Bubbleless membrane aeration for Chlorella vulgaris cultivation in urine at high CO2 supply

Microalgae cultivation in urine with CO2 supply has gained popularity because this bioenergy with carbon capture and storage technology can achieve the win-win of waste management and key elements cycling. However, the conventional sparging method has significant limitations in delivering CO2 from the fuel gas. In this study, we have developed a bubbleless membrane aeration photobioreactor for Chlorella vulgaris cultivation in synthetic human urine at high CO2 supply (30 %–100 %). The effects of light intensities, urine dilution factors and CO2 concentrations on the C. vulgaris growth and nutrient removal were compared between the conventional and membrane aeration methods. Results showed that membrane aeration can efficiently deliver CO2 to the culture at negligible energy cost. More importantly, membrane aeration can alleviate the CO2 stress and reduce the negative impacts of pure CO2 supply on the cultivation. Through combining a pH control strategy, sustained algal growth (>3 h−1) and high ammonia removal (88.3 %) was achieved using 10 times diluted urine. Proteomics analysis demonstrated that pH control in membrane aeration could further regulate the antioxidant, peroxidase and oxidoreductase activities, facilitating the metabolisms for photosynthesis and nutrient uptake. Chlorella cultivation also showed the same performance by using real human urine. Results of this study demonstrate that this novel approach holds great promise for algae cultivation in urine at high CO2 supply, opening a new pathway toward sustainable CO2 and waste management.