One of the awesome things about living in the time we do is also one of the things that no one ever seems to mention – the sewer systems. The pipes and drains are below our feet, doing their thing every day, and a lot of us kind of seem to take it for granted. There’s quite a bit of energy that goes into processing and disposing of waste, though, which just makes the announcement at the 243rd National Meeting & Exposition of the American Chemical Society (ACS) that much greater: there is a new and efficient version of a machine that both processes sewage and makes electricity doing it, and that device could be commercially viable.
From Taking Energy to Making It
Current wastewater treatment tech has a lot of steps: separation, settling, filtration, biological digestion, and chemical treatment. There’s a lot of equipment, too, including settling tanks, macerators, membranes, and so on. At least one evaluation has estimated that wastewater treatment uses 2% of the United States’ overall energy consumption. It’s not the first waste-fueled machine in the United States, but it does seem to have the broadest potential application.
The machine in question, presented by Orianna Bretschger, Ph.D., is a new and improved version of a previous prototype. It’s a microbial fuel cell (MFC), and it has a 13% energy recovery capacity. That’s a pretty major improvement over the initial prototype, which had a 2% energy recovery capacity. Bretschger, when presenting the report, mentioned that this could have a significant impact on water treatment and availability, particularly in developing countries:
“We’ve improved its energy recovery capacity from about 2 percent to as much as 13 percent, which is a great step in the right direction. That actually puts us in a realm where we could produce a meaningful amount of electricity if this technology is implemented commercially. Eventually, we could have wastewater treatment for free. That could mean availability for cleaner water in the developing world, or in southern California and other water-short areas of the United States through the use of more wastewater recycling technologies.”
What’s A Microbial Fuel Cell?
An MFC is exactly what it says on the tin – it’s a biological fuel cell. Where traditional fuel cells convert fuel into electricity without igniting it (combining hydrogen and oxygen, as in the hydrogen fuel cell), an MFC uses organic matter as the fuel and microbes to break them down. As the microbes break down the organic matter, electrons (the movement of which constitutes electricity) are produced.
Bretschger’s revised MFC uses sewage from a bog standard sewage treatment plant. It’s made of a sealed container and an unsealed container, separated by a membrane. The microbes grow in a film on an electrode in the sealed chamber, sending electrons to the electrode and protons to the unsealed container. Oxygen in that container plus microbes on a second electrode plus the electrons from the sealed chamber combine to produce things that are not sewage and generate some electricity in the process (remember, electricity is electrons moving from point A to point B, which is pretty much what’s happening here).
The Final Results
The new prototype is less expensive than the first one, since initial titanium components have been replaced with PVC and graphite (although, it’s still six or seven times the cost per gallon of conventional water treatment tech). The Bretschger’s team hopes to keep bringing the cost down. The team also hopes to further improve energy recovery efficiency – right now, it’s at 13%. Bretschger thinks that if they can get a big enough device going at maybe 20-25% (the same numbers as some current mass-produced solar cells), they could actually power a conventional sewage treatment plant.
The device also removes the vast majority of organic matter and potentially disease-causing microbes, Bretschger also pointed out. Although, it’s not quite at the point of creating drinkable water along with electricity:
“We remove about 97 percent of the organic matter. That sounds clean, but it is not quite clean enough to drink. In order to get to potable, you need 99.99 percent removal and more complete disinfection of the water.”
Life is a cycle, guys. I don’t think any one single clean energy technology is going to be the salvation wave breaking us free of fossil fuels; rather, I think a lot of types of tech working in tandem will eventually do the trick. This particular little machine uses a resource that is never, ever going to be used up, and I’d say that makes it a pretty viable area for further research. What do you think? Let us know in the comments, below.
Don't want to miss a cleantech story? Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!
Have a tip for CleanTechnica, want to advertise, or want to suggest a guest for our CleanTech Talk podcast? Contact us here.