Integrated cultivation of Euglena gracilis in urban wastewater: pilot-scale evaluation of organic matter removal, carbon capture and biomass valorization

This study evaluated the cultivation of Euglena gracilis in real urban wastewater as a strategy for organic matter removal, carbon capture, and biomass valorization. Cultivation was conducted at laboratory and pilot scales using different proportions of urban wastewater and a mineral nutrient medium as control. E. gracilis successfully adapted to the wastewater from a university wastewater treatment plant, showing growth kinetics at pilot scale comparable to laboratory-scale systems. High removal efficiencies were achieved for chemical oxygen demand (up to 98.0%) and ammoniacal nitrogen (up to 91.6%), demonstrating the potential of this organism for organic load reduction. Cultivation in undiluted wastewater enhanced carbon incorporation into the biomass, reaching values above 43%, indicating strong carbon assimilation under mixotrophic conditions. The biochemical composition of the biomass varied according to the culture medium, with a clear metabolic shift from protein-rich biomass in mineral medium to carbohydrate accumulation (up to 40.8%) in wastewater-based cultures. These results demonstrate the feasibility of integrating E. gracilis cultivation into urban wastewater systems at pilot scale, combining organic matter removal with carbon capture and the generation of biomass with biotechnological potential.