Identification of the bacterial community of a pilot-scale thermophilic aerobic bioreactor treating sewage sludge

•A pilot-scale thermophilic aerobic digester was studied for treating sewage sludge.•The system provided a highly selective milieu.•Firmicutes and Deinococcus-Thermus constituted the main phyla in the system.•Predominance of Firmicutes potentially contributed to thermophilic sludge degradation.

The goal of this study was to investigate the bacterial community associated with a pilot-scale thermophilic aerobic digestion (TAD) reactor treating sewage sludge. The digestion system removed up to approximately 30% of volatile solids (VS); VS and total solids (TS) decreased from 38.4 to 26.9 g/L and from 51.2 to 43.8 g/L, respectively, and the ratio of VS/TS declined from 75.4% to 62.8%. Coincident with the thermal reduction of sludge, 16S rRNA clone library data showed that a significant shift occurred in the bacterial community composition with the selection of the Firmicutes and Deinococcus-Thermus families as well as a marked decrease in the relative abundance of a large part of bacterial taxa such as Proteobacteria. A unique bacterial community in the TAD reactor developed resulting from specific environmental pressures such as thermal stress. A predominance of thermophilic bacteria belonging to Bacillus sp., Geobacillus sp., Thermaerobacter sp. and Thermus thermophilus sp. suggest their putative roles for potentially high thermophilic degradation of sewage sludge.