Having Your Manure and Energy, Too

John Davis

usda-logo2A new report from the USDA says that farmers and ranchers could turn manure into energy without taking too much of it out of the fertilizer market.

This story from Biomass Magazine says the report, entitled “Manure Use for Fertilizer and for Energy,” points out that turning manure into energy is really underused in this country:

Interest is growing in manure-to-energy systems, but implementation remains scarce in the United States. Anaerobic digestion and combustion are the most common processes used to obtain carbon dioxide and methane for electricity generation, the report says. Most digesters are on-farm systems at dairy and hog farms and combustion can be beneficial to fuel large power plants with poultry litter and fed cattle manure, which have higher energy and lower moisture content. Only one combustion plant operates in the U.S., using litter from 6.6 percent of turkey production. Digestion systems cover less than 3 percent of dairy cows and less than 1 percent of hogs, according to the report.

Using manure for energy won’t impose substantial constraints on manure for fertilizer supplies, the report says, because the technologies do not consume the nutrients that are beneficial for plant growth. In anaerobic digestion, the nitrogen, phosphorus and potassium remain in the effluent to be spread on fields. Digestion also eliminates odors and nearly eliminates pathogens, according to the report. Combustion plants do burn nitrogen nutrients, but leave the phosphorous and potassium in concentrated form in the ash residues. In addition, manure-to-energy projects function in markets for fertilizer and energy and will be most economical in those areas where acquisition costs of manure are lowest, the report says. In turn, manure costs will be lowest where manure is in excess supply, with the least value as fertilizer, the report said.

The report goes on to say that economics is still the big stumbling point for wider implementation. Just 91 commercial dairy farms and 17 hogs farms were using digesters to turn the manure into energy, and there are few commercial combustion plants in the U.S. But it does believe that will change if there’s more public support for such ventures.

biomass, biomethane