Modeling Ammonium Adsorption on Broiler Litter and Cake

Ammonia emission from broiler houses is a major concern because of its impacts on the environment. To reduce ammonia emissions, it is necessary to understand the fate of ammonia/um in the broiler waste. In broiler waste, uric acid and urea hydrolyze to ammonia (NH₃) and a fraction of NH₃ converts to ammonium (NH₄ ⁺) depending on pH and temperature. Further, NH₄ ⁺ undergoes solid–liquid partitioning and the ammonia fraction is partitioned among the solid, liquid, and gas phases in the waste. Ammonium partitioning between solid and liquid phases in broiler cake and litter were measured at pH of 4, 6, and 7. Ammonium adsorption increased with pH in both broiler litter and cake. Adsorption capacity of the litter was much lower than broiler cake. Six NH₄ ⁺ adsorption/desorption isotherms (linear, Langmuir, Freundlich, Temkin, Redlich–Peterson, and Toth) were evaluated. The isotherm that provided the best fit for partitioning NH₄ ⁺ in litter or cake for each pH value was selected by comparing up to six sets of parameters modeled using linear and nonlinear (with five error functions) regressions. Despite high R ² values obtained using linear regression, linearizing the models introduced an offset into the model reducing their accuracy. The sum of normalized error was used to select the most suitable parameter set for each isotherm. While the nonlinear error functions were the more suitable for developing parameter sets in broiler litter, for cake, linear regression generally provided the most optimum parameter sets. Whereas the Freundlich, linear, and Temkin isotherms were the most suitable for broiler litter for pH of 4, 6, and 7, respectively, for the cake, the linear isotherm was the most suitable for the entire range of pH evaluated. Overall, due to its simplicity, the linear isotherm seems suitable for partitioning NH₄ ⁺ in the adsorbed and dissolved phases for simulating nitrogen fate and dynamics in broiler waste more accurately.