Jul
13
2010

The cornucopia of the 21st century is a cow’s rear-end

Brown gold!: This is actually the solid byproduct of a manure-to-methane operation. As you can see, it holds no fear for the owner of this bare hand.
Brown gold!: This is actually the solid byproduct of a manure-to-methane operation. As you can see, it holds no fear for the owner of this bare hand.Courtesy kqedquest
We’ve talked about the delights of cow feces before on Science Buzz, but mid-July always puts me in the mind of “brown gold” (coincidentally, the last occasion it came up was exactly four years ago today), and any time there’s talk of turning an animal into a fuel source, I get excited. (Remember that fuel cell that ran on the tears of lab monkeys? Like that.) Why not take another look?

So here you are: another wonderful story of cows trying their best to please us, before they make the ultimate gift of allowing their bodies to be processed into hamburgers and gelatin and cool jackets.

Poop jokes aside (j/k—that’s impossible), it is a pretty interesting story. The smell you detect coming from cattle farms is, of course, largely from the tens of thousands of gallons of poop the cattle produce every day. The decomposing feces release lots of stinky methane. (Or, to be more precise, the methane itself isn’t smelly. The bad smell comes from other chemicals, like methanethiol, produced by poop-eating bacteria along with the methane.)

Aside from being, you know, gross, all of that poop is pretty bad for the environment. The methane is released into the atmosphere, where it traps heat and contributes to global warming (methane is 20 to 50 times more potent than carbon dioxide as a greenhouse gas), and the poop itself is spread onto fields as fertilizer. Re-using the poop as fertilizer is mostly a good idea, but not all of it gets absorbed into the soil, and lots of it ends up getting washed away into rivers, lakes, and streams, where it pollutes the water.

Some farms have managed to address all of these problems, and make money while doing it.

Instead of spreading the manure onto fields right away, the farms funnel all the poop into swimming pool-sized holding tanks, where it is mixed around and just sort of stewed for a few weeks. All of the methane gas produced by bacteria as it breaks down the manure is captured in tanks. What’s left is a fluffy, more or less sterile, solid that can be used as bedding for the animals, or mixed in with soil, and a liquid fertilizer that can be spread onto fields.

The methane can then be used on-site to generate electricity, either by burning it in a generator, or using it in a fuel cell. (The methane is broken apart and combined with oxygen from the air to produce electricity, water, and carbon dioxide.) A large farm will produce enough electricity to power itself and several hundred other houses. (The extra electricity is just put back into the power grid and sold to the power company.)

Whether the methane is burned or used in a fuel cell, the process still creates carbon dioxide. However, CO2 isn’t nearly as bad as methane when it comes to trapping heat, and because the original source of the carbon was from plant-based feed, the process can be considered “carbon-neutral.” (Although one might argue that the fossil fuels involved in other steps of the cattle farming process could offset this. But let’s leave that be for now. It’s complicated.)

The downside is that setting up an operation to capture and process manure, and to generate power by burning it is expensive—it took about 2.2 million dollars to do it at the farm covered in the article, with about a third of that coming from grants. Still, the byproducts (electricity, fertilizer, soil/bedding) are profitable enough that the system could pay for itself over the course of a few years.

It’s amazing, eh? Out of a cow’s butt we get soft, clean bedding, liquid fertilizer, and electricity, all without the bad smell. What a world.

Your Comments, Thoughts, Questions, Ideas

bryan kennedy's picture

If plans like this are implemented, which sounds like a great idea, we are going to have to figure out how to make sure that all the methane produced here is very tightly contained.

Since methane is a a more evil* greenhouse gas, even small leaks can end up doing more harm than good. Some studies have shown that we can surely get better at not leaking this valuable resource out into the atmosphere, but we'll need to keep an eye/nose on methane leaks as it become a more important fuel.

* - OK, going a bit crazy with the personification.

posted on Tue, 07/13/2010 - 2:25pm
JGordon's picture
JGordon says:

It's a remarkable sort of project, isn't it? I've been thinking a lot about energy lately, and how we do or do not make the most out of the byproducts of energy-intensive operations, and this seems to fit pretty well with that.

One of the complaints leveled against the meat industry is that we put a lot of energy into raising animals (in the form of feed and all the fossil fuels it takes to grow, process, and transport the feed and meat), and we get relatively little energy out of it (in the form of meat). Installing biogas digesters in farms would take us a little way, at least, toward reclaiming some of the energy that goes into the whole operation. (And a high-quality energy at that.)

I suppose it would be dizzyingly complicated to try to calcuate all of the energy inputs and outputs of raising meat, but it would be interesting to see how much more efficient, overall, recapturing methane makes the process.

I also wonder how large a farm has to be for this sort of thing to be practical.

posted on Tue, 07/13/2010 - 2:54pm
Shana's picture
Shana says:

This is super cool. I dig how one of the final products is sterile fertilizer--the thought of growing vegetables to eat raw with raw dung has always sounded like a terrible idea to me. Plus I just dig the frugality of it.

I've been reading that methane is also a serious problem with rotting waste food--I wonder if there are similar systems that compost food and capture the methane?

posted on Wed, 07/14/2010 - 9:58am

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