# Biochar from Agro-Forest Residue: Application Perspective Based on Decision Support Analysis
## 3 Results and Discussion
### Decision Analysis  
Independent studies investigate the significance of the ash content and ash-forming elements of biomass envisaged to be used as solid biofuels [77; 78]. [PERSON] et al. [77] identify correlations and associations among the ash yields and contents of the general ash-forming elements of a huge variety of biomass. Thus, the origin and the role of these elements (grouped as follows: (1) Si-Al-Fe-Ti, (2) Ca-Mg-Mn, and (3) K-P-S-Cl-Na) are determined along with the benefits and the obstacles of their associations for biofuel combustion. For instance, the enrichment of elements from group (3) is generally associated with the most critical technological and environmental challenges during biomass thermochemical conversion. The results from the decision support analysis, based on the experimentally measured biochar characteristics, are shown in Tables S1-S4, Supplementary material. Table S1 presents a summary of the results, obtained in terms of biochar potential application as biofuel. The biochar from cherry stones showed the highest potential application as fuel since most of its parameters dominated among the rest of the investigated biochar (number of weak domination events--meaning that cherry stones have better values in 34 situations or in single variables comparison). It showed the most beneficial balance between all parameters reading the distance metric. However, both feedstock and biochar appeared rich in K and P, which according to [PERSON] et al. [77] is a good reason for exploring other utilization pathways. In this point of view, independent studies consider biochar as valuable energy carrier, suitable not primarily for direct combustion but rather as a resource or even additive that facilitates the production of liquid or gaseous biofuels [79]. The results from the decision support analysis regarding the possible char application as catalyst are generalized in Table S2, Supplementary material. In this case, grape pomaces appear to have the highest potential, closely followed by peach stones and cherry stones. The conclusion is based on the obtained higher number of domination events, balanced by the distance metric, which seems to be concurrent. Although peach stones dominated in most solutions, it is the cherry stones and grape pomace that achieved better balance among all variables. Both peach stones and grape pomace can be considered the most advantageous for this application. [PERSON] et al. [67] provided a detailed literature review and experimental research focused on the application opportunities of biochar as a catalyst suitable for various processes. The authors suggest that biochar can act as a promising low-cost adsorbent for CO\({}_{2}\) capturing due to its highly porous structure and sorptive capacity. They further propose the subsequent conversion of the absorbed CO\({}_{2}\) to fuel, although detailed research is required on the process parameters and kinetic mechanisms that enhance the catalytic conversion of CO\({}_{2}\) to biofuels. [PERSON] et al. [80] investigate biomass-derived CaO sorbent for CO\({}_{2}\) capture and conclude that the examined material is suitable for producing CO\({}_{2}\) adsorbents. All six types of biomass analyzed in the present study showed a relatively high content of CaO. [PERSON] et al. [81] summarize detailed studies on currently investigated carbon-based materials, obtained by biomass carbonization and/or activation. The authors state that activated carbons, known for having versatile properties (e.g., specific surface area, significant porosity, heteroatoms in their graphene matrix, etc. ), are highly valued materials for the production of electrochemical capacitors. According to [82], each biochar is unique, having different chemical and physical properties which depend on the feedstock and the applied technology/operating parameters for biomass conversion.