IMPACT OF CYCLIC VOLTAMMETRY ON MIXED CULTURE SINGLE CHAMBER MICROBIAL FUEL CELL PERFORMANCE AND ANODIC BACTERIAL VIABILITY

Open Access
- Author:
- Red Cloud-Owen, Susan S.
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Clinton Matthew Mench, Thesis Advisor/Co-Advisor
Matthew M Mench, Thesis Advisor/Co-Advisor - Keywords:
- curve-crossing
microbial fuel cell
cyclic voltammetry
biofilm
MFC - Abstract:
- Microbial fuel cells (MFCs) produce electricity by employing microorganisms that can oxidize organic material. Research pertaining to MFCs is rapidly increasing and involves researchers from several different fields, due to its bioelectrochemical nature. Many groups are looking at ways in which to increase and evaluate MFC performance, once of which is to use electrochemical techniques that are widely used in non-microbial fuel cell studies. Cyclic voltammetry (CV) is gaining in popularity as a rapid method of evaluating the performance of electron transfer mechanisms that are used in the cell. Since this is a relatively new application of CV involving living organisms which can be sensitive to voltage levels, there have not been any guidelines set for its appropriate use. The main purpose of this study was to determine if, and at what applied potential, CV affects MFC performance and bacterial viability of the anodic biofilm. Six identical single-chamber air-cathode acetate-fed cube MFCs were constructed for use in this study, and inoculated with an uncharacterized mixed anaerobic consortium obtained from the Penn State Wastewater Treatment Plant’s primary digester. CV was performed at a fixed scan rate of 5 mV s-1. Two cells were repeatedly tested at high applied voltage ranges up to +/- 1600 mV, with one consistently being exposed for 5 cycles and the other for 50 cycles. Another cell was tested at a low applied voltage range (-500 to 400 mV) for 50 cycles, and a different cell was tested only once at +/- 1500 mV for 50 cycles. It was determined that the point at which CV affected MFC performance was +/- 1500 mV. Three cells were exposed to this range, with the following results: the cell exposed to 5 cycles returned from CV at 91% of pre-CV power output; the cell exposed to 50 cycles in fresh substrate returned at 0.52% power output; and the cell exposed to 50 cycles in partially-consumed substrate returned at 18.8% of its full power output. When another experiment was performed using a +/- 1600 mV range, the cell exposed to 5 cycles returned at 27% power and the cell exposed to 50 cycles returned at 0.30% power output. All cells with reduced power output were fully recovered within three days. While this CV exposure did reduce the power production of the MFCs, Laser Scanning Confocal Microscopy (LSCM) images indicated that the power loss was not due to death of bacteria. In fact, the MFC that was tested at +/- 1500 mV immediately before LSCM imaging had an almost equal percent viability to the untested control. The cyclic voltammograms in this study were not typical of others found in literature due to the multiple anodic-cathodic curve-crossings. It is proposed that the very high acetate concentration, combined with the low scan rate, produced these results. The mechanisms that induced the curve-crossings at this high acetate concentration need to be investigated further.