Evaluation of Alternative Approaches for Developing Growth-Stage-Specific Ammonia Emission Factors for Swine Feeding Operations

Concentrated animal feeding operations (CAFOs) are potentially significant sources of ammonia emissions. Because of the number and proximity of swine CAFOs in North Carolina, the emissions and subsequent deposition of ammonia from these operations may lead to the eutrophication of North Carolina streams and estuaries. Accurate emission inventories are needed to assess the environmental impact of these swine CAFOs. In efforts to improve ammonia emission inventories in North Carolina, a mass-balanced emission inventory was developed based on growth-stage-specific nitrogen excretion rates. This paper addresses the ammonia data available from monitoring studies of CAFOs and methods of selecting growth-stage-specific emission factors from the data set. Three approaches for developing emission inventories for North Carolina swine CAFOs are then presented and compared. For each approach, ammonia emissions are evaluated for five model CAFOs: three single growth-stage CAFOs (farrow-to-wean, wean-to-feed, and feed-to-finish) and two multiple growth-stage CAFOs (farrow-tofeed and farrow-to-finish). The results of the different emission inventories are compared and evaluated, and the advantages and limitations of the different emission factor approaches are discussed. INTRODUCTION The purpose of this paper is to develop a technique to estimate CAFO-specific ammonia emission estimates. The need for this technique arose from using the information available in North Carolina’s database of swine CAFOs. The state conducted a survey, collecting general information about the size and locations of CAFOs actively operating in North Carolina. For each CAFO, this information included location; growth stage(s) raised; and size of the CAFO. The information collected did not include site-specific data on the type of confinement house or the types of waste management units or disposal systems. The two primary pieces of information available in the database from which to develop site-specific emission inventories are growth stages raised at each CAFO and the size of the CAFO (in number of head of swine and steady-state live weight). Therefore, an emission inventory methodology was sought to take advantage of these two pieces of data. A process-specific emissions model is the best approach to predict emissions from the wide variety of confinement housing and waste management systems used at the CAFOs, especially where various growth stages are produced. However, the detailed site-specific data needed to apply a growthstageand process-specific emissions model are not currently available. To fill this gap, RTI developed an approach to derive emission factors based on growth stage and waste management process. We assessed the relative magnitude of CAFO emissions by evaluating the three primary emission sources for North Carolina swine operations: the animal confinement house, the lagoon waste storage/treatment unit, and the sprayfield (or land application area). These emission sources occur in series, so that ammonia released at one source is not available for release from downstream sources. * RTI International is a trade name of Research Triangle Institute. 1 Most monitoring studies investigate only specific emission sources at a CAFO rather than characterizing all emission source at a CAFO. The utility of these one-source monitoring data are further limited by a variety of site-specific factors, including animal type and growth stage, confinement housing type, waste management system configuration, and meteorological conditions present during the study. As a result, considerable uncertainty is associated with the emission factors available for CAFOs, and indiscriminate use of reported emission factors developed from different CAFO studies can lead to inaccurate emission inventories. RTI carefully assessed emission factors reported for various one-source monitoring studies before using those in its emission inventory. A mass-balanced emission inventory approach was desired to facilitate the evaluation of alternative waste management or control techniques for reducing CAFO emissions. Synthetic membrane covers, for example, may reduce ammonia emissions effectively from a waste storage/treatment lagoon but this suppression control technique will tend to cause higher ammonia emissions during subsequent spray application. The net ammonia emission reduction achieved by the waste management or control technique, considering all CAFO processes (i.e., the life cycle of the waste material), is needed to properly assess the environmental impacts and benefits achieved by emission reduction strategies. Mass-balance approaches have been proposed by Doorn et al. (2002) and Webb and Misselbook (2004), but none were found that specifically addressed differences in growth stage. This paper presents RTI’s approach to filling the gap in growth-stage-specific emission factors while incorporating a technique that includes a mass balance evaluation of the entire operation from point of waste generation to final disposal. The approach consists of three steps: • Develop model CAFOs • Review literature data on emissions specific to waste management process and growth stage • Fill data gaps. The results are presented as a comparison of three emission estimating techniques: by live weight, by head of swine, and by percentage ammonia loss across waste management unit. Discussion then follows on the benefits of RTI’s technique to emission estimation. APPROACH Swine CAFOs can be characterized based on the age range of the animals raised. “Farrows” are newborn piglets that initially nurse from their mother. After about 3 weeks, the piglets are weaned from their mothers and nursed using mechanical milk dispensers; these piglets are termed “weans. ” After 7 to 8 weks, the young pigs can eat solid food and are called “feeder” pigs. “Finish” pigs are grown pigs ready for market. A CAFO that breeds sows to produce new litters of piglets are termed farrow-to-wean operations (i.e., they raise farrow piglets until they are weaned from their mothers). CAFOs that take newly weaned piglets and raise them until they can eat solid food are termed wean-to-feed operations. Some CAFOs may raise the piglets from birth until they can eat solid food; these are termed farrow-tofeed operations. CAFOs that take feeder pigs and raise them until they are ready to market are termed feed-to-finish operations. Some CAFOs may raise pigs from birth to market; these are termed farrowto-finish operations. Develop Model CAFOs RTI classified the swine CAFOs from the state survey database into one of five growth stage categories based on the growth stages reported by each CAFO: