TY - BOOK

T1 - Life Cycle Perspectives on Nutrient Recycling Systems

T2 - Environmental Benefits and Impacts in Regional Contexts

AU - Rydgård, Maja Karolina

PY - 2024

Y1 - 2024

N2 - 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 fertilisers, the PLCI 2.0 model, was developed from the original PLCI model that previously was parameterised for Denmark.The PLCI model was further developed to be applicable to regions in all EU countries by considering parameters that describe region-specific conditions affecting the loss of P, crop P uptake and potential mineral fertiliser substitution. In a case study of the Copenhagen region in Denmark and the Piedmont region in Italy, the PLCI 2.0 model showed that P loss and mineral fertiliser substitution were greatly affected by the varying soil erosion rates and fertilisation practices in the respective regions. Sensitivity analysis supported the reliability of the model, although the whole model could not be validated. In conclusion, the new PLCI 2.0 model provides a dynamic tool for LCA practitioners to estimate inventory factors for bio-based P fertilisers, capturing differences between fertilisers and between regions in the EU.An LCA case study was conducted for sewage sludge pyrolysis in a region of southern Sweden. The PLCI 2.0 model was used to calculate the impacts of field application of sludge and sludge biochar-P. The LCA showed that pyrolysis could lead to reduced impacts on global warming and human toxicity. However, the impacts increased in other categories, including land and water use, due to the lower yields in the case of biochar application, as estimated through modelling. As the short-term plant-availability of P in biochar may be low, biochar application may be associated with a risk of lower yields when the P application is restricted based on total P. In summary, pyrolysis of sewage sludge may be environmentally favourable, especially in contexts where biochar can be applied to fields that are not heavily reliant on high immediate P availability for sustained crop yields.Anaerobic digestion of agricultural residues was investigated in an LCA case study of an organic dairy farm in Denmark. Harvesting and ensiling of cover crops and cereal straw for co-digestion with cattle manure was compared with mono-digestion of manure. Co-digestion increased biogas production and thereby increased benefits for the climate because of the potential to substitute the use of fossil natural gas. However, the impacts increased in several other impact categories compared with direct incorporation of the residues and no biogas production, due to emissions from heat and electricity production for biogas plant operation, changes in cereal yield and emissions from ensiling. The results point to a need for further research to improve understanding and mitigate emissions and dry matter losses during ensiling. Finally, the study emphasises that the environmental advantages depend on effective fossil gas substitution, which requires support from appropriate policy instruments.In conclusion, the implementation of technologies for nutrient recycling can offer environmental benefits, but can also shift burdens to affect the environment negatively in other ways. The environmental impacts depend on the regional context in which the technology is implemented, and where the fertiliser is applied. This thesis highlights the importance of considering not just the technology itself, but the effects on the broader agricultural system as well. The results should provide support for environmentally friendly decision-making in the development towards a circular economy for nutrients.

AB - 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 fertilisers, the PLCI 2.0 model, was developed from the original PLCI model that previously was parameterised for Denmark.The PLCI model was further developed to be applicable to regions in all EU countries by considering parameters that describe region-specific conditions affecting the loss of P, crop P uptake and potential mineral fertiliser substitution. In a case study of the Copenhagen region in Denmark and the Piedmont region in Italy, the PLCI 2.0 model showed that P loss and mineral fertiliser substitution were greatly affected by the varying soil erosion rates and fertilisation practices in the respective regions. Sensitivity analysis supported the reliability of the model, although the whole model could not be validated. In conclusion, the new PLCI 2.0 model provides a dynamic tool for LCA practitioners to estimate inventory factors for bio-based P fertilisers, capturing differences between fertilisers and between regions in the EU.An LCA case study was conducted for sewage sludge pyrolysis in a region of southern Sweden. The PLCI 2.0 model was used to calculate the impacts of field application of sludge and sludge biochar-P. The LCA showed that pyrolysis could lead to reduced impacts on global warming and human toxicity. However, the impacts increased in other categories, including land and water use, due to the lower yields in the case of biochar application, as estimated through modelling. As the short-term plant-availability of P in biochar may be low, biochar application may be associated with a risk of lower yields when the P application is restricted based on total P. In summary, pyrolysis of sewage sludge may be environmentally favourable, especially in contexts where biochar can be applied to fields that are not heavily reliant on high immediate P availability for sustained crop yields.Anaerobic digestion of agricultural residues was investigated in an LCA case study of an organic dairy farm in Denmark. Harvesting and ensiling of cover crops and cereal straw for co-digestion with cattle manure was compared with mono-digestion of manure. Co-digestion increased biogas production and thereby increased benefits for the climate because of the potential to substitute the use of fossil natural gas. However, the impacts increased in several other impact categories compared with direct incorporation of the residues and no biogas production, due to emissions from heat and electricity production for biogas plant operation, changes in cereal yield and emissions from ensiling. The results point to a need for further research to improve understanding and mitigate emissions and dry matter losses during ensiling. Finally, the study emphasises that the environmental advantages depend on effective fossil gas substitution, which requires support from appropriate policy instruments.In conclusion, the implementation of technologies for nutrient recycling can offer environmental benefits, but can also shift burdens to affect the environment negatively in other ways. The environmental impacts depend on the regional context in which the technology is implemented, and where the fertiliser is applied. This thesis highlights the importance of considering not just the technology itself, but the effects on the broader agricultural system as well. The results should provide support for environmentally friendly decision-making in the development towards a circular economy for nutrients.

M3 - Ph.D. thesis

BT - Life Cycle Perspectives on Nutrient Recycling Systems

PB - Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen

ER -