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

David G. Weissbrodt, Samuel Lochmatter, Sirous Ebrahimi, Pierre Rossi, Julien Maillard, Christof Holliger

    Research output: Contribution to journalArticleScientificpeer-review

    49 Citations (Scopus)

    Abstract

    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 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, orwhen reactors were operated at 30oC. Fast-settling dense granules were obtained with 4.0 cms1 SAV, or when the inoculation sludge was taken from a WWTP removing all nutrients biologically. However, only carbon was aerobi-cally 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 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.

    Original languageEnglish
    JournalFrontiers in Microbiology
    Volume3
    Issue numberSEP
    DOIs
    Publication statusPublished - 2012

    Keywords

    • Aerobic granular sludge
    • Bacterial selection
    • Biological wastewater treatment
    • Granule formation
    • Nutrient removal limitations
    • Wash-out dynamics

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