Four of the nine planetary boundaries (Planetary Boundaries 2.0) defined by a global alliance of scientists as deleterious to Planet Earth, have already been crossed; namely the thresholds in the areas of climate change, biodiversity, land use and biogeochemical cycles. Biomass has a role to play in all four of these areas. In this context, scientists at the Universities of Stuttgart and Tübingen are investigating how biomass should be classified and assessed at the regional level. The researchers’ work is part of a project called “Indicators for the Utilisation of Biomass Baden-Württemberg 2.0” that will be funded by the Baden-Württemberg government for three years and will help improve the utilisation of biomass in the future.

Project manager Dr. Ludger Eltrop from the Institute for Energy Economics and Rational Energy USE (IER) at the University of Stuttgart explains why this is so important. "Over the last 15 years, major priority has been put on using biomass for the generation of energy - high compensation levels for growing renewable raw materials that can be used for energy generation have been a clear incentive for this. Current focus needs to shift to developing the use of biomass in a slightly different way, raising awareness of the material use of biomass and establishing a good balance between using biomass for material and energetic purposes. The potential of biomass - especially for material use - has not yet been fully exploited. The focus needs to be on achieving a stable balance."

Care must be taken to quantify material and energy utilisation paths as comprehensively as possible in order to be able to evaluate the utilisation of biomass more efficiently. The project team has defined economic, ecological and social key indicators. This is where the project partners led by Prof. Dr. Thomas Potthast from the International Centre for Ethics in the Sciences and Humanities (IZEW) at the University of Tübingen become involved. "The IZEW complements the quantitative analyses carried out by the Stuttgart researchers. The project partners from Tübingen deal with and evaluate the work from an ethical perspective, examining, for example, whether sustainability issues are given adequate consideration,” says Eltrop. When can a product in the biomass chain be called sustainable? The difficulty of answering this question becomes obvious when the overall context is taken into account. Using maize instead of petroleum for plastic production could potentially reduce the quantity of greenhouse gases. However, excessive maize cultivation has a negative effect on biodiversity. The project partners from Tübingen and Stuttgart aim to jointly shed light onto these issues.

The team from Stuttgart brings its skills in life-cycle analyses to the project. “The holistic approach of looking into the life cycle of a product is a good starting point, but is in no way comprehensive. We have subjectively chosen just a few categories to look at in order to make the whole venture manageable,” says Eltrop. Natalia Matiz Rubio from the IER is working on the project as part of her doctoral thesis and explains the approach taken by the researchers from Stuttgart University: "We are looking at economic, ecological and social indicators. But we are looking at them in combination rather than separately. We are particularly concentrating on environmental aspects. We are defining environmental impact indicators based on the critical biophysical processes that correspond to the environmental boundaries.” The material and energetic pathways will also be evaluated in combination rather than separately.

Matiz Rubio illustrates this "cascade use" with a case study on the utilisation of maize: “One of the issues that we are investigating is the effects of grain maize when used as raw material for plastic and when used as raw material for bioethanol production. We also take into account the effects of the disposal or combustion of plastic and when the combustion of plastic generates energy.” With both material and energetic products at the end of the chain, the scientists always take into account substitution issues. Eltrop comments: “We examine which products, both simple and valuable, are substituted in the process chains. Pathways can also be connected with side paths, which means that we are also examining the “biorefinery” approach which focuses on the use of all individual biogenic raw material components.” Using maize once again as example, the energetic use of biomass is a relatively simple chain whereas processing maize into plastics in a cascade process would be associated with high added value.

It is now around six months before the project ends, and the scientists have already worked on some utilisation pathways to the extent that they can be evaluated. Although not all indicators have yet been evaluated, Matiz Rubio cites one example that shows that CO₂ equivalents have the potential to be used as performance indicators for climate change. “The energetic use of maize is a simple chain and must be regarded as rather negative. Only power, heat and fuels can be substituted. In contrast, maize used for producing plastics has a positive balance, as this pathway also enables plastics to be substituted with other materials.”

Further indicators, e.g. nitrogen equivalents as indicators of eutrophication, are still in the pipeline for a variety of biomass utilisation pathways. In order to be able to make comparative statements, the team is also pursuing an approach that involves monetarising environmental effects, although this method has its limitations. All units or equivalents are converted into a monetary unit, namely the euro. As far as the selection of indicators is concerned, statements can be made on which of the utilisation pathways examined are better for certain agricultural raw materials such as maize. Such evaluations provide a solid basis for decision recommendations in government, business and research, with the overall goal of making biomass utilisation and a biobased economy more efficient.