Animal Feed from Microalgae Grown on Biogas Digestate as Sustainable Alternative to Imported Soybean Meal

Abstract This work investigates the environmental potential to develop a circular economy solution to create benefit from agricultural waste by integrating microalgae technology into the nutrient-rich digestate (NRD) stream from anaerobic digestion plants. Different environmental benefits can be captured by algal uptake of nitrate and the scarce resource phosphorus from biogas digestate. First, unwanted excess nutrients polluting groundwater are reduced and second, the algal animal feed can substitute soybean meal (SM) imported to North-Western Europe (NWE). That allows a decentralised circular bio-economy and avoids deforestation of rainforests due to SM overseas import. Life cycle assessments were conducted based on novel data from engineers in academia and industry, acquired through pilot-scale research facilities in United Kingdom, France, and Belgium. The findings of this study highlight the environmental impacts of three different technologies with varying scales of production and offer recommendations based on sensitive analysis for more sustainable pathways. In this study, a pilot-scale bio-refinery is considered a promising solution to excess nutrients in fertilisers in the NWE and an alternative source for imported SM as an animal feed source, having a comparable environmental footprint.