Modelling ammonia emission from swine slurry based on chemical and physical properties of the slurry

The slurry pit is one of the main sources of ammonia emission in swine enterprises. Ammonia emission from slurry is considered a convective mass transfer process, but there are different methods to predict the mass transfer coefficient and the amount of ammonia in the gas film at the slurry surface. The objective of this research is to develop a new model to simulate the ammonia emission rate from swine slurry that can be applied to slurries of varying physical and chemical composition (i.e., pH, temperature, concentration, etc.). Slurry samples were collected from pigs fed diets differing in crude protein and sugarbeet pulp content and placed in emission boxes where the headspace ammonia concentration was measured and used to calibrate and validate a new ammonia emission rate model for slurry. The new model relates the fraction f) of ammonia in the slurry relative to the total ammoniacal nitrogen concentration (TAN) as a linear function of pH and TAN, based on both single and multiple variable regression analyses. The average bias between the simulated and measured emission box concentration levels for seven datasets was -3%. The new model was deemed accurate for slurry with TAN concentration levels between 0.3 and 1.0 mol l^-1, and pH levels between 8 and 9. Because the value f is based on a linear relationship with pH, the ammonia emission rate from slurry is less sensitive to changes in pH compared with previous models that used an exponential relationship between f and pH.