Ammonia Fate and Transport Mechanisms in Broiler Litter

摘要

Ammonia (NH_3) emission from poultry houses is a major air quality concern. In poultry litter, uric acid converts to urea which hydrolyzes to NH_3, a fraction of NH_3 protonates to ammonium (NH_4~+). Moisture content (MC), dissociation constant, and Henry's law constant affect NH_3 partitioning among solid, liquid, and gas phases. The dissociation constant (K_d) and Henry's Law constant (K_h) that are so well known for dilute aqueous solutions may not apply to broiler litter which has much higher ionic concentration. We quantified K_d, K_h, and NH_3 sorption at different MC in broiler litter in replicated lab experiments. Dissociation constant in litter slurry was 1.02 × 10~(-10), 20 % of the dissociation constant in aqueous solution, which may be due to NH_3/NH_4~+adsorption and reduced activities of the dissolved ions. Henry's Law constant (0.0158 atm/M) in litter slurry was 4 % lower than K_h in dilute aqueous solution. Ammonia sorption increased linearly with MC from 0 to 55 %, whereas 0 % MC litter adsorbed 5 % of its background total ammoniacal N (TAN) concentration as NH_3, litter with 55 sorbed 266 % its background TAN concentration mostly as NH_4~+. We have improved the understanding of NH_3 sorption in litter as function of MC. However, improved sensors that can measure TAN and pH in unsaturated matrices are required to improve quantification of N fate and transport.