Abstract The synergistically optimized nitrogen removal strategy emerges from the co-treatment of municipal wastewater with the effluent from partial nitrification (PN) of high-ammonia wastewater through a partial denitrification-anaerobic ammonium oxidation (PDA) process. However, maximizing PDA efficiency remains a critical challenge. In this study, a two-stage partial nitrification-partial denitrification-anaerobic ammonium oxidation (PN-PDA) integrated system was developed to regulate synergistic granule-biofilm architecture in the second stage to enhance PDA. After 160-day operation, the system showed excellent nitrogen removal, with effluent nitrogen at 5.6 ± 2.9 and 5.2 ± 2.0 mg/L in two phases. In-situ activity assays revealed that anammox rate in granular sludge (9.6 mg N/(L·h)) was significantly higher than that in biofilms (1.8 mg N/(L·h)). Fluorescence in-situ hybridization analysis demonstrated a distinct spatial distribution, with PD functional bacteria Thauera dominating granule outer layer, while Ca. Brocadia was enriched in the inner layer. Metagenomic sequencing further confirmed that Ca. Brocadia accounted for 9.8% and 4.1% in granules and biofilms, respectively. Anammox-related genes ( hzs , hdh ) showed significantly higher abundance in the granules. This study offers a novel framework for concurrent high-strength and municipal wastewater treatment while providing critical insights into granule-biofilm engineering for nitrogen removal intensification.
Bai et al. (2026) studied this question.