Heterotrophic Anodic Denitrification in Microbial Fuel Cells

Nowadays, pollution caused by energy production systems is a major environmental concern. Therefore, the development of sustainable energy sources is required. Amongst others, the microbial fuel cell (MFC) seems to be a possible solution because it can produce clean energy at the same time that waste is stabilized. Unfortunately, mainly due to industrial discharges, the wastes could contain nitrates, or nitrates precursors such ammonia, which could lead to lower performance in terms of electricity production. In this work, the feasibility of coupling anodic denitrification process with electricity production in MFC and the effect of the nitrates over the MFC performance were studied. During the experiments, it was observed that the culture developed in the anodic chamber of the MFC presented a significant amount of denitrificative microorganisms. The MFC developed was able to denitrify up to 4 ppm, without affecting the current density exerted, of about 1 mA/cm2. Regarding the denitrification process, it must be highlighted that the maximum denitrification rate achieved with the culture was about 60 mg·NO3−·L−1·h−1. Based on these results, it can be stated that it is possible to remove nitrates and to produce energy, without negatively affecting the electrical performance, when the nitrate concentration is low.Hoy en día, la contaminación causada por los sistemas de producción de energía es una gran preocupación ambiental. Por tanto, se requiere el desarrollo de fuentes de energía sostenibles. Entre otras, la pila de combustible microbiana (MFC) parece ser una posible solución porque puede producir energía limpia al mismo tiempo que se estabilizan los residuos. Desafortunadamente, debido principalmente a descargas industriales, los desechos podrían contener nitratos, o precursores de nitratos como el amoníaco, lo que podría conducir a un menor rendimiento en términos de producción de electricidad. En este trabajo se estudió la viabilidad de acoplar el proceso de desnitrificación anódica con la producción de electricidad en MFC y el efecto de los nitratos sobre el desempeño de MFC. Durante los experimentos, se observó que el cultivo desarrollado en la cámara anódica del MFC presentó una cantidad significativa de microorganismos desnitrificantes.2 . En cuanto al proceso de desnitrificación, cabe destacar que la tasa máxima de desnitrificación alcanzada con el cultivo fue de unos 60 mg · NO 3 - · L −1 · h −1 . Con base en estos resultados, se puede afirmar que es posible eliminar nitratos y producir energía, sin afectar negativamente al rendimiento eléctrico, cuando la concentración de nitrato es baja

The Influence of External Load on the Performance of Microbial Fuel Cells

In this work, the effect of the external load on the current and power generation, as well as on the pollutant removal by microbial fuel cells (MFCs), has been studied by step-wise modifying the external load. The load changes included a direct scan, in which the external resistance was increased from 120 Ω to 3300 Ω, and a subsequent reverse scan, in which the external resistance was decreased back to 120 Ω. The reduction in the current, experienced when increasing the external resistance, was maintained even in the reverse scan when the external resistance was step-wise decreased. Regarding the power exerted, when the external resistance was increased below the value of the internal resistance, an enhancement in the power exerted was observed. However, when operating near the value of the internal resistance, a stable power exerted of about 1.6 µW was reached. These current and power responses can be explained by the change in population distribution, which shifts to a more fermentative than electrogenic culture, as was confirmed by the population analyses. Regarding the pollutant removal, the effluent chemical oxygen demand (COD) decreased when the external resistance increased up to the internal resistance value. However, the effluent COD increased when the external resistance was higher than the internal resistance. This behavior was maintained in the reverse scan, which confirmed the modification in the microbial population of the MFCEn este trabajo se ha estudiado el efecto de la carga externa sobre la generación de corriente y potencia, así como sobre la eliminación de contaminantes por pilas de combustible microbianas (MFC), modificando paso a paso la carga externa. Los cambios de carga incluyeron un escaneo directo, en el que la resistencia externa se incrementó de 120 Ω a 3300 Ω, y un escaneo inverso posterior, en el que la resistencia externa se redujo de nuevo a 120 Ω. La reducción de la corriente, experimentada al aumentar la resistencia externa, se mantuvo incluso en la exploración inversa cuando la resistencia externa disminuyó gradualmente. En cuanto a la potencia ejercida, cuando la resistencia externa se incrementó por debajo del valor de la resistencia interna, se observó una mejora en la potencia ejercida. Sin embargo, cuando se opera cerca del valor de la resistencia interna, se ejerce una potencia estable de aproximadamente 1. Se alcanzaron 6 µW. Estas respuestas de corriente y potencia pueden explicarse por el cambio en la distribución de la población, que cambia a un cultivo más fermentativo que electrogénico, como lo confirmaron los análisis de población. En cuanto a la remoción de contaminantes, la demanda de oxígeno químico del efluente (DQO) disminuyó cuando la resistencia externa aumentó hasta el valor de resistencia interna. Sin embargo, la DQO del efluente aumentó cuando la resistencia externa fue mayor que la resistencia interna. Este comportamiento se mantuvo en el análisis inverso, que confirmó la modificación en la población microbiana del MFC. la demanda de oxígeno químico del efluente (DQO) disminuyó cuando la resistencia externa aumentó hasta el valor de resistencia interna. Sin embargo, la DQO del efluente aumentó cuando la resistencia externa fue mayor que la resistencia interna. Este comportamiento se mantuvo en el análisis inverso, que confirmó la modificación en la población microbiana del MFC. la demanda de oxígeno químico del efluente (DQO) disminuyó cuando la resistencia externa aumentó hasta el valor de resistencia interna. Sin embargo, la DQO del efluente aumentó cuando la resistencia externa fue mayor que la resistencia interna. Este comportamiento se mantuvo en el análisis inverso, que confirmó la modificación en la población microbiana del MFC

