- Christian Zörb &
- Iris Lewandowski
Biobased resources are all resources containing non-fossil, organic carbon, recently (<100 years) derived from living plants, animals, algae, microorganisms or organic waste streams. These are summarized in the term “biomass”. This section describes the formation of biomass through the process of photosynthesis. Biobased resources can be classified and characterized according to their origin (e.g. plant, animal) and the sector (agriculture, forestry or waste) in which they are produced. However, for the integration into specific biobased product chains, the most relevant classification of biomass is according to its major component, i.e. starch, sugar, lignocellulose, oil or protein.
There are various options for tailoring biomass properties to user demands. This section considers breeding, green biotechnology and genetic engineering. Synthetic biology uses the tools of genetic engineering and biotechnology to construct completely new functional units or systems with desired properties. The bioeconomy also makes use of biological knowledge, described here as the combination of biological data and its interpretation, often by means of bioinformatics, and the understanding of naturally occurring mechanisms (bionics).
Biomass; Biomass production; Biobased resources; Biomass use; Plant modification
After studying this chapter, you should:
Understand the process of biomass formation.
Be able to characterize the resource base of the bioeconomy.
Have gained an overview of techniques to design biomass characteristics.
Understand the concept of biological knowledge.
Biomass Concepts: Different Perspectives
The concept of biomass was introduced in the year 1927 by a publication of the German zoologist Reinhard Demoll (1882–1960): “By biomass we term the quantity of substance in living organisms per unit of surface or volume” (Demoll 1927). Currently, there is no consensus on the general definition of “biomass”. A simple and widely used biological definition is “organic matter derived from living, or recently living organisms”. This definition may be too broad to be of use as an exact definition for this bioeconomy textbook. Let us focus on different perspectives of what constitutes biomass. Even in ecology, there is no standard definition of biomass. One reason is that biomass changes as organisms interact with each other and with their abiotic environment. Instead, a colourful variety of ecological biomass concepts exists side by side.
A Biologist’s Perspective
When considering the term “biomass”, a biologist would first think of carbohydrates (e.g. starch, sugar), proteins (e.g. storage proteins from grains), fats and oils (e.g. from oil seeds) and other secondary plant compounds. These substances are secondary metabolites of (plant) tissue, many examples of which can be found in biochemistry textbooks. Primary plant metabolites are compounds produced from the sugars formed by photosynthesis and used for metabolism. By contrast, secondary metabolites are not involved in primary metabolism but are responsible, for example, for the structure and functioning of a cell or organism. Higher plants probably build around 100,000–150,000 different secondary compounds including a diverse range of proteins, sugars, sugar alcohols, vitamins, fats, oils, amino acids, organic acids, nucleic acids, phenolic compounds, odours, pigments, etc. There are many interesting substances within these classes that may be (re)discovered in the bioeconomy as valuable compounds for polymer chemistry or possibly even pharmacy.
A Chemist’s Perspective
A chemist would like to see a molecular formula to describe carbohydrates, proteins, fats and other secondary substances showing the chemical elements incorporated by autotrophs (see Fig. 5.1 and section “Photosynthesis”) together with an amount of binding energy. However, unfortunately, there is no chemical formula for the general definition of biomass. Physicists or agronomists may calculate the energy value of a certain biomass fraction, from a maize field, for example, using an equation for the heating value of biomass based on its components, but this is also only part of the “what is biomass” story.
A Technologist’s Perspective
Technologists see biomass as a source of energy. Therefore, they mostly think of plant-based materials not used for food or feed applications, specifically lignocellulosic biomass. Although technical biomass definitions include only biotic substances that can be used as energy sources, a number of different energy-related biomass terms and definitions still exist. Biomass can be used for energy either directly via combustion to produce heat or indirectly after conversion to various forms of biofuel. There are several methods of converting biomass into biofuels, and these are broadly classified into thermal, chemical and biochemical methods (see Chap. 7 for description of conversion technologies).
Our Definition of Biomass
In Sect. 2.2, biobased resources were defined as all resources containing non-fossil, organic carbon, recently (<100 years) derived from living plants, animals, algae, microorganisms or organic waste streams. These are summarized in the term “biomass”. Biomass can be further defined as plant or animal tissue or tissue-based material, microorganisms and the substances produced from them as well as organic molecules (primarily) formed by (photosynthetic) organisms such as carbohydrates (e.g. sugars), proteins, fats, fibre, vitamins and other secondary plant metabolites. This includes edible biomass, such as starch-, sugar- and oil-rich biomass and nonedible lignocellulosic biomass from dedicated crop production, residues and organic wastes. Today, the term “biomass” is most frequently used to refer to organic material utilized for energy production and other nonfood applications such as the production of biogenic materials and chemicals. In the following text, we use a more general definition of biomass, which includes edible as well as nonedible organic material.
