Environmental impacts of combining pig slurry acidification and separation under different regulatory regimes – A life cycle assessment

Global livestock production is increasing rapidly, leading to larger amounts of manure and environmental impacts. Technologies that can be applied to treat manure in order to decrease certain environmental impacts include separation and acidification. In this study, a life cycle assessment was used to investigate the environmental effects of slurry acidification and separation, and whether there were synergetic environmental benefits to combining these technologies. Furthermore, an analysis was undertaken into the effect of implementing regulations restricting the P application rate to soils on the environmental impacts of the technologies. The impact categories analysed were climate change, terrestrial, marine and freshwater eutrophication, fossil resource depletion and toxicity potential. In-house slurry acidification appeared to be the most beneficial scenario under both N and P regulations. Slurry separation led to a lower freshwater eutrophication potential than the other scenarios in which N regulations alone were in force, while these environmental benefits disappeared after implementation of stricter P regulations. With N regulations alone, there was a synergetic positive effect of combining in-house acidification and separation on marine eutrophication potential compared to these technologies individually. The model was sensitive to the chosen ammonia emission coefficients and to the choice of inclusion of indirect nitrous oxide emissions, since scenarios changed ranking for certain impact categories. •In-house and field acidification of slurry could be used to decrease ammonia emissions.•Slurry separation led to the lowest freshwater eutrophication under N regulation.•In-house acidification and separation had a synergetic effect on marine eutrophication.•Introducing P regulation led to equal freshwater eutrophication for all scenarios.•Results were sensitive to NH3 emission coefficients and the inclusion of indirect N2O.