Methanogenic population dynamics during startup of a full-scale anaerobic sequencing batch reactor treating swine waste

Changes in methanogenic population levels were followed during startup of a full-scale, farm-based anaerobic sequencing batch reactor (ASBR) and these changes were linked to operational and performance data. The ASBR was inoculated with anaerobic digester sludge from a municipal wastewater treatment facility. During an acclimation period of approximately 3 months, the ASBR content was diluted to maintain a total ammonia-N level of approximately 2000 mg l−1. After this acclimation period, the volatile solids loading rate was increased to its design value of 1.7 g l−1 day−1 with a 15-day hydraulic retention time, which increased the total ammonia-N level in the ASBR to approximately 3600 mg l−1. The 16 ribosomal RNA (rRNA) levels of the acetate-utilizing methanogens of the genus Methanosarcina decreased from 3.8% to 1.2% (expressed as a percentage of the total 16 rRNA levels) during this period, while the 16 rRNA levels of Methanosaeta concilii remained low (below 2.2%). Methane production and reactor performance were not affected as the 16 rRNA levels of the hydrogen-utilizing methanogens of the order Methanomicrobiales increased from 2.3% to 7.0%. Hence, it is likely that during operation with high ammonia levels, the major route of methane production is through a syntrophic relationship between acetate-oxidizing bacteria and hydrogen-utilizing methanogens. Anaerobic digestion at total ammonia-N levels exceeding 3500 mg l−1 was sustainable apparently due to the acclimation of hydrogen-utilizing methanogens to high ammonia levels.