Two-stage anaerobic digestion of fruit and vegetable wastes

The objective of this work was to determine the maximum organic load that can be treated in a two-stage anaerobic system for the stabilization of fruit and vegetable waste (FVW). The hydrolysis-acidogenesis step was carried out in a batch-operated stirred tank reactor (STR) and the methanogenic step was carried out in an up flow anaerobic sludge blanket reactor (UASB). This separation favored the environmental conditions of the microbial groups present in each stage and had a better control over the global variables of the process. The easily biodegradable fraction imposed (as volatile solid, VS) the maximum organic loading rate (OLR) of the overall process (13 g VS/L·d), in addition to conditioning the maximum input load of volatile fatty acids (VFA) to the methanogenic reactor 3.5 g/L·d. These conditions allow to highlight the benefit of separating the stages. The productivity reached was 3.0 LCH4/L·d with a chemical oxygen demand (COD) removal of 80 %.