Pilot-scale sulfur-fed vibrating membrane bioreactor for efficient mainstream autotrophic nitrogen removal

Sulfur autotrophic denitrification (SADN) coupled with membrane retention is promising for low carbon to nitrogen (C/N) waterwater treatment. However, limitations in anoxic membrane fouling control and sulfur powder deposition constrain scale-up. In this study, a sulfur-fed vibrating membrane bioreactor (S-VMBR) was developed at pilot scale. Intermittent recirculation, elevated sludge concentration, and extended hydraulic retention time (HRT) improved denitrification with low energy consumption. The maximum nitrogen removal rate reached 0.32 kg N·m^-3·d^-1 and was constrained by membrane flux. Sulfur utilization was evidenced by biocorrosion pores and biofilm attachment, with Thiobacillus and Sulfurimonas enriched to 62.9%. Long-term operation induced community differentiation. The sulfur biofilm was dominated by autotrophic denitrification with a mixotrophic strategy, whereas the sludge community supported cross-feeding. Stable performance was attributed to syntrophy between the two communities. This study presents a scalable strategy for autotrophic denitrification and provides insights into the coexistence of autotrophic and heterotrophic communities.