## 3 Results and Discussion
### Second Experimental Cycle  
The average results and their standard deviation for every phase of the second experimental cycle are presented in Table 6.  
In Figure 11, the daily production of biogas and biomethane in the reactor per experimental phase shows increase in biogas production after the first experimental phase and then a significant reduction in the beginning of the third experimental phase. In the middle of the third experimental phase, the reactor increased again its biogas generation, and during the 56 th day of operation reached the maximum production recorded (81.3 L biogas). During the last experimental phase (HRT 1 d) the reactor showed greater stability both in terms of biogas and biomethane production. The same pattern is shown in Figure 12, where the daily methane percentage in the generated biogas is depicted. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Second Experimental Cycle** & \multicolumn{3}{c}{**Experimental Phases**} \\ \hline
**Characteristics** & **1 st** & **2 nd** & **3 rd** & **4 th** \\ \hline Biogas Production (L/d) & 58.1 \(\pm\) 3.1 & 68.0 \(\pm\) 4.1 & 71.6 \(\pm\) 8.6 & 66.8 \(\pm\) 2.3 \\ Biomethane Production (L/d) & 42.9 \(\pm\) 7.4 & 44.6 \(\pm\) 6.4 & 42.3 \(\pm\) 4.5 & 41.1 \(\pm\) 3.5 \\ CH\({}_{4}\) Biogas content (\%) & 71.7 \(\pm\) 11.2 & 65.07 \(\pm\) 7.5 & 60.01 \(\pm\) 5.3 & 61.6 \(\pm\) 4.7 \\ sCOD Feedstock (g/L) & 3.89 \(\pm\) 0.10 & 2.92 \(\pm\) 0.30 & 2.05 \(\pm\) 0.12 & 1.03 \(\pm\) 0.15 \\ sCOD Effluent (g/L) & 0.82 \(\pm\) 0.04 & 0.48 \(\pm\) 0.17 & 0.24 \(\pm\) 0.10 & 0.27 \(\pm\) 0.06 \\ COD removal (\%) & 78.9 & 83.5 & 88.3 & 73.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Average daily results of the second experimental cycle phases. Figure 11: Daily biogas and biomethane production. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **Compartment a** & \multicolumn{2}{c}{**Compartment b**} & \multicolumn{2}{c}{**Compartment c**} & \multicolumn{2}{c}{**Compartment d**} & \multicolumn{2}{c}{**Effluent**} \\ \hline
**Exp.** & **TSS** & **VSS** & **TSS** & **VSS** & **TSS** & **VSS** & **TSS** & **VSS** & **TSS** \\
**Phase** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** & **(g/L)** \\ \hline
1 st & 0.98 & 0.79 & 0.63 & 0.43 & 0.57 & 0.33 & 1.16 & 0.99 & 0.75 & 0.63 \\
2 nd & 0.61 & 047 & 0.64 & 0.52 & 0.60 & 0.54 & 0.63 & 0.54 & 0.58 & 0.49 \\
3 rd & 0.50 & 0.31 & 0.44 & 0.26 & 0.55 & 0.35 & 0.50 & 0.31 & 0.48 & 0.32 \\
4 th & 0.50 & 0.35 & 0.43 & 0.31 & 0.46 & 0.31 & 0.50 & 0.32 & 0.48 & 0.32 \\
5 th & 0.30 & 0.20 & 0.32 & 0.31 & 0.33 & 0.23 & 0.34 & 0.21 & 0.45 & 0.28 \\
6 th & 0.12 & 0.24 & 0.20 & 0.13 & 0.24 & 0.13 & 0.20 & 0.15 & 0.25 & 0.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Average daily TSS and VSS concentration in feedstock, reactor’s compartments and effluent. Regarding the COD consumption in this experimental cycle, again a significant reduction was presented in the reactor's effluent. Although reduction levels reached 88.3% (2d HRT), the effluent still does not reach the criteria for disposal. The lower effluent COD concentration achieved is that of 240 mg/L in the third experimental phase and the highest value in COD effluent was observed during the first experimental phase 820 mg/L. The daily sCOD values of each compartment are presented in Figure 13, while the daily sCOD values of the feedstock and the effluent are presented in Figure 14. The sCOD concentration of the effluent in the last experimental phase shows that a significant reduction is obtained (73.7%). However, as in the previous cycle, the effluent is not directly disposable. The pH of the process observed in Figure 15 was fairly constant during all experimental phases of the cycle for all compartments, without any significant fluctuation.