Document ID: EPA-R09-OAR-2015-0432-0208
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2016-02-09T05:00Z

Evaluation of Potential Ammonia Reductions from Covering 
   Manure Storage Ponds & Manure Storage Piles in the San Joaquin Valley

As previously demonstrated in Chapter 2 of the San Joaquin Valley Air Pollution Control District 2015 PM2.5 Plan, reducing ammonia (NH3) is not an effective strategy to reduce PM2.5 concentrations in the San Joaquin Valley because of the abundance of ammonia in comparison to other precursors that react with ammonia to form fine particulate.  However, the District has adopted stringent regulations that have significantly reduced ammonia emissions in the San Joaquin Valley as explained in Appendix C of the San Joaquin Valley Air Pollution Control District 2015 PM2.5 Plan.[1]  In addition to these stringent regulations, the following analyses evaluates the potential for further ammonia reductions that could result from requiring Confined Animal Facilities cover stored liquid manure systems and stored solid manure piles.  The District has evaluated these options and found that there is no decisive evidence that covering manure storage ponds or solid manure piles will result in meaningful reductions in ammonia emissions from Confined Animal Facilities in the San Joaquin Valley.

Evaluation of Covers to Reduce Ammonia from Stored Liquid Manure

Manure storage covers have not been conclusively demonstrated to reduce total ammonia emissions from Confined Animal Facilities.  One study performed to evaluate the effectiveness of porous covers for control of emissions from hog manure storage lagoons in Missouri found "no statistically significant reduction of ammonia emissions" from any of the lagoon covers because of consistently low emission rates of ammonia. The consistently low ammonia emissions observed in the study may be the result of the high solubility of ammonia in water.  

Installing impermeable plastic covers over storage liquid manure systems (lagoons/ponds) would effectively convert these manure storage ponds into covered lagoon anaerobic digesters due to the San Joaquin Valley's warm climate.  A number of experts and researchers have stated that anaerobic digestion of manure actually increases ammonia emissions.  Covering a manure storage lagoon or pond with an impermeable cover will result in greater reductions of the organic matter in the manure.  Organic carbon will be converted to methane and organic nitrogen will be converted to ammonia nitrogen.  This leads to greater concentrations of ammonia in the liquid manure.  The cover prevents the ammonia from being released directly from the covered areas of the pond, but the greater concentration of ammonia in the lagoon increases the amount of ammonia released from uncovered areas and from the effluent.  The digested manure will also have a higher pH, which will result in a greater fraction of the ammonia nitrogen in the form of volatile NH3 rather NH4[+] that remains in the liquid manure.  

There have also been studies that support that anaerobic digestion of manure increases ammonia emissions.  One study compared ammonia volatilization from undigested and digested manure from a dairy in Washington found that anaerobic digestion of dairy significantly increased the ammonia volatilization potential from liquid dairy manure. Factors that contributed to increased volatilization of ammonia from the digested manure include: increased concentration of ammonia nitrogen, higher pH, and a greater fraction of the ammonia nitrogen as NH3 because of the higher pH and ionic strength of digested manure.  Another study presented at the 2013 eXtension Waste to Worth Conference indicated that anaerobically digested manure may result in greater nitrogen loss in the form of ammonia than raw manure. Some simulations using process-based models have also indicated that installation of anaerobic digesters at Confined Animal Facilities can increase ammonia emissions.  The United States Department of Agriculture (USDA) Agricultural Research Service (ARS) Dairy Gas Emissions Model (GEM) Reference Manual indicates that the digestion process affects the nitrogen fractions in the manure, a greater portion of the organic nitrogen in the raw manure is converted to total ammoniacal nitrogen (TAN), and that "this increase in TAN potentially increases the ammonia emissions from the storage and field applied effluent."  This is shown in a presentation in which the USDA Dairy GEM model indicated that installation of an anaerobic digester at a dairy farm in New York would increase total ammonia emissions. 

