The dynamics of ammonia release from animal wastewater as influenced by the release of dissolved carbon dioxide and gas bubbles

The largest global source of atmospheric ammonia is animal wastewater. Previous models to predict the release of ammonia from animal wastewater have focused on undisturbed conditions. However in animal facilities the surface of wastewater is constantly disturbed due to liquid addition and wastewater management. This paper presents a gas emission-pH-film model (GE-pH-film model) that describes the dynamics of ammonia release from swine wastewater after surface liquid disturbances, considering volatilization of dissolved carbon dioxide, surface pH changes, bubble-enhanced ammonia volatilization and surface film formation. The GE-pH-film model improved the accuracy of estimated ammonia release during the first 10 h after liquid disturbance, from an averaged error of 82% (gas emission model) to 25% (GE-pH-film model). Neglecting the bubble-enhanced NH3 volatilization and the surface film formation (i.e. GE-pH model), led to an averaged error on NH3 release of 43%.

► Animal slurry in farms is frequently disturbed.
► The release of NH3 immediately after disturbances is minimum.
► Then NH3 release increases until it reaches a steady condition.
► This pattern is related to the release of dissolved CO2 and surface film formation.
► A model describing this process is presented.