Microalgae grow on source separated human urine in Nordic climate: Outdoor pilot-scale cultivation

Human urine contributes approximately 80% of nitrogen and 50% of phosphorous in urban wastewaters while having a volume of only 1-1.5 L/d per capita compared to 150-200 L/d per capita of wastewater generated. There is interest to study source separation of urine and search methods to recover the nutrients form the urine. In this study, the objective was to use the nutrients in source separated urine for outdoor cultivation of microalgae in Nordic climate. A freshwater green microalga Scenedesmus acuminatus was grown in different dilutions (1:20 and 1:15) of source separated human urine, in a semi-continuously operated outdoor raceway pond with a liquid volume of 2000 L, at hydraulic retention time of 15 d. The microalgae could remove 52% nitrogen and 38% phosphorus even at culture temperatures as low as 5 °C, while obtaining a biomass density of 0.34 g VSS/L. Harvested microalgal biomass could be used to produce methane with a yield of 285 L CH₄/kg volatile solids.