## 3 Results and Discussion
### Lipid Extraction Maximization  
As discussed earlier, ultrasonication was found to be more conducive to extracting the microalgae oil compared to other processes. Both ultrasonication and the Soxhelt extraction process were further carried out to maximize the oil yield. Ultrasonication extraction was investigated with varying amplitudes to maximize the oil yield. Different amplitudes were tested, ranging from 50% to 90%. The results of this work are shown in Figure 5. It is to be noted that, for these cases, a percentage increase in the oil yield compared to baseline was presented. The percentage yield of crude oil was observed to increase continuously as the amplitude increased. A higher amplitude enhances the disruption efficiency of the cell wall for both species of microalgae. For _Chlorella_ sp., the percentage oil yield continues to increase up to the 90% amplitude, reaching about 36%. On the other hand, at the 70% amplitude, ultrasonication of _Spirulina_ sp. resulted in a 30% oil yield. After that, any increase in amplitude did not affect the oil yield significantly and remained nearly identical. Thus, the 70% amplitude maximizes _Chlorella_ sp. lipid extraction without significantly affecting output, whereas a 90% amplitude is required for _Spirulina_ sp. lipid extraction. Lipid maximization for Soxhelt extraction was investigated with a combination of solvents at different ratios to enhance the extraction process, and the results are shown in Figure 6. Since hexane resulted in a poor oil yield of both species of microalgae, different solvents were used to extract the microalgae cells. Instead of using a single solvent, a mixture of solvents was used based on the recommendations \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Species**} & **Amount of Dried** & \multirow{2}{*}{**Soxhlet Extraction**} & \multirow{2}{*}{**Ultrasonication**} & \multirow{2}{*}{**Solvent Extraction**} & \multirow{2}{*}{**Reference**} \\  & **Microalgae Used** & & & & \\ \hline \multicolumn{5}{c}{**Oli Yield in Percentage (\%)**} \\ \hline _Chlorella_ sp. & 30 g & 3.5 & 9.4 & 2.7 & This study \\ _Spirulina_ sp. & 30 g & 4.1 & 6.6 & 2.5 & This study \\ _Chlococcicum_ sp. & 4 g & 0.8 & - & - & [52] \\ _Chlococcicum_ sp. & 200 mL stock culture & - & 4.5\% & - & [56] \\ _Birdococcus_ sp. & 0.5 g & - & \(<\)9\% & - & [20] \\ _Chlorella vulgaris_ & 0.5 g & - & \(<\)9\% & - & \\ _Scenedesmus_ sp. & 0.5 g & - & \(<\)9\% & - & \\ _Birdysaccus bmunti_ & - & - & 16\% & - & [57] \\ _Chlorella pyrerooides_ & - & 2.2 & - & - & [18] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison study of the percentage oil yield based on different extraction methods. Figure 4: Percentage of oil yield for different extraction processes. of previous research [17; 58]. The goal of using a mixture of polar and non-polar solvent was to achieve maximum extraction efficacy compared to an earlier stage where only non-polar hexane was used. As seen in Figure 6, a C:H:M ratio of 1:1:1, 2:1:3, 3:2:1, and 1:2:3 resulted in about a 15.3%, 10%, 14%, and 13.3% percentage oil yield for _Chorella_ sp. On the other hand, a C:H:M ratio of 1:1:1, 2:1:3, 3:2:1, and 1:2:3 resulted in about a 23.3%, 12%, 15%, and 20% percentage oil yield for _Spirulina_ sp. respectively. The higher percentage yield of oil was extracted from both species of microalgae compared to the hexane-only extraction. The combination of chloroform, hexane, and methanol at a ratio of 1:1:1 gave a maximum yield of crude oil for both species of microalgae. When comparing the yield of two species, _Spirulina_ sp. showed a higher yield for every solvent combination ratio of chloroform, hexane, and methanol, as shown in Figure 6. Appendix B discusses the SEM images of dried microalgae after the Soxhlet extraction maximization process with 1:1:1 C:H:M.  
Figure 5: The percentage yield of crude oil for ultrasonication extraction.