(558d) Development of a 3D Computational Fluid Dynamics Model for Microbial Fuel Cells

Development of a 3D Computational Fluid Dynamics Model for Microbial Fuel Cells

Xianhua Li, Robert Ferrari, Jaclyn Guglielmi, Zuyi (Jacky) Huang

Department of Chemical Engineering, Villanova University, PA, 19085

Abstract:

Wastewater is an important new source of substantial energy. The energy potential contained in wastewater and its biosolids exceeds by 10 times the energy used to treat it [1]. However, conventional wastewater treatment currently consumes about 3% of all electrical power produced [2] and costs more than $25 billion annually in the United States [3]. Therefore, cost-effective methods are in high demand for converting the chemical energy contained in wastewater into bioenergy to address the energy crisis nowadays. Microbial fuel cell (MFC) is a bio-electrochemical system that is capable of producing electricity from wastewater under ambient conditions through the biodegradation of organic compounds by exoelectrogenic microorganisms [4]. Specific species of bacteria such as Geobacter and Shewanella spp. can transfer electrons directly to the anode by membrane-bound cytochromes through anaerobic respiration [5]. The generated electron flow can be used by an external electrical circuit as power supply. In the meanwhile, protons migrate to the cathode and react with oxygen to form water. While bench-scale MFCs have been studied for decades, for the practical implementation of MFCs in wastewater treatment plants, it is still challenging to scale up MFCs [6]. Regarding the complex multi-layer structure, fuel composition and electrochemical reactions in MFCs, a robust computational model will be helpful to direct the scaling up of MFCs.

This study aims to investigate the performance and scalability of MFCs with a three-dimensional computational fluid dynamics (CFD) model. In the CFD model, dynamic electricity generation data that was used for model validation was obtained from experiments conducted in different scales of single-chamber air-cathode MFCs with working volumes of up to one liter. Based on existing one-dimensional mathematical models that have been published [7-9], an integrated and advanced three-dimensional model with complex geometry specifications has been developed for the first time in CFD. User defined functions have been developed and compiled to CFD to accurately analyze process properties such as mass transfer rates, diffusion rates, electrochemical reactions, biofilm formation, bacterial endogenous metabolism, internal and external ohmic resistance. As a result, the 3D CFD model can quantify and visualize the MFC performance by showing electric potential, electrode surface potential, current density and species concentration distribution in any designated cross section across a MFC. From the model, the influence of current density, substrate concentration and conductivity on the long-term dynamics of power generation and coulombic efficiency has been revealed, thus optimal operational conditions have been identified. The developed three-dimensional MFC CFD models will be of great benefit for predicting and evaluating the scaling up of MFCs in the future.

References:

[1] W. E. R. Foundation, "Energy management exploratory team report executive summary," March 23, 2011.

[2] B. E. L. a. K. Rabaey, "Conversion of wastes into bioelectricity and chemicals by using microbial electrochemical technologies," Science, vol. 337, pp. 686-690, 2012.

[3] R. R. Hong Liu, and Bruce E. Logan, "Production of electricity during wastewater treatment using a single chamber microbial fuel cell," Environ. Sci. Technol., vol. 38, pp. 2281-2285, 2004.

[4] "Exoelectrogenic bacteria that power microbial fuel cells," Nature Reviews Microbiology, vol. 7, pp. 375-381, 2009.

[5] Liang Shi, David J. Richardson, S. N. K. Zheming Wang, J. M. Z. Kevin M. Rosso, and J. K. Fredrickson, "The roles of outer membrane cytochromes of shewanella and geobacter in extracellular electron transfer," Environmental Microbiology Reports, vol. 1, pp. 220–227, 2009.

[6] B. E. Logan, "Scaling up microbial fuel cells and other bioelectrochemical systems," Appl Microbiol Biotechnol, vol. 85, pp. 1665-71, Feb 2010.

[7] R. P. Pinto, B. Srinivasan, M. F. Manuel, and B. Tartakovsky, "A two-population bio-electrochemical model of a microbial fuel cell," Bioresour Technol, vol. 101, pp. 5256-65, Jul 2010.

[8] C. Picioreanu, I. M. Head, K. P. Katuri, M. C. van Loosdrecht, and K. Scott, "A computational model for biofilm-based microbial fuel cells," Water Res, vol. 41, pp. 2921-40, Jul 2007.

[9] C. Picioreanu, K. P. Katuri, M. C. M. van Loosdrecht, I. M. Head, and K. Scott, "Modelling microbial fuel cells with suspended cells and added electron transfer mediator," Journal of Applied Electrochemistry, vol. 40, pp. 151-162, 2009.