CONVERGENT DEVELOPMENT OF MICROBIAL COMMUNITIES IN MICROBIAL FUEL CELLS

Open Access
Author:
Yates, Matthew D
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 09, 2011
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
Keywords:
  • convergence
  • mfc
Abstract:
Microbial fuel cells (MFCs) are often inoculated with rich sources of microorganisms from a single wastewater source, but it is not known to what extent this inoculum choice affects community development or power production. The temporal development of microbial communities in MFCs was examined using inocula from three different sources: a local wastewater treatment plant known to produce consistent power densities; a second nearby wastewater treatment plant; and an anaerobic bog sediment. The bog inoculum MFCs initially produced much higher power densities than the wastewater samples, but after 60 d all MFCs on average converged to similar voltages (0.47 ± 0.02 V, 1000 Ω external resistor) and maximum power densities (590 ± 170 mW/m2). While voltages produced by MFCs inoculated with bog sediment were not significantly different among triplicate reactors, one of the MFCs inoculated with wastewater produced substantially less voltage. Denaturing gel gradient electrophoresis (DGGE) profiling showed the development of a stable exoelectrogenic biofilm in all samples after 30 d, consistent with an analysis using 16S rRNA clone libraries. After 60 days, 58 ± 10% of clones had a high similarity to Geobacter sulfurreducens. Analysis using a FISH probe for G. sulfurreducens confirmed the predominance of this microbe in the anode communities (63 ± 6% of all microbes). One of the wastewater inoculated MFCs that produced less voltage than other MFCs (UAJA3) had a significantly lower percentage of 16S clones similar to G. sulfurreducens (36%) with an increased number of Bacteroidetes (36%). This suggested that a high predominance of G. sulfurreducens was needed for convergent power densities and that an overabundance of Bacteroidetes could be harmful, although a lower percentage of this microbe in the UAJA3 MFC could not be verified by FISH analysis. These results suggests that MFC replicates need not be sampled and analyzed for their individual microbial communities when exhibiting similar performance, but sub-optimal performance can arise from a lack of predominance of specific microorganisms in the anode communities. The extent to which this finding can be generalized for MFCs needs to be further examined for other substrates, inocula, and reactor types.