Welcome to Exploring Renewable Energy Technology from Bounce Energy! Because the ERCOT portion of Texas can be thought of as a “walled garden,” renewable energy sources in Texas now make up a significant portion of the energy supply mix. It’s also a dynamic technology with new innovations, discoveries, and issues arising every week. Each month, we will examine the latest news in the industry to better understand what (if any) changes might come to the Texas energy supply.

Microbial Electricity Production

At first glance, the idea that tanks of green and brown bacterial slime powering homes might have some folks running to get spray bottles of disinfectants. From a young age, we are taught to fear Bacteria as a source of bloating stomach ailments, painful skin infections, and furious deadly plagues —and not as a source of light, entertainment, and air conditioning.

But for several years now, Microbial Fuel Cell (MFC) technology has been expanding as totally green energy source that makes electricity from organic sources. Electricity comes from feeding: anaerobic bacteria colonies live on the anode (negative) end of the fuel cell, feasting on organic compounds. The bacteria process their food through oxidation, which releases electrons to the anode. The anode’s electrode is connected to the circuit outside the cells, and electrons flow out as electrical current into that circuit, ultimately returning to the MFC’s cathode (positive) electrode to complete the circuit.

Voltage output of a MFC varies greatly depending on the bacteria, what they eat, ambient temperature, and the biofilm they live on. Power output isn’t much (averaging 1/2 volt) but, like batteries and solar cells, MFCs are stackable. And because of the endless food supply, wastewater treatment (particularly for breweries) is usually thought to be their ideal application site.

But new uses are showing up in all sort of places.

The Germ of an Idea

What if your oil well is producing methane but conditions are such that building a pipeline to transport the gas is more expensive than the gas is worth? Meanwhile, the price for electricity to run your wellhead is also expensive enough that it’s ruining your profits.

Researchers at Penn State University have created what they call a “consortium of bacteria” to process methane into electricity. One type of bacteria has synthesized DNA based on a species that eats methane but lives at the bottom of the Black Sea. Apart from electrons, this bacteria releases acetate, which is conveniently a food source for naturally occurring Geobacter type bacteria. Still, one more bacteria found in anaerobic digester sludge was introduced because it produced a chemical that could efficiently shuttle electrons to the electrode. While power output is quite high for a microbial fuel cell, it is still very low for practical deployment.

The U.S. Naval Research Laboratory (NRL), Center for Biomolecular Science and Engineering , has received a U.S. patent for a solar microbial fuel cell (SMFC). While that sound all very techno-speak, the marvel of it is that this microbial fuel cell is self-assembling, self-repairing, self-contained, and driven entirely by sunlight and microorganisms. Under abundant sunlight, the sealed fuel cell’s microbes generate electricity at the same time they produce glucose and oxygen at the electrodes. This means the microbes can continually remake food and oxidant for making electricity from their waste products.

Again, while power output for each individual cell is low, these cells are stackable, and like regular solar cells in a solar panel, they can be connected to each other to increase their overall output.

Back in 2015, Bristol University researchers devised a self-propelled robot that could swim around like a water bug, making it’s own electricity in its own microbial fuel cell-stomach just by gulping dirty water.

Dubbed the “Row Bot” because of it’s little oar-like paddles, the main practical use for it is to clean up pollution in lakes and ponds. Groups of Row Bots could spend months swimming and feeding in contaminated waters, gradually restoring them. Interestingly enough, research interest has drifted towards using the microbial fuel cell-stomach to help power low voltage “soft robots” made of artificial muscle materials and other similar robots that autonomously forage. The reason? Foraging will let such robots function independently for long periods of time in environments that are too dangerous for humans to explore.