## 3 Results and Discussion
### Anaerobic Digestion Process
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values \(\pm\) SD (\%; w/w)** \\ \hline Solids totals & 14.82 \(\pm\) 2.81 \\ \hline Volatile solids & 12.25 \(\pm\) 0.54 \\ \hline Fixed solids & 2.57 \(\pm\) 0.96 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Characterisation of substrate (cow manure + corncob hydrolysate). Figure 1: Comparison of different pretreatments in the production of biogas from corncob. Table 5 makes clear that the concentration of total reducing sugars is one of the factors that can affect methanogenic production in the anaerobic digestion process, directly and correlationally [32]. The consumption of TRS and total sugars during the anaerobic digestion was 96.8% and 85.75%, respectively. The COD was reduced to 79% with a COD reduction of 7.9 g, which is proportional to 639.24 NmLbiogas/g COD. Clearly confirming the influence of sugars in biogas production, the sugar content had the maximum reduction on the final day, demonstrating the potential of corncob residues, rich in sugars, as viable substrates in biogas production. Table 6 shows the results obtained from the daily biogas production and composition. The biogas composition was CH\({}_{4}\) with a concentration of 35.7% to 72.80% (v / v), CO\({}_{2}\) of 63.8% to 26.18%, and 0.5% to 1% (v/v) for other biogas (H\({}_{2}\), O\({}_{2}\), etc.) during anaerobic digestion (15 days). The CH\({}_{4}\) concentration is in line with values reported by previous studies of the contents of biogas, ranging from 50% to 65% (v/v) for CH\({}_{4}\) and from 35% to 50% (v/v) for CO\({}_{2}\) during sludge anaerobic digestion [33]. The production of CH\({}_{4}\) indicated the presence of methanogens, and the anaerobic digestion was effective. Other important parameters during anaerobic digestion are the concentrations of volatile fatty acids (VFA), which increased with respect to the values obtained in the recovery of the substrate material. This is a clear indicator of the microbiological activity of the system during the time of the experimentation with a single feeding and periodic evaluation of the volume of biogas. During anaerobic degradation, complex organic matter is hydrolys and fermented in low-molecular-weight compounds, including short-chain fatty acids (C\({}_{2}\)-C\({}_{6}\)). As shown in Table 7, the VFAs found in both the substrate (initial) and digestate (day 17) were acetic acid in the highest proportion, followed by butyric and propionic acid and lesser quantities of furfural. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Stage**} & \multicolumn{2}{c}{**TRS**} & \multicolumn{2}{c}{**TS**} & \multicolumn{2}{c}{**COD**} \\ \cline{2-7}  & **(g/L)** & **\%** & **(g/L)** & **\%** & **(g/L)** & **\%** \\ \hline Initial hydrolysate & 65.84 \(\pm\) 3.92 & 100 & 157.70 \(\pm\) 7.88 & 100 & 10 \(\pm\) 0.01 & 100 \\ \hline Final digestate & 2.11\(\pm\) 0.10 & 3.20 & 22.48 \(\pm\) 1.2 & 14.25 & 2.10 \(\pm\) 0.10 & 21 \\ \hline Total degradation & 63.73 & 96.80 & 135.22 & 85.75 & 7.9 & 79 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of concentrations of total reducing sugars (TRS), Total sugars (TS) and chemical oxygen demand (COD) of the digestate with respect to the substrate. Figure 2: Cumulative biogas production in daily and total accumulated intervals. During the hydrolytic-acidogenic stage, different organic acids are generated and even biogas rich in H\({}_{2}\), depending on the operating conditions. Table 7 shows the concentration of the main metabolic intermediaries detected at this stage. These precursors are metabolised to CH\({}_{4}\) during the methanogenesis stage. It should be noted that during the assays, about 70% of the volume of biogas corresponded to CH\({}_{4}\), which implies benefits for its subsequent exploitation. Finally, no accumulation of organic acid was detected throughout the methanogenesis operating period, indicating that the anaerobic digestion process was carried out efficiently with an overall COD balance of 79%.