Isolation and characterization of filamentous bacteria present in bulking activated sludge

Summary Several types of filamentous microorganisms were observed and identified in samples of poorly settling (bulking) activated sludge. The major types encountered and the frequency (percentage) of appearance in the total of all treatment plants sampled were: Eikelboom type 0041 (60), type 1701 (45), Haliscomenobacter hydrossis (35), type 021N (30), Thiothrix spp. (20), and Sphaerotilus natans (20). Isolation techniques and culture media were developed and used to recover 42 axenic strains of filamentous bacteria from sludge samples collected. The isolates were identified as strains of Thiothrix, Beggiatoa, S. natans, and Eikelboom types 021N, 1701, 0041, and 0803. Nutritional and differential characterization of the bacteria was important to the differentiation of groups which could not be easily distinguished on the basis of morphology. Although certain treatment plant operating parameters (organic loading) seemed associated with the presence of specific filamentous organism types, possible interaction among factors precluded definite establishment of a cause and effect relationship for most of the treatment plant characteristics and organisms observed.