Performance and microbial community analysis of a microaerophilic sulfate and nitrate co-reduction system

The succession of complex internal sulfur cycles and sulfide-oxidizing bacteria community has been observed during wastewater treatment under microaerophilic conditions or denitrifying conditions. However, research on the microbial community involved in sulfur cycles under microaerophilic denitrifying conditions is scarce. In this study we characterized the dominant bacteria and microbial community structure stimulated by microaerophilic conditions in a sulfate and nitrate co-reduction system. Full denitrification was accomplished and the sulfate removal efficiency ranged from 79.93% to 96.81% for all the tested scenarios, with the degree of sulfate reduction slightly decreased with higher O₂ feeding rate. The proportion of S⁰ to influent SO₄²⁻ was much greater at microaerophilic stages (27.5–69.2%) versus the anaerobic stage (11.1%). The peak S⁰ recovery (69.2%) was achieved at O₂ = 4.0 mL/min. Illumina sequencing technology was used to characterize the bacterial community and the results indicated that Bacteroidetes, Firmicutes, Proteobacteria, Spirochaetae and Synergistetes members were dominant in microbial communities, however the variation of these dominant members across all the operating conditions did not well respond to reactor performance. Further analysis revealed that the structure of the microbial community, including community richness and evenness, might better respond to reactor performance, which deserves more research in future.