Techies 37: Generating Energy From Poop and much more

Engineers at Stanford University have devised a new way to generate electricity from sewage using naturally-occurring “wired microbes” as mini power plants, producing electricity as they digest plant and animal waste.

In a paper published today in the Proceedings of the National Academy of Sciences, co-authors Yi Cui, a materials scientist, Craig Criddle, an environmental engineer, and Xing Xie, an interdisciplinary fellow, call their invention a microbial battery.
One day they hope it will be used in places such as sewage treatment plants, or to break down organic pollutants in the “dead zones” of lakes and coastal waters where fertilizer runoff and other organic waste can deplete oxygen levels and suffocate marine life.
At the moment, however, their laboratory prototype is about the size of a D-cell battery and looks like a chemistry experiment, with two electrodes, one positive, the other negative, plunged into a bottle of wastewater.
Inside that murky vial, attached to the negative electrode like barnacles to a ship’s hull, an unusual type of bacteria feast on particles of organic waste and produce electricity that is captured by the battery’s positive electrode.
"We call it fishing for electrons," said Criddle, a professor in the department of civil and environmental engineering and a senior fellow at the Stanford Woods Institute for the Environment.
The tubular growth depicted here is a type of microbe that can produce electricity. Its wire-like tendrils are attached to a carbon filament. This image is taken with a scanning electron microscope. More than 100 of these "exoelectrogenic microbes" could fit side by side in a human hair.  (Xing Xie, Stanford Engineering)
Scientists have long known of the existence of what they call exoelectrogenic microbes – organisms that evolved in airless environments and developed the ability to react with oxide minerals rather than breathe oxygen as we do to convert organic nutrients into biological fuel.
During the past dozen years or so, several research groups have tried various ways to use these microbes as bio-generators, but tapping this energy efficiently has proven challenging.
What is new about the microbial battery is a simple yet efficient design that puts these exoelectrogenic bacteria to work.
At the battery's negative electrode, colonies of wired microbes cling to carbon filaments that serve as efficient electrical conductors. Using a scanning electron microscope, the Stanford team captured images of these microbes attaching milky tendrils to the carbon filaments.
"You can see that the microbes make nanowires to dump off their excess electrons," Criddle said. To put the images into perspective, about 100 of these microbes could fit, side by side, in the width of a human hair.

Self Regenerating polymer

Researchers at IK4-CIDETEC have created a polymer capable of self-repairing at room temperature without the need of any catalysts or any external stimulus. After being cut in half, the material is able to regenerate itself in just two hours, fully recovering its mechanical properties. 

This new polymer is based on a poly(urea-urethane) type composition, a material which is widely used in industry. Therefore, and because it can be easily scaled-up, this new development is expected to reach the markets shortly. Its discovery opens a wide range of industrial applications in the use plastic components, in both electrical and automotive sectors, as well as in construction and in the development of biomaterials.

The work, which was published in the journal Materials Horizons from the Royal Society of Chemistry, was developed in the framework of the SHINE European project, where IK4-CIDETEC participates as a partner in a consortium of various European companies, research centres and universities.

IK4-CIDETEC plans to continue working in this field, with the aim of developing harder self-repairing materials through the incorporation of reinforcements or the use of other technologies.