The addition of Fe2O3 nanoparticles to microalgae cultures has gained popularity since it has been demonstrated to enhance microalgae growth and metabolite accumulation. However, most of the literature has been focused on small batch laboratory-scale studies under controlled conditions and the need of continuous studies under real environmental conditions is needed to demonstrate the feasibility of this process. In this study, the effect of Fe2O3 nanoparticles on the metabolism and nutrient uptake of a microalgae-cyanobacteria consortium cultivated in wastewater was elucidated. Different concentrations of Fe2O3 nanoparticles (10, 20, 30 and 70 mg L−1) were assessed at least for 21 days in outdoor cylindrical PBRs at 7 days of hydraulic retention time. No significant difference in microalgae growth, microalgae biomass composition and nutrient uptake was observed at concentrations <30 mg L−1. Moreover, when 30 mg L−1 were added to the culture, the carbohydrate content increased up to 38 % but a decrement in biomass concentration of 18 % was observed by the deposition of nanoparticles on the cyanobacteria cell wall. The addition of 70 mg Fe2O3 L−1 reduced the content of carbohydrate and biomass concentration but did not influence the nutrient uptake from wastewater. In brief, Fe2O3 NP supplementation at 30 mg L−1 can be added as a strategy to stimulate carbohydrate content during microalgae-based wastewater treatment.
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