A Novel AOA-SNDPRr Process for Simultaneous Wastewater Treatment, Phosphorus Recovery, and In Situ Sludge Reduction with Ultralong Sludge Retention Time

Successive side-stream phosphorus recovery challenges the stable enhanced biological phosphorus (P) removal process due to stripping of P from sludge. In this study, a novel anaerobic/oxic/anoxic simultaneous nitrification, denitrification, and phosphorus removal integrating side-stream recovery process (AOA-SNDPRr) was proposed and operated under ultralong sludge retention time (SRT, 120–140 d). Results showed that effective and stable carbon, nitrogen, and P removal was obtained. High P contents within sludge (15–30 mg P/g MLSS) were kept even after an 80 day continuous extraction, thus supporting considerable anaerobic P concentrations (10–30 mg/L). Up to 81.60% of influent P was harvested, and in situ sludge reduction by 63.2% was enhanced with a low observed sludge yield (Yobs) of 0.015 g MLSS/g chemical oxygen demand under a 50% extraction ratio. Interestingly, a long-time operation witnessed spontaneous sludge granulation. Abundant extracellular polymeric substances (EPS), particularly viscous polysaccharides (PS), were stimulated. A 16S rDNA sequence demonstrated that overwhelmingly dominated Candidatus_Competibacter soared to 20.18%–25.91% without deteriorating biological P removal. Negligible impact on functional genes for poly-P/Gly synthesis and decomposition was found. Overall, the AOA-SNDPRr process with long SRT was proved to be a sustainable approach targeting three goals of reliable wastewater treatment, efficient phosphorus recovery, and dramatic in situ sludge minimization.