Plastic and sustainable bioeconomy - How does that fit?

BioSC International Summer School 2023
May 8-12, 2023
RWTH Aachen | Forschungszentrum Jülich

The BioSC International Summer School 2023 took place from 8-12 May at the Invention Center Aachen with participants from all over the world and lecturers from a wide range of disciplines. Numerous aspects of the topic of plastics were highlighted, from the extraction of various monomers from different bio-based resources, through polymerisation, to the degradation of the polymers and the recycling of the monomers with chemical and biological systems. The problem of plastic as waste in the environment, in waste water and in waste disposal systems was also addressed.

Programme

The Summer School started on Monday with a comprehensive introduction by Prof. Lars Blank and Prof. Nick Wierckx. Lars Blank's sentence: "If you use plastic, you will lose plastic" outlined the basic problem: The recycling rate of plastic is far too low and huge amounts end up uncontrolled in the environment. Pure plastic waste can be reused, but plastic mixtures are still problematic. Nick Wierckx pointed out that plastics are polymers and that the degradation of polymers by biological systems is generally possible, as the examples of cellulose and lignin show. Current research is pursuing the approach of specifically evolving organisms and enzymes for the degradation of plastics.

In the afternoon, Dr. Harald Ruijssenaars from the company Corbion presented the production of various bio-based plastics, some of which can already be manufactured competitively with petroleum-based products. Prof. Nick Wierckx then stated that biobased plastics are only sustainable if a true circular economy can be established with them. Using the example of Pseudomonas putida, he vividly demonstrated the development of microorganisms for the bio-upcycling of plastic hydrolysates. Dr. Stephan Noack outlined the importance of process optimization for CO₂-neutral and sustainable production. Automated systems with a high throughput in production strain optimization and phenotyping can make a crucial contribution here.

On Tuesday morning, Prof. Andreas Jupke first gave an overview of the various steps in the production of bioplastics and the associated problems. Currently, the share of bioplastics in total plastic production is still vanishingly small and the use of biobased raw materials is also only around 10% - often because the process steps have not yet been optimized and are therefore not competitive. The major challenges here are: Usability of non-food biomass and residual streams, production strain development for high-yield production, zero-waste processes, and scalability of production processes. The challenges mentioned were addressed in the following three contributions by Prof Nick Wierckx, Katharina Saur and Tabea Helm using the concrete example of itaconic acid production with Ustilago maydis.

On Tuesday afternoon, the focus was on chemical processes. In her introduction, Prof. Sonja Herres-Pawlis pointed out that in the case of "bioplastics" a distinction must be made between biobased and biodegradable plastics and that polylactide (PLA) combines both properties. She reported on the development of novel chemical catalysts that significantly accelerate the polymerization of lactide and have a controllable effect on the properties of the resulting polymer, but can also be used for chemical depolymerization. The afternoon was rounded off with a laboratory tour before meeting for a networking dinner in Aachen's old town in the evening.

Wednesday was a lab day in the institutes of Prof. Lars Blank and Prof. Ulrich Schwaneberg. Dominik Steffens (AG Blank) led experiments on the isolation and degradation of plastics with bacterial strains, and provides the participants with a hands-on experience in the lab. Dr. Francisca Contreras and Dr. Yu Ji (AG Schwaneberg) introduced the possibilities of identifying and sorting micro- and nanoplastics using specific fluorescently labeled peptides and accompanied the participants to demonstration experiments.

On Thursday, the first topic was plastic waste. Prof. Jürgen Pettrak explained that microplastics in wastewater in Germany are largely sedimented with sewage sludge. Nevertheless, considerable amounts of plastic still enter the water cycle. In particular, when rainwater and household wastewater are routed through the same system, heavy rainfall repeatedly leads to system overload. Worldwide, the plastic load in the oceans is enormous and huge plastic islands have already formed.

Kevin Carl addressed the issue of thermal treatment of plastic waste. Large quantities of plastic waste are still incinerated, which will continue to be necessary in the case of medical waste, simply for hygienic reasons. But also industrial plastic waste, such as that generated by vehicle recycling, will have to be disposed of thermally for a very long time to come due to its complexity and many contaminants. The goal here must be to generate heat and electricity and to optimally prevent the release of flue gases and toxic substances, such as those produced by additives.

When it came to the topic of Life Cycle Assessment (LCA) in the afternoon, Prof. Grit Walther impressively showed the complexity of an economic, social and ecological evaluation of products and manufacturing processes. All steps of production including individual components, transport, use and disposal have to be taken into account. In LCA analyses conducted by themselves and guided by Veis Karbassi (AG Walther) with specific software and databases, the participants could experience both how great the variance of the influencing variables is and what relevance the initial question has for the LCA analysis.

The last day was dedicated to group work and summarizing what had been learned. The participants worked in small groups on presentations on ecotoxicological aspects of micro- and nanoplastics, the use of CO₂ for the production of bio-based plastics as well as the carbon footprint, the use of lignocellulose as a raw material and the types of plastics and their advantages and disadvantages. In the final discussion, a clear mandate was given to policy makers to contribute to the development of bio-based and sustainable plastic use through restrictive regulation, as well as incentives.