## 3 Results and Discussion  
### Proximate and Ultimate Analysis and Higher Heating Value  
The results concerning the proximate and ultimate analyses, as well as the moisture, density and heating value, are shown in Table 1.  
Concerning the moisture obtained, there was a variation (depending on the kind of waste) from 7.15 to 11.30%, but less than 15%, which is the recommended value for \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \begin{tabular}{c} **Moisture** \\ **\% wb** \\ \end{tabular} & \begin{tabular}{c} **Density** \\ **kg/m\({}^{3}\) wb** \\ \end{tabular} & \multicolumn{5}{c}{**Ultimate Analysis (\% db)**} & \multicolumn{5}{c}{**Proximate Analysis (\% db)**} & \multicolumn{2}{c}{\begin{tabular}{c} **HHV** \\ **MJ/kg db** \\ \end{tabular} } \\ \cline{3-10}  & & **C** & **H** & **N** & **S** & **O** & **Ash** & \
\begin{tabular}{c} **Volatile** \\ **Matter** \\ \end{tabular} &
\begin{tabular}{c} **Fixed** \\ **Carbon** \\ \end{tabular} & \\ \hline Ma 1 & 11.30 & 220.02 & 41.57 & 6.48 & 0.35 & 0.04 & 51.56 & 1.92 & 85.79 & 12.29 & 16.54 \\ Ma 2 & 10.37 & 204.80 & 42.20 & 6.35 & 0.34 & 0.04 & 51.07 & 1.98 & 86.72 & 11.30 & 16.72 \\ Ma 3 & 9.23 & 121.80 & 41.44 & 6.37 & 0.54 & 0.07 & 51.58 & 4.41 & 80.72 & 14.87 & 16.52 \\ Ma 4 & 7.15 & 96.86 & 39.98 & 5.87 & 0.50 & 0.08 & 53.57 & 9.68 & 79.75 & 10.57 & 16.37 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Proximate and ultimate analyses (db: dry basis, wb: wet basis). subsequent pelletizing, according to the standard [19]; it did not need any previous drying process. Regarding density, there were clear differences among the four residues, due to their different natures, and therefore the densification ratios will be very different. [PERSON] et al. [34] obtained densities of 282.38 kg/m\({}^{3}\) (for corncob waste) and 127.32 kg/m\({}^{3}\) (for stalk); these values were very similar to those obtained in this work. With regard to the ultimate analysis, it is interesting to focus on N and S content, due to the possible NOx and SO\({}_{2}\) emissions. For nitrogen, the values ranged from 0.35% to 0.5%, whereas in the case of sulfur, the range was from 0.039 to 0.080%. In both cases, the values were higher in the wastes that contained corn stalk. Nevertheless, the results were below the upper limit established by the standard [19]. Regarding the proximate analysis, in the case of volatile matter, the residues containing corncob waste had a higher value, whereas for corn stover this content was lower (79.75%). Other authors like [PERSON] et al. [35] obtained a volatile matter of 81.1% for corn stover, very similar to the result obtained in the present study. Regarding ash content, lower values were observed for the residues containing corncob waste than for those containing corn stalk. Moreover, the influence of leaves on the corncob waste was not significant when it came to ash content. In the case of Ma1, Ma2 and Ma3, ash content was 1.92%, 1.98% and 4.41%, respectively; compared to other biofuels, it can be observed that other herbaceous biomass, such as rice husk or wheat straw, had ash contents of 18.91% [15] and 9.28% [36], respectively, whereas in woody biomass, such as the biomass from eucalyptus or stone pine, the ash content was 7.21% and 3.03% [28], respectively. Therefore, the ash content of the analyzed samples had suitable values for thermal use. Taking into account the standard required to use these wastes as biomass, class A pellets would be obtained from Ma1, Ma2 and Ma3 residues [19]. On the other hand, ash content considerably increased for Ma4, which remained on the soil and was degraded over time, and directly baled on the ground (implying higher amounts of impurities). These high ash values showed that this kind of waste would not be a suitable material for its thermal use in densification. If the results related to corn stover are compared with other studies, [PERSON] et al. [15] obtained ash content values of 11.80% for corn stover, whereas [PERSON] et al. [16] obtained a value of 8.18%.