Featured Research

from universities, journals, and other organizations

Scientists use 'wired microbes' to generate electricity from sewage

Date:
September 16, 2013
Source:
Stanford School of Engineering
Summary:
Engineers 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.

The release describes nature of these microbes; more than 100 can fit side by side in the width of a human hair; the microbes are white tubes; they are attached to the carbon filaments of the battery; the tendrils are the "wires" referred to; images were taken by scanning electron microscope.
Credit: Xing Xie, Stanford University

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.

Related Articles


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.

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.

As these microbes ingest organic matter and convert it into biological fuel, their excess electrons flow into the carbon filaments and across to the positive electrode, which is made of silver oxide, a material that attracts electrons.

The electrons flowing to the positive node gradually reduce the silver oxide to silver, storing the spare electrons in the process. According to Xie, after a day or so the positive electrode has absorbed a full load of electrons and has largely been converted into silver.

At that point it is removed from the battery and re-oxidized back to silver oxide, releasing the stored electrons.

The Stanford engineers estimate that the microbial battery can extract about 30 percent of the potential energy locked in wastewater. That is roughly the same efficiency at which the best commercially available solar cells convert sunlight into electricity.

Of course, there is far less energy potential in wastewater. Even so, the inventors say the microbial battery is worth pursuing because it could offset some of the electricity now use to treat wastewater. That use currently accounts for about three percent of the total electrical load in developed nations. Most of this electricity goes toward pumping air into wastewater at conventional treatment plants where ordinary bacteria use oxygen in the course of digestion, just like humans and other animals.

Looking ahead, the Stanford engineers say their biggest challenge will be finding a cheap but efficient material for the positive node.

"We demonstrated the principle using silver oxide, but silver is too expensive for use at large scale," said Cui, an associate professor of materials science and engineering, who is also affiliated with the SLAC National Accelerator Laboratory. "Though the search is underway for a more practical material, finding a substitute will take time."


Story Source:

The above story is based on materials provided by Stanford School of Engineering. The original article was written by Tom Abate. Note: Materials may be edited for content and length.


Journal Reference:

  1. Xing Xie, Meng Ye, Po-Chun Hsu, Nian Liu, Craig S. Criddle, and Yi Cui. Microbial battery for efficient energy recovery. PNAS, September 16, 2013 DOI: 10.1073/pnas.1307327110

Cite This Page:

Stanford School of Engineering. "Scientists use 'wired microbes' to generate electricity from sewage." ScienceDaily. ScienceDaily, 16 September 2013. <www.sciencedaily.com/releases/2013/09/130916161733.htm>.
Stanford School of Engineering. (2013, September 16). Scientists use 'wired microbes' to generate electricity from sewage. ScienceDaily. Retrieved November 23, 2014 from www.sciencedaily.com/releases/2013/09/130916161733.htm
Stanford School of Engineering. "Scientists use 'wired microbes' to generate electricity from sewage." ScienceDaily. www.sciencedaily.com/releases/2013/09/130916161733.htm (accessed November 23, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Sunday, November 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Newsy (Nov. 23, 2014) Microsoft has robotic security guards working at its Silicon Valley Campus. Video provided by Newsy
Powered by NewsLook.com
Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

AFP (Nov. 21, 2014) Toyota presented its hydrogen fuel-cell compact car called "Mirai" to US consumers at the Los Angeles auto show. The car should go on sale in 2015 for around $60.000. It combines stored hydrogen with oxygen to generate its own power. Duration: 01:18 Video provided by AFP
Powered by NewsLook.com
Google Announces Improvements To Balloon-Borne Wi-Fi Project

Google Announces Improvements To Balloon-Borne Wi-Fi Project

Newsy (Nov. 21, 2014) In a blog post, Google said its balloons have traveled 3 million kilometers since the start of Project Loon. Video provided by Newsy
Powered by NewsLook.com
Raw: Paralyzed Marine Walks With Robotic Braces

Raw: Paralyzed Marine Walks With Robotic Braces

AP (Nov. 21, 2014) Marine Corps officials say a special operations officer left paralyzed by a sniper's bullet in Afghanistan walked using robotic leg braces in a ceremony to award him a Bronze Star. (Nov. 21) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins