PhD defence by Maja Rydgård

Life Cycle Perspectives on Nutrient Recycling Systems: Environmental Benefits and Impacts in Regional Contexts

Nutrients derived from organic waste streams can be recycled for use in agriculture as bio-based fertilisers, offering a more sustainable alternative to conventional synthetic fertilisers. Technologies for recycling of nutrients from agricultural and urban wastes provide circular solutions with environmental benefits, but the resources used for the operation of a technology and the emissions throughout the life cycle also have an environmental cost. A life cycle assessment (LCA) can be conducted to assess whether the technology results in an overall improvement for the environment and to identify potential trade-offs. In this thesis, two technologies for nutrient recycling were assessed using LCA. The first was pyrolysis of municipal sewage sludge, and the second was anaerobic digestion of agricultural residues typically available on an organic dairy farm, including animal manure, straw and cover crop cuts. Since the environmental impacts depend on where the technology is implemented and where the bio-based fertiliser is applied, region-specific information is needed. Bio-based fertilisers give rise to emissions from the field that depend on site-specific parameters such as soil type, climate and management practices. To account for such parameters on a regional scale, a regional inventory model for bio-based P fertiliser application in European regions, the PLCI 2.0 model, was developed from the original PLCI model that previously was parameterised for Denmark.

Supervisors

Professor Sander Bruun, PLEN, University of Copenhagen, Denmark Professor Lars Stoumann Jensen, PLEN, University of Copenhagen, Denmark​