Growth and Nutrient Removal Characteristics of Chlorella Cultivated in Resource-Separated Human Urine Mixed with Soap Wastewater

Human urine, which accounts for approximately 80% of the nitrogen and 50% of the phosphorus in domestic sewage, could be a high-quality medium for cultivating microalgae. However, soap wastewater (SW) is constantly mixed with human urine. This work explored Chlorella pyrenoidosa and Chlorella sp. culture using a high-loaded urine-SW mixture under non-sterilization, less inoculation dosage, and medium illumination. The Chlorella yields at human urine to blue-green algae medium (BG11) ratios of 3:6 and 4:5 were superior to those obtained at higher ratios of 5:4, 6:3, and 7:2 and even exceeded those with pure BG11. SW inhibited the production of Chlorella cultured in human urine. Although an SW-to-BG11 ratio of 1:49 was optimal, a higher ratio was acceptable for Chlorella sp., even as high as 5:45. The optimum yields and protein contents under SW addition were 0.57 g/L and 60.32% for Chlorella pyrenoidosa and 0.96 g/L and 53.55% for Chlorella sp. The maximal nitrogen, phosphorus, and chemical oxygen demand removals surpassed 74%, 74%, and 44% for Chlorella pyrenoidosa and 94%, 94%, and 86% for Chlorella sp. Studies elucidated the viability of microalgae culture using human urine sewage containing SW, accelerating low-cost production of microalgae and high-valued utilization of source-separated human urine.