ENVIRONMENT ▶▶▶
associated with additional labour and a slurry pumping sys- tem required for its implementation, it performed poorly from an economic perspective (~€ 553,000 over a 25-year time horizon) and therefore ranked low in cost-effectiveness.
6. Diluting slurry with water Slurry dilution is an easy-to-implement strategy targeting ammonia emission reductions, with abatement potential for the acidification (-5.29%) and eutrophication (-0.850%) im- pact categories. However, it is particularly expensive (~€ 907,000 over a 25-year time horizon) due to the large amounts of water input required to achieve an effective level of dilution and, more importantly, the greatly increased costs for transporting the more voluminous slurry for field applica- tion. Because its poor economic performance outweighed its environmental benefits, increased slurry dilution was not identified as a particularly cost-effective strategy, incurring an abatement cost of € 5,670 per tonne SO2 per tonne PO4
eq. and € 186,032 3- eq. respectively.
Combined implementation The study further showed that combining the potential en- vironmental abatement strategies tested can significantly improve their cost-effectiveness in most cases. For example, combinations of anaerobic digestion and improved insula- tion or increased ventilation system efficiency performed significantly better than implementing anaerobic digestion as a standalone investment. Based on these findings, the study suggests that further research should be conducted to investigate synergistic effects between environmental mitigation measures, as this might unlock potential benefits of combinations between larger investments (i.e. anaerobic
digestion of acidified slurry) that are currently not viewed as sustainable solutions.
Important trade-offs identified This study identified important trade-offs in the implementa- tion of environmental mitigation strategies within pig farming systems. First, there are the trade-offs between the two pillars of sustainability: environment and economy. Then, there are many trade-offs within the environmental aspect of sustainability, which the study has highlighted. For example, while implementing anaerobic digestion of slurry helps reduce system global warming potential, applying nutri- ent-enriched digestate that is higher in nitrogen and phospho- rus significantly contributes to problems of acidification of ter- restrial ecosystems and eutrophication of freshwater bodies. Furthermore, although slurry acidification improves system performance for acidification and eutrophication potentials, it has important negative consequences for global warming potential, as well as for animal welfare and farm worker health due to increased sulphuric emissions in the closed space of a pig barn. Slurry dilution also increases system impact for global warm- ing potential and can negatively impact its water footprint. Further consideration and analysis of such trade-offs is a criti- cal aspect in future efforts to improve sustainability of the pig farming sector and are important for policymakers to consid- er when shaping relevant agri-environmental policies and investment support schemes.
The Newcastle University research was part of EU project PigSys – Improving pig system performance through a whole system approach.
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▶PIG PROGRESS | Volume 36, No. 10, 2020 17
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