Coupling of wastewater treatment and algal biomass cultivation and valorisation: a Life Cycle Assessment

The scientific interest about microalgae has significantly increased in recent years due to their potential sustainability. Among the new promising valorisation routes, microalgae can be useful to produce biostimulants. This research evaluates the environmental benefits and impacts associated with the cultivation of microalgae integrated in a wastewater treatment plant (WWTP), including different subsequent valorisation routes of the residual algal biomass: direct use in agriculture, energy recovery, and production of biostimulants to be used in agriculture. When compared to the WWTP without the integration of the algal system, only the scenario in which the residual algal biomass is valorised to produce biostimulants allows for benefits in most of the examined impact categories, showing a negative normalised and weighted impact (-22 mPt for the treatment of 1,000 m3 of wastewater). This is possible by assuming that biostimulants can avoid the use of 5% of fertilisers on crops. Accordingly, biostimulants production can be seen as a promising valorisation route for the algal biomass. Future research should further quantify and correlate impacts for the production of biostimulants and actual benefits on crops.