# Biochar from Agro-Forest Residue: Application Perspective Based on Decision Support Analysis
## 3 Results and Discussion
### Biochar Characterization Using Proximate, Ultimate, Calorimetric, BET, and Combined pH/EC Analyses  
The results from biochar proximate, ultimate, and calorimetric analysis are summarized in Table 4.  
The biochar, derived from biomass containing kernel, showed the highest fixed carbon content, although the effect cannot be directly related to the concentrated carbon \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Biochar**} \\ \hline
**Colza** & **Cherry Stones** & **Peach Stones** & **Grape Pomace** & **Softwood** & **Sunflower Husks** \\ \hline \multicolumn{6}{c}{Proximate analysis (wt. \%)} \\ \hline Moisture & 5.32 & 4.49 & 4.95 & 2.84 & 5.38 & 9.33 \\ Ashes (db) & 7.08 & 4.47 & 1.92 & 12.44 & 1.29 & 4.83 \\ Volatile matter (db) & 32.10 & 25.86 & 30.57 & 17.91 & 40.49 & 44.13 \\ Fixed carbon * (db) & 55.51 & 65.18 & 62.57 & 66.81 & 52.85 & 41.71 \\ \hline \multicolumn{6}{c}{Ultimate analysis (wt. \%, db)} \\ \hline C & 73.52 & 67.01 & 81.56 & 77.61 & 82.35 & 76.76 \\ H & 3.66 & 3.22 & 3.61 & 3.52 & 3.78 & 3.50 \\ N & 1.97 & 4.28 & \textless{}0.10 & 2.64 & 0.97 & 2.24 \\ O* & 8.25 & 16.33 & 7.66 & 0.75 & 6.04 & 3.13 \\ S & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 \\ Cl & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 & \textless{}0.10 \\ HHV, MJ/kg & 24.94 & 28.62 & 33.34 & 28.11 & 30.88 & 31.05 \\ Specific surface area & 252.30 & 265.74 & 306.72 & 293.27 & 331.62 & 278.25 \\ (m\({}^{2}\)/g), S\({}_{\text{SET}}\) & 0.1585 & 0.4455 & 0.4301 & 0.3737 & 0.2028 & 0.2700 \\ pH & 9.70 & 9.55 & 9.10 & 11.08 & 8.38 & 9.93 \\ EC (\(\mu\)S/cm) & 1015 & 372 & 84 & 1960 & 56 & 897 \\ Salt content (ppm) & 508 & 186 & 42 & 980 & 28 & 448 \\ \hline \hline \end{tabular} \({}^{*}\)by difference.  
\end{table} 
Table 4: Biochar characteristics. Figure 4: SEM images of the biochar morphology. content. The descending order of the fixed carbon per biochar type is as follows: grape pomace > cherry stones > peach stones > > colza > softwood > sunflower husks. As expected, the opposite trend was observed regarding the content of volatile matter. Figure 5 shows the Van Krevelen diagram, according to [PERSON] and [PERSON] [64], and [PERSON] et al. [65], of the used raw biomass and the obtained biochar. The comparison of the hydrogen/carbon (H/C) and the oxygen/carbon (O/C) atomic ratio was considered in order to verify the elements' selective loss during the process of dehydration and carbonization [66]. Biochar showed considerably lower H/C, and O/C ratios. According to [PERSON] et al. [67], the fuels with low H/C and O/C ratios are preferable due to their low smoke, water vapor production, and energy losses. The H/C ratio is often seen as an indicator for carbon stability in biochar [68], which together with the O/C ratio is directly associated with the aromaticity, biodegradability, and polarity of biomass and biochar [66; 69]. According to other authors [62; 66; 69; 70], the higher the carbonization temperature is, the lower the observed H/C and O/C ratios are in the resulting biochar samples. The conversion of agricultural biomass residue to biochar in pyrolytic conditions is proposed as a promising option for feedstock utilization for various sustainable purposes such as a substitution of renewable and environment-friendly energy source [38; 71], e.g., for household briquette production [72]. Expectedly, the measured biochar HHV (Table 4) increased on average by 30-50% in comparison to the biomass; the effect was observed also in [38; 71; 73]. The biochar HHV, proximate, and ultimate analyses confirmed the conclusion of [PERSON] [74], concerning its considerable potential to be used as a renewable energy carrier. However, the biochar thermal and surface stability and reactivity are dependent on the feedstock type and conversion temperature [75]. Recently, in focus is the biochar's prospect of becoming a low-cost sorbent for CO\({}_{2}\) capturing [38]. [PERSON] et al.