Context. Aerobic granular sludge (AGS) bioprocess allows to remove nutrients from wastewater. AGS can be obtained from enhanced biological phosphorous removal reactors after applying specific operational conditions for granulation.
Gap. Functional activities and microorganisms involved in the nutrient removal were mainly studied using synthetic wastewater containing acetate and propionate as carbon source.
Aim. Better understand the activity of the microbiome composing granules using more complex carbon substrates is of high importance to obtain an efficient process.
Methods. The sensitivity of the granules facing a progressive modification of the substrate composition, from volatile fatty acids (VFA) to fermentable monomeric (CM) and polymeric (CP), was studied in a sequencing batch reactor. In addition, the reversibility of the microbial community was studied by returing to VFAs. 16S amplicon sequencing was done on regular basis, and metagenomics and -transcriptomics analyses were carried out for each influent during anaerobic and aerobic phases.
Findings. Nutrient removal performances and settling properties were mainly modified after CP implementation without modifying the microbial community structure. Differentially expressed genes between anaerobic and aerobic phases were identified for each influent (Table 1), representing 8-12% of the global dataset. Upregulated genes in the aerobic phase were mainly involved in the energy production and growth metabolisms, except in CP. However, genes involved in the polyhydroxy-alkanoate or phosphorous metabolisms represented less than 1% of the DGE. The complexification of the influent seemed to induce a modification in the microbial metabolisms. Differential gene analysis showed that 28 to 51% of genes were different between CP and respectively CM and VFA (both phases), while CM vs VFA had 22% of differential genes. Further expression analyses are at present carried out to determine the metabolic pathways involved in the decomposition of the different substrates and in the nutrient removal, as well as the microorganisms metabolically active in these pathways.
