S⁰-driven partial denitrification coupled with anammox (S⁰PDA) enables highly efficient autotrophic nitrogen removal...

This study proposed a novel strategy that integrates S⁰ particles (diameter: 2-3 mm) and granular sludge to establish S⁰-driven partial denitrification coupled with anammox (S⁰PDA) process for autotrophic nitrogen removal from NH₄⁺- and NO₃^--containing wastewaters. This process was evaluated using an up-flow anoxic sludge bed bioreactor, operating continuously for 240 days. The influent concentrations of NH₄⁺ and NO₃^- were 29.9 ± 2.7 and 50.2 ± 2.7 mg-N/L, respectively. Throughout the operation, the hydraulic retention time was shortened from 4.0 h to 2.0 h, while the effluent concentrations of NH₄⁺ and NO₃^- were maintained at a desirable level of 1.45-1.51 mg-N/L and 4.46-6.52 mg-N/L, respectively. Despite an autotrophic process, the nitrogen removal efficiency and rate reached up to 88.5 ± 2.0 % and 1.75 ± 0.07 kg-N/(m³·d), respectively, indicating the remarkable robustness of the S⁰PDA process. Autotrophic anammox and sulfur-oxidizing bacteria (Candidatus Brocadia and Thiobacillus) were the predominant bacterial genera involved in the S⁰PDA process. Candidatus Brocadia was primarily enriched in the granular sludge, with a relative abundance of 6.70 %. Thiobacillus occupied a unique niche on the S⁰ particles, with a relative abundance as high as 57.6 %, of which Thiobacillus thioparus with partial denitrification function (reducing NO₃^- to NO₂^- without further reduction to N₂) accounted for 78.0 %. These findings challenge the stereotype of low efficiency in autotrophic nitrogen removal from wastewater, shedding fresh light on the applications of autotrophic processes.