Behavior of methanogens during start-up of farm-scale anaerobic digester treating swine wastewater

• We have operated a farm-scale anaerobic digester for 591 days.
• The methanogenic community structure was investigated under process events.
• Changes in operating temperature caused domination of hydrogenotrophic methanogens.
• Methanobacteriales was better survived than other methanogens under starvation.
• HRT and influent pH significantly correlated with methanogenic communities.

The aim of this study was to monitor the changes in methanogenic community structures in an anaerobic digester (250 m3 working volume) during start-up including prolonged starvation periods. Redundancy analysis was performed to investigate the correlations between environmental variables and microbial community structures. The anaerobic digester was operated for 591 days at alternating operating temperatures. In initial start-up period at stage I (35 °C), growth of various species of mesophilic aceticlastic methanogens (AMs) and hydrogenotrophic methanogens (HMs) was observed. Methanobacteriales species survived better than other methanogens under long-term starvation conditions. In stage II (50 °C), HMs became dominant over AMs as the operating temperature changed from mesophilic to thermophilic due to increase of ammonia inhibition. In stage III (35 °C), only the Methanomicrobiales population significantly increased during 50 days of HRT while Methanobacteriales dominated over 15 days of HRT. The influent pH negatively correlated with all methanogenic populations especially in stage II.