Enrichment, Performance, and Microbial Diversity of a Thermophilic Mediatorless Microbial Fuel Cell

Abstract

A thermophilic mediatorless microbial fuel cell (ML-MFC) was developed for continuous electricity production while treating artificial wastewater concurrently. A maximum power density of 1030 +/- 340 mW/m2 was generated continuously at 55 degrees C with an anode retention time of 27 min (11 mL h(-1)) and continuous pumping of air-saturated phosphate buffer into the cathode compartment at the retention time of 0.7 min (450 mL h(-1)). Meanwhile, about 80% of the electrons available from acetate oxidation were recovered as current. Denaturing gradient gel electrophoresis (DGGE) and direct 16S-rRNA gene analysis revealed that the bacterial diversity in this ML-MFC system was lower than the inoculum. Direct 16S rDNA analysis showed that the dominant bacteria representing 57.8% of total population in anode compartment was phylogenetically very closely related to an uncultured clone, clone E4. Two sheets of graphite used as the anode showed different dominant bacterial population. For the first time, it is shown that thermophilic electrochemically active bacteria can be enriched to concurrently generate electricity and treat artificial wastewater in a thermophilic ML-MFC.

A novel ecological role of the Firmicutes identified in thermophilic microbial fuel cells

“…Two Gram-positive phyla, Firmicutes (11 OTUs, 234 clones, 79% of clones) and Coprothermobacteria (two OTUs, 48 clones, 16% of clones), represented 95% of the clone sequences. Coprothermobacter species were previously identified by culture-independent molecular techniques in an MFC study with acetate as an electron donor and a thermophilic anaerobic digester inoculum (Jong et al, 2006). In that study, Coprothermobacter sequences represented 15.1% of the community.…”

“…This is further supported by culture-independent studies, which indicate that the phylogenetic diversity of MFC microbial communities far exceeds that of electrochemically active isolates. Unfortunately, these community studies (Bond et al, 2002;Lee et al, 2003;Holmes et al, 2004;Kim et al, 2004;Rabaey et al, 2004;Aelterman et al, 2006;Jong et al, 2006;Kim et al, 2006) were hampered by the use of lowresolution DNA fingerprinting techniques targeting the 16S ribosomal RNA gene (16S rDNA), the presence of which does not necessarily demonstrate electrochemical activity but may simply be an artifact of gene persistence in the environment (Manefield et al, 2002). Furthermore, because these studies focused on gene presence (16S rDNA) rather than gene expression (16S rRNA) they could not elucidate active members of the anode biofilm.…”

“…To expand the known phylogenetic diversity of electricityproducing organisms, we concentrated on MFCs operated at 55 1C, under which conditions neither Geobacter nor Shewanella species can survive (Lovley, 2000). Moreover, as Proteobacteria represent a minor constituent of thermophilic anaerobic digester microbiota (Sekiguchi et al, 1998;Jong et al, 2006), MFCs inoculated with thermophilic digester sludge offer a high likelihood of isolating novel electricity-producing bacteria. Additional benefits also exist for operating fuel cells at elevated temperatures including potentially higher energy yields, easier maintenance of anaerobic reducing conditions because of the lower solubility of O 2 at elevated temperatures and thermal removal of most known pathogens (Jong et al, 2006).…”

Performance improvement of whey-driven microbial fuel cells by acclimation of indigenous anodophilic microbes

“…Applied Biosytems 2720 Thermal Cycler was used for PCR and set at the following parameters: initial denaturation at 95°C for 3 min, followed by 35 cycles of denaturation (30 s at 94°C), annealing (45 s at 60°C and extension, 90 min at 72°C) and a final extension at 72°C for 7 min before storage at -4°C. The products were electrophoresed on an agarose gel to confirm their presence, quality and purity (Jong et al, 2006).…”

Bioelectrochemical analysis of a hyperthermophilic microbial fuel cell generating electricity at temperatures above 80 °C

“…8) Several studies have shown that thermophilic MFCs, which are inoculated with thermophilic microorganisms (with optimal growth temperature between 45 and 80°C), exhibit good performance at operating temperatures approximately 55-60°C. 6,[9][10][11][12][13] However, compared to mesophilic systems, MFCs with higher operation temperatures remain underexploited. For example, exoelectrogenic activity has been reported in more than 20 bacterial species, but most are mesophilic species affiliated with the phylum Proteobacteria.…”