Biodiesel production from wet microalgae: Progress and challenges

Microalgae are promising renewable feedstocks for producing biodiesel as an alternative to conventional diesel. However, the major bottleneck in microalgal biodiesel production is a rather high energy consumption and production costs, which limit the economic feasibility and industrial commercialization. In microalgal downstream processing, biomass dewatering and drying constitute the major challenge in terms of cost and energy. In this regard, several techniques have been developed to produce biodiesel from wet biomass, but the cost of biodiesel production is still higher than that of diesel. To date, reviews in this field generally focus on methods of producing biodiesel from wet microalgae and do not compare the different methods in terms of operation and efficiency. Here, we investigated and summarised different biodiesel production techniques from wet microalgae, and reviewed factors affecting cell wall disruption, lipid extraction, and lipid conversion. Further, challenges that hinder the industrial-scale production of biodiesel from wet microalgae are critically analysed in terms of production costs, production processes, and environmental concerns. We also provided a critical and in-depth insight into the challenges of microalgal biodiesel production and identified pragmatic strategies to put forward with the current research for economical biodiesel production from microalgae.