## 3 Results and Discussion
### Production and Composition of Biogas  
Table 6 shows the accumulated biogas production and composition, as well as the bioH\({}_{2}\) volumetric production (VHP) rate, bioH\({}_{2}\) yield (\(\eta_{bioH2}\)), and available energy. The HRT6 (OLR: 10.6 g VS.L\({}^{-1}\).d\({}^{-1}\)) was not effective in the production of bioH\({}_{2}\) (H\({}_{2}\): 5\(\%\)\(\circ\)/\(\
u\); \(\eta_{bioH2}\): 1.64 L H\({}_{2}\).kg\({}^{-1}\) VS\({}_{\text{influent}}\); VHP rate: 0.02 L H\({}_{2}\).L\({}^{-1}\)\({}_{\text{bioreactor}}\).d\({}^{-1}\)). This can be explained by the development of methanogenic bacteria as CH\({}_{4}\) was detected (18\(\%\)\(\circ\)/\(\
u\)) in the biogas collected during this experimental trial. Although the pH was kept at 5.1 \(\pm\) 0.7, the HRT of 6 days was high enough to allow the development of hydrogenotrophic methanogens which contribute to bioH\({}_{2}\) consumption and CH\({}_{4}\) production. Additionally, it should be noted that the redox potential during the HRT6 assay (\(-\)110 \(\pm\) 12 mV) was significantly lower compared to the HRT5 (\(-\)56 \(\pm\) 26 mV) and HRT4 (\(-\)47 \(\pm\) 38 mV) assays, which may have contributed to the use of CO\({}_{2}\) as the final electron acceptor instead of H\({}^{+}\), providing the necessary conditions for CH\({}_{4}\) production and H\({}_{2}\) consumption. It is also important to notice that the anaerobic sludge used as inoculum in the present work was composed of biological anaerobic flocs. The floc structure protects the cells located in the inner part of the flocs. Therefore, even if the medium pH is not favorable to methanogens, the floc structure allows them to remain active inside the flocs. When the HRT is sufficiently high to allow the methanogens' growth inside the biological flocs, then significant H\({}_{2}\) consumption may occur and CH\({}_{4}\) will be detected in biogas. For all these reasons, the results obtained in the HRT6 assay were very different from those reported by [PERSON] et al. [35]. These authors investigated the effect of different OLRs in the DF of OFMSW under thermophilic conditions. At an OLR of 13 g VS.L\({}^{-1}\).d\({}^{-1}\) and an HRT of 6 d, these authors reported an H\({}_{2}\) content of 36 \(\pm\) 5\(\%\)_v/v_ and a VHP rate of 0.27 L H\({}_{2}\).L\({}^{-1}\).d\({}^{-1}\). The trial with the HRT of 4 d and OLR of 23.6 g VS.L\({}^{-1}\).d\({}^{-1}\) showed much better results (H\({}_{2}\) content: 25\(\%\)_v/v_; \(\eta_{bioH2}\): 8.48 L H\({}_{2}\).kg\({}^{-1}\) VS\({}_{\text{influent}}\); VHP rate: 0.20 L H\({}_{2}\).L\({}^{-1}\)\({}_{\text{bioreactor}}\).d\({}^{-1}\)) than with the HRT of 6 d. The biogas calorite value was 123 kJ.kg\({}^{-1}\) VS\({}_{\text{influent}}\) which is equivalent to a thermal energy potential of 34.2 kW.t\({}^{-1}\) VS\({}_{\text{influent}}\). This experimental trial did not reach the best results, maybe due to the excessive organic load applied to the bioreactor and the high concentration of acetic acid that was present in the feedstock. [PERSON] et al. [40] performed a study on the impact of OLR in the DF of glucose. The following conditions were tested: fluidized-bed reactor; temperature of 37 \({}^{\circ}\)C; OLR of