Environmental Impacts and Costs for Manure Management with and without Anaerobic Digestion for Heat and Power

摘要

Anaerobic digestion of manure and energy recovery is generally viewed as a positive environmental approach to increase the use of renewable energy. In this study, life cycle assessment (LCA) methods were utilized to investigate the net benefits of these energy recovery systems. Environmental impacts of business-as-usual manure management were compared with those of a manure management operation incorporating anaerobic digestion with combined heat and power generation (AD-CHP). Impacts related to fossil fuel use decreased in the AD-CHP system due to decreased consumption of grid-based electricity and increased use of renewable biogas. However, these benefits were small compared to the increased impacts from nitrogen compounds. Nitrogen-related impacts include eutrophication, acidification, and human health impacts. Most importantly, high ammonia emissions from manure spread on fields can cause significant human health impacts. Because a greater fraction of the nitrogen in digested versus raw manureis present in the reduced ammonia species, the human health impacts for spreading digested manure are greater than for raw manure. External environmental costs were also calculated. As with the environmental impacts, ammonia emissions and costs associated with the risk of mortality are the most significant impact associated with anaerobic digestion and energy recovery from dairy manure.