Session: General Posters:

Aerobic granulation is an emerging microbial process in wastewater treatment that has shown to improve the efficiency of the conventional activated sludge system by accelerating sedimentation and increasing microbial tolerance to toxic elements found in wastewater. To date, granulation can only be achieved in sequence batch reactors, which are largely incompatible with the continuous flow model used in modern wastewater treatment plants. Recent research demonstrated that a proper combination of feast and famine conditions is able to promote aerobic granulation in a continuous flow system composed of a series of completely stirred tank reactors. The goal of the present study is to understand the mechanisms of aerobic granulation present in the continuous flow reactor by determining changes in the microbial community composition in aerobic granules compared to conventional microbial flocks. A metagenomic analysis was conducted using 16S rDNA sequencing on aerobic granules and conventional activated sludge samples fed by the same wastewater. Taxonomic identification and functional metagenomics were completed with bioinformatics software tools Bioconductor, QIIME, and PICRUSt. Results showed that the microbial class assortment distribution across all eight chambers of the continuous flow reactor was fairly similar, suggesting homogeneous microbial composition. The aerobic granules showed a predominance of Gammaproteobacteria (32%), Bacteroidia (28%), Alphaproteobacteria (6%), and Campylobacteria (5%). This microbial composition was quite different from the microbial community in activated sludge fed with the same wastewater which contained the following classes: Gammaproteobacteria (22%), Bacteroidia (24%), Polyangia (12%), Alphaproteobacteria (10%), Parcubacteria (3%), Saccharimonadia (3%) and Campylobacteria (0.9%). It was observed that filamentous bacteria such as Parcubacteria, Saccharimonadia, Deltaproteobacteria, and Actinobacteria were four to ten times more abundant in conventional activated sludge compared with aerobic granules. Additionally, microbial structure appeared to shift from filamentous bacteria to EPS-producing bacteria, which are essential in promoting granulation. These findings suggest that the presence of filamentous bacteria hinder the formation of aerobic granules in the activated sludge. Furthermore, the feast-famine causes a shift of the microbial community towards EPS-producing bacteria, therefore promoting aerobic granulation.

Benoit Van Aken

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