GROWTH REQUIREMENTS OF FILAMENTOUS BACTERIA ISOLATED FROM BULKING AND SCUMMING SLUDGE

A total of 68 strains of filamentous bacteria belonging to the genera Sphaerotilus and Haliscomenobacter, Eikelbooms types 021N, 1701, some nocardioform organisms in addition to some unidentified, Gram-negative pink-pigmented isolates were studied qualitatively and quantitatively for their growth requirements and growth response to different nutrients. With the exception of type 021N, all isolates grew better with D-fructose and D-glucose, than with acetate as sole carbon source. Acetate concentrations > 1.0 gl(-1) inhibited all isolates and Haliscomenobacter and the pink-pigmented strains did not grow at all with acetate. With the exception of Haliscomenobacter isolates, growth of the majority of strains was stimulated by low peptone and yeast extract concentrations (0.05-0.5 gl(-1)). Haliscomenobacter strains did not grow in the presence of yeast extract and peptone. For all isolates a strict requirement for calcium, and (to some extent) magnesium was observed. Below a concentration of 20 mg l(-1) Ca and 0.1 mg-l(-1) Mg only few strains were able to show visible growth. The Haliscomenobacter isolates were not able to grow in media containing < 25 mg l(-1)Ca and 5 mg l(-1) Mg. All isolates did not grow in media containing < 1 mg l(-1) NH4-N, and 2.5 mg l(-1) P. Often group or genus specific growth requirements were recorded, indicating that the occurrence of one type of filamentous organisms in bulking sludge can be associated with a specific nutrient mixture in the activated sludge.