Electron transfer kinetics at anode interface in microbial electrochemical systems

Abstract

Microbial electrochemical system (MES) is favored by its wide applications for wastewater treatment but demands a better understanding of its reaction kinetics for system development. Herein, we have performed Tafel analysis to understand the anodic reaction kinetics in MES. In addition to use the widely adopted Butler-Volmer-Monod model, we applied the Marcus-Hush-Chidsey (MHC) model with fewer adjustable parameters to understand the anodic kinetics. After fitting the data at three months of cultivation, where the current production reached the apex that indicated the maturation of the biofilm, our results showed that MHC curves match better with a multi-electron transfer mechanism than with an one-electron transfer mechanism. The experiment and fitting results agree better at three and five months, indicating that MHC model is only applicable to the anode with fully cultivated biofilms. Additionally, the reorganization energy determined from fitting with the MHC model is in the range from 5 to 10 under various transferred electron number with mature biofilm, consistent with the theoretical estimation. The good fitting performance of MHC model was also supported by the low root mean square errors of 7.4–22.9%. This work provides new insights to the reaction kinetics in MES and paves the way for the accurate systematic modeling works towards MES development.