Abstract
Electro-fermentation is a novel process that consists in coupling a microbial fermentative metabolism with an electrochemical system. In such a process, the electrodes act either as the electron sinks or sources modifying the fermentation balance of a microbial fermentative metabolism and provide new options for the control of microbial activity. A theoretical framework for the analysis and control of fermentations using electro-fermentation is currently lacking. In this paper, we propose a simple electro-fermentation model in which a population of fermentative bacteria switch between two metabolic behaviors in response to different electrode potentials. We then mathematically analyze optimal strategies to maximize the production of one of the rising products in a batch fermentation using Pontryagin’s Maximum Principle. The obtained results show that, in some experimental configurations, a dynamic control of the electrode potential is required for the maximization of the desired product. Consequences of the obtained optimal strategy for driving electro-fermentation experiments are discussed through a realistic example. This analysis also highlights that the transition rates between fermentation and electro-fermentation behaviors are currently unknown and would be crucial to quantify in order to apply such a control approach.
Highlights
The knowledge of electroactive microorganisms has rapidly grown over the last 20 years with the development of microbial electrochemical technologies such as microbial fuel cells (MFC) and microbial electrolysis cells (MEC) for the production of electricity or hydrogen from organic matter [1]
The obtained results show that the optimal strategy is not trivial, in the sense that the control is not always constant, where in some cases the metabolic behavior f1 should be visited by the fermentative bacteria
We have proposed a model describing the effect of electro-fermentation on the metabolic profile of a fermentative bacteria in a batch culture
Summary
The knowledge of electroactive microorganisms has rapidly grown over the last 20 years with the development of microbial electrochemical technologies such as microbial fuel cells (MFC) and microbial electrolysis cells (MEC) for the production of electricity or hydrogen from organic matter [1]. The application of an external potential through the implementation of an electrode in the bioreactor leads to a switching of the metabolism between two different metabolic pathways This EF effect is modeled by considering two microbial subpopulations producing different metabolites ( f1, f2) giving rise to two different products (s1, s2). The bioreactor equations in batch culture are used to establish the model [18] Based on this model, an optimal control problem for the maximization of the production of s2 is formulated. The obtained results show that the optimal strategy is not trivial, in the sense that the control is not always constant (equal to that which correspond to f2), where in some cases the metabolic behavior f1 should be visited by the fermentative bacteria.
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