Microbial fuel cell: influence of temperature and external resistance on electrogenic activity

The microbial fuel cell (MFC) is a technology that enables the conversion of organic matter into electrical energy. Thus, this project aimed to analyze the influence of temperature for the removal of organic matter and energy generation together with the optimization of the resistance applied to the external circuit (Rext). The study was carried out with a tubular MFC, in bench scale, applied to the treatment of synthetic effluent simulating vinasse from bioethanol production. Six MFC prototypes were built and operated under continuous flow, studied in 3 conditions/phases. Phase 1 is configured as the startup, adjustments and standardization of all units. Phase 2 with Rext reduction from 300 &#937 to 22.5 &#937, in mesophilic (25.5°C) and thermophilic (55.2°C) conditions. For both phases, the MFCs were fed with synthetic effluent with 5 gCOD/L. For phase 3, the concentration of organic matter (OM) was increased, so the reactors started to operate with 20 gCOD/L with the functionality to evaluate the effect of the organic load on the Coulomb efficiency (CE) and the tension of the MFC. The evaluation of the wastewater treatment efficiency was carried out through the analysis of physical-chemical and electrochemical parameters. For internal resistance resistance (Rint) polarization curves and electrochemical impedance spectroscopy were used. Phase 1 results indicated that the units operated as replicated had similar behavior, with total potential above 600 mV, with power density between 2.7 3.5 W/m3 and Rint below 13 &#937. Rext reduction in phase 2 resulted in increased current density, with average values up to 38.6 ± 4.21 A/m³ and 14.69 ± 3.38 CE. MFCs operated at 55°C demonstrated 1.8 times greater OM removal compared to mesophilic units. However, a high internal resistance was observed, associated with the saturation of oxygen stored in the cathode. For phase 2, the mesophilic condition at 22.5 &#937 showed greater efficiency for internal resistance and CE parameters. In phase 3, the intensification of the OM concentration allowed the MFCs to reach the highest values of power density among the previous MFC phases at 55°C with 22.5 &#937 with a value of 14.4 ± 2.36 W/m3. Mesophilic units showed lower OM removal and energy generation, with limitations associated with diffusion resistance related to biofilm growth caused by OM emission. Therefore, in the third phase, the most efficient configuration in terms of energy generation was identified in thermophilic MFCs (AU)