Bacterial populations associated with the development of aerobic granules in column-type sequential aerobic sludge blanket reactors fed with a synthetic acetate-based wastewater were monitored also by microscopy and ribosomal RNA-targeted fluorescence in situ hybridization (FISH) using group specific probes. The reactor biomass initially consisted of pin-point flocs which later developed into well-settling granules. Filament counts and SVI decreased rapidly from 389 ± 26 |xl-1 and 341ml g-1 on day 2 to 14 ± 26 |xl-1 and 111 ml g-1on day 16. Filamentous bacteria fitting the morphological descriptions of Sphaer3tilus natans and Type 1863 were observed on day 2 in sludge flocs after seeding of reactor. However, filament counts decreased due to rapid filament washing out and proliferation of floc-forming bacteria.
FISH determination revealed that gram-positive bacteria with high G+C content and $-Pmte3bacteria were the dominant sub-populations in flocs, and their relative abundances increased in granules sampled on day 23. Gram-positive bacteria with low G+C content, a-, and Y-Pr3te3bacteria were minor constituents in both floc and granules, while Archaea were not detected at all.
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