Characterization of sulfate-reducing granular sludge in the SANI

The Sulfate reduction, Autotrophic denitrification and Nitrification Integrated (SANI) process is a sulfur cycle-based biological carbon and nitrogen removal process that has been developed in Hong Kong to close the loop between the hybrid water supply and saline sewage treatment. The major bioreactor of this new technology is a Sulfate-Reducing Up-flow Sludge Bed (SRUSB) that convers organics and provides the electron donor for subsequent autotrophic denitrification. In order to minimize footprint and maximize operation resilience granulation of sulfate reducing bacteria (SRB) in the SRUSB was recently conducted. This study investigates the biological and physicochemical characteristics of the granular sulfate-reducing sludge. A lab-scale granular sludge SRUSB reactor was operated with synthetic saline sewage for 368 days. At 1 h nominal hydraulic retention time (HRT) and 6.4 kg COD/m 3 -d organic loading rate, the SRUSB reactor achieved 90% COD and 75% sulfate removal efficiencies. Granular sludge was observed within 30 days, and became stable after 4 months of operation with diameters of 400−500 mm, SVI5 of 30 ml/g, and high cohesion resisting breakage with a shear force G > 3400 s -1 . Pyrosequencing analysis of the 16S rRNA gene in the sulfate-reducing granules on day 90 indicated that the microbial community consisted of diverse SRB genera, namely Desulfobulbus (18.1%), Desulfobacter (13.6%), Desulfomicrobium (5.6%), Desulfosarcina (0.73%) and Desulfovibrio (0.6%). These genera accounted for 38.6% of total operational taxonomic units at genus level and no methanogens were detected. The microbial population and physicochemical properties of the granules explained clearly the excellent performance of the granular SRUSB reactor.