From linear to circular bioeconomy: Case study and life cycle assessment of integrating small-scale freshwater aquaculture with microalgae cultivation

This study deals with the use of microalgae cultivation system to treat effluents from a small, artisanal fish farm that breed “red tilapia” in Colombia. These types of “aquafarms” have limited technology and high production costs, particularly regarding aquaculture feed inputs. The proposed integrated “aquaculture-microalgae” process aims to recover nutrients and rationalise freshwater intake, whilst the harvested algae biomass partially offsets commercial feed and provides fish farmers with extra income. In this way “circular bioeconomy” notions are brought to this traditional form of aquaculture. The results of this study comprise a life cycle assessment (LCA) based on data extracted from a fully integrated pilot system for fish farming and microalgae (Spirulina) production, using a 6.6 m 3 open-raceway pond bioreactor; it also covers the validation of aquafeed replacement with microalgae. LCA methodology has provided a more comprehensive view of the environmental trade-offs and co-benefits associated with the proposed shift from a traditional, linear model of aquaculture to a circular bioeconomy, but it also reveals areas requiring attention for its full maturation and potential replication. The environmental midpoint indicators used to analyse local water pollution, climate change and resource use, return lower values in circular bioeconomy scenarios with “enhanced circularity”, than in the baseline scenario (traditional fish farming). Although the circular bioeconomy model and reference scenario display similar toxicity indicator results, positive change is possible in this respect. Lastly, it is suggested using the harvested biomass for basic “in situ” applications, without major downstream refinement, to be sustainable in isolated, low-income contexts.