Integrating dairy and bioenergy systems to achieve environmental sustainability: The influence of different lifecycle pathways on energy, greenhouse gas emissions, and nutrients

With an increasingly growing and wealthier population that demands more food and fuel, the pressure on the planet's ecosystems threatens to reach levels that cannot be sustained. Animal agriculture presents multiple challenges for sustainability and the dairy sector alone contributes 30% of agricultural greenhouse gas (GHG) emissions. This dissertation contributes to the debate on the sustainability of agricultural systems and integrates dairy and bio-energy systems to address global warming and energy security using lifecycle techniques.;Chapter two evaluates how including dry distillers grains with solubles (DDGS) and soybean meal into the dairy diet affect energy intensity, GHG emissions, and direct land-use of milk production. This is done by conducting a cradle-to-farm gate lifecycle assessment and by expanding the system boundaries of the dairy farm to include ethanol and biodiesel production. Results show that scenarios that maximize DDGS in the dairy diet achieve lower GHG emissions and energy intensity, but lead to higher land area requirements.;Chapter three develops a novel method combining subdivision and allocation concepts to reduce the variability when partitioning the environmental impacts of a multi-functional system producing cheese, dried whey, and whey cream. After running several sensitivity tests, it is shown that the variability of results is significantly reduced with the new method when compared to the traditional allocation methods.;Chapter four combines process-based and LCA techniques to test the environmental impacts of different manure processing pathways that include anaerobic digestion (AD) and solid-liquid separation (SLS). Findings suggest that AD has the largest reductions in GHG emissions and depletion of fossil fuels, but also the largest increases in ammonia emissions. The study highlights the need of using multiple sustainability indicators to evaluate and understand the trade-offs between manure pathways.;Chapter five evaluates different AD pathways to reduce environmental impacts and increase energy production. Pathways are defined based on multiple management practices, co-digestion strategies, and energy conversion processes. Results show that management practices can achieve significant reductions in GHG and ammonia emissions, and can increase energy production as well.