Abstract Microalgae represent an outstanding renewable resource for the sustainable production of biohydrogen, owing to their rapid growth rates, efficient carbon fixation, and adaptability to various aquatic environments, as well as their low nutritional demands and minimal land requirements. Nonetheless, their commercial viability is hindered by challenges such as low hydrogen yields and high production costs. Recent advancements have actively addressed these challenges by prioritizing the maximization of hydrogen yields through improved cultivation techniques, effective pretreatment strategies, and state-of-the-art integrated bioelectrochemical systems. This review provides a comprehensive analysis of the latest breakthroughs in biohydrogen production using microalgae, highlighting innovative pretreatment methods, significant progress in genetic engineering, efficient microbial immobilization techniques, and hybrid biohydrogen fermentation systems that significantly enhance hydrogen yields. Moreover, the review underscores the critical importance of advanced reactor designs, such as microbial electrolysis cells (MECs) and hybrid systems utilizing microalgae hydrolysate, which play a pivotal role in boosting biohydrogen production. Consequently, microalgae are positioned as a vital component in advancing a sustainable hydrogen economy. Beyond hydrogen production, algal biomass can assimilate nutrients and yield economic benefits through the generation of value-added products such as biodiesel, pigments, and various secondary metabolites. Additionally, the integration of microalgae in microbial fuel cells (MFCs) effectively mitigates greenhouse gas emissions and promotes carbon sequestration. Currently, microalgal-based wastewater treatment technology is gaining considerable attention as a green solution aligned with the principles of the circular bioeconomy. The capacity of microalgae to produce oxygen eliminates the necessity for external aeration processes, resulting in enhanced economic advantages. Photosynthetic MFCs emerge as a robust solution for integrating bioenergy production, pollutant removal, recovery of valuable byproducts, and effective wastewater treatment and management, all in alignment with the ambitious goals of a circular bioeconomy.
Usharani Rathinam Krishnaswamy (Mon,) studied this question.