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Dairy Manure Collaborative:
Technologies for Treating Dairy Manure
Technology Assessment
Many technologies are currently promoted for treatment of dairy manure, and it can be difficult to determine their practical feasibility. The Agriculture Program and the California Air Resources Board co-chaired the Dairy Manure Technology Feasibility Assessment Panel 
. This panel evaluated and published a report on technologies for managing dairy manure under conditions prevalent in California's San Joaquin Valley. The University of California Cooperative Extension is currently evaluating additional technologies. We will post the results from that process here. Other groups are also conducting technology assessments, notably Farm Pilot Project Coordination, Inc., which evaluates technologies and funds pilot projects to treat all types of manure.
Treatment Systems and Pilot Projects
Many of the available technologies address only a portion of dairy manure, leaving the rest untreated. For example, anaerobic digestion converts organic carbon in manure to carbon dioxide and methane; this "bio-gas" can be burned to generate electricity and heat. But the process does not treat the dissolved nutrients and salts that can degrade water and soil quality. Combinations of complementary technologies could comprise a comprehensive dairy manure treatment system. Below is a generalized model of such a system; many variations are certainly possible.
Blue boxes indicate processes. Green boxes indicate products with economic value. *Current practice on California dairies or pilot project in place. Entire flow diagram, PDF (1 pg, 12K) About PDF
Several projects in California that incorporate one or more dairy manure treatment technologies are currently under construction or in operation. Information about the components of a potential comprehensive system or projects that implement these technologies are linked to the Comprehensive Manure Treatment diagram.
This diagram shows some possible technologies that could be combined into a comprehensive treatment system. No dairy is likely to use all of these; rather, the diagram indicates possibilities that could be combined as appropriate for the specific needs of each dairy.
- Solids can be composted to make bedding and soil amendments or converted to energy and byproducts through anaerobic digestion or gasification/pyrolysis.
- Liquids can be used for irrigating and fertilizing crops or recycled to flush the barns. When used for irrigation, available technology (flow meters, monitoring of nitrogen content in lagoon water, timing to crop needs, etc.) can ensure that nutrients are applied to crops at agronomic rates, preventing leaching and run-off.
- The liquid can be further treated by denitrification to make inert N2 gas, and/or by treatment with chemicals to precipitate the phosphorous and fine particulates, and/or by reverse osmosis to remove and concentrate the salts. Both denitrification and reverse osmosis require large amounts of energy, which could be supplied by the digester or the gasifier.
- Biogas from digesters and syngas from thermal conversion processes produce electricity, heat, and fuel that can be sold into the grid, or used on the dairy, possibly to power further treatment processes.
Many Additional Components Could be Added:
- feed and drinking water management to reduce nutrients in manure
- improved lagoon design (size, shape, lining, etc.) to prevent leaching and overflows
- frequent collection of manure to reduce off-gassing of VOCs
- collection and bio-filtration of gases from feed and cows
These technologies all exist. The challenge is to adapt them to conditions on dairies and connect them into a comprehensive system.
For More Information
- EPA National Agriculture Compliance Assistance Center's Animal Feeding Operations topic
- EPA Region 9 Animal Waste topic
- ManureNet Canada Manure Processing Technologies. A staggering amount of information, somewhat lacking in organization and search capability.
- North Carolina State University, Development of Environmentally Superior Technologies for Swine Waste Management
- Waterkeeper Alliance, Citizen's Guide to Manure Treatment Technologies
- National Dairy Environmental Stewardship Council, Cost-effective and Environmentally Beneficial Dairy Manure Management Practices (PDF) (28 pp, 4M, About PDF)
- Sustainable Conservation, Strategies for Increasing Implementation and Fostering Innovation in Dairy Manure Management (PDF) (18 pp, 56K)
- National Livestock and Poultry Environmental Learning Center