to two levels of temperature (ambient; infrared heater warming) and two nitrogen levels (0 or 25 g m⁻²year⁻¹ N). We used a free air temperature increase from an overhead infrared heater to raise both air and soil temperature by 2.1 and 2.6°C, respectively. The results showed that warming alone significantly increased total biomass, coarse root biomass and fine root biomass of P. asperata seedlings. Both total biomass and fine root biomass were increased, but coarse root biomass was significantly decreased by nitrogen fertilization and warming combined with nitrogen fertilization. Warming induced a prominent increase in soil organic carbon (SOC) and NO₃ ⁻-N of rhizosphere soil, while nitrogen fertilization significantly decreased SOC and NH₄ ⁺-N of rhizosphere soil. The warming, fertilization and warming × N fertilization interaction decreased soil microbial C significantly, but substantially increased soil microbial N. These results suggest that nitrogen deposition combined with warmer temperatures under future climatic change possibly will have no effect on fine root production of P. asperata seedlings, but could enhance the nitrification process of their rhizosphere soils in subalpine coniferous forests.     

An Indian scenario on renewable and sustainable energy sources with emphasis on algae

India is the fifth largest primary energy consumer and fourth largest petroleum consumer after USA, China, and Japan. Despite the global economic crisis, India’s economy is expected to grow at 6 to 8?%/year. There is an extreme dependence on petroleum products with considerable risks and environmental issues. Petroleum-derived transport fuels are of limited availability and contribute to global warming, making renewable biofuel as the best alternative. The focus on biogas and biomass-based energy, such as bioethanol and biohydrogen, will enhance cost-effectiveness and provide an opportunity for the rural community. Among all energy sources, microalgae have received, so far, more attention due to their facile adaptability to grow in the photobioreactors or open ponds, high yields, and multiple applications. Microalgae can produce a substantial amount of triacylglycerols as a storage lipid under photooxidative stress or other adverse environmental conditions. In addition to renewable biofuels, they can provide different types of high-value bioproducts added to their advantages, such as higher photosynthetic efficiency, higher biomass production, and faster growth compared to any other energy crops. The viability of first-generation biofuels production is, however, questionable because of the conflict with food supply. In the future, biofuels should ideally create the environmental, economic, and social benefits to the communities and reflect energy efficiency so as to plan a road map for the industry to produce third-generation biofuels.