Imagine Magazine - Johns Hopkins - Demo - (Page 12)

UG JUICE Bug Juice: How Bacteria Bug Juice: Might Fuel the Future by Kartik Madiraju A s part of a prize I won in my eighth-grade science fair, I got to visit the major hydroelectric power plants near James Bay in northern Quebec. One researcher said something that revolutionized my thinking about energy. He told me that at the pace humans are consuming energy, it would take four planet Earths to support our appetite for fossil fuels, land, water, and other natural resources. My interest in renewable energy was ignited. There are many renewable sources of energy, and humans have tapped into most of them for practical use. But current sources of renewable energy have disadvantages. Solar-powered cells produce no emissions, but they are currently much too expensive for widespread use. Nuclear reactors could support whole cities, but one meltdown would spell disaster, and the radioactive waste has to be stored somewhere. Hydroelectric turbines provide a lot of power, but damming rivers can harm ecosystems. While we figure out how to overcome these disadvantages, I realized, it makes sense also to look for additional energy sources. Living Fuel Cells When I returned home to Montreal, I began reading about renewable energy technologies. Days of pondering turned into weeks. Thoughts of a pending energy crisis were swirling around in my head as I flipped through a 2003 issue of Nature Biotechnology. One article describing the concept of a microbial fuel cell (MFC) caught my eye. I could hardly believe what I was reading: bacteria could produce electricity in a fuel cell with no polluting side effects. Operating principles of an MFC (not to scale). A bacterium in the anode compartment transfers electrons obtained from glucose to the anode electrode. During electron production, protons are also produced in excess. These protons migrate through the cation exchange membrane into the cathode chamber. The electrons flow from the anode through an external resistance (or load) to the cathode where they react with the final electron acceptor (oxygen) and protons. Reprinted with permission from Environ. Sci. Technol., 40 (17), 5181–5192, 2006. Copyright 2006 American Chemical Society. To understand the science behind MFCs, you need only basic knowledge of cellular respiration and electric principles. The process begins inside the bacterial cell. During cellular respiration, all organisms, including bacteria, decompose molecules of glucose by stripping high-energy electrons off the atoms in its structure. These electrons cascade down an “energy staircase” known as the Electron Transfer Chain, losing a bit of energy at each step on the staircase. The energy is used to synthesize ATP, the primary molecule that provides energy for biological reactions in all organisms. At the end of the staircase, the electrons are donated to a final electron acceptor: if the organism is aerobic, like humans, the electrons are donated to oxygen; if the organism is anaerobic (survives without oxygen), such as the Rhodoferax used in most MFCs, the electrons are donated to metals such as manganese or iron. Since these metals are not within their cells, bacteria that rely on these metals as electron acceptors have developed electrically conductive structures, known as pili, that protrude from their membranes to connect them to metal ions. If we place an electrode from one end of a circuit inside a culture of anaerobic bacteria that produce pili, the electrode would attract electrons from the bacterial cells. And there you have it. These electrons will conduct through the electrode, generating a current and creating a rudimentary microbial fuel cell. Lucky Break After several sleepless nights contemplating whether MFCs could be the ideal renewable energy resource, I decided to test the principle myself. In my basement, I fashioned a fuel cell out of an empty Coke bottle, using the graphite rods from pencils as electrodes. My goal was simply to familiarize myself with the MFC concept, but I was fortunate that I’d later be able to test my model experimentally. Hoping to build an MFC using recyclable materials, I had been looking for researchers doing work related to fuel cells who might mentor me. I discovered that MFC research was being considered at the Biotechnology Research Institute (BRI) in Montreal, a branch of the Canadian National Research Council. I contacted the researcher in charge, who agreed to mentor my project. This was a lucky break: I had no lab experience and I was only 14. March/April 2008 12 imagine

Table of Contents Feed for the Digital Edition of Imagine Magazine - Johns Hopkins - Demo

Imagine Magazine - March/April 2008 Contents Letters Big Problems Big Picture In My Own Words Putting E-Waste in Its Place Big Juice Making Waves What Does "Green" Mean? Into the Woods Swimming with Whale Sharks Crash Course in Costa Rica Selected Opportunities & Resources Hooked on Logistics Off the Shelf Word Wise Middle Ground One Step Ahead Exploring Career Options Planning Ahead for College Students Review Creative Minds Imagine Sudoku Knossos Games

Imagine Magazine - Johns Hopkins - Demo

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