[Investigation on enhanced conditions for the densification of filamentous sludge]

A new approach was investigated for controlling sludge bulking by using enhanced conditions for densification of filamentous sludge. Several methods, including elevated dissolved oxygen, increased superficial velocity, elevated calcium concentration, extended starvation time, have been employed to reveal when and how filamentous sludge could be denser in terms of settleability. It showed that increased superficial velocity improved the settleability and event triggered filamentous granulation in a short term, i. e., sludge volumetric index (SVI) decreased from 800 mL/g to 350 mL/g, and it became less effective in a long term, as the SVI increased to approximately 800 mL/g after a short period of stable operation. Elevated calcium concentration also improved the settleability by clustering the mycelium of filamentous microorganisms, and then SVI decreased to 300 mL/g gradually, but no granulation was observed. However, negligible changes were observed by elevated dissolved oxygen or extended starvation time, as the decrease of SVI value could not be significantly observed. Additionally, relationship between ovality of filamentous mesh and sludge volumetric index was also examined. It was found that the clustered growth that brought about high ovality (approximately 1.5) could improve the settleability. Additionally, acidic condition may damage the mycelium aggregation, and alkaline condition and divalent cation concentration were insignificant for mycelium aggregation.