A 2013 report to the California Energy Commission (CEC) on the performance of six dairy digesters operating in California found that the digesters increased the amount of nitrogen in the manure converted to ammonia nitrogen. The document determined this was a positive impact because it reduces the risk of nitrogen impacting water quality but the document did not discuss the potential for higher ammonia emissions (possibly because this has traditionally also been considered beneficial to water quality near farms).  A Michigan Biomass Energy Program Anaerobic Digester FAQs document specifically states that anaerobic digestion produces ammonia.  Like the CEC document, this document mentions the benefits of reduced leaching of nitrogen to water but does not discuss the potential for higher ammonia emissions.  The Penn State Extension document "The Fate of Nutrients and Pathogens During Anaerobic Digestion of Dairy Manure (G-71)" specifically states that "Ammonium is not destroyed during the digestion process, but rather, organic N is converted to ammonium during protein degradation.  Hence, the ammonium level in the digester effluent is typically higher than raw manure." and "When digester effluent is field applied, much of the ammonium will be released as a gas (ammonia) unless it is incorporated into the soil." It is often not practical to incorporate dilute liquid manure into the soil.  In addition, the stringent regulations to protect water quality in the San Joaquin Valley limit the times that manure can be applied and limit when manure can be incorporated into the soil.    

It must be emphasized that covering ponds and lagoons will not reduce the amount of nitrogen in the manure but will increase the fraction of nitrogen that is in the form of volatile ammonia.  The cover may suppress ammonia from manure storage but this ammonia is likely to be released when the manure exits the digester.  If a flare or other combustion device is used to dispose of the gas from the covered lagoon some of the ammonia may even be converted to NOX during combustion.  Any increases in NOX are detrimental to the plans for attainment of air quality standards for ozone and fine particulate matter in the San Joaquin Valley.  

As explained above, at this time there is no definitive evidence that that covering liquid manure storage ponds and lagoons will decrease ammonia emissions from Confined Animal Facilities in the San Joaquin Valley; however, there is evidence that covering liquid manure storage ponds and lagoons may increase overall ammonia emissions in the San Joaquin Valley.  Therefore, requiring Confined Animal Facilities in the San Joaquin Valley to incur costs to cover manure storage ponds and lagoons as a means to reduce ammonia emissions is not reasonable and may even be counterproductive.

Evaluation of Covers to Reduce Ammonia from Solid Manure Storage Piles

Generally two types of solid manure are stored at dairies in the San Joaquin Valley: 1) separated solids, which are solids that have been removed from a liquid manure stream by a separation system, and 2) manure scrapings from corrals and exercise pens.  Studies have generally shown the VOC and ammonia emissions from separated solids to be very low or negligible because the majority of the VOCs emitted from cow manure, such as alcohols and Volatile Fatty Acids, and ammonia are highly soluble in water and will remain in liquid when the solids are removed.  Studies have also shown that emissions from other types of stored dairy manure (i.e. corral scrapings) are also very low.  

One study performed at a San Joaquin Valley dairy for the California Air Resources Board (ARB) to characterize emissions from different processes at California dairies found that ammonia emissions from separated solids piles were below the detection limit. 

The District's current dairy ammonia emission factors for separated solid piles and other types of stored solid manure from milk cows are as follows:
   * Separated solids piles: 0.38 lb-NH3/(milk cow-yr)  - 0.53% of total dairy emissions
   * Solid manure storage piles: 0.95 lb-NH3/(milk cow-yr)  -  1.3% of total dairy emissions

Given the very low ammonia emissions from solid manure storage piles, it would be difficult to justify costs of covers or other controls to reduce ammonia emissions from solid manure storage piles.  There are also major safety concerns related to covering manure piles that are not completely dry because heat generated by biological activity in the manure piles will be trapped by the covers and this will increase the chances that the manure piles may spontaneously combust.  This safety concern is not an issue once the piles have dried and biological activity has lessened; however, during this period, due the low moisture content of the manure and decreased biological activity, ammonia emissions are likely to be low.  There are also practical concerns related to the costs of the materials and labor required for large manure storage piles.

