A Model for Overall Mass Transfer Coefficient of Ammonia from Dilute Dairy Manure Slurries

Abstract

Available data indicate that about 75-80% of total nitrogen (N) entering a dairy operation is lost as ammonia (NH3) from an anaerobic dairy lagoon and other similar manure storages. Direct measurement of NH3 emissions from manure holding systems can be complicated and expensive. Process-based emission models can be used to provide a cost effective alternative method for NH3 emissions estimation. The overall mass transfer coefficient (KoL) of NH3 is an important component of any NH3 emission process-based model. Models relying on purely theoretically derived KoLs of NH3 from livestock manures have not adequately predicted NH3 emissions. In this study, the KoL of NH3 from dilute dairy manure slurries was modeled empirically, in a laboratory convective emission chamber (CEC), to determine realistic NH3 KoL values under typical conditions of the Pacific Northwest. The KoL of NH3 increased with both liquid temperature (TL), and air velocity (Vair), but decreased with increase in both air temperature (Tair), and concentration of total solids (TS). The KoLs of NH3 ranged from 1.4110-6 to 3.7310-6 m/s. The obtained non-linear empirical model of KoL of NH3 from dilute dairy manure slurries had a coefficient of determination (R2) of 0.83. This model is thus reliable for determining KoL of NH3 in NH3 emissions process-based models over the range of the experimental conditions considered in this study. The sensitivity of the KoL of NH3 to the four model parameters, in descending order was: TL, Tair, Vair and TS concentration, respectively.