Nutrients and Waste Management

Nutrients Management
 
Take nitrogen (N) as an example. N arrives on farm generally in the five forms as shown in the following figure. Within the boundaries of the farm, there is a “Recycling” of nutrients between the livestock and crop components. Manure nutrients are recycled, at least in part, for crop production. Feed crop nutrients are in turn recycled as animal feed for livestock or poultry production. It is preferable that nutrients leave a livestock operation as “Managed Outputs” including meat, milk, eggs, crops, or manure transferred to an off-farm user. The balance between N inputs and managed outputs defines the quantity of N lost to the environment. Livestock operations that achieved a balance represent a potentially sustainable production system. In contrast, livestock operations with a significant imbalance can cause increased risk to environmental quality. Much of the N loss to air can are in forms of NH3 or N2O.

 

 

Waste Management

Animal manure is one important source of air pollutants. Producers face challenges associated with manure accumulation, storage and disposal. Proper waste management is needed to control odor and dust; to prevent waste from impacting water quality; and to recycle the nutrients in waste.

  • Nutrient management plan
  • Runoff control
  • Seepage control
  • Feedlot solid manure collection
  • Design  and maintenance of storage facility
  • Aerobic or anaerobic system
  • Land application management of liquid and solid manure
  • Crop utilization
  • Composting
  • Energy conversion: anaerobic digestion, combustion or gasification

Anaerobic Digestion of Livestock Manure

Anaerobic digestion (AD) of livestock manure offers a management option for livestock producers to generate energy from manure. The AD decomposes manure and converts it into a more stable material with reduced odor and pathogens while generating biogas. The primary component of the biogas is methane (CH4), which is a greenhouse gas (GHG) if released into air, but also could be a promising source of energy if captured. The biogas generated from AD can be burned directly for on farm applications (e.g., producing hot water or heat to maintain temperature of the digester), or be used to fuel generators to produce electricity. The digested manure has nutrient value as fertilizer. Dairy based AD can have the potential added benefit of reusing digested fibers for bedding. 

Even though AD is a century-old process, the technology is still evolving to adapt the process successfully on the commercial scale for producing energy. U.S. Environmental Protection Agency (EPA) estimated that AD systems are technically feasible at more than 8,000 U.S. dairy and swine facilities (AgSTAR, 2010). However, only 3% of these facilities currently have operational AD systems and failures of AD systems have been reported. One of the main reasons for failures was inadequate management of the system. A small mistake in maintenance can result in a significant decline in biogas production and require months to correct. Other reasons include excessive operating costs and unreliable market for biogas. Recently, interest in AD of livestock manure has been renewed with evolving market for “carbon credit” as well as biogas energy. Both financial support from government and the number of designers available for service in the U.S. has increased significantly.

A cooperative effort among the U.S. Departments of Agriculture, Energy and the EPA to promote bio-gas projects is known as the AgSTAR. The Program offers a variety of tools, resources, and events to increase the use of AD systems. It is the premier U.S. resource for information and assistance with regard to AD of livestock manure. There are multiple grant and cost-share programs available for farm operators who are interested in AD. For detailed information on funding programs, see the AgSTAR funding database, Funding On-Farm Biogas Recovery Systems: A Guide to Federal and State Resources (http://www.epa.gov/agstar/tools/funding/index.html) and the factsheet Funding Programs for Developing Anaerobic Digestion Systems (http://www.epa.gov/agstar/documents/agstar_federal_incentives.pdf).

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