Environmental Consequences of Pig Slurry Treatment Technologies: A Life Cycle Perspective

Research output: Book/ReportPh.D. thesisResearch

Manure is a valuable fertiliser since it contains nutrients that are crucial for crop growth. Furthermore soil
quality might be maintained or improved by the use of manure instead of mineral fertiliser, due to the
presence of organic matter in manure. On the other hand, emissions to the environment occur during manure
storage and after field application. The main emissions are ammonia, nitrous oxide, methane, carbon dioxide,
nitrate, phosphorus and odour. Slurry treatment technologies have been and are being developed in order to
reduce the environmental impacts of manure. However, it is important to analyse whether total impacts are
reduced or merely result in burden shifting with impacts occurring in other life cycle stages or other impact
categories instead. Therefore, in the present thesis, life cycle assessment (LCA) was used in three separate
studies to analyse the environmental consequences of slurry acidification, separation and anaerobic digestion.
The functional unit that formed the basis of the life cycle assessments in this thesis was the management of
1000 kg of slurry excreted by fattening pigs under prevailing Danish conditions. A total of ten treatment
scenarios were compared with a reference scenario. The treatment scenarios were field acidification, in-house
acidification, screw press separation with and without composting of the solid fraction, decanter centrifuge
separation with and without ammonia stripping of the liquid fraction, and four anaerobic digestion scenarios
with different co-substrates. These co-substrates were straw that would otherwise have been left on the field,
straw that would otherwise have been incinerated, the organic fraction of household waste and the solid
fraction of slurry. The impact categories analysed were climate change potential including and excluding
biogenic carbon, marine and freshwater eutrophication potential, terrestrial acidification and eutrophication
potential, and fossil resource depletion potential.
The different types of treatment technologies showed varying environmental profiles, meaning that one type
of technology was beneficial for one impact category, but disadvantageous for another, while another type
showed the opposite trends. Slurry acidification was the preferred technology for reducing terrestrial
acidification and eutrophication potential, while slurry separation performed best for freshwater
eutrophication, and anaerobic digestion showed the lowest impact potential for fossil resource depletion and
marine eutrophication. For climate change potential, whether a beneficial or disadvantageous impact potential
was revealed depended on the specific technology (moment of acidification, separation and fraction upgrading
technology, or co-substrate for anaerobic digestion). With respect to odorous emissions, an LCIA method was
developed, but due to a lack of data it proved difficult to include odour in LCA. Regulations appear to have an
influence on the environmental impacts of slurry treatment. A decrease in N application limits favours slurry
acidification, but an increase in these limits is disadvantageous for acidification. This is due to the higher N
content in acidified slurry resulting in higher yields at limited N application rates. Furthermore, regulations are
a restricting factor for increasing pig production at single farm level.
In conclusion, treatment had an influence on the environmental profile of pig slurry, but the choice of an
appropriate slurry treatment technology depended on many considerations, e.g. local policy, cost and
Original languageEnglish
PublisherDepartment of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen
Publication statusPublished - 2015

ID: 144795381