Dissociation Constant of Ammonium and Henry's Law Constant of Ammonia in Broiler Litter

Abstract

Ammonia (NH3) emission from poultry houses is a major air quality concern. In poultry litter, uric acid and urea hydrolyze to ammonium (NH4+) and a fraction of NH4+ coverts to NH3; the NH4+- NH3 equilibrium in the litter depends on pH, temperature, moisture content, ionic concentration, carbon/nitrogen (C/N) ratio, oxygen level, substrate concentration, and some cations. The dissociation constant (Kd) that controls NH4+- NH3 equilibrium developed for aqueous solutions may not apply to broiler litter which has much higher ionic concentration. Similarly, Henrys law constant (Kh) which describes the equilibrium of NH3 between the liquid and gas phases in aqueous solution with free liquid surface may not apply to broiler litter. Values of Kd and Kh developed for aqueous solutions are not appropriate for modeling the fate of NH4+ and NH3 in litter system. The research qualified Kd and Kh in broiler litter in replicated lab experiments. Dissociation constant in litter slurry was 1.02, 20% of the dissociation constant in aqueous solution, which may be due to the ammonia/um adsorption and reduced activity coefficient. Henrys Law constant (0.0158 atm/M) in litter slurry was similar to Kh (0.0164 atm/M) in aqueous solution. Determination of dissociation constant and Henrys constant for broiler litter will allow more accurate simulation of litter nitrogen dynamics.