Bacterial selection during the formation of early-stage aerobic granules in wastewater treatment systems operated under wash-out dynamics

Bacterial selection during the formation of early-stage aerobic granules in wastewater treatment systems operated under wash-out dynamics

Blog Article

Aerobic granular sludge is attractive for high-rate biological wastewater treatment.Biomass wash-out conditions stimulate the formation of aerobic granules.Deteriorated performances in biomass settling and nutrient removal during start-up have however often been reported.

The effect of wash-out dynamics was investigated on bacterial selection, biomass settling behavior, and metabolic activities during the formation of early-stage granules from activated sludge of two wastewater treatment plants (WWTP) over start-up periods of maximum 60 days.Five bubble-column sequencing batch reactors were operated with feast-famine regimes consisting of rapid pulse or slow anaerobic feeding followed by aerobic starvation.Slow-settling fluffy granules were formed when read more an insufficient superficial air velocity (SAV; 1.

8 cm s-1) was applied, when the inoculation sludge was taken from a WWTP removing organic matter only, or when reactors were operated at 30°C.Fast-settling dense granules were obtained with 4.0 cm s-1 SAV, or when the inoculation sludge was taken from a WWTP removing all nutrients biologically.

However, only carbon was aerobically removed during start-up.Fluffy granules and dense granules were displaying distinct predominant phylotypes, namely filamentous Burkholderiales affiliates and Zoogloea relatives, respectively.The latter were predominant in dense granules independently from the feeding regime.

A combination of insufficient solid retention time and of leakage of acetate into the aeration phase during intensive biomass wash-out was the cause for read more the proliferation of Zoogloea spp.in dense granules, and for the deterioration of BNR performances.It is however not certain that Zoogloea-like organisms are essential in granule formation.

Optimal operation conditions should be elucidated for maintaining a balance between organisms with granulation propensity and nutrient removing organisms in order to form granules with BNR activities in short start-up periods.