Effects of feed pattern and dissolved oxygen on growth of filamentous bacteria

The association of filamentous microorganisms with bulking in activated sludge systems has been well documented by a number of researchers.1"3 Papers published during the last 15 years have broadened understanding of the filamentous bulking phenomenon and have suggested remedial control actions.4"6 Several papers concluded that reactor feed patterns have a large impact on sludge settleability and on the predominance of fil amentous versus nonfilamentous growth in an activated sludge system.7"9 Eikelboom10"12 used microbial morphology and staining techniques to develop reliable procedures to identify, by type, filamentous microorganisms in activated sludge. By identifying filaments found in various bulking sludges and investigating prevalent process conditions, Eikelboom discovered that certain filament types could act as indicator organisms for those process conditions.11 More recently, Strom and Jenkins13 conducted a laboratory examination of sludge samples from a number of U. S. wastewater treatment plants and attempted to correlate filament types with various process conditions. That study con cluded, for example, that the growth of Type 02 IN, Sphaerotilus spp., Type 1701, Type 1863, and Thiothrix (also a sulfide in dicator) is stimulated by maintenance of low reactor dissolved oxygen (DO) concentrations, while, M. Paricella, Nocardia spp., and Type 0041 filaments predominate in activated sludge sus pensions with low food-to-microorganism ratios (F:M). This paper provides results of an investigation of the responses of Type 1863 and "protruding from the floe" Type 0961 (Ei kelboom nomenclature12) filament growth to changes in reactor feed pattern and DO concentration. The purpose of the inves tigation was to gain more information on plant process condi tions that enhance the growth of various filamentous microor ganisms and on organism response to alteration of those con ditions.