Biobased fertilisers from fishery side-streams: an environmentally friendly alternative to mineral fertilisers?

Commercial fertilisers have been shown to contribute substantially to crop yields and thus to satisfying the needs of a growing world population (Stewart et al., 2005). However, the production and application of mineral fertilisers is connected to several sustainability issues. For example, the Haber–Bosch process to manufacture nitrogen fertilisers requires a high energy input (Chojnacka et al., 2020). So far, production relies mostly on natural gas thus contributing to global warming. Furthermore, nitrogen fertiliser prices can fluctuate substantially (e.g. increase by 300% in 2021) with variations in natural gas prices (Chojnacka et al., 2024) posing an economic risk for farmers. On the other hand, phosphorus fertilisers are produced from a finite source of phosphate rock (Hernandez-Mora et al., 2024). The widespread application of nitrogen and phosphorus fertilisers strongly contributes to transgressing planetary boundaries (te Wierik et al., 2025). Fertiliser-related emissions lead to eutrophication, global warming, air pollution as well as acidification of terrestrial and aquatic habitat (de Vries, 2021; Richardson et al., 2023; Shukla et al., 2019; Ti et al., 2019).

To reduce the dependence on non-renewable resources in agriculture and mitigate the nutrient excess within Europe, nutrient recovery from organic waste streams is increasingly seen as an alternative to mineral fertiliser production. The European Updated Bioeconomy Strategy (European Commission, 2018) identified nutrient recycling as one of the levers for future proofing of the European food and farming systems. The European Union therefore aims to stimulate markets for recovered nutrients (European Commission, 2022), boost research in this field (European Commission, 2018) and regulate (Regulation (EU) 2019/1009, 2019) market access of biobased fertilisers (BBFs; Cucina et al., 2021). However, also BBFs require energy and material inputs during production and cause emissions of greenhouse gases and pollutants when being applied on the field. To understand the environmental performance of BBFs, life cycle assessment (LCA) is a typically applied methodology.

In the past, LCA studies on organic waste analysed ways to reduce environmental impacts of waste management (e.g. composting vs. incineration or landfilling) or of energy production, considering nutrient recovery as a secondary function of biorefineries (Egas et al., 2023; Lam et al., 2020). In recent years, LCA studies on BBF production from important organic waste streams, such as municipal biowaste, sewage sludge and animal manures, have been conducted (Egas et al., 2023; Tanzer et al., 2021). For other relevant organic waste streams, studies are scarce. For example, to our knowledge, no LCA studies have been conducted so far on side-streams from the fish industry. In addition, LCA studies on BBFs often do not consider the main function of fertilisers, i.e. crop production, but only compare environmental impacts related to the production, but not the application of the BBFs (Egas et al., 2023).

Globally, discards from large-scale fisheries and on-shore fish processing side-streams (from both large-scale capture fisheries and aquaculture) amounted to a total of 11.7 million tons of non-edible loss in 2021 (excluding aquaculture production loss and valorised side-streams; WEF, 2024). In the EU, the non-edible discards were around 1.2 million tons for the same year (WEF, 2024). The side-streams from aquaculture and capture fisheries (hereinafter defined as fishery) shows high nutrient contents and fertilisers produced from them showed a similar or better agronomic performance compared to mineral fertilisers (Zhang et al., 2023).

These potential advantages of nutrient recovery from fishery side-streams can be leveraged by novel processing approaches that go beyond the traditional processing technologies such as composting by fractionating side-streams and concentrating nutrients. This study therefore aims to address the question whether the resulting BBFs from such valorisation can be an environmentally friendly alternative to mineral fertilisers. In a first step, the environmental impacts of producing three novel BBFs from aquaculture side-streams are assessed as an example for novel processing pathways that valorise the untapped potential of fishery side-streams. In a second step, data from an agronomic field trial are integrated into an agricultural LCA model to analyse and compare the environmental performance of broccoli grown with BBFs or with mineral fertilisers.