Abstract:

The filamentous bulking of sludge is directly associated with specific influent characteristics and operational regime.In order to understand whether the types of carbon source can cause filamentous sludge bulking and lead to the formation of dominant filamentous bacteria, their long-term effects on sludge settleability and filaments growth as well as the competition between filaments and floc-formers were investigated.Three lab-scale sequencing batch reactors under controlled conditions were operated by using acetate, glucose and starch as carbon sources, respectively.When the storage capability of microorganisms was limited by decrease of substrate concentration gradient, there appears a great quantity reproduction of filamentous bacteria i.e.filamentous bulking (sludge volume index, SVI>600 ml·g^-1）for acetate- and glucose-fed systems.SVI was kept below 300 ml·g^-1 for starch-fed reactor,although much open, fluffy and porous flocs were formed, and settling performance had no serious deterioration.The results from  staining reactions and fluorescent in situ hybridization showed that the first dominant filament was Thiothrix nivea for the acetate-fed reactor, S.natans for the glucose-fed reactor, N. limicolaⅡ and M.parvicella for the starch-fed reactor.So, it was demonstrated that various carbon sources can lead to different metabolic characteristics for various substrates, and the occurrence of filamentous bulking was closely associated with kinetics and storage properties of microorganisms.