Manure Could Provide U.S. Power

Taxing greenhouse gas emissions would allow manure to compete economically with fossil fuels and to produce 5.5% of U.S. electricity needs by 2050, according to a new analysis (Environ. Sci. Technol., DOI: 10.1021/es104227y).

Today, a tiny fraction of the manure from the nation’s 2.2 million cattle, pigs, and chickens is fed into power plants called anaerobic digesters. Bacteria in the digesters break down the waste to produce methane, which the plants burn to generate electricity. There are about 150 anaerobic digesters in the U.S., which produce power at about double the average cost of energy from fossil fuels.

David P.M. Zaks of the University of Wisconsin, Madison, and his colleagues wanted to know whether power from anaerobic digesters became more economically viable under different energy policies. Using data from anaerobic digesters such as their capital costs, costs of hauling manure to the plants, and their emissions savings, the researchers employed the MIT Emissions Prediction and Policy Analysis model, a well-known computer simulation of the world economy.

They found that a climate policy similar to the so-called “cap and trade” one that Congress considered but failed to pass, says Zaks, would have made power from anaerobic digesters profitable in replacing 5.5% of the country’s energy needs. In the policy, a nationwide limit on emissions would make energy from fossil fuels progressively more expensive, peaking in 2050 at $316 per ton of carbon dioxide.

In addition to replacing fossil fuels, the digesters would provide the benefit of reducing methane release from manure, Zaks says. The http://www.epa.gov/climatechange/emissions/usinventoryreport.html that the methane from livestock manure currently makes up 0.8% of the country’s greenhouse gases. If digesters produced 5.5% of U.S. electricity, the researchers found, they would also reduce emissions from livestock by the equivalent of 151 million metric tons of CO₂.