## 3 Results and Discussion
### Proximate Analysis and Ultimate Analysis  
Thermogravirometric analysis (TGA) provides critical insights into the composition of biomass and serves as a key parameter in evaluating its suitability as a biofuel feedstock by quantifying moisture, volatile matter (VM), and ash content. Among these, the moisture content should remain below 10% to avoid the need for additional drying, which would increase processing costs and reduce conversion efficiency [62]. _Desmodesmus_ sp. KNUA231 exhibited a moisture content of 4.04 \(\pm\) 0.51% (wt) (Table 5), which falls within the acceptable range, ensuring its efficient utilization in biofuel applications without supplementary drying. A high volatile matter (VM) content enhances fuel reactivity, lowers the ignition temperature, and improves overall combustion efficiency. Many conventional lignocellulosic biomass materials, such as agricultural residues (65.15%) [24] and fuel briquettes (65.99%) [63] derived from biomass residues, exhibit lower VM levels compared to microalgae-derived biomass. In contrast, _Desmodesmus_ sp. KNUA231 demonstrated a VM content of 89.56 \(\pm\) 1.11%, indicating superior combustion efficiency and enhanced thermal energy output.  
A detailed analysis also allows for the determination of CV, which represents the energy released during combustion. _Desmodesmus_ sp. KNUA231 exhibited a CV of 25.49 \(\pm\) 0.28 MJ kg\({}^{-1}\), which is substantially higher than that of conventional biomass feedstocks such as bamboo (15.66 MJ kg\({}^{-1}\)) and corn cobs (19.23 MJ kg\({}^{-1}\)) [64]. A higher CV indicates greater energy density, positioning _Desmodesmus_ sp. KNUA231 as a promising candidate for biofuel production. The CV of biofuels is predominantly influenced by carbon and hydrogen content, with higher values correlating with increased energy density. The  
\begin{table}
\begin{tabular}{c c c c} \hline  & _Desmodesmus_ sp. & & \\  & **KNUA231** & & & \\ \hline \hline \begin{tabular}{c} Saponification value (mg KOH g\({}^{-1}\)) \\ \end{tabular} & 167.29 & & & \\ \begin{tabular}{c} Iodine value (g I\({}_{2}\) 100 g\({}^{-1}\) fat) \\ \end{tabular} & 169.04 & \(\leq\)120 & & \\ \begin{tabular}{c} Cetane number \\ \end{tabular} & 38.19 & \(\geq\)51 & \(\geq\)45 \\ \begin{tabular}{c} Degree of unsaturation \\ Cold filter plugging point (\({}^{\circ}\)C) \\ \end{tabular} & \(-\)9.4 & \(-\)20–0 & & \\ \begin{tabular}{c} Oxidation stability (110 \({}^{\circ}\)C, h) \\ Kinematic viscosity (mm\({}^{2}\) s\({}^{-1}\)) \\ \end{tabular} & 5.0 & \(\geq\)6 & \(\geq\)3 \\ \
\begin{tabular}{c} Kinematic viscosity (mm\({}^{2}\) s\({}^{-1}\)) \\ Density (15 \({}^{\circ}\)C) (g cm\({}^{-3}\)) \\ \end{tabular} & 3.28 & 3.5 & 1.9–6.0 \\
\begin{tabular}{c} Density (15 \({}^{\circ}\)C) (g cm\({}^{-3}\)) \\ \end{tabular} & 0.89 & 0.872–0.878 & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Biodiesel quality properties of _Desmodesmus_ sp. KNUA231 compared with EN14214 and ASTM D6751 standards.  
\begin{table}
\begin{tabular}{c c} \hline  & _Desmodesmus_ sp. KNUA231 \\ \hline \hline \begin{tabular}{c} Proximate analysis (wt\%) \\ \end{tabular} & & 4.04 \(\pm\) 0.51 \\ \begin{tabular}{c} Volatile matter \\ \end{tabular} & 89.56 \(\pm\) 1.11 \\ \begin{tabular}{c} Ash \\ Ultimate analysis (wt\%) \\ \end{tabular} & 6.40 \(\pm\) 1.40 \\ \begin{tabular}{c} Carbon (C) \\ \end{tabular} & 53.14 \(\pm\) 0.16 \\ \begin{tabular}{c} Hydrogen (H) \\ \end{tabular} & 7.67 \(\pm\) 0.16 \\ \begin{tabular}{c} Oxygen (O) \\ \end{tabular} & 25.16 \(\pm\) 0.01 \\ \begin{tabular}{c} Nitrogen (N) \\ \end{tabular} & 8.80 \(\pm\) 0.04 \\ \
\begin{tabular}{c} Sulfur (S) \\ \end{tabular} & 0.30 \(\pm\) 0.05 \\
\begin{tabular}{c} CV * (M) kg\({}^{-1}\)) \\ \end{tabular} & 25.49 \(\pm\) 0.28 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Proximate and ultimate analyses of _Desmodesmus_ sp. KNUA231 biomass.  
exceptional CV observed in _Desmodesmus_ sp. KNUA231 underscores its potential as a high-energy-density biofuel that is comparable to or exceeds existing biomass feedstocks (Table S4).