Rapid initiation of partial denitrification with different seeding sludge and carriers: Responses of wastewater treatment performance, microbial composition, and functional genes

Partial denitrification (PD) can facilitate the widespread application of anaerobic ammonium oxidation (anammox) by stably providing nitrite. However, research on its seeding sludge mainly focuses on activated sludge from various treatment processes. In this study, activated sludge obtained from three municipal wastewater treatment plants was inoculated into three sequencing batch reactors, which were then fed with nitrate- and acetate-containing wastewater. The nitrate-to-nitrite transformation ratios increased to 64.2 %, 73.0 % and 59.5 % in 35 days with the effluent nitrite peaking at 67.5, 76.8 and 62.4 mg N/L, respectively. Carriers were added to three sequencing batch reactors at a filling ratio of 30 % and after two months of idleness, the PD process was recovered in only 6 days with NTR above 57 %. Further 16S rRNA gene amplicon sequencing revealed that the relative abundance of the dominant microbial genus Thauera was closely correlated with the NTR. The metagenomic analysis presented that Thauera carried the majority of denitrifying enzymes of the community, especially nar and nap. This study demonstrates the feasibility of rapidly initiating the PD process by using different activated sludge, which could be favorable for the application of mainstream anammox processes.