# Biochemical Methane Potential of Cork Boiling Wastewater at Different Inoculum to Substrate Ratios
## 3 Results and Discussion
### Production of Biogas and Biomethane  
The accumulated production of biogas can be seen in Figure 1; the production started in the first days. The solids for both ratios were reduced, with the production of biogas derived from the solids added to the reactor. Figure 1: Accumulated biogas for the tests (**a**) anaerobic digestion (AD) of different ratios of mixture of inoculum and cork boiling wastewater (Ino/CBW); (**b**) anaerobic digestion of different ratios of mixture of inoculum, cork boiling wastewater, and food waste (Ino/CBW:FW); (**c**) anaerobic digestion of different ratios of mixture of inoculum, cork boiling wastewater, and cow manure (Ino/CBW:CM). For each ratio studied, the tests were performed in duplicate. For the Ino/CBW 1:1 ratio, biogas production was 274.5 \(\pm\) 0.5 mL, and the production in relation to the added volatile solids was 99.94 \(\pm\) 0.18 mL.g.SV\({}_{\text{added}}\)\({}^{-1}\). Regarding the 2:1 ratio, biogas production was 317.43 \(\pm\) 7.48 mL, and the production in relation to the added volatile solids was 155.60 \(\pm\) 3.67 mL.g.SV\({}_{\text{added}}\)\({}^{-1}\). Compared with the literature, these values are much lower than expected. Food waste has the characteristic of having good biodegradability. In order to have a good performance in relation to the degradation of organic matter, the system needs enough nutrients and minerals for the correct development of microorganisms to occur. Inhibitions can occur when digesting large amounts of food waste for long periods of operation. The reasons for the occurrence of inhibition are related to the imbalance of nutrients during the fermentation process--insufficient elements (zinc, iron, molybdenum, among others) and excess micronutrients (sodium, potassium, among others) [40]. In order to avoid problems arising from inhibition, several authors have suggested that FW with two or more substrates be used in the process in order to achieve better performance with the mixtures. The substrates must compensate for the nutritional deficiencies that the FW has, in addition to helping the growth of microorganisms [41, 42, 43]. For the tests carried out, the accumulated biogas for the tests with both mixtures (2/0.7:0.3 and 2/0.5:0.5) can be seen in Figure 1. For the ratio of 2/0.7:0.3 of Ino/CBW:FW, the production of biogas was 695.12 mL, and specific production in relation to VSs was 101.04 mL. g.VS\({}_{\text{add}}\)\({}^{-1}\). For the ratio of 2/0.5:0.5 of Ino/CBW:FW, accumulated biogas production was 330.83 mL, and production in relation to VSs was 32.98 mL g.VS\({}_{\text{add}}\)\({}^{-1}\). It is possible to note that the biogas production for the second test was lower, indicating that an inhibition may have occurred, as previously mentioned. Cow manure is used as fertilizer in the fields; however, the deposition of this material without pretreatment increases the potential for contamination and puts the health of the animals at risk [44]. The use of treatments that aim to reduce contaminants is of fundamental importance for the production of fertilizers from this type of waste [45]. The use of CM in anaerobic digesters is an alternative to potentiate an effluent with low methane production potential. Codigestion can increase biogas production by approximately 44% [46]. Figure 1 shows the accumulated volumes of biogas for the BMP tests of Ino/CBW:CM codigestion in the ratios of 2/0.7:0.3 and 2/0.5:0.5, with a duration of 40 days. For the 2/0.7:0.3 ratio tests, accumulated biogas production was 1261.15 mL, and cumulative production in relation to VSs was 372.76 mL.g.SV\({}_{\text{added}}\)\({}^{-1}\). For the ratio of 2/0.5:0.5, accumulated biogas production was greater than 10% in relation to the test with a ratio of 2/0.7:0.3. The accumulated biogas was 2611.23 mL, with an accumulation in relation to VSs of 533 mL.g.SV\({}_{\text{added}}\)\({}^{-1}\).