WHAT DO FILAMENTS LIKE TO EAT? USING DGGE AND FISH TO TEST THE EFFECT OF CARBON SOURCE AND SEED SLUDGE ON FILAMENTOUS GROWTH IN ACTIVATED SLUDGE

The effects of eight carbon sources and three inoculum sources on the growth of filamentous bacteria were tested in lab scale sequencing batch reactors. Microscopic (Gram and Neisser staining) and molecular methods (Denaturing Gradient Gel Electrophoresis [DGGE], Fluorescent in Situ Hybridization [FISH]) were used to track the microbial population changes in the reactors. Sludge volume index (SVI) measurements were used to monitor bulking in the reactors. DGGE and sequencing results indicated the presence of the filamentous bacteria Sphaerotilus natans and Thiothrix. S. natans grew in glucose-, acetate-, and sucrose-fed reactors, regardless of the inoculum source. It also grew in propionate- and pyruvate-fed reactors inoculated with the sludge from the Neuse River Wastewater Treatment Plant (WWTP). Thiothrix was detected in propionate- and pyruvate-fed reactors inoculated with sludge from the South Cary WWTP. In addition to these two filaments, Gram and Neisser staining indicated the presence of Nostocoida limicola in Neuse River WWTP inoculated reactors. The presence of S. natans and Thiothrix (T. nivea) was confirmed with FISH. SVI measurements were consistent with the level of bulking, showing an increase as the number of filaments in the reactors increased.