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Effects of carbon dioxide emission, kinetically-limited reactions, and diffusive transport on ammonia emission from manure

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010  1008895.(doi:10.13031/2013.29750)
Authors:   Sasha D Hafner, Felipe Montes, C Alan Rotz
Keywords:   Ammonia emissions, cattle manure, emission model

Volatilization of ammonia from animal manure causes significant loss of fixed N from livestock operations. Ammonia emission from manure is the culmination of biological, chemical, and physical processes. In this work we present a speciation and transport model for simultaneous CO2 and NH3 emission from manure. Our model was implemented using the geochemical software PHREEQC in order to assess the importance of CO2 volatilization, equilibrium speciation, kinetically-limited reactions, and aqueous diffusion on NH3 emission dynamics from thin layers (1-10 mm) of dairy cattle manure. Preliminary predictions show that emission of CO2 leads to a rapid increase in manure pH, which causes a substantial increase in NH3 flux. Kinetic limitations on conversion of carbonic acid to dissolved CO2 was predicted to significantly influence NH3 emission by limiting the effect of CO2 volatilization on solution pH, therefore these reactions should be considered in the development of chemical models of NH3 emission. For the limited number of conditions studied in this work, diffusion of solution species through the aqueous phase had only small effects on NH3 emission from 1 and 5 mm layers. However, aqueous-phase diffusion can be limiting for thicker layers or for conditions that cause higher convective mass transfer from the surface. Additional work is needed to assess the importance of the processes studied here for different conditions.

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