1.1 Biomass: Its Origin and Characterization
Primary production is the process that directly or indirectly supports virtually all life on Earth. Primary biomass is formed by the conversion of carbon dioxide (CO2) and water through the autotrophic processes of photosynthesis (performed by plants and green algae) and chemosynthesis (performed by some microorganisms). Of these two processes, photosynthesis is the more important. In this process, autotrophic organisms take up CO2 and water and convert them into carbohydrates with the help of light energy (photons). Thus, light energy is converted into chemical energy through the integration of carbon (C) into the organism’s substance (assimilation). The final products of photosynthesis are C6 sugars (hexoses) and oxygen. Figure 5.1 shows the chemical equation summarizing the complete process.
Glucose is used as a resource in internal plant biochemical processes to form various other molecules through subsequent biochemical reactions, which also incorporate macro- and micronutrient elements into the plant substance. It is estimated that plants can build up around 100,000–150,000 different chemical substances, many of which have not yet been identified but could be interesting in a future bioeconomy. However, not all of these substances are available in sufficiently high quantities or concentrations. Biotechnological methods may make it possible to increase the production and concentration of target molecules by plants and microorganisms.
The first step in biomass formation is the absorption of light by the chlorophyll molecule. Photosynthetic electrons are used for the assimilation of CO2 and the formation of carbohydrates such as sugars in plant cells. However, not all absorbed energy electrons can be converted to chemical energy in the form of sugars. There are energy losses in the process of photosynthesis, for example, the heat produced by metabolism, and energy consumption through photorespiration and other processes such as the Mehler reaction (for further information, see Taiz et al. 2015). Therefore, the maximal efficiency of photosynthesis is estimated to be about 12%. However, this is a theoretical maximum (Radmer and Kok 1977) that can never be achieved by a growing crop, even if all adverse factors such as disease, predation, inadequate inorganic nutrient supply and suboptimal water supply are mitigated. Wilhelm and Selmar (2011) calculated a conversion efficiency of photosynthetic energy into biomass of only about 8% (Fig. 5.2).
Given the above-mentioned energy losses in biomass formation, it is of vital importance that available biomass is used as efficiently as possible. Here, three approaches for efficient biomass production and use are suggested:
Focusing on the production of valuable (biochemical) substances by plants and algae. An effective strategy would be the production of valuable organic substances (such as glycolate, omega-3 fatty acids, lutein) by algae. Microalgae in particular have a higher photosynthetic efficiency because the light absorption of small algal cells (unicellular algae) is generally better than that of larger algae.
Supporting the efficiency of crop production through optimal crop management, improved harvest technologies and the avoidance of biomass losses in the supply chain (see Sect. 6.1).
Applying breeding and biotechnological methods to supply varieties that make optimal use of factors necessary for growth and that are tailored to the production of specific products (e.g. metabolites, proteins) at high concentrations in the biomass.
All biological material (or biomass) is essentially derived from inorganic molecules or ions that are assimilated into the biological tissue of autotrophic (primary) organisms (plants and microorganisms) through photosynthetic or chemosynthetic processes. Organisms that perform primary production are called “autotrophs” because they are self-feeding and use light as an energy source. In the process of photosynthesis, they take up CO2 and convert it into chemical energy with the help of sunlight. These organisms provide the basis for secondary biological organisms, i.e. heterotrophs. Heterotrophs (animals, humans, fungi, most bacteria) rely on the consumption of either the products of autotrophs or whole autotrophic organisms.
Biomass is formed primarily from carbon (C), oxygen (O) and hydrogen (H) (Fig. 5.1). These are assimilated from air and water. In addition, mineral macronutrients are essential for plant growth and development and thus biomass formation. The main macronutrients necessary for the production of biomass by primary organisms are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). These elements are also the major components of plant fertilizers, mostly in the form of ammonium, nitrate, urea, phosphate and potassium salts. Further important elements are the so-called plant micronutrients, which are essential but only in very small quantities—mostly at concentrations three orders lower than that of macronutrients. They include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl) and nickel (Ni). Other elements that can be beneficial for plant growth in niche environments are silicon (Si), cobalt (Co), selenium (Se) and sodium (Na) (Fig. 5.3).
Biomass resources can be classified according to their origin, i.e. whether they come from plants, animals or microorganisms. Not only the requirements for their production (see Sects. 6.1.9, 6.1.10 and 6.4) are different but also the characteristics of their products. This is not only relevant from a processing point of view but also from an ethical point of view, for example, meat is not an “acceptable” biomass for vegetarians.
