NEW MODEL OF HYDROLYSIS IN THE ANAEROBIC CO-DIGESTION OF BOVINE MANURE WITH VEGETABLE WASTE: MODIFICATION OF ANAEROBIC DIGESTION MODEL No. 1

The anaerobic digestion processes are a sustainable strategy for manure (M) management. However, due to its structural characteristics, this substrate leads to low biogas yields. A solution strategy is its co-digestion, where mathematical models are a fundamental tool for the selection of suitable co-substrates. In this work, a new model of co-digestion and of the disintegration and hydrolysis stages, following the classical Anaerobic Digestion Model No.1 (ADM1) structure, is presented. In the proposed model, substrate-microorganism relationships are represented using the Contois equation. The model was validated via the anaerobic co-digestion of vegetable (V) and M with variations in the V/M ratio in the feed. The reaction system consisted of a continuously stirred tank reactor with an operating volume of 5L, a hydraulic retention time of 20d, and a constant temperature of 35 degrees C. The highest biogas yield was observed at a feed ratio of 1:1, lower values of this ratio decrease the biogas yield. The model explains the low digestibility of M as a consequence of unfavorable substrate-microorganism relationships, which cause disintegration to become a limiting stage in the process. The biogas production in the new model is primarily associated with carbohydrate degradation, as well as low concentrations and rapid consumption of intermediary metabolites, which do not favor the proliferation of acetanogenic or methanogenic communities.