RESUMEN
This study examines methanogen activity in microbial fuel cells when exposed to various environmental stresses, such as oxygen, low pH, low temperature, inhibitor (2-bromoethanesulfonate (BES)), and variations in external resistance. Controlling methanogenesis resulted in an increase in Coulombic efficiency (CE) because it was a major cause of electron loss. Methane was mainly produced from aceticlastic methanogenesis, rather than by syntrophic acetate oxidation, with Methanosarcinaceae being the primary contributor. Lowering the resistance from 600 to 50 Omega reduced the methanogenic electron loss by 24%; however, changing the temperature or pH level had little effect. A BES injection was the most potent strategy for the selective inhibition of methanogens without damaging exoelectrogens. The addition of 0.1-0.27 mM BES increased the CE from 35% to 70%. Oxygen stress successfully inhibited methanogens, while slightly suppressing the exoelectrogens, and is believed to be a practical option due to its low operating cost.
Asunto(s)
Fuentes de Energía Bioeléctrica , Biotecnología/métodos , Metano/química , Acetatos/química , Biotecnología/instrumentación , Electrones , Ambiente , Concentración de Iones de Hidrógeno , Oxígeno/química , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Temperatura , Factores de TiempoRESUMEN
To better understand microbial community in sulfur-based nitrate removal process, comparative molecular analyses were performed with the biofilm formed on sulfur particles that were obtained from different bed-heights of a laboratory-scale reactor employed for the process. Microbial community in the reactor showed vertical heterogeneity in terms of total cell count and nitrate removal activity. DAPI (4',6-diamidino-2-phenylindole) staining revealed that total cell count (per g sulfur particle) gradually decreased as bed height increased until reaching approximately middle of the reactor bed, showing a nearly plateau afterward. This result partly supported ion chromatography result that most nitrate removal activity was found in the lower part of the reactor bed. Phylogenetic composition of bacterial community in the biofilm was almost similar regardless of bed height as determined by whole cell hybridization using group-specific probes. Cells affiliated with the beta- and gamma-Proteobacteria were the most abundant proteobacterial groups throughout the bed, although their fractions were fluctuating along the bed height. Total number of the two major groups decreased as bed height increased, showing similar trend to total cell count and nitrate removal activity. Denaturating gradient gel electrophoresis revealed similar profiles of nitrous oxide reductase gene (nosZ) fragments from denitrifying populations at the different bed-heights, suggesting similar diversity of the nosZ fragments regardless of bed height.