As an alternative feedstock for biodiesel production, microalgae have the following advantages over conventional oil crops such as soybeans: (1) microalgae have simple structures, but high photosynthetic efficiency with a growth doubling time as short as 24 h. Moreover, microalgae can be produced all year round. Some data in Table 1 [4] show microalgae are the only source of biodiesel that have the potential to completely displace fos­sil diesel. (2) The species abundance and biodiversity of microalgae over a broad spectrum of climates and geographic regions make seasonal and geographical restrictions much less of a concern compared with other lipid feedstocks. Microalgae may be cultivated on freshwater, saltwater lakes with eutrophication, oceans, marginal lands, deserts, etc. (3) Microalgae can effectively remove nutrients such as nitrogen and phosphorus, and heavy metals from wastewaters. (4) Microalgae sequester a large amount of carbons via photosynthesis, for example, the CO2 fixation efficiency of Chlorella vulgaris was up to 260 mgL-1h-1 in a membrane photobio­reactor [5]. Utilization of CO2 from thermal power plants by large-scale microalgae production facilities can reduce a great deal of the greenhouse gas emissions blamed for global warming. (5) The production and use of microalgae biodiesel contribute near zero net CO2 and sulfur to the atmo­sphere. (6) Microalgae can produce a number of valuable products, such as proteins, polysaccharides, pigments, animal feeds, fertilizers, and so on. In short, microalgae are a largely untapped biomass resource for renew­able energy production.

However, commercialization of microalgae biomass and biofuel pro­duction is still facing significant obstacles due to high production costs and poor efficiency. In face of these challenges, researchers are undertak­ing profound efforts to improve microalgae biomass production and lipid accumulation and lower downstream processing costs.