## 3 Results and Discussion
### Kinetic Parameters of Fermentation
The effect of the fermentation time on the glucose concentration at various fermentation temperatures can be seen in Figure 3c. Based on Figure 3c, glucose concentration tends to decrease with longer SSF times. This may occur because the glucose produced in enzymatic hydrolysis will be used directly by cells for growth processes and to produce bioethanol [39; 40]. The decrease in glucose concentration showed the same tendency at each SSF reaction temperature. This indicates that in the SSF process, glucose that has been formed as a result of enzymatic hydrolysis will be used directly by yeast as a carbon source to form bioethanol. 30 \({}^{\circ}\)C was the temperature that showed the lowest glucose concentration at the end of the SSF reaction. This happened because, at this temperature, yeast cells make optimum use of glucose, which can be characterised by high ethanol concentrations. The effect of the fermentation time on the bioethanol concentration at various fermentation temperatures can be seen in Figure 3a. Based on Figure 3a, the highest bioethanol concentration was 0.70 g/L. The longer reaction time of SSF produces lower bioethanol concentrations. The lower bioethanol concentration produced in this study was different from that produced in previous studies because, in general, the concentration of bioethanol will increase with longer fermentation times. The lower bioethanol concentration in this study could be due to the vaporisation of the ethanol. The effect of temperature on bioethanol concentrations is quite significant. Figure 3a shows that a temperature of 30 \({}^{\circ}\)C with a 24-h reaction time produced bioethanol at around 0.70 g/L. At 32 \({}^{\circ}\)C and 35 \({}^{\circ}\)C with 24-h reaction time, the concentration of bioethanol dropped significantly to 0.26 g/L and 0.17 g/L, respectively. This might have occurred because higher reaction temperatures can make fermentation processes ineffective. High temperatures can affect cell transport activity and the occurrence of ribosomal and enzyme denaturation and can cause fluidity problems in cell membranes [41]. Yeast optimally ferment glucose into bioethanol at 30 \({}^{\circ}\)C. Based on data obtained from the laboratory, the bioethanol concentration was very small. Therefore, the influence of bioethanol as an inhibitor in the SSF kinetics equation can be ignored. Based on Figure 4 above, the kinetic model optimisation of cell, glucose and bioethanol concentrations shows some results that are not optimal. This could be due to the composition of the raw materials used in this study. The raw material used in this study was OPEFB, which consists of cellulose, hemicellulose and lignin. The hemicellulose and lignin contents in the raw material could have inhibited the enzymatic hydrolysis process and the fermentation process. However, overall, the kinetics model that was used in this study is suitable for experimental data and can describe the SSF process. From the results of the kinetic model optimisation with cell, glucose and bioethanol concentrations, various kinetic constants on the bioethanol reaction can be obtained. The kinetics constants for the bioethanol fermentation reaction can be seen in Table 4 below. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Kinetic Parameters**} & \multicolumn{3}{c}{**Temperature (\({}^{\circ}\)C)**} \\ \cline{2-4}  & **30** & **32** & **35** \\ \hline \(\mu\)max (h\({}^{-1}\)) & 0.009 & 0.013 & 0.018 \\ \(ks\) (g/dm\({}^{3}\)) & 0.004 & 0.010 & 0.025 \\ \(kd\) (h\({}^{-1}\)) & 0.009 & 0.009 & 0.213 \\ \hline \end{tabular}
\end{table} 
Table 4: Determined kinetic parameters for bioethanol production. Based on Table 4, it can be seen that higher temperatures will increase the value of various reaction constants, such as \(\mu\) max (maximum specific growth rate), \(k\)s (Monod constant), \(kd\) (cell death rate constant) and m (maintenance cell constant). One parameter that influences cell growth is \(\mu\) max. The effect of ethanol on cell growth can be seen through the \(\mu\) max parameter.