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Doctoral thesis2014Open access

Recycling plant nutrients from waste and by-products : a life cycle perspective

Spångberg, Johanna


Chemical fertilisers contribute to greenhouse gas emissions, fossil fuel use, use of non-renewable phosphate rock and a flow of reactive nitrogen to the biosphere, exceeding the planetary boundaries. Recycling of plant nutrients from waste and by-products from society would reduce the use of chemical fertilisers. These plant nutrient sources are also of interest for organic farming, where chemical fertilisers are not allowed, especially organic farms without access to manure. This thesis assessed the environmental impact of systems recycling plant nutrients from slaughterhouse waste, toilet waste fractions, digested food waste and mussels too small to be used in food production. The methodology used was life cycle assessment (LCA) and the functional unit was production of 1 kg plant-available nitrogen. The environmental impact categories studied were primary energy use, global warming potential (GWP), potential eutrophication and potential acidification. Flow of cadmium to arable soil, use of non-renewable phosphate rock and potential carbon sequestration were also assessed. In addition, additional functions such as phosphorus added to arable soil, energy production, removal of nitrogen and phosphorus from wastewater streams etc. were considered. The reference scenario for all comparisons was the production and use of chemical fertilisers. In general, storage and spreading of the organic fertilisers contributed greatly to potential eutrophication and acidification, except in the case of meat meal fertiliser, which was in a pseudo-stable form. All investigated fertilisers gave rise to goal conflicts as none of the fertilisers reduced the impact for all impact categories studied. The urine fertiliser reduced the largest amount of impact categories and added the least amount of cadmium to arable soil. Meat meal reduced, or had similar results as the reference scenario, for all impact categories except primary energy use and potential eutrophication. For digested food waste, chemical fertiliser use was an environmentally better option for all impacts. Composting gave rise to large nitrogen emissions, thus anaerobic storage was a better environmental option for mussel treatment. Due to the large amount of phosphorus per kg nitrogen in the compost, the reference scenario used the largest amount of non-renewable phosphate rock. A need for applicable methods and data for estimating emissions in LCA of agricultural systems was identified.


Organic fertilisers; Life cycle assessment; Recycling; Waste

Published in

Acta Universitatis Agriculturae Sueciae
2014, number: 2014:20ISBN: 978-91-576-7988-8, eISBN: 978-91-576-7989-5
Publisher: Department of Energy and Technology, Swedish University of Agricultural Sciences