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Bioeconomy as a residue utilisation strategy

Every day we read in the newspaper that we are wasting precious resources such as oil, coal or natural gas without being sufficiently aware of their finiteness and associated consequences. With the bioeconomy, a promising idea seems to be emerging, showing how resources of plant, animal and microbial origin can become part of resource management and how they might be able to replace some of our remaining fossil reserves. A bioeconomy is the introduction of a biobased economy and the promise of sustainably manufactured goods. The head of the Institute of Forest Utilisation at the University of Freiburg, Prof. Dr. Gero Becker, examines the efficiency and sustainability of the provision of timber and forestry products, and focusses on the issue as to how wood residues can be industrially recycled.

Motor-manual timber harvesting in a deciduous forest. © Christian Suchomel, University of Freiburg

Researchers around the world are pondering about optimal biomass production and which plants are suitable for what purpose. Normally, one associates the term “biomass” with agricultural crops. “Many discussions focus on whether the use of agricultural land for bioeconomic, i.e. non-nutritional, purposes are in contradiction with food security measures,” says Becker, who proposes two strategies to mitigate this conflict. One involves the use of residual materials, i.e. not the corn itself, but the maize straw or coconut processing residues, and the second involves the use of woody plants, i.e. plants that are not used for the production of food. Since humans cannot digest wood, woody plants are a cheap raw material source that is not in competition with food production. However, wood is already used for a broad range of applications, in construction and for the production of furniture and paper. 

Wood – one of nature’s smart inventions

Traditional way of storing logs for the production of firewood. © Christian Suchomel, University of Freiburg

“Trees are frugal and can colonise larger areas than crop plants,” Becker explains. “But there is a natural limit in terms of productivity; trees do not grow in the sky.” In the final analysis, forest production is always in competition with food production. A hectare of land can only be used for the production of one or the other. Land that is used for growing trees cannot be used for growing corn. 

Wood is difficult to use in industrial applications due to its chemical composition. The molecular constituents of wood that give trees their durability and rigidity can only be isolated using complex methods. “Nature is relatively clever,” says Becker. “She has invented cellulose and lignin molecules in such a clever way that it is difficult to break them down without destroying their good properties.” Therefore, biotechnological methods for breaking down wood into its molecular constituents need to be far more sophisticated than those used for sugar or starch derived from agricultural crops. Nevertheless, lignin and cellulose have huge potential as they can be used for the production of plastics-like durable products. Technical methods that are suitable for breaking down wood and thus isolate and produce nanocellulose for bioeconomic applications are still in the research stage and are not yet applicable on the industrial scale. 

Where do we get the raw material from?

Sawmill residues used as the basis for pellet production. © Dr. Benjamin Engler, University of Freiburg

Large-scale production implies that large quantities of raw materials are needed. “As far as biomaterials are concerned, the use of large quantities always implies that the material needs to be collected from distant places,” Becker says. Concepts that involve the collection of wood from German forests for use in refineries have to take into consideration the need for large areas where, however, saw- and paper mills also get the wood for the production of timber and paper from. So the question is: is there any wood left for the bioeconomy? “It seems cheaper to transport wood chips by boat from Brazil or the USA than to collect or bundle brushwood in Germany,” says Becker. A sharp contrast appears to be emerging between ideology and economic reality and the contrast becomes even more striking if the price of wood, including transport costs, is taken into account.

“If we say that the shift from a fossil-based to a biobased economy requires cheap raw materials which can be turned into a great product with high technological effort, this certainly does not apply to wood. The price of wood is just too high,” says Becker pointing out that although large quantities of wood are available, the harvesting, transport and delivery costs would be far too high and would not leave any margin for paying for the actual material. What if the material is not from the local region, but is imported from far-off countries? What about the ecological consequences and hence the bioeconomy? “As far as the supply of raw materials is concerned, making the bioeconomy sustainable is a huge challenge,” Becker says. “The calculations must be very accurate. Otherwise we will produce skewed results and life cycle assessments would later end up being much worse than initially expected.”

Special applications instead of mass application

Harvest on a short-rotation plantation. © Dr. Janine Schweier, University of Freiburg

One of Becker’s research topics involves examining and improving the sustainability of wood provision. His major concern is the development of cost- and energy-efficient harvesting methods with the least possible impairment of soil, water and biodiversity. Does he see a possibility that this may happen despite the conflict between ideology and economic reality? “There are no absolute answers,” Becker says.

One issue is the order of magnitude of the methods used in a bioeconomy. “It will not be so much about replacing mass products, but more about special applications in which the biomaterial used has a qualitative and ecological advantage over other materials,” says Becker. “There are applications that are very attractive and lucrative, but that do not necessarily involve large quantities.” Nanocellulose such as that produced by Prof. Marie-Pierre Laborie's Forest Biomaterials group at the University of Freiburg is one such example. Nanoscale cellulose fibres are a new development with numerous applications. They can be mixed with plastics or added to paper, thereby reinforcing the resulting materials and giving them a high tensile strength. 

The reservation of marginal soils for the cultivation of fast-growing trees such as poplars and willows is one approach for expanding the raw materials base. Marginal land, which often has poor soil and is found at the edge of desolate areas, is unsuitable for the profitable production of food crops. In fact, it would not be ethically problematic to use this marginal land in Germany for bioeconomic purposes. Short-rotation plantations have already been established on such land, in particular in northeast Germany.

The second strategy relates to the intensive use of residuals. Using wood chips, sawdust and bark that arise in sawmills as a byproduct of timber production for bioeconomic purposes is quite a promising approach. Sweden already appears to be reacting to the decline in the consumption of print media: “Swedish paper mills are equipping their facilities with bioeconomy departments in which residual materials are used for the manufacture of bioeconomic products,” Becker said highlighting that part of the energy required for the chemical digestion of wood has already been invested. “Concepts which involve such cascade use are ecologically and economically sustainable,” concludes Becker. 

Further information:
Prof. Dr. Gero Becker
Institute of Forest Utilisation and Work Science
University of Freiburg
Werthmannstr. 6
79085 Freiburg
Tel.: +49 (0)761/203 - 3771
E-mail: gero.becker(at)fobawi.uni-freiburg.de

Website address: https://www.biooekonomie-bw.de/en/articles/news/bioeconomy-as-a-residue-utilisation-strategy