The Effect of Anode Surface Structures on Microbial Fuel Cells

Abstract

Wastewater treatment uses 3-4% of all electrical energy (approximately 820 million to 1.1 billion kWh) in the United States annually and is a promising source for energy and nutrient reclamation through microbial fuel cells (MFCs). MFCs are bio-electrochemical devices that use specific species of electrochemically-active bacteria as transporters of electrons for electrical power generation. The current maximum MFC power density of 3.32 kWm-3 is low compared to its theoretical maximum of 53 kWm-3, leaving much room for improvement. In this honors thesis, we hypothesized adding surface structures to the anode would tune shear rates at the anode surface independently of inlet flow rates, generating a more robust biofilm and, therefore, higher power output. The objective of this project was to design a continuous-flow MFC with structured anodes and determine the effect of anode surface structures on power output. A single chamber MFC was designed with three anode types: flat, patterned cylinders, and patterned cones. Designs were tested first in batch and then in continuous-flow at three flow rates: 0.12 mLmin-1, 0.21 mLmin-1, and 0.73 mLmin-1. In batch, the cones and cylinders designs had thirteen and four times the peak power output of the flat design (0.27 mWm-2) with 3.44 mW∙m-2 and 1.19 mW∙m-2, respectively. In continuous-flow, maximum attainable power density (MAPD) was highest for the cones design at all flow rates (3.75 mWm-2, 3.23 mWm-2, and 3.69 mWm-2 from low to high flow rates) and was significantly larger than the MAPD of the cylinders (1.48 mWm-2, 0.65 mWm-2, 0.86 mWm-2) and flat (1.09 mWm-2, 1.31 mWm-2, 1.15 mWm-2) anode designs. From this research, it was determined that anode geometry does affect power output. The patterned cone design was selected as a potential design feature for future MFCs to increase overall power output while the patterned cylinders design was rejected. Overall, this work motivates further investigation into unique anode geometries as a design aspect for microbial fuel cells as a method of increasing power output.