Combined effects of volume ratio and nitrate recycling ratio on nutrient removal, sludge characteristic and microbial evolution for DPR optimization

The optimization of volume ratio (VAn/VA/VO) and nitrate recycling (R) in a two-sludge denitrifying phosphorus removal (DPR) process Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor (A2/O-MBBR) was investigated. results showed that prolonged anaerobic retention time (HRTAn: 1.25→3.75 hr) exerted favorable effect on chemical oxygen demand (COD) (57.26%→73.54%), poly-β-hydroxyalkanoates (PHA) synthesis (105.70→138.12 mgCOD/L) PO43− release (22.3→38.9 mg/L). However, anoxic (HRTA) R exhibited positive correlation with PHA utilization (43.87%-81.34%) potential (ΔNO3−/ΔPO43−: 0.57-1.34 mg/mg), leading to dramatical TN variations from 68.86% 81.28%. Under the VAn/VA/VO 2:6:0, sludge loss deteriorated nutrient removals but bioactivity quickly recovered when oxic zone recovered. characteristic microstructure gradually transformed under dissolved (DO) control (1.0-1.5→1.5-2.0 mg/L), terms index (SVI: 194→57 mL/gVSS), median-particle-size (D50: 99.6→300.5 μm), extracellular polymeric substances (EPS) (105.62→226.18 mg/g VSS) proteins/polysaccharides (PN/PS) (1.52→3.46). Fluorescence situ hybridization (FISH) accumulation organisms (PAOs) (mainly Cluster I Accumulibacter, contribution ratio: 91.79%-94.10%) dominated superior DPR performance, while glycogen accumulating (GAOs) Competibacter, 82.61%-86.89%) responsible for deteriorative removals. optimal HRTA assembled around 5-6.5 hr 300%-400% based DRP zones also contributed although it low dependence DO concentration (HRTO).