For these complex wastes the use of COD methods to estimate anaerobic digestion does not fit with the experimental results, although this method outlines co-digestion 1 as the optimum

mixture for obtaining higher productivities as is indicated in the experimental results while the other methodologies practically do not show any increases for the co-digestions. Labatut et al. [24] obtained similar results studying the BMP of complex substrates such as dairy manure or corn silage. Two different models first-order MK0683 model (FO) and Gompertz model (GM) were applied to the experimental BMP results to determine the optimum equation to fit with these kind of wastes and evaluate the parameters that had influence on the anaerobic digestion process. Both models were studied and the maximum methane MDV3100 production was predicted in diverse points of the experiment (3, 7, 13, 23 and 39 days). The final methane production achieved from the experimental BMP assays was then compared with the maximum methane production (γ) obtained

by applying both models to the different points of the experiment ( Table 6). Generally the Gompertz model fits better than the first-order equation for the experimental values, with the exception of biological sludge and co-digestion 4, which has a high biological sludge content (80%) that is better suited with the first-order model. These models can explain 99% of the BMP results. Similar kinetics are observed between the sole substrates and mixtures in both models,

although it is noticed a growth of K and μ was noted with the increase in the proportion of biological sludge in the co-digestion mixtures. The same behavior occurs with the lag phase parameter that decreases with the diminution in the proportion of biological sludge. In this manner the model results indicate co-digestion 4 is the substrate that is more easily biodegradable and has quicker biodegradability periods. During the first 3 days the kinetics and productivities are better for biological sludge, and the methane production of the mixtures increases with the proportion of biological sludge. However after the 7th day the behavior changes and the co-digestion mixtures’ productivity increases through with the proportion of OFMSW. This performance could be explained by the fact that biological sludge contains easily biodegradable material while OFMSW has less readily biodegradable material, such as fiber, which makes the process slower at the beginning. Therefore, we can confirm that the lag phase of the Gompertz equation is related to the fiber content, increasing with the proportion of this material as is the case of OFMSW, which has a higher lag phase but is still negligible. For the OFMSW and the co-digestion mixtures, the Gompertz Eq.