## 3 Results and Discussion
### Physical Properties of the Biochars  
Figure 2b shows SEM images of samples of biochars obtained from bamboo and pinewood. Visible macroporosity (<10 \(\upmu\)m) inherently associated to the original structures of the xylem conducting tissue appear in BB1, in agreement with earlier observations [16; 31]. Following Wildman and Derbyshire [21], no pretreatment was used for the removal of debris, in order to avoid artifacts. Observable fine particles below 3.0 \(\upmu\)m were fragmented char derived from tissue walls, attributable to rapid devolatilization during pyrolysis. As can be seen in Figure 2b,d, greater and more irregular micro and mesoporosity was present in the pinewood biochar (see also Table 3). This might owe to higher temperatures during charring (see Table 2), though also to the structure and composition of the feedstock biomass. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Feedstock** & **Cellulose** & **Hemicellulose** & **Lignin** & **Moisture** & **Volatiles** & **Ash \%** & **hhv** & **(mj/kg)** & **Cite** \\ \hline _Guadua angustifolia_ & n.a. & n.a. & n.a. & 9 & 75 & 5.7 & 18.8 & [39] \\ Kunth & 52.6 & 19.7 & 27.6 & n.a. & n.a. & n.a & n.a & [40] \\ \hline  & n.a. & n.a. & n.a. & 7.8 & 75.8 & 3.8 & 19.1 & [41] \\ \hline  & n.a. & n.a. & n.a. & 9.1 & 74.1 & 2.9 & n.a. & [42] \\ \hline _Guadua_ & 47.8 & 26.3 & 21.5 & 8.1 & 86.8 & 2.2 & & [43] \\ \hline _Bambusa vulgaris_ & n.a & n.a & n.a & 7.14 & 74.35 & 1.49 & n.a & [44] \\ \hline _Phylosclachys_ & 44.2–47.7 & 26.7–28.6 & 25.4–27.3 & n.a. & 80–84 & 0.50–1.3 & 19.1–19.6 & [45] \\ \hline _Dendrocallanus gigantetus_ & 47.5 & 15.35 & 26.25 & 9.37 & 70.31 & 2.57 & n.a. & [46] \\ \hline Pine wood & 42.1 & 27.7 & 25.0 & n.a. & n.a. & n.a. & n.a. & [47] \\ \hline Pine wood & 43.74 & 16.20 & 29.14 & n.a. & 84.05 &.31 & n.a. & [48] \\ \hline _Cupressus_ & 64.7 &
\begin{tabular}{c} Under \\ cellulose \\ \end{tabular} & 31.4 & n.a. & n.a. & 0.18 & n.a. & [49] \\ \hline Spruce wood & 41.1 & 20.9 & 28.0 & n.a. & n.a. & 0.30 & 19.25 & [47] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of selected properties from selected feedstocks. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & **BB1** & **BB2** & **BB3** & **WB1** & **WB2** & **WB3** & \(p\)**-Value** \\ \hline  & & & \multicolumn{6}{c}{Temperature (\({}^{\circ}\)C)} \\ \hline
**Thermocouple I (13 cm)** & Average & 335 & 534 & 519 & 558 & 546 & 654 & 0.1643 \\  & Maximum & 782 & 752 & 756 & 685 & 836 & 854 & 0.6300 \\
**Thermocouple II (18 cm)** & Average & 258 & 439 & 417 & 554 & 549 & 547 & 0.0351 \({}^{\star}\) \\  & Maximum & 662 & 694 & 726 & 683 & 767 & 718 & 0.4015 \\ \hline  & & \multicolumn{6}{c}{Time to reach 500 \({}^{\circ}\)C (min)} \\ \hline
**Thermocouple I (13 cm)** & & 36 & 7 & 14 & 3 & 17 & 7 & 0.6193 \\
**Thermocouple II (18 cm)** & & 42 & 7 & 14 & 3 & 12 & 7 & 0.4782 \\ \hline \hline \multicolumn{7}{l}{\({}^{\star}\): is the \(p\)-value with significant difference (\(p<0.05\)). One-way ANOVA was measured between the two groups BB} and WB.  
\end{table} 
Table 2: Summary of temperatures and time to reach 500 \({}^{\circ}\)C in a TLUD stove, during preparation of biochars from bamboo (BB) and pinewood (WB). A-BET specific surface area (SSA, A-BET) was higher for pinewood biochars, ranging from 234 to 267 m\({}^{2}\)/g, as compared to that of bamboo biochars, ranging from 54 to 144 m\({}^{2}\)/g (Table 3). Most of A-BET apparently corresponds to internal surface area of microporosity. These results are consistent with A-BET values found for wood biochar by [PERSON] et al. [20] at temperatures ranging from 600 to 700 \({}^{\circ}\)C and by [PERSON] [17] for cellulose produced at 700 \({}^{\circ}\)C. On the contrary, [PERSON] et al.