Manure.....its greener then you'd think

By: Liz Staples
Student ID: 0725141

Animal manure has the potential of reducing net GHG emissions by up to 3.9%, says study. This, found in Environmental Research Letters, comes from the paper written by Amanda Cueller and Micheal Webber of the University of Texas titled “Cow power: the energy and emissions benefits of converting manure to biogas”. It states that by anaerobically digesting animal manure, which is the decomposition by bacteria into its basic elements, the biogas that results can be used to substitute a percentage of coal electricity used today.

In the United States alone, livestock produce over 1 billion tons of manure on a yearly basis. This manure is stored outside, left to decompose emitting foul odours and pollutants, contaminating water sources, and even emitting various greenhouse gases. When manure sits or is spread over fields, it releases methane and nitrous oxide which have an immense global warming potential then that compared to carbon dioxide.

In 2005 alone, the EPA (Environmental Protection Agency) reported that 7% of GHG emissions in the US were from the agricultural sector, equivalent to 536 million metric tons. And of this, up to 118 million metric tons came from sitting manure.

“Finding other approaches to manure management that decrease these emissions represents a valuable starting point for mitigating concerns about global climate change in the agricultural sector,” said Cueller, who goes on to say that biogases greatest potential is in replacing coal in electricity generation. Using two scenarios, Cueller compares the treatment of livestock manure. Scenario A, being ‘business as usual’: manure sits and coal is burned, and Scenario B, burning biogas produced from the manure to offset coal-fired power.

The MREC (Midwest rural energy council) of the University of Wisconsin-Madison estimates that one kW requires 5 to 8 dairy cows. Cueller, using various mathematical relationships and following the methods and results of scientific studies before, shows that when total livestock is taken into account, the energy possible from poultry biogas alone ranges from 9.2- 14.7 billion kWh annually, while dairy cows range from 6.8 to 10.8 billion kWh. As the United States consumes 3.8 trillion kWh annually, total biogas from all livestock can reduce up to 2.9% of this staggering amount.

But how does biogas really work? Combustion of the methane found in biogas, converts energy stored in the bonds of molecules into useable energy.
This combustion of methane results in a release of carbon dioxide into the atmosphere, however this output proves to be less then that which results from burning coal. Data comparing Scenario A and Scenario B show that net emissions of carbon dioxide can be reduced by up to 157.5 billion kg from the usage of biogas in Scenario B. Of course these values are affected by efficiency of the conversion, and the percentage of methane in the resulting biogas. With increased efficiency and methane percentages, carbon dioxide emissions decreased.

Scenario B effectively replaces two sources of Greenhouse gas emissions, manure and the burning of coal, with a more ‘friendly’ source, biogas.

There are huge benefits for farmers when converting from old smelly habits to new biogas technology. With the new, odours, pathogens, contaminants and pollution is reduced so all that is left is to gain!! And these farmers will gain in time, heat and of course some in the wallet too.

Many farmers have begun to realize the efficiency of this renewable ‘poop-power’ as Mark St. Pierre, a farmer new to this method says, “One thing for sure we can count on is a constant supply of it.”

And while there seems to be nothing but good things coming from these operations, Cueller recognizes that the logistics of widespread biogas production must be determined at the local level before implementing such a plan. “Other issues such as best methods to process and distribute biogas should also be analyzed before biogas production and use are implemented in widespread fashion.” Cueller says that more research is needed to consider such an objective, but who knows maybe soon, the world will be run on this new ‘poop energy’.


Scientific Journal Article:
Dr. Michael E. Webber and Amanda D Cuellar. Cow Power: The Energy and Emissions Benefits of Converting Manure to Biogas. Environmental Research Letters, 3 034002 (pp), July 24, 2008. http://iopscience.iop.org/1748-9326/3/3/034002/fulltext

Other information found from:
http://www.usatoday.com/news/nation/2006-12-03-cow-power_x.htm

http://www.mrec.org/anaerobicdigestion.html