Microbial fuel cells (MFCs) are bioelectrochemical systems that exploit microbial respiration for the conversion of organic compounds into electrical energy.  Within a typical system, electrochemically active microorganisms extracellularly transfer electrons released during the oxidation of organic compounds to the anode surface. The electrons travel from the anode, across an external load to the cathode, where they react with the terminal electron acceptor (e.g. oxygen from air). MFCs are a promising means for wastewater treatment and as a source of renewable energy.  The operational mode of the MFC can directly control microbial metabolism and respiration and thus define the wastewater treatment rate, energy recovery and final products from wastewater treatment.

Despite the advantages, MFCs are not yet a viable solution for large-scale wastewater treatment and energy generation.  Extensive research must still be conducted to optimize the system including MFC start-up time, stability and treatment rates. MFC start-up time is widely variable depending on external conditions, inoculum source and substrate. There are challenges associated with stability and reproducibility of the system. Finally, wastewater treatment rates using MFCs still are not comparable to conventional wastewater treatment methods, and the magnitude of energy recovery is not at a meaningful scale. 

In this study, we evaluated different enrichment and operational strategies to optimize MFC performance.  At the beginning of the experiment, during the enrichment phase, the anode potential was modulated either by an external resistor or an applied voltage.  It has been previously shown that the anodic community composition and biomass formation changes according to the external resistor or potential applied [1,2]. Under such operational conditions, a faster start up time can also be achieved [3]. In addition, start-up time and overall performance will also be impacted by inoculum source and substrate selection. Previous reports addressed MFC performance as a function of operation and startup time using either a defined media and single carbon substrate [2] or a single enrichment strategy with primary clarifier effluent as the single inoculum and substrate [1]. Therefore our evaluations addressed a highly diverse inoculum source including lagoon sediment and swine waste and different methodologies for enrichment to expand the knowledge base about what enrichment strategies may be best for a given wastewater treatment application.

Varying ranges of external resistors and applied voltages were tested.  A periodically induced open circuit condition was also evaluated to study its effect on MFC output.  With these experimental conditions, we are aiming to identify an optimal strategy for MFC start-up and operation, and evaluate the long-term effects on MFC performance including the electrochemical performance, community taxonomic dynamics, biomass formation, and wastewater treatment rate. 

References:

[1] Shun’ichi Ishii, Shino Suzuki, Trina M Norden-Krichmar, Tony Phan, Greg Wanger, Kenneth H Nealson, Yuji Sekiguchi, Yuri A Gorby,  and Orianna Bretschger; Microbial population and functional dynamics associated with surface potential and carbon metabolism

[2] Sokhee Jung and John M. Regan; Influence of External Resistance on Electrogenesis, Methanogenesis, and Anode Prokaryotic Communities in Microbial Fuel Cells

[3] Xin Wang, Yujie Feng, Nanqi Ren, Heming Wang, He Lee, Nan Li, Qingliang Zhao; Accelerated start-up of two-chambered microbial fuel cells:Effect of anodic positive poised potential