Collaborative Research: Microbial Fuel Cell Optimization through Digital Microfluidic Electrochemistry in Single-Bacterial Drops

University Of Cincinnati Main Campus, Cincinnati OH

Investigators

Abstract

Municipal wastewater treatment processes consume significant amounts of energy. However, the organic materials fed into the waste treatment process offer the potential for energy-positive waste water treatment if this waste organic material can be converted into energy. Many bacteria that grow in waste water can be harnessed to consume these organic contaminants to clean up the water and at the same time generate electrical current from their metabolism. These bacteria are bound within an electrode of a device called a microbial fuel cell to harvest this current as electrical power. To achieve maximum power output from microbial fuel cells, it must be determined how many species of bacteria, when organized into complex colonies known as biofilms, collaborate to convert organic matter into electricity. This project will study this collaborative metabolism within a novel miniaturized culture system capable of high-through analysis to accelerate the screening process. This miniature culture system will be capable of measuring metabolism of a single bacterial species, as well as in small mixed colonies of many bacteria, from a single drop of culture. This information will be used to determine how the electrical current produced and the organic matter consumed depends on bacterium type, as well as the potential synergy between many types of bacteria. The educational activities inspired by this project feature a hands-on teaching module for high school girls, who will build a simple microbial fuel cell to power a light-emitted diode (LED) or a digital watch. It is hoped this activity will illustrate to high school girls the potential of renewable green energy and biotechnology as exciting future career choices. The microbial fuel cell system components, which include electrodes, membranes, and bacteria, must be carefully engineered to achieve optimal power generation. This project will focus on genetic optimization of the bacteria within the electrode. This optimization is challenging given the interconnected manner in which wastewater bacteria grow. Towards this end, the proposed research has two primary objectives. The first objective is to develop a high-throughput digital microfluidic (DMF) platform for studying microbial fuel cell metabolism and electrical current evolution from single species of bacteria or small colonies of mixed bacteria. The second goal is to optimize the bacterial communities for high power density through high-throughput analysis of single bacterium electron transfer limitations. The DMF chip will be fabricated with droplet actuation electrodes, nanostructured electrochemical electrodes, and isolated on-chip microwell cell culture chambers. The droplet actuation electrode deposits a culture droplet into the microwell, and nanostructured electrodes within the culture microwell will enable the detection of single bacterium output current as well as measurement of specific cell culture contents using cyclic voltammetry. Bacteria known to consume organic matter in waste water and convert it into electrical current through microbioelectrochemical metabolic processes, including P. aeruginosa, Geobacter (G. sulfurreducens) and Shewanella (S. oneidensis) will first be studied as the model exoelectrogens in single species culture. By selectively increasing complexity and heterogeneity in the culture systems, beginning with isolated single species and moving to mixed bacterial colonies, a better understanding of the synergism among bacteria can be systematically determined. Through this study, it also is hoped that the DMF chip will become established as a new tool for studying electron transfer processes in bioelectrochemically-active bacteria.