Katharina Oehlenschläger

• Biotechnological processes provide a unique platform for the production of bulk and fine chemicals from renewable feedstocks but are often constrained by low yields and limited efficiency. Process intensification aims to fundamentally improve bioprocesses through more integrated and efficient process concepts, thereby enhancing their economic competitiveness compared to conventional petrochemical processes. This work presents and explores selected process intensification strategies at different process levels, including biocatalyst engineering, innovative cultivation strategies and integrated process concepts. Valuable insights can be derived from ABE fermentation with clostridia, a historically established and extensively studied bioprocess. The process intensification strategies developed in this context range from genetic modifications and optimized cultivation strategies to highly integrated continuous process concepts, providing important impulses for the efficient utilization of complex substrates. A key approach to process intensification is process integration, which is discussed in this work through the combination of microbial cultivation and enzymatic biocatalysis. Based on these insights, an integrated process for the production of ethyl butyrate was developed. Here, a microbial co-culture was combined with enzymatic esterification, with the produced ester being continuously removed via in-situ extraction. The limited acid tolerance of the yeast was identified as a key bottleneck in this process. Adaptive laboratory evolution emerged as a promising strategy to overcome this limitation, enabling the rapid development of robust biocatalysts tailored to specific process conditions. Overall, the present results highlight both the potential and the limitations of process intensification and underline the need for a holistic approach to the design of future bioprocesses. In this context, this work aims to provide new impetus for bioprocess intensification and to further strengthen the industrial relevance of biotechnological processes.