Bioelectrical reactors (BER) have potential to be utilized in a wide variety of industrial applications. This work explores the kinetics involved with reduction of electron mediators (anthraquinone disulfonate and methyl viologen) in bioelectrical reactors. It also discusses on possible application of BER technology to produce ethanol from CO2 and electricity. It is established that Clostridium ragdahlei is capable of sustaining life and product formation with CO2 as the only carbon source. This means it is theoretically possible to utilize CO2 as he source of carbon and electricity as the source of reducing equivalents for bacterial growth and product formation. A three-step mechanism composed of adsorption, surface reaction, and desorption is developed to model the reaction of dissolved electron mediators at the electrode surface of the BER. The proposed mechanism is then utilized to build a mathematical model to describe the kinetics of the BER system. This model is used to gain greater understanding of experimental kinetic data of electron mediator reduction at different voltage potentials. It is determined that voltage potential has very small effect on the initial rate of reaction in the reactor. However, thermodynamic equilibrium is affected by the change in voltage, resulting in longer sustained initial rate at higher overpotential. Mathematically, this change affects the modeled rate constants by increasing the reverse rate constant of the rate limiting step, and also by affecting the ratio of the thermodynamic equilibrium constants of adsorption. This results in a larger amount of oxidized electron mediator adsorbed to the electrode surface at higher overpotentials, leading to the initial rate persisting further into experimental runs. One key portion of these findings was the determination that the surface reaction step is the rate limiting step of the kinetic mechanism. This has great ramifications on future research and on future considerations for reactor design. This insight allows for better understanding of the key and fundamental workings of BER technology.
College and Department
Ira A. Fulton College of Engineering and Technology; Chemical Engineering
BYU ScholarsArchive Citation
Hoeger, Christopher D., "Foundational Work in Bioelectrochemical Anaerobic Reactor Design with Electron Mediators" (2013). All Theses and Dissertations. 3481.
bioelectrical reactor, kinetics, electrode surface reactions, Clostridium ragsdahlei