Effect of different acetate:propionate ratios on the methanogenic community during thermophilic anaerobic digestion in batch experiments

• Investigation of different acetate:propionate ratios for AD (75 days).
• Acetate:propionate ratio of 2 resulted in highest methane production.
• Differences between ratios ≤ 1 and ≥ 2 on metabolic level.
• Metabolic changes hardly reflected in DNA level investigations.

The present study investigated the metabolism of different acetate:propionate ratios (0.25, 0.33, 0.5, 1.0, 2.0, 3.0, 4.0) in equimolar carbon concentration during an anaerobic decomposition process under defined laboratory conditions and evaluated the engaged methanogenic community. Significant differences on a metabolic level (gas production, gas composition, volatile fatty acid (VFA) concentration) were observed between acetate:propionate ratios ≤1 and ≥2. Generally ratios ≥2 resulted in a faster methane production and VFA decomposition compared to ratios ≤1. Regarding the composition of the methanogenic community as well as the abundance of Methanosarcinales these differences were not reflected in an appropriate manner when DNA based methods (dHPLC and qPCR) were applied. However, by a culture based approach these differences could be documented showing a significant difference in the number of cultivable methanogens between initial acetate:propionate ratios ≤1 and ≥2.