Effect of post-digestion temperature on serial CSTR biogas reactor performance

The effect of post-digestion temperature on a lab-scale serial continuous-flow stirred tank reactor (CSTR) system performance was investigated. The system consisted of a main reactor operated at 55 °C with hydraulic retention time (HRT) of 15 days followed by post-digestion reactors with HRT of 5.3 days. Three post-digestion temperatures (55 °C, 37 °C and 15 °C) were compared in terms of biogas production, process stability, microbial community and methanogenic activity. The results showed that the post-digesters operated at 55 °C, 37 °C and 15 °C gave extra biogas production of 11.7%, 8.4% and 1.2%, respectively. The post-digester operated at 55 °C had the highest biogas production and was the most stable in terms of low VFA concentrations. The specific methanogenic activity tests revealed that the main reactor and the post-digester operated at 55 °C and 37 °C had very active acidogens and methanogens. In contrast, very low methanogenic activity was observed at 15 °C.