Control of activated sludge bulking

The settling properties of the activated sludge cultivated in both single and multiple compartment systems were thoroughly investigated under various BOD/N ratios in the wastewater and at a hydraulic retention time of 24 hr. The present study found that the compartmentalized system could not only achieve a better effluent quality but also produce a higher sludge settle- ability if the BOD/N ratio was not in excess of 130:1. The performance of the compartmentalized system highly depended upon the physical arrangement of the reactor compartments or the value of the dispersion number, that is, the higher the compartment number or the lower the dispersion number, the higher the percentage organic substrate removal. This result was mainly due to the fact that both the sludge settling and the substrate utilization rates were higher when the mixed activated sludge culture was cultivated in the compartmentalized system with low dispersion number. The major filamentous microorganisms which were observed in the conventional single-stage reactor system were: Sphaerotilus sp. form I (S. natans), and form II, Type 0961, Type 021N, Type 0581 and Type 0803. These causative filamentous microorganisms could exist even when the activated sludge system was operated under the DO sufficient condition.