Design and characterization of reactor concepts for microbial electrochemical technologies

Abstract

One of the existing challenges for implementing bioelectrochemical systems (BES) in a new bioeconomy is shifting the technology towards industrial use and engineering reactor systems at adequate scales. The goal of this study was to establish and define a rational knowledge-based process design for bioelectrochemical systems. Process development should start with the selection and engineering of the catalysts (electroactive microorganisms or enzymes), followed by first synthesis and optimizations in lab-scale reactors. Modeling and simulation is important to elucidate interactions between the electrochemical and biological component and to support the process design. The last stage is the scale-up of the BES into pilot plant applications and an economic evaluation. The most important open questions of different BES were identified at the start of this work to gain more insight into relevant parameters. A flat-plate microbial fuel cell was designed and the influence of two different inlet setups on performance was investigated. Perpendicular flow through the anode increased the performance 1.8 fold vs. parallel flow. Finite element method simulation revealed that substrate distribution is influenced by the change of inlet setup and is responsible for the improved experimental performance. In recent years, assemblies to host electrodes in bioreactors have been developed. The resulting electrobioreactors also possess the advantages of bioreactors like good scalability and comparability during production processes. Two assemblies enabling a separated and non?separated electrochemical operation, respectively, were designed and extensively characterized. Electrochemical losses over the electrolyte and the membrane were comparable to H?cells, the bioelectrochemical standard reaction system. Current production by the electroactive model organism Shewanella oneidensis was improved by the separation of anodic and cathodic chamber by a Nafion membrane. To date, the products of microbial electrosyntheses are rather limited to simple chemical structures. In this work the electroactive microorganism Cupriavidus necator was genetically engineered and used in BES for production of the terpene humulene from CO2 and electricity. This work serves as proof of concept that also more complex and valuable compounds can be produced in BES. Electrobiotechnology is a wide spread field. This work shows the development potential and offers solutions for the selected process steps.