ABSTRACT
Microalgal biodiesel provides advantages of the economical feedstock that does not compete with food resources. However, there are several challenges that should be overcome to be commercialized. One of the greatest challenges is harvesting of microalgae that accounts for 20–30% of the total production costs of algal biodiesel production. The details of the harvesting costs are explained in addition to the pros and cons of economical methods including bioflocculation and autoflocculation. Extraction of the lipid content from the algae biomass is another serious bottleneck to more economical production of algal biodiesel. Strategies for more effective extraction are addressed along with the introduction to general algal biodiesel manufacturing processes. For the conversion of algal lipids to biodiesel, both chemical and thermochemical methods are explained and compared. Hydrothermal liquefaction (HTL) process is introduced in more detail. Fatty acid profiles of microalgal biodiesel from different algae species, S. obliquus SJTU-3, Chlorella sp. TISTR 8990 and Nannochloropsis oculata, are described and compared with the fatty acid profiles of biodiesel from vegetable oils and animal fats. Differences of biodiesel properties caused by the feedstock are compared between microalgal biodiesel, diesel, and soybean-based biodiesel (100%, 20%, and 6%). Microalagal biodiesel shows much higher values in flash point (115 °C) and Cetane number (60.73) than the others. It also shows a superior oxidation stability.
