Abstract
The replacement of mineral fertilisers by biobased fertilisers (BBFs) produced from organic waste streams is promoted by the European Union to reduce political dependencies and nutrient excess. Life cycle assessment (LCA) studies have so far been mainly conducted on BBFs produced from municipal biowaste, sewage sludge and animal manures, primarily considering their production phase. This LCA study compares for the first time environmental impacts of three BBFs produced from fishery side-streams against those of mineral fertilisers assessing both BBF production (per kg N) and application (per kg broccoli), assuming burden-free side-streams. Compared to mineral fertilisers, two BBFs (one from fish sludge, the other from fish frames and heads) had a 3-62% (per kg N) and 11% (per kg broccoli) lower global warming potential and a 1-12% (per kg N) and 7-13% (per kg broccoli) lower mineral resources use. However, the third BBF from fish viscera showed overall higher impacts than the mineral fertiliser highlighting the importance of optimising the production of BBFs and their agronomic performance. Levers for optimisation include establishing the BBF production close to the location of the side-stream, implementing energy-efficient drying technologies and appropriate BBF application techniques. Methodological challenges such as modelling field emissions of BBFs and lacking harmonization of LCA methodology for the assessment of BBFs are discussed. By considering both production and application of BBFs, this study shows that BBFs from fishery side-streams can provide environmental benefits when used as a substitute for mineral fertilisers and identifies optimisation potential along the life cycle.
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Context
Agroecological innovations are seen as solutions to reduce environmental impacts of agriculture but can potentially lead to trade-offs with food production. Appropriate tools are needed to better understand synergies and trade-offs among environmental issues, resource efficiency and food production.
Objective
This study presents the FarmLCA tool, which models farms as interconnected crop-livestock systems and assesses environmental impacts from farms and farm-inputs. A mixed beef farm serves as case study to assess synergies and trade-offs of avoiding human edible feed in beef production.
Increasing global food demand has led to an intensive use of synthetic fertilisers. In this regard, the use of non-conventional streams such as swine wastewater (SW) and urban sewage sludge liquid fraction (USS) for the production of bio-based fertilisers can increase the sustainability of both the fertiliser industry and agriculture while reducing the reliance on imported nutrients. In this work, USS and SW were assessed for the production of struvite at different PO4 3−:Mg2+ ratios. Significant differences were found in terms of struvite crystals’ shape and size among both feedstocks due to the different saturation indexes, and it was concluded that PO4 3−:Mg2+ ratios of 1:2 for SW and 1:1 for USS were the most suitable for obtaining big crystals suitable to be used for direct fertilisation.
In addition, it was observed that the crystallisation process is highly dependent on the presence of interfering ions (mainly Ca) that can result in the formation of hydroxyapatite instead of struvite. Finally, recovering struvite from SW and USS could potentially reduce the European import of P by up to 6.5%.
