Timing of slurry acidification and its environmental consequences from a life cycle perspective
Livestock manure is responsible for approximately 40% of ammonia emissions in the world, 70% of ammonia emissions in Europe and 75% of ammonia emissions in Denmark (Bouwman et al., 1997; Hutchings et al., 2001; Van der Hoek, 1998). Slurry acidification is a technique that can be used for reducing ammonia emissions. Slurry acidification can be done at different stages in the manure handling chain. Acidification in the animal houses involves pumping acidified slurry into the area beneath the slatted floors. Another approach is to add the acid during field application. Technologies for both of these approaches are commercially available, and are increasingly applied in Danish agriculture.
Other effects of slurry acidification are a) reduced greenhouse gas emissions (methane and nitrous oxide emissions during storage and carbon dioxide and nitrous oxide emissions after soil application), b) increased sulfur and nitrogen fertilizer value, and c) increased amount of dissolved P in slurry (Berg et al., 2006; Eriksen et al., 2008; Hjorth et al., 2010; Kai et al., 2008). Uncertainty exists about odorous emissions from acidified slurry. Some researchers indicate that odorous emissions were not affected significantly by acidification (Kai et al., 2008), while others argue that increased volatilization and loss of smelly fatty acids is to be expected (Eriksen et al., 2012; Ottosen et al., 2009).
The objective of this study was to compare impact potentials of slurry acidification at the pig housing and field application stage with conventional slurry management (reference scenario) using a Life Cycle Assessment (LCA) framework.
The analysis was performed using consequential LCA and system expansion was used whenever additional processes were included compared to the reference scenario. The analysis assesses the treatment of 1000 kg of slurry ex animal and provides an overview of natural resource consumption and potential impacts. Impact categories that were analyzed are (a) terrestrial acidification potential, induced by ammonia emissions, (b) climate change potential, caused by methane, nitrous oxide and carbon dioxide emissions, and (c) eutrophication potential caused by nitrogen (marine waters) and phosphorus (freshwater) losses from soils. Furthermore, a newly developed method for characterization of odorous emissions was included.
For every scenario, areas in the life cycle of the slurry technologies can be identified, which show relatively high environmental impacts. Additionally, technologies can be compared, and environmentally preferred technologies can be distinguished. Overall, slurry acidification at pig housing appears the most favorable from an environmental point of view, with the lowest terrestrial acidification, climate change and marine eutrophication potential.
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