# Use of Invasive Acacia Biomass to Produce Biochar and Solid Biofuels
## 3 Results and Discussion
\begin{table}
\begin{tabular}{l l c c c c} \hline \hline  & \multicolumn{4}{c}{**Elaborated Products**} \\ \hline \multirow{2}{*}{**Material**} & **Moisture** & **Bulk Density** & \multirow{2}{*}{**pH (\%)**} & **Volatile Matter (\%)** & **Ash (\%)** & **Fixed Carbon (\%)** \\  & **Content (\%)** & & & & \\ \hline D-biochar-wood & & 162.4 \(\pm\) [11.46] & 8.0 \(\pm\) [0.14] & 31.6 \(\pm\) [1.52] & 2.39 \(\pm\) [1.55] & 66.0 \(\pm\) [2.86] \\ D-biochar-branch/leaf & & 192.0 \(\pm\) [0.57] & 7.5 \(\pm\) [0.00] & 46.3 \(\pm\) [1.94] & 3.07 \(\pm\) [1.88] & 51.0 \(\pm\) [3.84] \\ M-biochar-wood & & 159.9 \(\pm\) [1.27] & 9.5 \(\pm\) [0.16] & 21.5 \(\pm\) [3.92] & 11.75 \(\pm\) [9.90] & 66.8 \(\pm\) [3.80] \\ M-biochar-branch/leaf & & 150.9 \(\pm\) [2.12] & 8.1 \(\pm\) [0.04] & 34.0 \(\pm\) [0.76] & 4.96 \(\pm\) [3.60] & 61.0 \(\pm\) [4.36] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean and standard deviation values of the different tests carried out on the elaborated products. The usual densities obtained with biquettes elaborated with industrial hydraulic systems vary usually between 600 and 1000 kg m\({}^{-3}\)[49]. \"Impact\" and \"extrusion\" biquetting devices usually generate densities of 800-1100 kg m\({}^{-3}\) and 1100-1200 kg m\({}^{-3}\)[50; 51], respectively, at room temperature. The physicochemical properties of briquetted biofuels are significantly influenced by biomass type--classified as herbaceous or woody, and further as hardwood or softwood--as well as by densification parameters, including temperature and applied pressure during compaction [41]. Previous works [51; 52] report that briquette bulk density is a key physical characteristic that varies substantially among different biomass categories. Herbaceous materials such as grasses generally display low bulk densities, typically between 40 and 150 kg m\({}^{-3}\), while agricultural residues tend to exhibit intermediate values, ranging from 80 to 100 kg m\({}^{-3}\). In contrast, woody biomass--owing to its more compact structure--demonstrates considerably higher bulk densities, commonly between 150 and 200 kg m\({}^{-3}\). According to these references, the values of densification obtained both in the briquettes and in the pellets (Table 2 and Figure 4) would allow considering the possibility of producing biofuels with the analyzed raw material. In the case of the briquettes, that is, high-quality briquette fuel without binders, a moderate density was obtained, due to the system used at room temperature (low-pressure hydraulic briquetting). In the production of pellets, high density and quality were obtained, with a density close to 1375 kg/m\({}^{3}\). Figure 4: Mean and standard deviation of the density obtained with the original biomass and the solid biofuels. Figure 3: Mean values of fixed carbon, volatile matter, ash, and pH. Biochar bulk density values were slightly lower than those of the original biomass, as expected (Figure 5). These values are in line with those obtained for biomass-derived biochar, although they are slightly lower than the values typically reported for coal and coke [53]. The Shapiro-Wilk method was employed, using a comparison of the quartiles to determine the normality of the original biomass bulk density groups. As the \(p\)-value was 0.146842 (\(\geq\)0.05), the idea that the groups come from a normal distribution cannot be rejected with 95% confidence interval. The fixed carbon value of the original material ranges between 14.8% and 17.7%, compared to 50.7% to 66.8% of the biochar (Figure 3). Previous works [43] with charcoal produced from the trunks of different acacia species, obtained a fixed carbon of around 20% in the biomass, and their biochar obtained a fixed carbon of 70%, elaborated with 500 \({}^{\circ}\)C (rate of about 25 \({}^{\circ}\)C/min) in an electric furnace. The one-way ANOVA for fixed carbon based on the normality of the groups showed significant differences. Furthermore, LSD and [PERSON]'s test were used to test the homogeneity of means and variance at 95% confidence level.