Continuous cultivation of microalgae in photobioreactors as a source of renewable energy: Current status and future challenges

Microalgae are promising sustainable energy sources for biodiesel production due to their rapid photosynthesis growth rate and capacity to be cultivated in wastewater, seawater, or freshwater. Moreover, microalgae could complete the entire growth cycle via photosynthesis reactions that convert light energy into renewable energy. The closed photobioreactor, PBR is resistant to infection from uninhabited algae species and allows frequent monitoring of various factors such as temperature, light intensity, and pH during the cultivation phase. Thus, this study focuses on continuous cultivation technology which produces higher biomass productivity with sustainable energy-saving operation as compared to batch culture. High productivity of microalgae biomass tends to accumulate higher concentrations of lipid and carbohydrates composition which is essential for the production of biofuels. The energy balance of numerous microalgae-based biofuels was discussed, and it was discovered that the net-energy ratio was greater than 1, indicating that the process is both commercially feasible and environmentally friendly. This study also summarizes the most recent discoveries on continuous cultivation constraints through photobioreactors, PBRs as well as potential challenges to tackle in scaling up the continuous sustainable culture mechanism. The research gaps, market opportunities, and future development directions of continuous photobioreactor systems are discussed to explore future development opportunities. A continuous photobioreactor, architecture is recommended for a pilot-scale trial, as a cost-benefit comparison would be beneficial in commercializing the framework.