Cyanobacteria cultivation on human urine for nutrients recovery

Urine is a nutrient rich stream; it accounts for 70% of the nitrogen load and 40% of the phosphorus load present in domestic wastewater while in volume it only represents 1%. Given the high concentrations of nitrogen (5–7 g N∙L⁻¹) and phosphorus (0.2–0.3 g P∙L⁻¹) in urine, it is more efficient to recover these nutrients from this concentrated stream than from domestic wastewater where they are more diluted. These nutrients can be recovered in form of biomass that could be a source of biobased compounds or could also be used as soil amendment or fertilizer. In this study, the model cyanobacterium Synechocystis sp. PCC6803 was cultivated on synthetic and real, source-separated human urine with different pretreatments to determine if real urine inhibits cyanobacterial growth. Additionally, the nutrient content of urine, including trace elements, was assessed to determine if these are sufficient to support growth to the biomass concentration needed for complete nitrogen and phosphorus recovery. Cultivation of Synechocystis sp. PCC6803 on source separated urine recovered up to 87% of the nitrogen and 99% of the phosphorus in form of biomass, reaching N:P ratios up to 43:1. The biomass reached similar specific growth rates on synthetic urine and source-separated urine demonstrating that there are no negative effects of real urine on growth of Synechocystis sp. PCC6803. Supplementing urine with sulfate, magnesium, iron and trace elements is necessary for balanced growth of Synechocystis sp. PCC6803 and high nutrient recovery.