[Effect of temperature on methanogenic pathway during household waste anaerobic digestion by stable carbon isotopic signature of CH4].

The methanogenic pathway during anaerobic digestion of household waste was investigated by stable carbon isotopic signature analysis, and testified by the analysis of gas production, leachate characteristics and microbial fluorescence in situ hybridization (FISH) methods. Furthemore, the difference of methanogenic pathway between mesophilic and thermophilic anaerobic digestion was also discussed. Results showed that under mesophilic conditions, the isotopic stable carbon signature of CH4 (delta13 CH4) initially decreased to -69.5 per thousand, indicating that CH4 was produced from CO2 and H2 by hydrogenotrophic methanogens. When active CH4 production phase started, the delta13 CH4 values quickly increased to -23.8 per thousand, which indicated more and more CH4 were formed by aceticlastic methanogens, dominantly the family of Methanosarcinaceae, shown by the FISH results. The delta13 CH4 values decreased successively and ultimately remained at -55 per thousand, indicating that the fraction of aceticlastic methanogenesis finally decreased to a steady level comparative with CO2-derived methanogenesis at the steady slow methane production phase. Under thermophilic conditions, the delta13 CH4 values remained at a level about -70 per thousand, showing that methane were solely produced from CO2 reduction, and acetate syntrophic oxidation happened during the active methane production phase.