Identifying the microbial communities and operational conditions for optimized wastewater treatment in microbial fuel cells

Microbial fuel cells (MFCs) are devices that exploit microorganisms as “biocatalysts” to recover energy from organic matter in the form of electricity. MFCs have been explored as possible energy neutral wastewater treatment systems; however, fundamental knowledge is still required about how MFC-associated microbial communities are affected by different operational conditions and can be optimized for accelerated wastewater treatment rates. In this study, we explored how electricity-generating microbial biofilms were established at MFC anodes and responded to three different operational conditions during wastewater treatment: 1) MFC operation using a 750 Ω external resistor (0.3 mA current production); 2) set-potential (SP) operation with the anode electrode potentiostatically controlled to +100 mV vs SHE (4.0 mA current production); and 3) open circuit (OC) operation (zero current generation). For all reactors, primary clarifier effluent collected from a municipal wastewater plant was used as the sole carbon and microbial source. Batch operation demonstrated nearly complete organic matter consumption after a residence time of 8–12 days for the MFC condition, 4–6 days for the SP condition, and 15–20 days for the OC condition. These results indicate that higher current generation accelerates organic matter degradation during MFC wastewater treatment. The microbial community analysis was conducted for the three reactors using 16S rRNA gene sequencing. Although the inoculated wastewater was dominated by members of Epsilonproteobacteria, Gammaproteobacteria, and Bacteroidetes species, the electricity-generating biofilms in MFC and SP reactors were dominated by Deltaproteobacteria and Bacteroidetes. Within Deltaproteobacteria, phylotypes classified to family Desulfobulbaceae and Geobacteraceae increased significantly under the SP condition with higher current generation; however those phylotypes were not found in the OC reactor. These analyses suggest that species related to family Desulfobulbaceae and Geobacteraceae are correlated with the electricity generation in the biofilm and may be key players for optimizing wastewater treatment rates and energy recovery in applied MFC systems.     

Inoculation procedures and characterization of membrane electrode assemblies for microbial fuel cells

Membrane electrode assemblies were prepared following procedures adopted in the fabrication of polymer electrolyte membrane (PEM) fuel fells and used in microbial fuel cells (MFCs) with Shewanella oneidensis MR-1 as a single culture and sodium lactate as the electron donor. Improved inoculation procedures were developed and fuel cell performance with the biofilm density of microbes over the anode is discussed. A novel procedure to condition the membrane is also presented. Polarization measurements were carried out and power density plots were generated. Power density values of 300 mW m⁻² are typically obtained while a maximum value of 600 mW m⁻² is demonstrated indicating good performance for a single cell culture.     

Knowledge diffusion and the development of regionsKnowledge diffusion and the development of regions

The economic prosperity of a region is largely dependent on the accumulation and diffusion of knowledge. In this paper, the scale effects as well as the resource reallocation effects of intra- and interregional knowledge transmission are analysed. Within a model, the optimal levels of knowledge diffusion are calculated. It is also shown that knowledge diffusion becomes more important if regions are more integrated in interregional goods trade. Free trade in goods can harm the development of a region if the interregional knowledge diffusion is not intensive enough. Received: October 1996 / Accepted: December 1997