Because of the extremely low ammonia emissions from solid manure, concerns about combustion of manure piles that are not dry, and additional costs for covering manure with negligible benefits in terms of ammonia reductions, requiring Confined Animal Facilities in the San Joaquin Valley to incur costs to cover manure storage piles to reduce ammonia emissions is not reasonable.  However, it should be noted that District Rule 4570 does contain mitigation measure options for Confined Animal Facilities that store solid manure onsite to cover dry solid manure or separated solids with a weatherproof covering from October through May.  In addition, Rule 4570 contains several measures that promote the drying of manure even prior to storage.  As stated earlier, drying of manure decreases biological activity and thus reduces or eliminates the formation of both ammonia and VOC emissions.  Examples of Rule measures included in Rule 4570 are as follows:

*          Freestall Barns (Dairy CAF):
      o                For a large dairy CAF, remove manure that is not dry from individual cow freestall beds or rake, harrow, scrape, or grade freestall bedding at least once every seven (7) days.
      o                For a medium dairy CAF, remove manure that is not dry from individual cow freestall beds or rake, harrow, scrape, or grade freestall bedding at least once every fourteen (14) days.
*          Freestalls (Other Cattle):
      o                Remove manure that is not dry from individual cow freestall beds or rake, harrow, scrape, or grade bedding in freestalls at least once every seven (7) days.
*          Solid Manure/Separated Solids (Dairy CAF, Other Cattle):
      o                Within seventy-two (72) hours of removal from housing, either:
            #                      Remove dry manure from the facility; or
            #                      Cover dry manure outside the housing with a weatherproof covering from October through May, except for times when wind events remove the covering, not to exceed twenty-four (24) hours per event.
      o                Within seventy-two (72) hours of removal from the drying process, either:
            #                      Remove separated solids from the facility; or
            #                      Cover separated solids outside the housing with a weatherproof covering from October through May, except for times when wind events remove the covering, not to exceed twenty-four (24) hours per event.
*          Solid Manure/Separated Solids (Layer & Broiler, Duck, or Turkey):
      o                Within seventy-two (72) hours of removal from housing, either:
            #                      Remove all litter/manure from the facility; or
            #                      Cover litter/manure outside the housing with a weatherproof covering from October through May, except for times when wind events remove the covering, not to exceed twenty-four (24) hours per event.
*          Solid Manure/Separated Solids (Beef Feedlot):  
      o                Within 72 hours of removal from animal housing, either remove dry manure from the facility or, during the months of October through May, cover dry manure pile with a weatherproof covering, except for times, not to exceed twenty-four (24) hours per event, when wind events remove the covering; or
      o                Manage moisture content of manure to less than 50%.
*          Land Application (Dairy CAF, Beef Feedlot, & Other Cattle):
      o                If the CAF applies solid manure, choose one of the following:
            #                      Incorporate all solid manure within seventy-two (72) hours of land application
            #                      Only apply solid manure that has been treated with an anaerobic treatment lagoon, aerobic lagoon, or digester system
            #                      Apply no solid manure with a moisture content of more than 50%
      
Rule 4550, Conservation Management Practices, also contains several measures to promote the drying of manure as follows:
      * CMPs for Dairies
            o Corral/Manure Handling; must select one of the following:
                  # Fibrous layer in dusty areas
                  # Freestall housing 
                  # Frequent scraping and/or manure removal
                  # Pull type manure harvesting equipment
                  # Scraping/harrowing (in morning hours)
                  # Shaded areas in open corrals
                  # Sprinkling of open corral
      * CMPs for Feedlots
            o Pens/Manure Handling; must select one of the following:
                  # Fibrous layer in working areas
                  # Frequent scraping and/or manure removal
                  # Shaded for animals
                  # Sprinkling
                  # Pull type manure harvesting equipment
      * CMPs for Poultry
            o Manure Handling and Storage; must select one of the following:
                  # Cleanout frequency
                  # Outdoor storage
                  # Time of manure spreading