Microbial Electrosynthesis—An Inventory on Technology Readiness Level and Performance of Different Process Variants

Abstract

The objective of microbial electrosynthesis (MES) is to combine the advantages of electrochemistry and biotechnology in order to produce chemicals and fuels. This combination enables resource-efficient processes by using renewable raw materials and regenerative energies. In the last decade, different MES processes have been described, for example, MES based on biofilms or mediators, electro-fermentation, and secondary MES. This review compares the MES technologies with regard to the reached process performances in terms of key process indicators (i.e., coulombic efficiency (CE), product titre, productivity) and technology readiness level (TRL). Often the underlying mechanism of electron transfer in biofilm-based processes has not been elucidated and can therefore not be optimized. Similarly, technical aspects of electro-fermentation processes and processes with soluble mediators are under investigation and techno-economic assessments are missing. In contrast, the electrochemical production of microbial substrates in secondary MES or hybrid systems show high key process indicators and TRLs up to 7. In summary, the different types of MES processes offer options for today's industrial use, as well as an exciting and future-oriented technology that can be applied in a medium-term perspective.

Bioelectrochemical systems (BESs) towards conversion of carbon monoxide/syngas: A mini-review

“…The exact way of how the cells metabolism is influenced by EF is not well known. However, it is known that various metabolic processes that compete for reducing power from the NADH/NAD + pool, can adversely affect the 1,3-propanediol production yield in glycerol fermentation [84]. Zhou and coworkers demonstrated that the use of an electrode to provide additional reducing equivalents resulted in an improvement of 25% (1 mM-4 mM) on 1,3-propanediol production possibly due to the enhance of NADH generation routes [85].…”

“…Zhou and coworkers demonstrated that the use of an electrode to provide additional reducing equivalents resulted in an improvement of 25% (1 mM-4 mM) on 1,3-propanediol production possibly due to the enhance of NADH generation routes [85]. The applied potential can impact the microbial population structure and also selects the microbial community composition on the electrode's surfaces influencing the intracellular redox regulations [83,84].…”

From Innovation to Application: Bridging the Valley of Death in Industrial Biotechnology

“…Heavily as industry has grown to depend on microorganisms, only one in 5000-10 000 biotechnology innovations derived from academia survives the long route from the initial findings to product commercialization [5]. Generally referred to as the 'Valley of Death' [6], the division between innovation and application starts at the different product development levels at which academia and industry operate, known as technology readiness levels (TRLs) [7]: typically TRL 1-3 in academia and TRL 8 and 9 in industry. At TRL 4-7, the discovery process is generally considered too applied for further scientific funding but too risky to fund for industrial market implementation.…”

Valorisation of CO2 into Value-Added Products via Microbial Electrosynthesis (MES) and Electro-Fermentation Technology

“…Alternatively, changes in the composition of the microbial community could also help. Intermixing of cultures or creating co-cultures can be used in biofilm-based MES to enhance the performance of the system as these cultures are robust to changes in the environment and are flexible with different types of substrates [65]. However, when present in abundant quantity, the species compete with one another for e − , leading to a decrease in the product specificity [66].…”

“…A potential solution for the same is enriching specific species by using electrochemically-driven reactions in the long run, along with the addition of supplements. Biofilm-based MES highlighting the different process performances have been explained by Fruehauf [65].…”