CHARACTERIZATION OF FILAMENTOUS BULKING IN ACTIVATED SLUDGE USING OLIGONUCLEOTIDE HYBRIDIZATION PROBES

The abundance of the filament Sphaerotilus natans in bulking and non-bulking full-scale activated sludge systems was determined using a species-specific 16S ribosomal RNA-targeted probe. Membrane hybridization results showed that other filamentous organisms, or other physical and chemical factors, may have greater effects on sludge settling in these plants, since a correlation between settling characteristics and S. natans rRNA levels was not found. A quantitative method for determining S. natans biomass in activated sludge was developed. The technique involves in situ hybridization with a species-specific fluorescently labeled oligonucleotide probe calibrated on pure cultures of S. natans. The results of this technique were comparable to results of membrane hybridization studies using a radioactively labeled oligonucleotide probe. The combined use of the two hybridization assays represents a new approach in studying bulking phenomena, and the approach may be applicable to other filament species or types.