Prospects and challenges of thermal hydrolysis pretreatment of microalgae for enhancing bioenergy and resource recovery in anaerobic bioprocesses

Microalgae have emerged as a promising feedstock for bioenergy production through anaerobic digestion and fermentation, gaining significant attention due to their rapid growth rate, ability to adapt to diverse environments, and rich biochemical composition. However, the recalcitrant nature of the microalgal cell wall necessitates pretreatment to enhance the accessibility of intracellular components and improve overall bioenergy yields from anaerobic digestion/fermentation. Among the various pretreatment methods, the thermal hydrolysis process has proven to be a promising strategy for enhancing the efficiency of bioenergy recovery from microalgal biomass. The benefits of thermal hydrolysis pretreatment of microalgae include improved organic matter solubilization, enhanced digestibility, and increased product yields in subsequent anaerobic digestion/fermentation processes for biomethane, biohydrogen, and volatile fatty acids production. However, thermal pretreatment poses challenges, such as forming future research by-products like furfural and ammonia, which can adversely affect microbial activities and reduce process efficiency. Thus, addressing its associated challenges is critical for maximizing its effectiveness in bioenergy and resource recovery. This review provides a comprehensive analysis of these challenges and offers recommendations for future research, emphasizing the need for optimized pretreatment strategies for advancing the sustainable and efficient use of microalgae in bioenergy production.