Biomass resources can also be classified according to the sector in which they are produced, e.g. as agricultural, forestry or waste biomass (Fig. 5.4). The biomass supply chains in each sector vary from a practical point of view. But also from an ethical point of view, it makes a difference whether biomass has been classified as waste or whether it comes from the agricultural sector. The use of waste biomass is generally considered beneficial, whereas agricultural biomass has the primary task of producing food. In the latter case, a careful decision needs to be made on the best use of the biomass to avoid competition with food supply. The energetic use of edible biomass, such as vegetable oil, for the production of biofuels has received particular criticism. For this reason, biomass is also classified into “edible” and “nonedible” in terms of suitability for human consumption.
The most relevant classification of biomass for its integration into specific biobased product chains is according to its major component, i.e. starch, sugar, lignocellulose (lignin + cellulose + hemicellulose), oil or protein (Table 5.1). All of these contain mainly C, H and O. Only proteins, being a combination of different amino acids, also contain N and some contain S (Table 5.1).
Figure 5.5 shows the major components of different biomasses. These vary considerably between lignocellulosic biomasses (such as wood and straw), starch-rich biomasses (e.g. wheat grain), oil-rich biomasses (e.g. rape seed), sugar-rich biomasses (e.g. sugar beet) and protein-rich biomasses (e.g. pig meat and fish).
Finally, biomass can also be characterized according to its physical conditions into “wet” and “dry” or “solid” and “liquid” biomass. The physical properties of biomass determine the requirements for its harvest, transport, storage and processing (see Sect. 7.3). Generally, wet biomass is more perishable than dry biomass. It requires a higher transport effort (because more water is transported) and additional processing before storage, such as drying or ensiling (e.g. maize is ensiled for feed and biogas applications).
Global Biomass Use
Currently, it is estimated that about 11.4 billion tonnes of biomass are produced annually on agricultural land and from forests. Of this, 18% stems from wood, 40% from agricultural production, 30% from pasture and 12% are by-products (FAOSTAT 2014; Raschke and Carus 2012). The largest part of this biomass is comprised of cellulose (5.62 billion tonnes, 49%). Other important biomass feedstocks are sugar/starch (2.63 billion tonnes, 23%), protein (1.23 billion tonnes, 12%) and fat (0.51 billion tonnes, 4%) (FAOSTAT 2014; nova Institut 2015). About three quarters of the total biomass produced by agriculture is used as feed to produce 115, 90 and 60 million tonnes of pig, chicken and cattle meat, respectively, and 640 million litres of milk (Fig. 5.6).
1.2 Techniques for Improving or Designing Biomass Characteristics
Humans started to cultivate plants as they began to settle about 10,000 years ago. It was beneficial for them to have food stored throughout the whole year, to consume when less or no freshly produced food was available. This enabled them to survive in unfavourable climates where naturally grown plant-based food was only available in a particular season. Early farmers already started breeding wild plants and selecting the genotypes with the best performance in terms of high yield, non-shedding seeds and resistance to biotic and abiotic stress (e.g. drought). They developed many of our most important plants, such as wheat, maize (corn), rape and rice. Today, breeding is still the most important prerequisite for sufficient and sustainable food production.
Breeding is the improvement of crop varieties and animal breeds—in terms of yield, resistance to pests and diseases, fertility, product quality or adaptation to different production conditions—through breeding methods. These are classified as either “conventional” or “genetic engineering” methods. Conventional breeding seeks to provide improved varieties or breeds by selection and directed crossing. Genetic engineering (or genetic modification) uses biotechnological techniques to alter the genome (genetic material) of the organism.
Biotechnology is “any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use” (UN Convention on Biological Diversity, Art. 2). Green biotechnology is the application of such techniques in agricultural processes. An example is the use of genetic engineering methods to design transgenic plants able to grow in particular environments characterized by the presence (or absence) of specific (bio)chemicals.
Genetically modified organisms (GMOs) are organisms that have had their genomes altered, either in a way that does not occur naturally or in a natural but accelerated way. To produce a GMO, specific characteristics can be changed using laboratory-based techniques to delete or alter particular sections of DNA (deoxyribonucleic acid, contains the genetic information, e.g. genes, regulatory elements). An organism’s characteristics can also be changed by introducing new pieces of DNA into its genome. These can originate from the same or another, non-related species. The latter results in a transgenic organism, i.e. one that contains genes from a different species. Breeding progress is usually faster and more specific when biotechnological methods are used.
