Advances in Cow Pie Energy

From my previous post, Dog Poop Park Lights, I introduced an interesting and creative way to use all that dog poop that fills the backyard and park trashcans. It may come as a surprise to some, but this is not the first idea or process that has used animal feces to obtain energy.

Dating back to the early 1700s, when warmth and light accounted for the majority of energy consumption in the American West, Native Americans would build pottery kilns using dried buffalo and cow pies. They would use the dung and stack it on all side of the pottery to build high temperature fires used to cure the pottery. You may ask why not use wood, or some other more conventional combustible material? Well, when out on the plains of the western United States, buffalo were much more abundant than trees, and plus the Native Americans were known for their ability to not let any part of the animal go to waste. Actually, the dried dung has a heating value that is very close to wood’s heating value. The heating value of different materials is the amount of heat that is produced from the combustion (burning) of a unit amount of that material. But the main reason buffalo or cow pies were used to cure pottery is due to the fact that they contain no sap, and primarily made up of undigested grass. When you burn wood, sap becomes very hot and stains the pottery. This is the same thing that happens when cheese or other foods bake onto the pan after being in the oven for a long time. The picture below shows a Native American woman with the pottery she baked using buffalo and cow pies (filling the wash tubs). 

Not only did the Native Americans make use of cow pies, but the early American settlers also used cow pies to heat their homes. Cow pies were allowed to dry out in the pasture and then collected. One good thing about burning cow pies was that you didn’t have to chop them up into manageable pieces, a necessary step in burning wood. The women and children of the house would usually be in charge of collecting this free fuel. A surplus of cow pies could be collected over the summer, to provide a nice and warm home during the winter months. The picture below shows one early settler’s wheelbarrow full of sun dried cow pies, ready to be used to heat their home.

So why haven’t many people heard of these very practical ways of using cow manure? Mostly because the discovery and use of other fossil fuels such as oil and coal stole the scene away from cow pies. So just recently, since issues such as global warming and rising fuel prices have occurred, alternative energy has made a comeback.

So how has waste to energy, in particular, cow pies or manure to energy grown to be able to compete with the energy giants? It all starts with a free feedstock that is produced 24 hours a day, 365 days a year, cow manure. The most obvious places that an abundance of cow manure is produced are at feedlots and dairies. The same process that was used to turn dog poop into methane and then burned to create light can be applied in a much larger scale at these locations. Manure is cleaned out of the corrals on a regular basis and stock piled in one area where the waste to energy process can proceed. There are several types of anaerobic digesters that can be used. Underground covered lagoons and aboveground vessels can both be used to hold the manure and water mixture (approximately 2 parts water and 1 part manure). By keeping the mixture agitated and warm (around 95 F) the manure under goes several reactions that eventually generates biogas (50 % methane/ 50% CO2). 

However, before the methane that is produced can be used it must be separated from the carbon dioxide that is also produced. Further processing can be done to remove other impurities such as hydrogen sulfide, a poisonous gas. Finally the methane is dried and all the water is removed from the vapor phase. This almost pure methane stream can then be used in several ways. The natural gas can be compressed and injected into a natural gas pipeline, used as a fuel to run an electrical generator, or used in household furnaces and ranges. Many times local power companies will even set up an agreement with feedlots and dairies to put the extra electricity generated back into the grid. 

Don’t forget that there is left over sludge that needs to be disposed of or used after the process is complete. Fortunately, cow manure has long been used as a fertilizer. The left over sludge still has all the essential components and compounds to be spread over fields to fertilize the next growing seasons crops. 

There are however some down sides to using this type of waste to energy process. First, large amounts of water are needed to prepare the feedstock. In places where water is not as easily obtained this process could no longer be economical. Also, the bacteria that digest the manure are very sensitive. These bacteria must be held at an almost constant high temperature and oxygen must be kept out of the system. Below is a photo of modern biogas plant used to turn cow manure into clean burning and efficient energy.