Efficient Energy Harvester for Microbial Fuel Cells Using Dc/Dc Converters

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Efficient Energy Harvester for Microbial Fuel Cells using DC/DC Converters Abstract— Microbial fuel cell (MFC) is an emerging technology for sustainable energy production. An MFC employs indigenous microorganisms as biocatalysts and can theoretically convert any biodegradable substrate into electricity, making the technology a viable solution for sustainable waste treatment or autonomous power supply. However, the electric energy currently generated from MFCs is not directly usable due to the low voltage and current output. Moreover, the output power can fluctuate significantly according to the operating points, which makes stable harvest of energy difficult. This paper presents an MFC energy harvesting scheme using two layers of DC/DC converters. The proposed energy harvester can capture the energy from multiple MFCs at the most efficient operating point and at the same time form the energy into a usable shape.

Zhiyong Ren, Ph.D.
Dept. of Civil Engineering University of Colorado Denver Denver, USA zhiyong.ren@ucdenver.edu

Figure 1. Schematic of a two chamber microbial fuel cell using ferricyanide as the electron acceptor.



The finite resource of fossil fuels and environmental pollution derived from their use are driving the search for renewable and clean energy alternatives. This replacement of fossil fuels will require the utilization of many energy sources suited to meet different end uses. Microbial fuel cell (MFC) technology has been intensively researched in recent years as a novel technology, because it offers a solution for environmentally sustainable energy by treating waste and recovering electricity simultaneously. MFCs use active bacteria to generate electrical energy from the environment electrochemically. MFCs offer a simple, direct method for converting environmentally available biomass into electricity and are very suitable for clean, distributed, and renewable energy source, for example, powering the remote sensors [1], [2]. However, like other micro energy sources such as ambient heat, vibrations, and lights, MFC reactors generate very low power and energy due to thermodynamic limitations and it has been reported that larger power production cannot be easily achieved by just building larger MFCs or simply connecting them in series or in parallel, because of the nonlinear nature of MFCs [3-5].

The power density from MFCs has increased by orders of magnitude in less than a decade of research. The reported maximum power density from lab scale air-cathode MFCs increased from less than 1 mW/m2 to 6.9 W/m2. [5-7]. This improvement can mainly be attributed to relieving physical and chemical constraints through electrode material and reactor architecture improvement, as well as optimization of operational conditions [2], [8]. However, the reported power output from many MFC studies is based on the power dissipated on a static external resistance instead of the actual attainable power in a usable form, which indicates one crucial missing part before the technology can be commercialized - how to efficiently convert the theoretical potential into a practically meaningful power output. A few energy harvesting systems for sediment MFCs have been reported: they can capture energy from the MFC and convert it into applicable voltage and current levels [9], [10]. However, control scheme that actively harvests energy at an optimal operating point especially from multiple MFCs has not been researched extensively. In this paper, an efficient MFC energy harvesting system using two layers of DC/DC converters is presented. The proposed system can capture the energy from multiple MFCs

Figure 2. Lab scale two-chamber MFC using ferricy yanide as electron acceptor (MFC#1, left) and single-chamber MFC usi air as electron ing acceptor (MFC#2, right).

n Figure 4. Polarization curves of MFCs used in the experiment. MFC#1 and MFC#2 denote two-chamber ferricyanide cath hode MFC and single-chamber...
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