GM techniques can be applied to crops to modify the chemical structure of polymers such as starch, lignin or other fibres. The modification of proteins or metabolites for use in the chemical industry, building industry or in pharmacy is also possible. The use of plant-based antibodies to human or animal diseases has been applied in practice for two decades. The advantage of using GM crops for pharmaceutical purposes is that the agents can be produced in greenhouses or fermenters, and official regimentation is much lower than for field trials. Most varieties of a number of major crops, including soybean, maize and cotton, commonly grown in the USA, Brazil, China, India or elsewhere, have been genetically modified. However, GM crops are usually not well accepted by the general public, and, in Europe, their production in the field is highly restricted. In addition, GMO production is not permitted in organic agriculture. The recently developed gene-editing method CRISPR/Cas9 used in plant breeding is a biotechnical method for cutting out (knocking out) genes without leaving a trace or for specifically altering or adding genes or gene pieces in order to introduce the desired properties. The status of crop varieties produced by this method is the subject of current discussion. The question arises whether these organisms should still be considered genetically modified if only parts of the genes have been cut out or altered without introducing genetic material from other organisms or if genetic material from other species was only temporarily introduced for intermediate breeding steps (e.g. early flowering in trees) and then removed again.
Breeding and genetic modification can be categorized according to the nature of the conferred traits. Input traits are those that affect crop performance without changing the nature of the harvested product. Examples include resistance to pests, viruses, bacteria, fungi or insects, tolerance to abiotic stresses (e.g. soil-borne metals, salinity, drought, heat) and a higher nutrient use efficiency resulting in higher yields of biomass or target products.
Output traits change the quality of the crop product itself, e.g. by altering the starch, protein, vitamin or oil composition to improve the nutritional value. This may be, for example, through an increase in vitamins, omega-3 fatty acids or antioxidants, a decrease in saturated fats or an improved amino acid balance. Other output-trait-related targets include an enhanced level of essential minerals (Fe, Zn), the elimination of allergenic proteins, improved taste, longer shelf life and the introduction of novel food products. Output traits may also focus on the (small-scale) production of biomass for biopharming, sold at premium price.
1.3 Biological Knowledge
The discipline of biology was established around 1800 as the “science of life”. Biological research produces large sets of data on different scales, ranging from genetic information to biodiversity and the interactions between species, landscapes and climates. Biological knowledge is the combination of biological data and the interpretation of its meaning. Traditionally, such data were interpreted by a person; however, today the interpretation of large-scale data sets is only possible with the help of computers due to the sheer volume of data. This is mostly done by bioinformatics—the use of computational and mathematical techniques to store, manage and analyse biological data (Kaminski 2000). A major area of bioinformatic application is the analysis of DNA and protein sequences and structures in order to characterize the linked functions. The term “omics data” is also used to refer to this type of bioinformation. There are data available for genomics, proteomics, metabolomics, ionomics and several other -omics. The term “big data” is also used for large quantities of biological data but can also be applied to other areas than genetic information, such as data for analysing human health and interactions with various factors including nutrition and the environment. Omics data are often used for breeding purposes, e.g. for the identification of genes that code for important traits such as crop resistance to pathogens, and animal health or quality parameters. Big data sets can be used, for example, to describe the pharmacological relevance of particular substances, e.g. those produced by plant cultures, either GM or conventional. This is of great value for a knowledge-driven, biobased economy because it can help to provide practical information for developments in medicinal or food crop production. An example is the use of biobased genomic data for the design of a plant-tissue-based antibody (immune globulin) for the treatment of cancer. For this purpose, the binding specificity of the antibody to its target was calculated from a bioinformatic-based data set (genomic and proteomic data). The designed gene sequence for the antibody was then introduced into tobacco cell culture in fermenters, where the protein (i.e. the antibody) was expressed (for further details, see Ma et al. 2005).
Biological knowledge also includes the understanding of naturally occurring mechanisms (bionics). A prominent example is the so-called lotus effect. This describes the self-cleaning properties of the lotus plant (Nelumbo nucifera) that results from the ultrahydrophobicity of its leaves. Technical application of this mechanism is used for paints, coatings, roof tiles, fabrics and other surfaces that can stay dry and clean themselves. Biologization is the integration of such natural concepts into economic development, the application of biological and life science innovations and the development of products and solutions by means of life sciences. Biologization and digitalization (seen in the example of bioinformatics above) are often considered as convergent and potentially synergetic processes.
Synthetic biology goes beyond the application of existing biological mechanisms and knowledge. It uses the tools genetic engineering and biotechnology to construct completely new, not naturally occurring biological functional units or systems with desired properties or remodel existing biological systems for new tasks (Kircher et al. 2017). For example, recent technological advances have enabled scientists to produce new sequences of DNA from scratch. Through the application of modern engineering principles and the use of computers and chemicals, organisms can be designed that are suitable for technical purposes, for example, the direct production of biofuels or precursor chemicals for pharmaceutical drugs. Synthetic biology offers new opportunities in the bioeconomy, e.g. for the supply of products that cannot be produced economically by chemical processes or for which there are no natural synthesis methods (Kircher et al. 2017).
What are the major resources used in the bioeconomy?
How can biological knowledge be applied?
Describe the energy balance of biomass production through the process of photosynthesis.
Which plant nutrients are important for biomass formation?
Which input and output traits are relevant for plant modification?