Growing wastewater-born microalga Auxenochlorella protothecoides UMN280 on concentrated municipal wastewater for simultaneous nutrient removal and energy feedstock production

Using wastewater to grow algae is probably the most promising route to reduce production costs associated with nutrients and water. In this study, a newly isolated facultative heterotrophic freshwater microalgae strain, Auxenochlorella protothecoides UMN280, was examined for algal growth, wastewater nutrient removal efficiency, and lipid accumulation in batch and semi-continuous cultivation with various hydraulic retention time using concentrated municipal wastewater (CMW) as cultivation media. The results of the 6 day batch cultivation showed that the maximal removal efficiencies for total nitrogen, total phosphorus, chemical oxygen demand (COD) and total organic carbon (TOC) were over 59%, 81%, 88% and 96%, respectively, with high growth rate (0.490 d−1), high biomass productivity (269 mg L−1 d−1) and high lipid productivity (78 mg L−1 d−1). Further fatty acid methyl ester (FAME) analysis showed that the microalgal lipids were mainly composed of C16/C18 fatty acids (accounting for over 94% of total fatty acid), which are suitable for high-quality biodiesel production. The system could be scaled up from 100 mL flasks to 25 L BIOCOIL reactors, and semi-continuously operated at hydraulic retention time of 3 days with a net biomass productivity of 1.51 g L−1 d−1 of dried algae.