Effluents from well-acclimated microbial fuel cells (MFCs) have been widely used as inocula to start up new MFC reactors. However, the actual cell concentrations and cell viability of exoelectrogens in these MFC effluents have not been well examined. In this study, concentrations of exoelectrogens in the effluent from acetate- or wastewater-fed MFCs were examined using a quantitative polymerase chain reaction (qPCR) method specific for Geobacter spp. that are usually the dominant genus in MFCs, and a non-specific WO3 nanocluster/most probable number (WO3/MPN) method for enumeration of viable exoelectrogens. Geobacter spp. concentrations in acetate-fed MFC effluents based on qPCR were 1.3 ± 0.2 × 108 cells/mL, slightly higher than those in the wastewater-fed MFC effluents (9.3 ± 3.5 × 107 cells/mL). However, exoelectrogen cell counts using the WO3/MPN method were several orders of magnitude lower for both MFC effluents (1.1 ± 0.3 × 104 cells/mL for acetate-fed; 1.4 ± 0.3 × 105 cells/mL for wastewater-fed). Live/dead cell staining suggested that most cells (85 %) in the effluents were inactive or dead, which could partly explain the lower numbers using the WO3/MPN method. These results suggest that both acetate- and wastewater-fed MFC effluents contain high numbers of Geobacter spp. although a high percentage of cells are not viable.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Biomedical Engineering