Hong Kong has used seawater as secondary quality water for toilet flushing for more than four decades, the resulted saline sewage contains 4000 to 6000 mg/L chloride and 500 mg/L sulfate on average. It is treated by conventional sewage treatment processes without problems. In order to further benefit Hong Kong from this water-saving practice, a novel sewage treatment process, namely SANI (Sulfate reduction, Autotrophic denitrification and Nitrification Integrated) process is developed by The Hong Kong University of Science & Technology. This novel process uses less sludge-yielding sulfate-reducing bacteria (SRB), autotrophic denitrifying bacteria (ADB) and nitrifiers, thus achieves a significant reduction in excess sludge production, treatment cost and space....[ Read more ]

Hong Kong has used seawater as secondary quality water for toilet flushing for more than four decades, the resulted saline sewage contains 4000 to 6000 mg/L chloride and 500 mg/L sulfate on average. It is treated by conventional sewage treatment processes without problems. In order to further benefit Hong Kong from this water-saving practice, a novel sewage treatment process, namely SANI (Sulfate reduction, Autotrophic denitrification and Nitrification Integrated) process is developed by The Hong Kong University of Science & Technology. This novel process uses less sludge-yielding sulfate-reducing bacteria (SRB), autotrophic denitrifying bacteria (ADB) and nitrifiers, thus achieves a significant reduction in excess sludge production, treatment cost and space.

SANI process consists of a sulfate reduction up-flow sludge bed (SRUSB), an anoxic bio-filter and an aerobic bio-filter. To improve the sulfate-reducing and denitrifying efficiencies, understanding of the microbial community structures in both the SRUSB and anoxic bio-filter biomass is deemed necessary. In this study, the microbial communities involved the SRUSB of a lab-scale and a pilot-scale SANI system and the anoxic bio-filter of the lab-scale system. Daily performance and batch test results showed that 85% COD was removed by sulfate-reducing bacteria (SRB) in the SRUSB of both systems. Molecular cloning analysis of the sludge samples revealed that a novel Bacteriodetes-like population and a Thermotogales-like population were predominant in the pilot-scale systems’ SRUSB, while in the lab-scale system’s SRUSB, a Desulforhopalus-like population was representative. No methanogens were detected in both reactors, indicating the predominance of SRB in the SRUSB microbial population. The sludge taken from the anoxic filter of the lab-scale system comprised both autotrophic and heterotrophic bacteria, the result of clone library and the results of previous kinetic studies comprehensively revealed the dominance of autotrophic denitrifying bacteria and its co-existence with other groups of bacteria.

Key words: Sulfate reducing up-flow sludge bed (SRUSB), sulfate-reducing bacteria (SRB), autotrophic denitrifying bacteria (ADB), 16s ribosomal RNA analysis, saline sewage, SANI process