## 3 Results
### Scanning Electron Microscopy Analysis  
The morphological properties for the blended ratio of sewage sludge and sugarcane bagasse torrefied at 200 \({}^{\circ}\)C, 250 \({}^{\circ}\)C, 300 \({}^{\circ}\)C and 350 \({}^{\circ}\)C were studied using SEM. Figures 3 and 4 present the surface morphology images of the torrefied blended samples at the same magnifi  
\begin{table}
\begin{tabular}{c c c c} \hline
**Correlation** & **Sample** & **HHV1 (MJ/kg)** & **HHV2 (MJ/kg)** \\ \hline \multirow{8}{*}{HHV1 = 0.3536 FC + 0.1559 VM \(-\) 0.0078 AC} & M\({}_{\rm a250}\) & 16.20 & 17.64 \\  & M\({}_{\rm a300}\) & 12.25 & 14.59 \\ \cline{1-1}  & M\({}_{\rm a300}\) & 17.41 & 18.75 \\ \cline{1-1}  & M\({}_{\rm a350}\) & 13.93 & 15.08 \\ \cline{1-1}  & M\({}_{\rm e200}\) & 13.43 & 15.06 \\ \cline{1-1}  & M\({}_{\rm e250}\) & 15.82 & 17.92 \\ \cline{1-1}  & M\({}_{\rm e300}\) & 13.66 & 14.98 \\ \cline{1-1}  & M\({}_{\rm e350}\) & 22.70 & 23.62 \\ \hline \end{tabular}
\end{table}
Table 2: Highest energy value (HHV) of the torrefied blend of SS and BG.  
cation. The observed physical changes were associated with alteration in cellular tissue and structures of the samples. Degradation phases of the blended biomass samples, as seen from the SEM images, were attributed to depolymerization, carbonization and devolatilization of the polymer components as well as lipids present in sewage sludge fraction.  
Figure 4: SEM images of 75% SS to 25% BG blended ratio of torrefied SS and BG.  
Figure 3: SEM images of 50% SS to 50% BG blended ratio of torrefied SS and BG.  
In the SEM image for M\({}_{\rm a200}\), a fibrous hollow-like particle structure can be noticed, indicating the initiation of the degradation process caused by torrefaction. The interspaces were very high at 200 \({}^{\circ}\)C. As the temperature increased to 250 \({}^{\circ}\)C represented by M\({}_{\rm e250}\), the sample fractured and broke up, resulting in a shrinkage of the hollow spaces within the fibers. It also caused a reduction in the particle size of the sample and gave medium interspaces between the particles. This can be attributed to the devolatilization of hemicellulose, which is less thermostable compared to the other polymers. At 300 \({}^{\circ}\)C (M\({}_{\rm e350}\)), the samples further disintegrated into a mixture of granular and fragmented particles that were rectangular. The interspaces decreased at this point. As the temperature rose to 350 \({}^{\circ}\)C, denoted by M\({}_{\rm e350}\), some of the particles aggregated into small lumps, but the sheet-like form and the particle size were further reduced with little interspaces between the particles.  
The morphological image in Figure 4 differed from Figure 3 as the sewage sludge content in the blend changed from 50% to 75%. For the torrefaction temperature of 200 \({}^{\circ}\)C (M\({}_{\rm e200}\)), the sample was observed to have a fiber-like dispersed structure with wide interspaces. Further increase in temperature as observed in M\({}_{\rm e250}\) resulted in a flake-like structure with irregular particle size. At 300 \({}^{\circ}\)C, the biomass gradually formed granules of bigger sizes and aggregated together with fewer interspaces. With more increase in temperature as observed from the M\({}_{\rm e350}\) SEM image, aggregation of the particles on the surface was higher because of lignin degradation. Lignin is reported to have the capacity to bind plant cells together. Hence, this was envisioned to improve the grinding ability of the solid fuel due to the binding nature of lignin. It is noteworthy to highlight that the deformation and shrinking of the cell structure observed in all samples will enhance gasification reactivity [13; 31].