Analysis of methanogenic activity in a thermophilic-dry anaerobic reactor: Use of fluorescent in situ hybridization

Methanogenic activity in a thermophilic-dry anaerobic reactor was determined by comparing the amount of methane generated for each of the organic loading rates with the size of the total and specific methanogenic population, as determined by fluorescent in situ hybridization. A high correlation was evident between the total methanogenic activity and retention time [−0.6988Ln(x) + 2.667] (R2 0.8866). The total methanogenic activity increased from 0.04 × 10−8 mLCH4 cell−1day−1 to 0.38 × 10−8 mLCH4 cell−1day−1 while the retention time decreased, augmenting the organic loading rates. The specific methanogenic activities of H2-utilizing methanogens and acetate-utilizing methanogens increased until they stabilised at 0.64 × 10−8 mLCH4 cell−1day−1 and 0.33 × 10−8 mLCH4 cell−1day−1, respectively. The methanogenic activity of H2-utilizing methanogens was higher than acetate-utilizing methanogens, indicating that maintaining a low partial pressure of hydrogen does not inhibit the acetoclastic methanogenesis or the anaerobic process.