The Rationale for Recovery of Phosphorus and Nitrogen from Dairy Manure

The Rationale for Recovery of Phosphorus and Nitrogen from Dairy Manure

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Georgine Yorgey, Associate in Research, Center for Sustaining Agriculture and Natural Resources, Washington State University, Craig Frear, Assistant Professor, Department of Biological Systems Engineering, Chad Frear, Director, Center for Sustaining Agriculture and Natural Resources, Tara Zimmerman, Associate in Research, Center for Sustaining Agriculture and Natural Resources
This publication explains the rationale for implementing emerging phosphorus and nitrogen nutrient recovery technologies on dairies, with a particular focus on the Western United States. The document covers manure management and environmental issues, the recovery, concentration and partitioning processes of nutrients from manures, and the role that nutrient recovery plays in achieving environmental quality. The Anaerobic Digestion Systems Series provides research based information to improve decision-making for incorporating, augmenting, and maintaining anaerobic digestion systems for manures and food by-products.
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This publication explains the rationale for implementing emerging phosphorus and nitrogen nutrient recovery technologies on dairies, with a particular focus on the Western United States. Although dairy operations are emphasized, the lessons learned are readily applicable to feedlot, swine, and poultry operations, as well as other industrial and municipal organic solids and wastewater treatment facilities. The specific technology requirements will vary, depending on the qualities of the waste streams being processed.

Manure Management and Environmental Issues in the United States

In one year, a dairy cow generates liquid and solid manure that contains 58 lb phosphorus, 168 lb ammonia (a form of nitrogen), and 336 lb total nitrogen (ASAE 2005). Dairy manure is expensive to transport, so it is generally applied to nearby fields, which sometimes leads to excess applications of nutrients. The ongoing trend of increased numbers of dairy cows per farm in the U.S. (USDA-NASS, 2010) results in greater concentrations of manure, bedding, and urine being produced by the dairy operation. This increases the transport distances (and costs) required for appropriate land applica­tion of manure. In 2000, only 1% of large dairies (those with more than 1000 animal units) were applying phosphorus at agronomic rates, while only 23% were applying nitrogen at agronomic rates (Ribaudo et al. 2003). More recent data indi­cate that larger operations apply manure to cropland at rates that are more than three times higher than smaller farms, suggesting that excess nutrient applications are still an issue, particularly for large operations (MacDonald and McBride 2009). This observation is also supported by a recent study of manure application to field corn (the receiving crop for more than half of all applied manure), which found that the vast majority of dairies applied manure to fewer acres than would be needed to meet best management practices for nutrient management (USDA ERS 2011).

The loss of phosphorus and nitrogen to the environment during manure management can contribute to a number of significant water and air quality concerns:

  • Phosphorus and Nitrogen Eutrophication. Both phosphorus and nitrogen can be lost through runoff or infiltration and leaching at manure stor­age locations and field application sites, as well as through soil erosion. Losses increase substantially as nutrient application exceeds the plant needs (Bock and Hergert 1991; Schlegel et al. 1996). Once lost from agricultural

systems, phosphorus and nitrogen can migrate to lakes, rivers, estuaries, and coastal oceans. Overabundant nutrients can then lead to excessive growth of algae and aquatic weeds and subsequent oxygen shortages (Carpenter et al. 1998), fish toxicity (Ward et al. 2005), habitat loss (NRC 1993; Jeppesen et al. 1998) and decreased species diversity (Sutton et al. 1993).

  • Nitrate Pollution of Water Sources. Infants under six months of age who ingest high levels of nitrates in the water supply can acquire blue baby syndrome. Symptoms include bluish skin, stupor, brain damage and in severe cases, death (US-EPA 1991).
  • Ammonia Volatilization. An estimated 70% of total manure nitrogen is lost as ammonia during manure management and application on U.S. dair­ies and feedlots (CAST 2002). Ammonia is highly reactive and contributes to the development of ultra-fine particulate matter (PM 2.5) in the atmo­sphere. PM 2.5 has detrimental effects on overall air quality and human and animal health (Erisman and Schaap 2004; McCubbin et al. 2002; Archi­beque et al. 2007).

Greenhouse gas emissions are also a concern of current manure management practices. Dairy cattle create direct and indirect emissions of greenhouse gases throughout the production process, with over half of direct emissions generated by manure management (US-EPA 2013a). There is significant variation in emissions depending on the types of manure management systems; with higher methane emissions coming from liquid manure management sys­tems. These liquid manure systems are increasingly used in dairy operations (US-EPA 2013a), leading to recent increas­es in greenhouse gases associated with manure manage­ment. In total, manure management for dairy cattle in the U.S. contributed an estimated 46% of the greenhouse gas emissions associated with manure management for all live­ stock and poultry in 2011; or 0.48% of gross greenhouse gas emissions in the United States (this was an estimated 32.4 million metric tonnes, MT; US-EPA 2013a).

Factors Contributing to Nutrient Overloading

Because phosphorus and nitrogen losses increase rapidly when they are applied in excess of plant needs, one strat­egy for minimizing losses to the environment is to ensure that manure applications do not provide more nutrients than can be taken up by the crops being grown on the land. However, there are

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Copyright 2014 Washington State University

Published June, 2014

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