Bioanode Extracellular Electron Transfer And Mechanism Of Enhanced Current Production From Phenol

Bioelectrochemical system (BES) is widely studied for its characteristics of simultaneous electricity production and wastewater treatment. More functions have been developed for BES. Bioanode is the key component in the whole system; and a comprehensive understanding of the property of bioanode is important for the optimization of bioanode performance.The outer-membrane intermediate is a key step for the electron transfer process of bioanode. Literatures have reported that there may be two or more outer-membrane intermediates transferring electron from electroactive bacteria to anode. However, little has been known about the exact attribution of different outer-membrane intermediates to the current production of bioanode; furthermore, researchers have rarely focused on the relationship between the maximum current density and the charge density accumulated in outer-membrane intermediates of bioanode. The first part of this dissertation has found that there are two types of outer-membrane intermediates in butyrate-fed bioanode:Omii and Omi2. Omi1 contributes a current up to 8.5 mA with a butyrate concentration of 5 mM, which is almost ten times higher than that contributed by Omi2. Moreover, we present a strategy to explore the correlation between the accumulated charge density (τ) and the maximum current density (jmax) of bioanode. Current production data and fitting results demonstrate that there is a linear correlation between τ and jmax for all five carbon-based bioanodes, with coefficients close to 0.64±0.05. We claim that τ is a key parameter estimating jmax in BES without the need for determining biomass and biofilm thickness.Bioanode extracellular electron transfer could be influenced by many operational factors. Though literatures have reported such influences based on the current-production performance of bioanode, a detailed interpretation regarding extracellular electron transfer behavior has rarely been studied. The second part of this dissertation has found that temperature (T), pH, heavy metal (Cd2+), dissolved oxygen and operational mode have significant impact on the current production of bioanode. Cyclic voltammetry and electrochemical impedance spectroscopy data suggest that:(1) T, pH and Cd2+ directly influence the electron transfer activity of outer-membrane intermediates, resulting in the increase of Rct of bioanode; (2) dissolved oxygen molecule may be able to directly contact with the outer-membrane intermediates and becomes a electron-acception competitor of anode; (3) operation mode (MFC, MSC and MEC) controls the bioanode potential which further determines the number of available outer-membrane intermediates during the current production process of bioanode.The third part of this dissertation has focused on identifying the pathway governing current production from phenol and proposing the mechanism of current production from phenol. The comparisons of current production profiles with phenol and acetate as the electron donnors and bacterial communities analysis reveals that phenol degradation via bioanode proceeds with two consecutive steps:(1) hydrolytic acidification with the help of phenol-degrading bacteria, and (2) anaerobic oxidation of small molecule (e.g., acetate) with the help of electroactive bacteria. Air exposure improves the bioanode current production from phenol because the solution forms two functional sections:enhanced hydrolytic acidification section and anaerobic oxidation section. The enhanced hydrolytic acidification section provides more available electron donors improving the anaerobic oxidation rate of bioanode.