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BACKGROUND Various mixes of seeds have been quasi-randomly selected to startup anaerobic digesters. In contrast, this study examines the impact of inoculating thermophilic anaerobic digesters with a designed mix of non-acclimated seeds based on their methanogen composition, using quantitative polymerase chain reaction ( QPCR) of 16S rRNA gene, to achieve high abundance and diversity of methanogens. RESULTS Based on QPCR results, two seed mixes were selected to inoculate two anaerobic digesters: digester (A) was inoculated with a control seed consisting of digestate, manure, and activated sludge; and digester (B) was inoculated with a further methanogen-enriched seed consisting of the control seed with added compost and leachate. Both seed combinations yielded a balanced microflora that is able to achieve a successful startup. However, upon reaching steady state, digester B exhibited lower propionate levels, resulting in lower volatile fatty acids ( VFAs) concentration and increased buffering capacity, indicating greater stability. Acetotrophs and hydrogenotrophs were dominated by Methanosarcinaceae and Methanobacteriales, respectively, in both digesters, exhibiting an average ratio of 66-to-34% in A and 76-to-24% in B during steady-state. CONCLUSION The inoculation strategy in digester B resulted in improved stability, lower propionate concentration and 10% higher relative abundance of acetotrophs. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

This study examines the stability and efficiency of thermophilic anaerobic digesters treating food waste under various mixing velocities (50–160 rpm). The results showed that high velocities (120 and 160 rpm) were harmful to the digestion process with 18–30% reduction in methane generation and 1.8 to 3.8 times increase in volatile fatty acids (VFA) concentrations, compared to mild mixing (50 and 80 rpm). Also, the removal rate of soluble COD dropped from 75 to 85% (at 50–80 rpm) to 20–59% (at 120–160 rpm). Similarly, interrupted mixing caused adverse impacts and led to near-failure conditions with excessive VFA accumulation (15.6 g l −1 ), negative removal rate of soluble COD and low methane generation (132 ml gVS −1 ). The best efficiency and stability were achieved under mild mixing (50 and 80 rpm). In particular, the 50 rpm stirring speed resulted in the highest methane generation (573 ml gVS −1 ). High-throughput sequencing of 16S rRNA genes revealed that the digesters were dominated by one bacterial genus ( Petrotoga ; phylym Thermotogae ) at all mixing velocities except at 0 rpm, where the community was dominated by one bacterial genus ( Anaerobaculum ; phylum Synergistetes ). The Petrotoga genus seems to have played a major role in the degradation of organic matter. [ABSTRACT FROM AUTHOR]