The invention discloses a method for producing biological diesel oil by two steps of culture of chlorellas, namely, autotrophy and heterotrophy, which belongs to the renewable biological energy field. Concentrated autotrophic
algae is put into a
fermentation tank to perform heterotrophic growth from the processes of autotrophic culture,
cell concentration and
fermentation pollution controlling of the chlorellas, to ensure the chlorellas to be synthesized into
neutral fat. Effective feeding strategy is established to ensure the fat to be synthesized into optimal after the optimization of the
fermentation conditions and the
process control. The
biomass can reach 108g.L-1, and the
grease content can reach 52 percent of
cell dry weight. After the culturing is finished, biological diesel
oil can be prepared after extracting algal oil and
transesterification reaction. The
cell concentration technology adopted by the invention can effectively avoid the problem of light restriction during the
high density culture process Not only is the
carbon dioxide emission reduced, but also the organic
carbon source consumption is reduced, thus the preparation cost of the biological diesel oil material is saved. The whole technical line is environmental friendly, high efficient, and can meet the industrial application requirements of the microalgae biological diesel oil.