Simultaneous nitrogen and phosphorus removal in the sulfur cycle-associated enhanced biological phosphorus removal (EBPR) process

Hong Kong has practiced seawater toilet flushing since 1958, saving 750,000 m3 of freshwater every day. A high sulfate-to-COD ratio (>1.25 mg SO42−/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 and oxygen demand. Recently, the SANI® process has been expanded to include Enhanced Biological Phosphorus Removal (EBPR) in an alternating anaerobic/limited-oxygen (LOS-EBPR) aerobic sequencing batch reactor (SBR). This paper presents further development – an anaerobic/anoxic denitrifying sulfur cycle-associated EBPR, named as DS-EBPR, bioprocess in an alternating anaerobic/anoxic SBR for simultaneous removal of organics, nitrogen and phosphorus. The 211 day SBR operation confirmed the sulfur cycle-associated biological phosphorus uptake utilizing nitrate as electron acceptor. This new bioprocess cannot only reduce operation time but also enhance volumetric loading of SBR compared with the LOS-EBPR. The DS-EBPR process performed well at high temperatures of 30 °C and a high salinity of 20% seawater. A synergistic relationship may exist between sulfur cycle and biological phosphorus removal as the optimal ratio of P-release to SO42−-reduction is close to 1.0 mg P/mg S. There were no conventional PAOs in the sludge.