A grey box model of glucose fermentation and syntrophic oxidation in microbial fuel cells

In this work, the fermentative and oxidative processes taking place in a microbial fuel cell (MFC) fed with glucose were studied and modeled. The model accounting for the bioelectrochemical processes was based on ordinary, Monod-type differential equations. The model parameters were estimated using experimental results obtained from three H-type MFCs operated at open or closed circuits and fed with glucose or ethanol. The experimental results demonstrate that similar fermentation processes were carried out under open and closed circuit operation, with the most important fermentation products being ethanol (with a yield of 1.81 mol mol−1 glucose) and lactic acid (with a yield of 1.36 mol mol−1 glucose). A peak in the electricity generation was obtained when glucose and fermentation products coexisted in the liquid bulk. However, almost 90% of the electricity produced came from the oxidation of ethanol

Parametric Analysis of Effective Material Properties of Thickness-Shear Piezoelectric Macro-Fibre Composites

A previous study on the characterization of effective material properties of a d(15) thickness-shear piezoelectric Macro-Fibre Composite (MFC) made of seven layers (Kapton, Acrylic, Electrode, Piezoceramic Fibre and Epoxy Composite, Electrode, Acrylic, Kapton) using a finite element homogenization method has shown that the packaging reduces significantly the shear stiffness of the piezoceramic material and, thus, leads to significantly smaller effective electromechanical coupling coefficient k(15) and piezoelectric stress constant e(15) when compared to the piezoceramic fibre properties. Therefore, the main objective of this work is to perform a parametric analysis in which the effect of the variations of fibre volume fraction, Epoxy elastic modulus, electrode thickness and active layer thickness on the MFC effective material properties is evaluated. Results indicate that an effective d(15) MFC should use relatively thick fibres having relatively high shear modulus and relatively stiff epoxy filler. On the other hand, the electrode thickness does not affect significantly the MFC performance.MCT/CNPq/FAPEMIG National Institute of Science and Technology on Smart Structures in EngineeringMCT/CNPq/FAPEMIG National Institute of Science and Technology on Smart Structures in Engineering [574001/2008-5

Parametric analysis of effective material properties of thickness-shear piezoelectric macro-fibre composites

A previous study on the characterization of effective material properties of a d15 thickness-shear piezoelectric Macro-Fibre Composite (MFC) made of seven layers (Kapton, Acrylic, Electrode, Piezoceramic Fibre and Epoxy Composite, Electrode, Acrylic, Kapton) using a finite element homogenization method has shown that the packaging reduces significantly the shear stiffness of the piezoceramic material and, thus, leads to significantly smaller effective electromechanical coupling coefficient k15 and piezoelectric stress constant e15 when compared to the piezoceramic fibre properties. Therefore, the main objective of this work is to perform a parametric analysis in which the effect of the variations of fibre volume fraction, Epoxy elastic modulus, electrode thickness and active layer thickness on the MFC effective material properties is evaluated. Results indicate that an effective d15 MFC should use relatively thick fibres having relatively high shear modulus and relatively stiff epoxy filler. On the other hand, the electrode thickness does not affect significantly the MFC performance