Improving life cycle inventories for nitrogen and phosphorus in sewage sludge used in agriculture
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Typ
Examensarbete för masterexamen
Program
Industrial ecology (MPTSE), MSc
Publicerad
2019
Författare
Karlsson, Amanda
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
When treating wastewater, large amounts of sewage sludge are generated. Sewage sludge
contains substances that may be of use, e.g. nutrients such as nitrogen and phosphorus, but also
substances that are harmful such as pathogens and heavy metals. In order to reuse the nutrients
in sewage sludge it can be used as a fertilizer on agricultural fields in Sweden but there are
regulations that specify how the sludge must be hygienized before use. One way of hygienizing
sewage sludge in Sweden is by storing it. However, this method will probably not will be
allowed as an hygienization method in the future, since the Swedish Environmental Protection
Agency has not listed it as one of the hygienization methods they recommended to be acceptable
in future legislation on the use of sludge in agriculture.
A way of assessing the environmental impact when sewage sludge is stored and applied to
agricultural fields as a fertilizer is by using life cycle assessment (LCA). Previous reviews of
LCAs performed in this field have shown a variety when it comes to which flows that are
included in the life cycle inventories, and there is a need to improve the data quality when the
flows are quantified. Therefore, this study was made to investigate if the life cycle inventory
for nitrogen and phosphorus compounds could be improved and if there are differences in the
characterization of nitrogen and phosphorus compounds in different methods, and what LCA
practitioners needs to be aware of when assessing this kind of system. The three impact
categories chosen were global warming potential, acidification potential and eutrophication
potential.
The study was performed by literature searches and by personal contact with experts on
nutrients and the practice when using sewage sludge in agriculture in Sweden. Also, an LCA
case study was performed to illustrate how choices of inventory data and LCIA methods affect
the environmental impact results.
The study concluded that sewage sludge storing and application to agricultural fields have a
significant environmental impact regarding the three impact categories and the used
characterization methods. The literature review combined with the personal contact and LCA
case study indicated that there are many factors that affect the emissions of nitrogen and
phosphorus from sewage sludge, e.g. soil type, soil chemistry, pH, how the sewage sludge has
been treated, when the sewage sludge is incorporated into the soil and weather conditions.
Therefore, it was shown that it is important to do a life cycle inventory for the specific system
and not to use generic numbers of emissions since it can vary a great deal.
Beskrivning
Ämne/nyckelord
Sewage sludge , Life cycle assessment , Nitrogen , Phosphorus , Mineral fertilizers , Agriculture , Storage