Comparison between wet and semi-dry anaerobic biogas diester under thermophilic and mesophilic conditions: Methane productivity and analysis of microbiota

The current practice of using stanchion breeding cow houses results in a semi-dry manure that ideally should be used as the substrate for the anaerobic fermentation. The conventional liquid-slurry biogas fermentation is disadvantageous with high running costs due to requirement such as water addition and running efficiency, among others. This study aimed to establish a high-speed semi-dry methane fermentation system for cow manure, by comparing productivity in wet and semi-dry conditions (> 90 and 83-85% water content, respectively), and mesophilic and thermophilic conditions (38 and 55°C, respectively). The highest methane productivity was obtained for 30 days in semi-dry or wet, thermophilic conditions (0.4-16.2 L‧Kg-1VS‧day-1). The highest accumulated production was 60 days (192.1 L‧Kg-1VS) in semi-dry thermophilic conditions. The pronounced difference in methane production at different temperatures in semi-dry digesters was studied by characterizing the microbial community changes in mesophilic and thermophilic digesters. For bacteria, the class Clostridia (including family Clostridiaceae and the genus Clostridium) was dominant in the thermophilic digester. In the thermophilic digester, a succession of taxa from the genus Methanobrevibacter and family Methanobacteriaceae to genus Methanoculleus in archaea was observed. The convergence of archaeal microbiota in thermophilic conditions was more pronounced than in mesophilic conditions. These results indicate that the proposed procedure is capable of improving methane productivity per scale and lowering the running costs concomitant and downsizing the fermentation scale.   Key words: Semi-dry fermentation, methane yield, anaerobic digestion, cow manure, biogas.