Electricity from Cellulose-Fed Microbial Fuel Cells: Comparing a Co-Culture of Clostridium Cellolyticum-Geobacter Sulfurreducens with An Undefined Mixed Culture

As the most abundant polymer on earth and a significant fraction of many waste streams, cellulose is an attractive renewable feedstock for energy production. Microbial fuel cells (MFCs) can be used to extract this energy from cellulose for direct electricity production or hydrogen generation. However, cellulose conversion in an MFC presents some interesting ecological challenges: it requires the use of an insoluble electron donor and acceptor, there are no known microbes capable of both cellulose hydrolysis and anode reduction, and cellulose hydrolysis kinetics are considerably slower than substrates more commonly used in MFCs. These constraints introduce operational considerations that must be addressed to achieve efficient conversion. Using insoluble MN301 cellulose and a binary culture comprised of Clostridium cellulolyticum and the exoelectrogenic Geobacter sulfurreducens, fluorescent in situ hybridization and real-time polymerase chain reaction analyses showed that anode biofilms were dominated by G. sulfurreducens, while C. cellulolyticum was more abundant in suspension. However, when soluble carboxymethylcellulose was used, both microbes cohabitated the anode. Subsequently, MFCs were operated as sequencing batch reactors with settling and supernatant decant to enhance the retention of cellulose degraders. There was little change observed in the performance of the defined binary culture. However, in undefined mixed-culture experiments with MN301, solids retention significantly impaired the performance relative to a system with complete replacement of the anode chamber contents with each batch. Chemical characterization and molecular examination of these communities is underway to determine the fate of cellulose products in these systems.