The Next Generation Feedstock of Biofuel: <i>Jatropha</i> or <i>Chlorella</i> as Assessed by Their Life-Cycle Inventories

Promising energy crops such as <i>Jatropha curcas Linnaeus</i> (<i>JCL</i>), which are planted on marginal lands, or microalgae such as <i>Chlorella</i>, which are cultivated in ponds located on mudflats or deserts, have been regarded with high hopes to solve the shortage of food crops and increase the amount of biodiesel (Fatty Acid Methyl Ester, FAME) production. However, the annual yields of biomass and transport fuels (t/ha) of both are still unclear and often exaggerated in the literature. Large portions of <i>JCL</i> biomass, including tree trunks and leaves, can also be used to generate electricity along with FAME, which is produced from seed lipids. Meanwhile, lipid extracted algae (LEA) are composed of proteins, polysaccharides, and lipids other than glycerides which are unable to be esterified to form FAME and much more abundant in the microalgae than oil cake in the oil crops. Therefore, it has been strongly suggested that not only transesterification or esterification but also Fischer-Tropsch (FT) process and bio-electricity generation should be considered as routes to produce biofuels. Otherwise, the yield of biofuel would be extremely low using either <i>JCL</i> or <i>Chlorella</i> as feedstock. The Life-Cycle Inventories (LCI) of the biofuel processes with whole biomass of <i>JCL</i> and <i>Chlorella</i> were compared based on their net energy ratio (NER) and CO₂ emission saving (CES). It was shown that the technological improvement of irrigation, cultivation, and processing for either economic-crops or microalgae were all necessary to meet the requirements of commercial biofuel production.