Microbial battery: Team uses 'wired microbes' to generate electricity from sewage

Sep 16, 2013
Stanford scientists have developed a "battery" that harnesses a special type of microbe to produce electricity by digesting the plant and animal waste dissolved in sewage. Credit: Xing Xie,Stanford Engineering

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 , and Xing Xie, an interdisciplinary fellow, call their invention a microbial battery.

One day they hope it will be used in places such as , or to break down in the "dead zones" of lakes and coastal waters where and other organic waste can deplete 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 to a ship's hull, an unusual type of bacteria feast on particles of 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.

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 into biological fuel.

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

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 , 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 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

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. "Though the search is underway for a more practical material, finding a substitute will take time."

Explore further: First-of-a-kind supercritical CO2 turbine

More information: Microbial battery for efficient energy recovery, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1307327110

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User comments : 14

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MR166
1.6 / 5 (19) Sep 16, 2013
There is a serious lack of absolute figures here. WOW there is a jar connected by clip leads to a resistor and I am supposed to be impressed. There must be better uses for an electron microscope than taking pictures for propaganda releases.
MR166
1.2 / 5 (18) Sep 16, 2013
Also, if you care to notice the clip leads are both "Green". Ah, green energy the salvation of mankind.
MikeBowler
2.5 / 5 (10) Sep 16, 2013
Also, if you care to notice the clip leads are both "Green". Ah, green energy the salvation of mankind.

two words: "shut up"
Jeddy_Mctedder
1.4 / 5 (16) Sep 16, 2013
the whole point is to make small modular bacterial fuel cells combined with some other type of treatment that allows you to to completely treat your 'waste' without needing access to a sewage pipeline.

at that point, no more money will need to be spent on maintaining sewage lines, or running sewage plants. or on running pumps to keep the entire hydraulic balance of a huge water pumping system in place

that's a massive savings. massive.

it might not be doable at the smallest scale of one house, but maybe 10 or 20 or 1000 houses. a passive micro-sewage system that runs on the electricity produced by the fuel cell is basically one that needs very little labor and is thus a huge savings economically.

the point of this technology is NOT to compete with electricity generation.
Lorentz Descartes
1.3 / 5 (13) Sep 17, 2013
"the biggest challenge is finding a cheaper positive node material than silver oxide" - I would like add another big challenge: How robust is this as a biological system? Because there are certainly challenges to a bacterial colony in sewage - diverse chemicals (disinfectant soap etc), not to mention a whole ecosystem of aggressive microorganisms.

And also, if these were not enough, what happens during the maturity of the electrode colony? Wouldn't it develop a mucus layer that isolates from the raw sewage, thus reducing effectiveness. Studies in laboratory conditions of the first few days of such a setup are nice and good, but they are still far from economical, even with a better electron receiver.
THEFORREAL
2.3 / 5 (3) Sep 17, 2013
what type of microbes were used? What is their scientific name?
Kiwini
1.2 / 5 (20) Sep 17, 2013
Also, if you care to notice the clip leads are both "Green". Ah, green energy the salvation of mankind.

two words: "shut up"


Dear Mr. Bowler-

On line forums like this one were created to allow/encourage discussion between its' members. Attitudes like yours would end that.

You must be a liberal, or a "progressive". Not a Democrat, a Republican, or an independent, just someone who will not tolerate any POV that isn't their own, ie: a conversation-killer in a place created to exchange ideas, not shovel dogma....

Piss off, you wanker.

MR166
1.4 / 5 (18) Sep 17, 2013
Just like any other religion, members of the green religion get very very mad when you question their dogma.
MikeBowler
1.5 / 5 (8) Sep 18, 2013
Just like any other religion, members of the green religion get very very mad when you question their dogma.

OK you want a proper reply ??

the clip sheaths and wire being green in color doesn't have a damn thing to do with our efforts to slow global warming, there are no ifs or buts about it, my keyboard is green but that doesn't mean it's trying to be more power efficient than any other keyboard (btw i'm actually not joking my keyboard is really green in color)
antialias_physorg
4.7 / 5 (3) Sep 22, 2013
Also, if you care to notice the clip leads are both "Green". Ah, green energy the salvation of mankind.

That has to be one of the dumbest arguments made. Ever.
What difference does it make what color leads they use?
hexafraction
1 / 5 (1) Sep 22, 2013
Now, generating a small amount of energy from sewage is interesting, but a converse could be even more economically useful. Given similar technology to interface at a microelectronic scale with microorganisms, the generation of glucose from CO2 could occur given an electrical input, and the glucose then fermented to ethanol for commercial purposes.
antialias_physorg
5 / 5 (1) Sep 23, 2013
the generation of glucose from CO2 could occur given an electrical input, and the glucose then fermented to ethanol for commercial purposes.

You don't need an electrical input for that. Humans have been doing this for millennia.
'Waste' in. Add microbes (yeast). Get fermented sugars out (alcohol).
Howhot
3.7 / 5 (3) Sep 24, 2013
Also, if you care to notice the clip leads are both "Green". Ah, green energy the salvation of mankind.

two words: "shut up"


Dear Mr. Bowler-

On line forums like this one were created to allow/encourage discussion between its' members. Attitudes like yours would end that.

You must be a liberal, or a "progressive". Not a Democrat, a Republican, or an independent, just someone who will not tolerate any POV that isn't their own, ie: a conversation-killer in a place created to exchange ideas, not shovel dogma....

Piss off, you wanker.


Blow off ya nard head. A twit of your level can only understand one word, "UNK".
Neinsense99
1 / 5 (4) Sep 29, 2013
the generation of glucose from CO2 could occur given an electrical input, and the glucose then fermented to ethanol for commercial purposes.

You don't need an electrical input for that. Humans have been doing this for millennia.
'Waste' in. Add microbes (yeast). Get fermented sugars out (alcohol).

The method you outline may also explain some of the posts here.