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A new biological phosphorus removal process in association with sulfur cycle

Di Wu, George A. Ekama, Hui Lu, Ho-Kwong Chui, Wen-Tso Liu, Damir Brdjanovic, Mark C.M. van Loosdrecht, Guang-Hao Chen
Water research 2013 v.47 pp. 3057-3069
acetates, biomass, carbon, chemical oxygen demand, crystals, denitrification, formaldehyde, freshwater, hydrolysis, nitrification, phosphorus, seawater, sewage, sludge, sulfur, China
Hong Kong has practiced seawater toilet flushing since 1958, saving 750,000 m3 freshwater every day. A high sulfate-to-COD ratio (>1.25 mg SO4/mg COD) in the saline sewage resulting from this practice has enabled us to develop the Sulfate reduction Autotrophic denitrification and Nitrification Integrated (SANI®) process with minimal sludge production. This study seeks to expand the SANI process into an enhanced biological phosphorus removal (EBPR) process. A sulfur cycle associated EBPR was explored in an alternating anaerobic/oxygen-limited aerobic sequencing batch reactor with acetate fed as sole electron donor and sulfate as sulfur source at a total organic carbon to sulfur ratio of 1.1–3.1 (mg C/mg S). Phosphate uptake and polyphosphate formation was observed in this reactor that sustained high phosphate removal (20 mg P/L removed with 320 mg COD/L). This new EBPR process was supported by six observations: 1) anaerobic phosphate release associated with acetate uptake, poly-phosphate hydrolysis, poly-hydroxyalkanoate (PHA) (and poly-S2−/S0) formation and an “aerobic” phosphate uptake associated with PHA (and poly-S2−/S0) degradation, and polyphosphate formation; 2) a high P/VSS ratio (>0.16 mg P/mg VSS) and an associated low VSS/TSS ratio (0.75) characteristic of conventional PAOs; 3) a lack of P-release and P-uptake with formaldehyde inactivation and autoclaved sterilized biomass; 4) an absence of chemical precipitated P crystals as determined by XRD analysis; 5) a sludge P of more than 90% polyphosphate as determined by sequential P extraction; and 6) microscopically, observed PHA, poly-P and S globules in the biomass.