Viscosity influence on kinetics parameters in dry anaerobic digestion

The viscosity that governs mass exchanges is a determining parameter of dry digestion kinetics. This observation leads to the measurement of viscosity influence on key kinetic parameters of digestion such as microbial growth, degradation of COD, biogas production and its CH4 quality. Thus, for limit viscosities at the beginning of digestion in batch mode at 37 °C and 55 °C of potato residues of 18–35 % TS content, the evolution of kinetic parameters is observed. The results show strong microbial growth for 4.39 × 10−2 Pa s and 7.5 × 10−2 Pa s in digestion at 37 °C and 4.12 × 10−2 Pa s in digestion at 55 °C. The reduction of COD is optimal for 7.50 × 10−2 Pa s at 37 °C and 6.57 × 10−2 Pa s at 55 °C. Biogas production is higher for 7.5 × 10−2 Pa s at 37 °C and 4.12 × 10−2 Pa s at 55 °C. Finally, the CH4 content of biogas is higher for 4.39 × 10−2 Pa s and 4.12 × 10−2 Pa s at 37 °C and 55 °C, respectively. These results show that optimal conditions for microbial growth and CH4 production are obtained with the 22 % TS scenario giving a viscosity of 4.39 × 10−2 Pa s at 37 °C and 4.12 × 10−2 Pa s at 55 °C. These results confirm the importance of the viscosity in biochemical kinetics in dry digestion.