## 4 Conclusions  
The HRT of 5 days, corresponding to an OLR of 18.0 g VS.L\({}^{-1}\).d\({}^{-1}\), presented the best results on the DF of OFMSW. The bioH\({}_{2}\) content in biogas (H\({}_{2}\): 32% \(v/v\)), the bioH\({}_{2}\) yield (\(\eta_{bioH2}\): 18.2 L H\({}_{2}\).kg\({}^{-1}\) VS\({}_{\text{influent}}\)), and the volumetric production rate (VHP: 0.32 L H\({}_{2}\).L\({}^{-1}\)\({}_{\text{bioreactor}}\).d\({}^{-1}\)) for this HRT were comparable or even higher than some experimental data reported in the literature. Additionally, these results are better than the experimental data obtained for the HRTs of 4 and 6 days. For the former HRT, an overload of organic matter may have occurred. For the latter HRT, H\({}_{2}\)-consuming methanogens gained importance in the microbial consortium, contributing to the appearance of CH\({}_{4}\) in  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Orgabit Schobate**} & \multirow{2}{*}{**Income**} & \multirow{2}{*}{**T**} & \multirow{2}{*}{**HRT**} & \multirow{2}{*}{**Bioreactor**} & \multirow{2}{*}{**OLR**} & \multirow{2}{*}{**H\({}_{2}\)**} & \multirow{2}{*}{**PineH2-1**} & \multirow{2}{*}{**VHP**} \\  & & & \(c^{\prime}\)**O** & & & & & & \\ \hline OFNSW & Model culture & 27 & 52 & 5.4 & CSTR & 18 & 32 & 18.2 & 0.02 & **Density** \\ OFNSW & Model culture & 55 & 5.5 & 5.4 & CSTR & 16 & 62 13.3 & 1045.54.54.59 & 27 & [28] \\ OFNSW & Model culture & 55 & 5.7 & 3.3 & 4.5 & CSTR & 16.8 & 38.55.97 & 80 & 275 & [11] \\ Synthetic OFNSW & Model culture & 34 & 5.5 & 0.5 h & CSTR & 45.4 & 30.4 \(\pm\) 0.7 & 133.3 \(\pm\) 1.04 & 0.00 & [9] \\  & & 5.3 & 6.6 & CSTR & 13 & 36 \(\pm\) 5 & 20.5 & 0.27 & [55] \\ OFNSW & Model culture & 55 & 4.4 & CSTR & 19 & 39 \(\pm\) 6 & 31 \(\pm\) 7 & 0.42 & \\  & & 5.8 & 3.4 & CSTR & 28 & 41 \(\pm\) 2 & 23 \(\pm\) 4 & 0.03 & \\ OFNSW & Model culture & 35 & 5.5 & 24 h & CSTR & 19 & 39 & 1.23 & 0.37 & [11] \\ OFNSW & Model culture & 35 & 5.0 & 8 h & 0.1 & 106 & 32 & 99.8 & 1.35 & [28] \\ \hline \hline \end{tabular}
\end{table}
Table 7: Comparison of the main experimental data obtained in the present work with the data available in some bibliographic references.  
the biogas and to lower bioH\({}_{2}\) production, eventually due to its consumption for CH\({}_{4}\) production. The overall conclusion is that the optimal conditions for bioH\({}_{2}\) production through the DF of OFMSW are significantly affected by the HRT and OLR, as these parameters are fundamental to establishing the metabolic pathway able to maximize bioH\({}_{2}\).  
By using the real samples of OFMSW characterized by high chemical variability, it is also possible to conclude that the characteristics of the substrate can drive the process of VFA accumulation, thus leading to some instability. Thus, the substrate variability becomes a parameter that must be controlled in the aim of maintaining optimized conditions for bioH\({}_{2}\) production.  
Conceptualization, E.S. and N.L.; methodology, I.M., E.S., M.V. and N.L.; validation, E.S. and N.L.; formal analysis, E.S. and N.L.; investigation, I.M.; resources, M.V. and N.L.; data curation, I.M.; writing--original draft preparation, I.M.; writing--review and editing, E.S., M.V. and N.L.; supervision, N.L.; project administration, N.L.; funding acquisition, E.S., M.V. and N.L. All authors have read and agreed to the published version of the manuscript. This work was supported by the Associate Laboratory for Green Chemistry--LAQV which is financed by national funds from FCT/MCTES (UID/QUI/50006/2019). Dr. [PERSON] also acknowledges the post-doc fellowship on the framework of the funds from the REQUIMTE 2020-2023 (UIDB/50006/2020) financed by FCT/MCTES.  
Not applicable.  
The authors acknowledge the Valorsul S.A. company for providing the OFMSW samples and anaerobic sludge that were used in the experimental assays.  
The authors declare that they have no conflict of interest.