# Biochemical Methane Potential of Cork Boiling Wastewater at Different Inoculum to Substrate Ratios
## 3 Results and Discussion  
### Characterization of Substrate  
Table 1 describes the characterizations performed on the substrate and inoculum used in the AD process. CBW has an acidic character, with a pH of 4.6. The Ino used was neutral, helping the CBW to reach the optimum pH (between 6.5 and 7.5) so that the AD process occurred favorably. CBW is rich in phenolic-polyphenolic compounds, which characterizes them as an acid effluent, with an acid pH between 4.5 and 5.5 [32; 33; 34]. The CBW substrate used had a COD of 7060.00 mg/L, which is in accordance with the literature. In some previous works, CBW effluent presented COD with very wide values, varying between 2600.00 and 12,600.00 mg/L [32; 35]. These values are dependent on the quality of the boards, the number of times the water is reused, and the location of the cork oak forest, among other factors that can change the characteristics of the raw material. According to [PERSON] et al. [36] and [PERSON] et al. [37], the conductivity of CBW varies between 1200 and 1500 \(\upmu\)S/cm. Additionally, according to [PERSON] et al. [37], the total solids of the effluents are in the order of 5200 mg/L. In their tests, [PERSON] et al. used the effluents from the associated plant of the cork industries of San Vicente de Alcantara. Despite being from different lots, the pH (5.0) and conductivity (1684 \(\upmu\)S/cm) values were relatively close. The authors characterized the amounts of polyphenols present in the effluent, being in the order of 455 mg/L. As they were effluents from the same region and produced by the same companies, it is possible that despite being from different lots, the conditions were as similar as possible compared to other effluents. According to [PERSON] et al., bovine manure has a high COD and a high amount of total solids. Those values are very close, in the order of 84,000.00 mg/L of COD and 110,000.00 mg/L of total solids [38]. The characteristics of food waste vary widely according to the components that are included in the waste. These variations make it difficult to compare with works carried out by other authors. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Unit.** & **CBW** & **Ino** & **FW** & **CM** \\ \hline pH & - & 4.6 \(\pm\) 0.2 & 6.7 \(\pm\) 0.2 & 6 \(\pm\) 0.2 & >> \\ Dissolved solids & mg/L & 740.00 \(\pm\) 60 & 2840.00 \(\pm\) 120 & 4440.00 \(\pm\) 180 & >> \\ Conductivity & \(\upmu\)S/cm & 1480.00 \(\pm\) 350 & 5770.00 \(\pm\) 980 & 8910.00 \(\pm\) 1080 & >> \\ C & (\%) & 44.17 \(\pm\) 0.43 & 35.08 \(\pm\) 2.08 & 46.29 \(\pm\) 1.67 & 39.56 \(\pm\) 0.94 \\ H & (\%) & 6.03 \(\pm\) 0.16 & 6.06 \(\pm\) 0.33 & 6.43 \(\pm\) 0.37 & 5.91 \(\pm\) 0.31 \\ N & (\%) & 3.7 \(\pm\) 0.57 & 7.52 \(\pm\) 0.52 & 4.79 \(\pm\) 1.67 & 3.44 \(\pm\) 0.16 \\ S & (\%) & 0 & 0 & 0 & 0 \\ O & (\%) & 29.96 \(\pm\) 0.64 & 11.42 \(\pm\) 0.38 & 28.74 \(\pm\) 0.55 & 27.31 \(\pm\) 0.35 \\ Ratio C/N & - & 12.06 \(\pm\) 1.74 & 4.66 \(\pm\) 0.05 & 9.66 \(\pm\) 0.59 & 11.51 \(\pm\) 0.05 \\ COD & mg/L & 7060.00 \(\pm\) 100 & 1639.50 \(\pm\) 13.75 & 8297.50 \(\pm\) 1500 & 84,475.00 \(\pm\) 1062 \\ Total solids & mg/L & 8375.00 \(\pm\) 25 & 14,525.00 \(\pm\) 575 & 79,575.00 \(\pm\) 3525 & 187,250.00 \(\pm\) 1150 \\ Total solids & (\%) & 0.87 \(\pm\) 0.00 & 2.00 \(\pm\) 0.72 & 6.9 \(\pm\) 0.02 & 27.96 \(\pm\) 0.86 \\ Volatile solids & mg/L TS & 6875.00 \(\pm\) 25 & 9500.00 \(\pm\) 300 & 68,925.00 \(\pm\) 3225 & 136,600.00 \(\pm\) 2400 \\ Volatile solids & (\% TS) & 82.09 \(\pm\) 0.05 & 65.43 \(\pm\) 0.52 & 86.60 \(\pm\) 0.22 & 729.00 \(\pm\) 0.83 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characterization of the substrate, inoculum, and cosubstrates used. The C/N ratio reflects the availability of nutrients in CBW, Ino, FW, and CM for the growth of bacteria. The low C/N ratio shows that the microorganism does not have adequate amounts of nutrients, especially carbon, for them to develop. [PERSON] et al.