Benefits and Challenges of Manure-Based Energy

Animal Manure Management March 14, 2016 Print Friendly and PDF

Manure-to-energy systems on farms can deliver a number of economic benefits for farmers. They can also increase the amount of renewable energy in the United States and, if handled correctly, protect streams and rivers from the polluting effects of surplus nutrients. (Related: Explore other manure treatment technologies).

Financial Benefits

A farmer with an on-site, manure-based energy system can generate heat for the farm’s buildings and equipment, generating significant annual savings in energy costs. This new source of heat could replace traditional propane heat in poultry houses, for use in:

BTU Values of Manure and
Other Feedstocks

Feedstock

(Btus/lb)*

Chicken Litter 6,500
Swine feces 8,000
Dairy manure 8,000
Feedlot manure 4,500
Wood 8,000
Municipal sewage 4,000-8,000
Coal, bituminous 12,000

Manure has enough energy to be valuable, providing moisture is at acceptable level.

* Values reported are based on dry matter basis

Source: Farm Manure-to-Energy Initiative

  • Air-to-air systems
  • Ceiling-mounted hot water hydronic heat exchangers
  • Hot water hydronic floor systems

A farmer can also sell ash and bio-char — two nutrient-rich co-products of the thermochemical process that can be used as fertilizer or soil amendments. Although markets are still emerging for these products, field research indicates that ash and biochar can be used as a substitute for commercial fertilizer to support row crop production. Over the long term, such phosphorus co-products could become increasingly valuable. World consumption of phosphate fertilizer is expected to increase, supplies are expected to decline over the next few decades. The United States is already dependent on phosphorus imports. In fact, our nation is the world’s leading importer of phosphate rock and our domestic production is expected to continue its recent decline. Globally, phosphorus from mined sources is predicted to peak around 2034. Although exploration and expansion of phosphate rock production continues, especially in Africa and Australia, phosphorus from other sources may have a growing value in the marketplace.

In the future, farmers may also be able to sell surplus electricity from energy production to utility companies that manage the local grid, or sell their entire supply on the wholesale market. Projects coupling thermal manure-to-energy technologies with electric generation are still in the research and development phase.

Other benefits that may be realized in the future include the sale of credits, such as those for renewable energy, carbon offsets, or nutrient reduction. Although the markets for these credits are still emerging, the potential for future growth is drawing the attention of entrepreneurs.

Water Quality Benefits

In some locations, animal production creates more manure nutrients (especially phosphorus) than can be effectively used as fertilizer. Rainwater carries surplus nutrients from fertilizer into streams, rivers, and bays, where high levels of nitrogen and phosphorus trigger harmful algae blooms. Manure-based energy provides another use for manure and converts the nutrients into ash and bio-char. These co-products are much easier and more cost-effective to transport for use in other locations where nutrients are needed in the soil.

Reliable, Renewable Energy

Energy produced from manure, a form of biomass, is one of the most dependable forms of energy in the United States. Wind, water, and solar sources of energy all produce an inconsistent flow that makes it more difficult to stabilize the regional energy grid.  The percentage of time in which these types of facilities operate at or near their designed capacity ranges from approximately 17 to 30 percent. In contrast, the capacity factor for biomass is 85.5 percent—second only to nuclear on a nationwide scale. As long as the American consumer relies on a steady diet of milk, meat and eggs, there will be a steady supply of animal manure as feedstock for energy projects. 

Challenges

On-farm manure-to-energy technologies are expensive and require initial investments in infrastructure as well as on-going maintenance and operation costs. Additionally, few vendors have a track record for long-term, successful on-farm performance with multiple farm clients. Most of these technologies are still in the early phases of commercialization, or in the research and development phase. Also, matching technologies to the needs of each unique farm, and customizing systems when necessary, takes time. Systems installed to produce heat will require more labor than traditional propane-fueled heating systems.

Manure-to-energy systems will not be right for every farm, or in every setting. For example, a farmer with more poultry litter than needed to fertilize his own fields typically sells it for use on surrounding farms. If the litter is used to produce energy, it loses its immediate value as a source of nitrogen fertilizer. Therefore, such systems may be most appropriate in regions with concentrated animal production and widespread surplus manure. In such a setting, poultry litter has less value as a fertilizer on nearby farms because high soil phosphorus levels limit how much manure most farms can use. Farmers may find that converting surplus litter to energy, and producing an ash or biochar co-product that can be transported long distances and sold, is a better choice.

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USDA / NIFA

This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.