Recent advances in biological pretreatment of microalgae and lignocellulosic biomass for biofuel production

Biological pretreatment (BP) is a promising approach for treating microalgae and lignocellulosic biomass (LCB) during biofuels production that uses mostly fungal and bacterial strains or their enzymes. Pretreatment with fungi requires long incubation time (weeks to months), whereas, bacterial and enzymatic pretreatments can be completed by only a few hours to days. Nevertheless, fungal pretreatment especially with white-rot fungi (WRF) is predominantly used in BP of biomass for its high efficiency and downstream yields. According to the recent reports, delignification of LCB by WRF may vary between 3% and 72% with a maximum 120% increase in the biofuel yield. Compared to the untreated microalgae biomass, the downstream yields of the respective biofuels were found to be increased by 22-159% after bacterial pretreatment, while enzymatic pretreatment improved as much as 485% of the final yield. Despite the results are promising, exploitation of BP on large scale is still bottlenecked by some technoeconomic hurdles, which need to be overcome through further fundamental and applied researches. This paper presents a comprehensive and in-depth review on BP for LCB and microalgae biomass by focusing on the relevant overviews and perspectives, technological approaches, mechanisms, influencing factors, and recent research progresses. Finally, challenges and future outlooks are discussed in the concluding sections.