Computational fluid dynamics simulation of temperature distribution in heated and stirred pilot-scale methanogenic reactor

Suppressing temperature stratification is crucial for pilot-scale methanogenic reactor (MR) in two-phase anaerobic digestion. In this study, computational fluid dynamics was utilized to simulate changes in temperature distribution under various heating and hydraulic stirring conditions within the MR. Elevating heating temperature accelerated the process of the MR reaching the set temperature (35.5 °C). However, excessively high heating temperature led to significant temperature differences. The maximum temperature difference varied from 2.15 °C to 4 °C when heating temperature ranged from 45 °C to 75 °C, respectively. Hydraulic stirring effectively mitigated temperature distribution, reducing the maximum temperature difference from 3 °C to 1 °C at stirring speed of 0.31 m/s when heating temperature was maintained at 55 °C. The standard deviation of the temperatures at points P1-P5 and the average temperature decreased from 0.22 at 0.11 m/s to 0.076 at 0.31 m/s. Consequently, cumulative biogas production of the MR increased from 8.085 m³ to 12.975 m³ after implementing hydraulic stirring. Microbial community analysis revealed that methanogens were more susceptible to the effects of temperature distribution compared to bacteria. This study provides guidance for practical project implementations.