Modeling the interaction of transport mechanisms through bedded manure to evaluate the effects on ammonia and greenhouse gas emissions

Understanding the characteristics of dairy farm manure and the interrelationship between mass transport mechanisms (diffusion and convection) contributing to the release of gaseous emissions is imperative to reducing the gas emissions from these sources. The major goals of this study were to characterize compacted dairy farm manure with various bedding materials (woodchips, sawdust, and hay mix), to measure ammonia and greenhouse gas emissions from the bedded manure while evaluating the effectiveness of compaction as a treatment for reducing emissions, and determine the rates of diffusion responsible for the release of ammonia and greenhouse gases.;The results of this study indicate that the permeability values for all bedding types pattern permeabilities between clean gravel and peat, 10 -7 -- 10-13 m2. This result also proved that the sawdust-bedded and hay mix-bedded manure samples followed Darcy's Law of permeability. The woodchip-bedded samples followed a modified Darcy's Law (Dupuit-Forcheimer) because of a lack of water absorbency. In terms of using compaction to reduce the permeability, the results revealed that the permeability was reduced for the sawdust-bedded samples but not for the woodchip and hay mix-bedded samples. Using compaction, the air-filled porosities of the bedded samples were significantly reduced for all bedding types. The woodchip-bedded manure had the lowest air-filled porosity of all bedded manures (within a range of 0.26 -- 0.43 m3 m -3 before compaction and 0.24 -- 0.40 m3 m -3 after compaction) because of the low water absorbency of the material. The hay mix-bedded manure had the highest air-filled porosities (0.73 -- 0.90 m3 m-3 before compaction and 0.57 -- 0.88 m3 m-3 after compaction).;The effects of compaction were inconclusive as a treatment for reducing ammonia and greenhouse gas emissions and compaction is not recommended as a treatment for reducing ammonia and greenhouse gas emissions. Specifically, the sawdust-bedded samples exhibited a decrease in gas emission rates for NH3, N2O, and CH4 after compaction, and N 2O and CH4 gas emission rates exhibited a greater change from the uncompacted samples when compacted at an applied stress of 6522 N m-2 (75 lbs). Statistically, there was no significant affect of compaction in decreasing NH3, CO2, and CH4 emission rates. However, N2O emission rates were significantly reduced by compaction. For the hay mix and woodchip-bedded samples, compaction caused an increase or insignificant change in CH4, NH3, and CO2 production.;The rate of diffusion was measured for each bedding type and the results indicated that for all bedding types the range of diffusion coefficients was the same magnitude throughout the trials with a slight trend of the diffusion coefficient decreasing with increased compaction. This trend was not consistent throughout the trials and for all the gases. The hay mix samples had higher overall range of O2 diffusion coefficients than the sawdust or woodchip-bedded samples because of the higher porosities within the samples before and after compaction. The resulting oxygen diffusion coefficients seem to reflect the theory of passive airflow even at high levels of compaction within the system. The determined effective diffusion coefficients in this study were compared to reference values of the diffusion coefficients of the gases, exposed to air and water. Based on the referenced diffusion coefficients, for all of the gases, the diffusion coefficients calculated through the bedded manure samples decreased with compaction to levels below the diffusion of each gas in air, but remained higher than the levels for diffusion of each gas in water.;Lastly, a parameter estimation was performed to determine whether diffusion conditions were truly maintained within the reactors, throughout the study. The results revealed that there was a presence of convection within the hay mix-bedded samples and that the error in the convection term was roughly between 10 -- 30%. This study also developed a methodology for determining the rates of non-diffusive processes within bedded manures from experimental data. (Abstract shortened by UMI.)...