Acidification

Application: used to reduce ammonia and methane emissions from manure storages

Pros

• Increase nitrogen retention in the manure.
• Improves in-barn air quality.
• Cost effective for solid manure systems.

Cons

• Safety concerns when dealing with concentrated acids.
• Reduced pH is conductive to volatilization of hydrogen sulfide and other odorous compounds.

Description

Ammonia emitted from livestock manure is not only an odor concern, it also is a financial loss as fertilizer value that could be utilized on farm or sold. Additionally, ammonia emissions are an environmental and human health concern. Thus, numerous strategies have been proposed to reduce ammonia emissions, one such method is acidification of the manure. This practice has become accepted and is practiced in many poultry facilities that utilize dry litter systems, but can also be applied to slurry manure.

Figure 1. Granulated ferric sulfate litter amendment which can improve in-barn air quality and reduce ammonia emissions. The product works by acidifying the manure.

Nitrogen exists in numerous forms in manures including proteins, ammines, urea, ammonia, and ammonium. Of these forms, ammonia is the most volatile and susceptible to loss from the manure. Manipulating the pH of the manure alters the balance between ammonia (NH3) and ammonium (NH4+), with ammonium (NH4+) favored at low pH (acidic) and ammonia favored at high pH (basic). As ammonia is the volatile of these two compounds, reducing the pH to change ammonia to ammonium can be effective at reducing loss of nitrogen. Additionally, the acidity can also create less favorable conditions for the bacteria and enzymes that contribute to ammonia formation.

Acidification of poultry litters has become relatively common with amendments such as aluminum chloride, aluminum sulfate, sulfuric acid, and ferric chloride available under trade names of Al+Clear (Alum – aluminum sulfate), Klasp (ferric sulfate), Poultry Guard (acidified clay, clay soaked in sulfuric acid), and Poultry Litter Treatment (sodium bisulfate). Acidification practices for slurry manure are less well developed due to the risk of foaming and because of the potential hazards associated with the use and storage of strong acids on farms.

Figure 2. Applying aluminum sulfate solution (Alum) to poultry litter. This treatment lowers the pH of the litter to reduce ammonia losses.

Strategies for acidifying the manure that have been attempted include dietary practices used to acidify urine (such as adding phosphoric acid to the diets or adding small amounts of fiber to the diet which reduces manure pH), dosing the manure with strong acids (often sulfuric acid or nitric acid), or weaker fermentable acids (lactic acid). Modifying dietary practices can be effective at acidifying manure at excretion, but during storage the manure pH tends to increase and as a result effectiveness at reducing ammonia loss decreases. Strategies of dosing acid to the manure can be more effective at maintaining acidic pHs. Recent works tends to suggest that adding about 33 to 50lbs of concentrated sulfuric acid (H2SO4) per 1000 gallons pig slurry reduces the slurry pH to between 5.5 and 6.0. The addition of these strong acids to manure slurries will typically cause a large amount of carbon dioxide to off-gas immediately after addition of the acid, which may cause some temporary foaming.

In poultry systems alum or other litter amendment are often applied between flocks of birds. Numerous application methods have been tried inducing de-caking machines as well as fertilizer, manure, and drop spreaders for granulated products. If using granulatedalum, it should be mixed into the litter prior to placing birds. Liquid alum in normally applied by certified applicators. The use of acidification in slurry manure storage systems is not as developed, but research has tended to indicate it can be effective; however, it is thought that acidification may cause the emission of more hydrogen sulfide.

Effectiveness

Cost Considerations

Cost of poultry litter treatment for broiler housing has been estimated to cost about $500 per barn, but research has tended to show improved bird performance and reduced energy costs are expected to save the producer $900. Additionally, improved nitrogen retention will make the litter a more valuable fertilizer amendment.

Costs and benefits of treating slurry manures are less well documented, but assuming an acid dosing rate of 4 lbs concentrated sulfuric acid per 1000 gallons of slurry as has been suggested would result in a cost of approximately $6000 per year for a 1000 head swine finishing barn to purchase the acid. If a 70% reduction in ammonia emissions were obtained the extra nitrogen present in the manure slurry at the time of application would provide approximately $4000 worth of nitrogen fertilizer value.

References

Eriksen, J., P. Sorensen, and L. Elsgaard. 2008. The fate of sulfate in acidified pig slurry during storage and following application to cropped soil. J. Environ. Qual.  37: 280-286.

Moore, P. Treating poultry litter with aluminum sulfate (Alum). Emissions Management Practice. USDA ARS.

Sommer, S.G. and N.J. Hutchings. 2001. Ammonia emission from field applied manure and its reduction – invited paper. European Journal of Agronomy 15: 1-15.

Vandre, R. & J. Clemens. 1997. Studies on the relationship between slurry pH, volatilization processes, and the influence of acidifying additives. Nutrient cycling in Agroecosystems 47: 157-165.

University of Arkansas:

Treating Poultry Litter with Alum

Purdue University:

Diet and Feed Management Practices Affect Air Quality from Poultry and Swine Operations