Journal Article

Efficiency and process development for microbial biomass production using oxic bioelectrosynthesis

Rosa, Luis F.M., Rominger, Leonie, Gescher, Johannes, Horn, Harald, Hackbarth, Max, Jung, Tobias, Scherzinger, Marvin, Kaltschmitt, Martin, Picioreanu, Cristian

2025

Overview

By using carbon dioxide (CO2) as carbon source, fossil sources can be replaced. In microbial electrosynthesis (MES), CO2 and in situ produced hydrogen (H2) are used for bacterial biofilm growth.Kyrpidia spormannii is a Knallgas bacterium with a protein content of 61% of its dry mass. It grows as a biofilm on the cathode in an oxic MES. The biomass can be used for the food and feed industry.A continuous process was established by applying a negative potential to harvest parts of the biofilm for use. The biofilm regenerated after being partly harvested.The system was operated at maximum coulombic efficiency, enabling the energy input to be minimized.A numerical model describing the growth of K. spormannii as a H2-oxidizing bacterium in an oxic MES system was developed. This helps predict growth behavior and efficiencies for further optimization. Autotrophic microbial electrosynthesis (MES) processes are mainly based on organisms that rely on carbon dioxide (CO2) as an electron acceptor and typically have low biomass yields. However, there are few data on the process and efficiencies of oxic MES (OMES). In this study, we used the knallgas bacterium Kyrpidia spormannii to investigate biomass formation and energy efficiency of cathode-dependent growth. The study revealed that the process can be carried out with the same electron efficiency as conventional gas fermentation, but overcomes disadvantages, such as the use of explosive gas mixtures. When accounting only for the electron input via electrical energy, a solar energy demand of 67.89 kWh kg–1 dry biomass was determined. While anaerobic MES is ideally suited to produce methane, short-chain alcohols, and carboxylic acids, its aerobic counterpart could extend this important range of applications to not only protein for use in the food and feed sector, but also further complex products. [Display omitted] Oxic microbial electrosynthesis (OMES) using Kyrpidia spormannii can match the electron efficiency of gas fermentation, without producing explosive gas mixtures. It uses solar energy efficiently and has the potential to produce complex products, such as proteins, for food and feed instead of methane and alcohols, which are typical products of anoxic MES. Oxic microbial electrosynthesis (OMES) is a relatively new technology, particularly in the context of biofilm-based processes, which is now achieving a Technology Readiness Level (TRL) of 3 in laboratory reactors. Similar to other biofilm-based technologies, OMES faces both challenges and opportunities. One of the primary challenges will be identifying a reactor design that maximizes electrode surface area while simultaneously maintaining a predictable fluidic regime. Since OMES relies on an electrochemical system, reactor configuration must also minimize electrochemical losses. If biomass is intended to be the end product, it is important to consider that, over the duration of the experiment, microorganisms are likely to adapt to the changing process conditions, potentially enabling evolution-based optimization of biocatalysts. In the future, OMES is likely to compete with processes relying on anaerobic gas fermentation as a first step and subsequent usage of end products from this first step as feed for a second reaction step likely involving aerobic microorganisms. Full economic and ecological process assessment based on larger scale reactors will be necessary to decide under which circumstances which technology might be superior.

• Publisher: Elsevier Ltd,Elsevier Limited
• Subject: Alcohols / Alternative energy sources / bacteria / Biocatalysts / Bioelectric Energy Sources - microbiology / Biofilms / Biogas / Biomass / Biomass energy production / biomass production / biotechnology / Carbon dioxide / Carbon Dioxide - metabolism / Carboxylic acids / Catalysis / Clostridiales - growth & development / Clostridiales - metabolism / coulombic efficiency / electric power / Electrodes / electrosynthesis / Energy demand / Energy efficiency / Enzymes / Fermentation / Gas mixtures / Genetic engineering / hydrogen-oxidizing bacteria / Internal Medicine / Kyrpidia spormannii / Methane / microbial biomass / Microorganisms / Organisms / oxic microbial electrosynthesis (OMES) / Photosynthesis / Process controls / Solar energy