Abstract
<abstract> <bold><sc>Abstract.</sc></bold> The goal of this study was to determine the effect of anaerobic digestion (AD) on ammonia volatilization from liquid dairy manure, in storage or treatment lagoon, prior to land application. Physical and chemical properties of liquid dairy manure, which may affect ammonia volatilization, were determined before and after AD. The properties of interest included particle size distribution (PSD), total solids (TS), volatile solids (VS), viscosity, pH, total ammoniacal nitrogen (TAN), and ionic strength (IS). The overall mass transfer coefficient of ammonia (K<sub>oL</sub>) and the NH<sub>3</sub> fraction of TAN (β) for the undigested (UD) and AD manures were then experimentally determined in a laboratory convective emission chamber (CEC) at a constant wind speed of 1.5 m s<sup>-1</sup> and fixed air temperature of 25°C at manure temperatures of 15°C, 25°C, and 35°C. The PSD indicated non-normal left-skewed distributions for both AD and UD manures particles, suggestive of heavier concentrations of particles toward the lower particle size range. The volume median diameters (VMD) for solids from UD and AD were not significantly different (p= 0.65), but the geometric standard deviations (GSD) were significantly different (p = 0.001), indicating slightly larger particles but more widely distributed solids in UD manure than in AD manure. Results also indicated significantly higher pH, TAN, ionic strength (IS), and viscosity in AD manure. The β for AD manure, determined under identical conditions (air temperature, liquid temperature, and airflow), was significantly higher (p < 0.001) than for UD manure. However, mass transfer of ammonia (K<sub>oL</sub>) was significantly lower for AD manure than for UD manure (p < 0.001). Overall, these findings suggest that AD of dairy manure significantly increased initial ammonia volatilization potential from liquid dairy manure, with the largest increase (~61%) emanating from increased ammonium dissociation. The initial flux of ammonia, at 15°C, was ~16% more from AD manure than from UD manure.
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