## 3 Results
### Characterization of Synergistic Effects  
To study the possible synergistic effects suggested by the interactions identified as acute effects in [PERSON] et al. [24], the ratios between the maximum MYs in the continuous operation and batch validation tests were compared using equation 5. The results are shown in Table 5.  
The MY ratio of the mixture with SWW was almost the same in both scales. The relative difference in the ratios obtained for the mixture with SBT was 7.01%. This confirmed the acute effects of adding a third substrate to the two-substrate mixture. The third substrate provided the same boost in the continuous stage and batch tests.  
Also, the methane yield ratio obtained during the transfer from batch tests to the continuous stage was between 0.72 and 0.78. It was expected that the obtained MY from the continuous stage would be smaller than the ultimate biomethane potential from the batch test described by [PERSON] and [PERSON] [11]. Similar intervals in the continuous stage to batch tests methane yields ratio have been identified in the literature. For example, [PERSON] et al. [57] obtained ratios from 0.73 to 0.8 from the use of different grass species. [PERSON] and [PERSON] [58] reached a ratio of 0.81 from the use of grape pomace. Meanwhile, [PERSON] and [PERSON] [59] used the mesophilic digestion of cattle dung in both batch and semi-continuous digestion with four reactors and six semi-continuous reactors, respectively.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Operating Points**} & \multicolumn{3}{c}{**Solid Retention Time to Hydraulic Retention Time Ratio**} \\ \cline{2-4}  & **R1** & **R2** & **R3** \\ \hline Start-up (15 d) & 1.10 & 1.29 & 1.24 \\ \hline Operating Point 1 (15 d) & 1.72 & 1.41 & 1.59 \\ \hline Operating Point 1 (15 d) & 0.82 & 1.83 & 1.16 \\ \hline Operating Point 4 (5 d) & 1.22 & 1.33 & 1.15 \\ \hline Reactor recovery (5 d) & 1.30 & 1.68 & 1.18 \\ \hline Operating Point 4 (5 d) & 1.20 & 1.42 & 1.99 \\ \hline Operating Point 5 (3 d) & 1.22 & 1.28 & 1.11 \\ \hline Average value & 1.23 & 1.32 & 1.20 \\ \hline \hline \end{tabular}  
* The red and green highlighted numbers were the lowest and highest values in the columns, respectively.  
\end{table}
Table 4: SRT/HRT results for the three reactors (R1, R2, and R3).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Mixture**} & **Maximum Methane** & **Methane Yield** & \multicolumn{2}{c}{**Methane Yield**} & \multirow{2}{*}{\
\begin{tabular}{c} **Methane Yield** \\ **Predicted by the** \\ **Model in Batch Tests** \\ **(L\({}_{\text{CH}}\)/kgys)** \\ \end{tabular} } & \multicolumn{2}{c}{**Methane Yield**} & \multirow{2}{*}{
\begin{tabular}{c} **Continuous to** \\ **Batch Methane** \\ **Yield Ratio** \\ \end{tabular} } \\  & **Tests** & **(L\({}_{\text{CH}}\)/kgys)** & & **Tests** & **Yield Ratio** \\ \hline PM+CWM & 265.70 & 1.00 & 342.83 & 1.00 & 0.78 \\ PM+CWM+SWW & 395.80 & 1.49 & 513.07 & 1.50 & 0.77 \\ PM+CWM+SBT & 382.50 & 1.44 & 530.76 & 1.55 & 0.72 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Methane yields and ratios based on piglet and cow manure yield in the batch and continuous tests.  
Their results showed higher rates in the semi-continuous operation; however, biogas yields were lower compared to the batch test. Their batch tests reached 67% COD efficiencies, which was lower than the results in this study. In addition, [PERSON] et al. [60] suggested that BMPs can be used to estimate biogas production at full scale; however, the BMP value should be multiplied by a factor of 0.8-0.9 to avoid overestimation.