Process modeling of ammonia volatilization from ammonium solution and manure surfaces

Authors: Montes, Felipe; Rotz, Clarence - Al; CHAOUI, HALA - PENN STATE UNIV

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2009
Publication Date: 12/1/2009
Citation: Montes, F., Chaoui, H., Rotz, C.A. 2009. Process Modeling of Ammonia Volatilization From aAmonium Solution and Manure Surfaces: A Review With Recommended Models. Transactions of the ASABE. 52(5):1707-1719.

Interpretive Summary: A growing concern over the impact of animal feeding operations on air quality has created a need for quantifying gaseous emissions from animal facilities. An important emission from animal-producing farms is ammonia. The amount of ammonia emitted is heavily influenced by management practices, which vary considerably among farms. Therefore, the use of emission factors such as a loss per animal unit can only provide a general estimate of the emissions from a given farm. A more accurate approach is to use computer simulation to estimate emissions where all of the important components of the farm and their interactions are considered. To further develop this computer simulation approach, better understanding of the fundamental processes of ammonia emission is needed, and more accurate models of these processes must be developed. An extensive review of existing research literature was conducted, summarized, and used to develop a robust model for predicting ammonia emission from the surface of an ammonium containing solution such as manure. This refined model of ammonia emission provides a key component for a software tool that is being developed to estimate gaseous emissions from dairy and beef farms. With this tool, producers and their consultants will be able to estimate ammonia emissions from specific farms as influenced by the management of each farm. Technologies and strategies for reducing emissions can also be evaluated to help develop more environmentally friendly and profitable farms. More sustainable farms will help assure a continued stable, safe, and secure food supply.

Technical Abstract: Ammonia emissions from animal feeding operations have become an important concern because of their potential effects on animal and human health and the environment. Emissions occur from manure surfaces on the barn floor, during storage, and following field application. To better quantify ammonia emissions from these sources, models are needed that accurately predict the dissociation of the ammonia from the ammonium in the manure and the emission rate of the ammonia leaving the manure surface. Based upon theoretical principles and associated published information on ammonia emission, relationships were refined for modeling the dissociation constant, Henry’s law constant, and mass transfer coefficient to better predict ammonia loss from manure surfaces. Refined expressions were obtained that relate these coefficients to the temperature, pH and electric conductivity of the material, and the air speed over the material. These expressions were tested by comparing predicted ammonia dissociation and emission rates against values measured in controlled laboratory experiments from buffered ammonium-water solutions and dairy cow manure. Experimental results compared well with values predicted using these expressions derived from ammonia volatilization literature. These process-based relationships provide a basis for developing predictive tools that quantify management effects on ammonia emissions from farms and thus assist in the development and evaluation of strategies for reducing emissions.