The analysis of volatile fatty acids (VFAs) revealed acetic acid and propionic acid as the primary components across all reactors, regardless of the inoculum source. The pH, acetate, and total VFA concentration values observed over time in each reactor are illustrated in Figure . In all three reactors, the pH of the nutrient media sump remained within the normal operating range (<8.5), supporting the activity of microorganisms involved in the biomethanation process .