Phosphorus (P) is the controlling factor for eutrophication in surface and marine waters. In Hong Kong, the southern waters, which were identified as P limiting, receive 70% of sewage treatment effluents. Thus, P removal from wastewater became a critical issue in Hong Kong. As an economical and highly efficient method for P removal & recovery from centralised sewage treatment plants, enhanced biological phosphorus removal processes (EBPRs), mediated by phosphate accumulating organisms (PAOs), were developed and applied elsewhere. However, current EBPRs did not favour the warm climate (sewage temperature 20-30 °C) that prevails in Hong Kong throughout the year. This unenviable scenario was because warm temperature induces intense competition of glycogen accumulating organisms (GAOs) agai...[ Read more ]

Phosphorus (P) is the controlling factor for eutrophication in surface and marine waters. In Hong Kong, the southern waters, which were identified as P limiting, receive> 70% of sewage treatment effluents. Thus, P removal from wastewater became a critical issue in Hong Kong. As an economical and highly efficient method for P removal & recovery from centralised sewage treatment plants, enhanced biological phosphorus removal processes (EBPRs), mediated by phosphate accumulating organisms (PAOs), were developed and applied elsewhere. However, current EBPRs did not favour the warm climate (sewage temperature 20-30 °C) that prevails in Hong Kong throughout the year. This unenviable scenario was because warm temperature induces intense competition of glycogen accumulating organisms (GAOs) against PAOs for organic carbon sources.

Hence, the development of a new EBPR process for such subtropical regions was deemed necessary. A possible solution is to explore new PAOs that would not compete with GAOs. Our recent studies revealed a possible shift of PAOs from carbon conversion to sulfur conversion when sulfate was abundant. Leveraging on 20% freshwater saving, seawater toilet flushing practice in place since 1958, 500 mg/L sulfate in the saline sewage provided a drive for the exploration of this new PAO for the purpose of developing new EBPR suitable for the warm temperature. In this thesis research, the interconnections between chemical compounds and sulfur-cycle communities were confirmed, and a new concept of simultaneous sulfide and VFA-carbon uptake/storage being responsible for the control of sulfide emission and luxury-uptake/release of phosphorus was found. The observations also suggested that the poly-S could act as an intracellular energy source for P-uptake and poly-P formation. Moreover, microscopic (CLSM and TEM) images indicated the presence of intercellular poly-P and poly-S. Metagenomics analyses were also done and concluded that poly-S can influence Poly-P accumulation in the system. In addition, we introduced multi-cycle operation to achieve higher system stability and higher removal efficiency. In conclusion, we confirmed the possibility of developing such new PAOs, named sulfur associated PAOs (SPAOs) which has the minimal formation of PHAs, but with high P removal potential at 30 °C, dissociated SPAOs and GAOs for organic carbon source competition completely.