This study investigates the effects of media recirculation on microalgal species C. sorokiniana growth in a pilot-scale algae photobioreactor (APB). Two culture conditions, freshwater and recirculated boiler water, were conducted on the APB to determine the effect of recirculation on algal growth. The results showed that microalgae cultivation under recirculation conditions was stable over a period of four months. Biomass productivities during the 1st through 4th months of recirculation (0.26, 0.23, 0.20, and 0.18 g L-1 d-1, respectively) were not significantly different from the culture on freshwater (0.22 g L -1 d -1). Furthermore, the relationship between eukaryotic and bacterial domains remained consistent throughout the four months of recirculation (80.7, 87.1, 83.1, and 82.1%, respectively and 19.2, 12.8, 16.9 and 17.8%, respectively). This was not significantly different from the abundance of each domain in freshwater cultivation (83.7% eukaryotic and 16.2% bacterial). A 1 m3 photobioreactor was then envisioned for mass, energy and exergy analyses. The mass balance analysis concluded that a 98% reduction in freshwater usage and 25% reduction in nutrients could be achieved during cultivation operating under recirculation conditions for a year, while maintaining a biomass productivity of 1.2 kg wet algal biomass and 0.4 kg CO2 sequestered per day. Both systems require an energy input of 219 kWh unit-1 d-1. The exergy balance analysis concluded that without considering solar irradiation, the rational exergy efficiency of the culture with water recirculation was more than double that of freshwater.
Read
