Stories tagged manure

Jul
13
2010

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.

Jul
13
2006

Cow Power: photo by Art Oglesby,    Cow manure can produce electricity.
Cow Power: photo by Art Oglesby, Cow manure can produce electricity.

What comes out of the back end of a cow?

Milk and manure. The cows at the Audet family's Blue Spruce Farm make almost 9,000 gallons of milk a day — and about 35,000 gallons of manure. With the help of their power company, Central Vermont Public Service Corp., the Audets have devised a way to extract methane from the manure and pipe it to a generator. They make enough electricity to power 300 to 400 average Vermont homes.

How can electricity be made from cow manure?

If cow manure is pushed into a long, narrow tank and held around 100 degrees, in about 20 days bacteria will digest the manure into methane gas and a liquid slurry. The methane can run an engine and generator to make electricity. A dry, odor-free, fluffy brown substance that is used as bedding for the cows can also be extracted. The remaining liquid contains enough nutrients that it can be used as fertilizer for the farm's feed crops.

Do farms in Minnesota make electricity from manure?

Since late 1999, the Haubenschild farm has been converting their cow manure into electricity. At first they, too, digested manure producing methane which fueled a generator to produce electricity. Then, on Jan. 27, 2005, for the first time anywhere in the world, the methane was fed into a fuel cell.
A fuel cell is like a battery. A chemical reaction generates the electricity. It is totally quiet, and the only waste product is clean water. Haubenschild said it costs 5.1 cents per kilowatt hour to produce electricity from the fuel cell and Great River Energy will buy the surplus electricity from the fuel cell for four cents per KWH. If Minnesota power companies can create a progam similar to Vermont's Cow power program, customers willing to pay a couple extra cents per KWH would allow farmers to make money instead of losing money.

What are the benefits of anaerobic digestion?

    Reduced odor and greenhouse gas emissions
    Fewer pathogens in the digested product
    Nutrient rich effluent to apply to crops
    Electricity to use and to sell
    Possible sale of separated solids as a garden amendment
    Good manure management
    Pay back on the investment

Read more about Cow power
Biosystems and Agricultural Engineering Department, Univ. of MN.
Princeton Union-Eagle
Pioneer Press
FAQ about CVPS Cow Power