3. Results and discussion
3.1. Pretreatment of microalgal biomass and wet oil extraction
Fig. 3 shows the effects of extraction time, extraction temperature
and the hexane-to-methanol ratio on oil recovery by the wet
oil extraction process. The results indicate that the oil recovery
increased rapidly with an increase in the extraction time, extraction
temperature, and the hexane-to-methanol ratio in the early
stage of the experiments. The increase in oil recovery then slowed
down as these parameters continued to rise, and finally reached a
maximum oil recovery level. The trends shown in Fig. 3 are quite
similar to those reported in a recent study (Dai et al., 2014). At
room temperature (25 C), the oil recovery increased along with
the extraction time, and reached a plateau starting at 80 min,
and thus this was selected as the suitable extraction time. As for
the extraction temperature, although the highest oil recovery
occurred when the temperature was increased to 65 C, when considering
the safety of an open extraction system, a lower temperature
of 45 C was selected for oil extraction. In addition, an increase
in the hexane/methanol ratio also led to an increase in oil recovery,
which reached the highest level of 96.2% when the hexane/
methanol ratio was 3:1 (12 mL:4 mL), and thus this was
selected as the suitable condition. In summary, the selected