Anaerobic Digestion and Related Best Management Practices: Utilizing Life Cycle Assessment

Anaerobic digestion of dairy manure with energy recovery through biogas combustion is generally viewed as a positive environmental approach to increase the use of renewable energy. However, there are potential negative impacts associated with emissions of methane and nitrogen species during digestion and after spreading of digester effluent that have the potential to counteract the environmental benefits of anaerobic digestion. To promote best management practices, assessment of environmental impacts and investigation of their causes should be conducted using a broad perspective. A life cycle assessment (LCA) comparing environmental impacts of business-as-usual manure management with those of a manure management operation incorporating anaerobic digestion with combined heat and power generation was conducted. The case study, based on a medium sized dairy farm in northern New York State, USA, showed benefits across multiple categories due to the displacement of fossil fuels, and reduction of related emissions. Knowledge gained from the LCA was used to assess the benefits associated with various management practices. For example, design and construction of biogas systems must minimize the potential for fugitive emissions of biogas that can easily out weigh the climate change related benefits associated with fossil fuel displacement. This paper defines and explains the environmental trade offs associated with various manure management and energy recovery systems.