The inclusion of phototrophic microorganisms is being studied with renewed interest for applications in secondary wastewater treatment. One manifestation, called oxygenic photogranules (OPGs), are granular biofilms of cyanobacteria, which surround populations of heterotrophs, autotrophs, and microalgae. In bench-scale reactors, OPGs have achieved 90% COD removal and 60% total nitrogen removal without external aeration. To better grow and maintain biomass in the proposed wastewater process, the elements of successful granulation need to be better understood. Availability of initial inorganic nitrogen was associated with successful cultivation of OPGs from activated sludge biomass. Using next generation amplicon sequencing of the 16S rRNA gene, the communities that successfully granulated had a greater relative abundance of OTUs associated with filamentous cyanobacteria genera Oscillatoria than the unsuccessful. A greater concentration of chlorophyll b in the unsuccessful OPG formation suggested a greater abundance of algal species. We hypothesized that successful static granulation is correlated to the proportion of cyanobacteria, microalgae, and initial nutrients present in the sludge inoculum. In a subsequent cultivation, ratios by wet-mass of Oscillatoria to activated sludge solids from Amherst, MA (5:95 (low) and 20:80 (high)) were combined with synthetic wastewater containing either 23 +/- 2.5 for high and 3.7 +/- 0.3 mg NH4+-N/L for low conditions. Results showed 90% granulation for vials inoculated with high initial Oscillatoria and high ammonia, 50% granulation for high Oscillatoria with low ammonia, and 30% granulation for low Oscillatoria with both high and low ammonia. Ammonia availability and abundance of filamentous cyanobacteria are key factors in the formation of OPGs and could be key to the maintenance of healthy populations of phototrophic granular biomass in reactor environments.

Formation of phototrophic granular biofilms for oxygenic wastewater treatment

256th National Meeting (2018)

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