Abstract
Recently, the use of phototrophs for wastewater treatment has been revisited because of new approaches to separate them from effluent streams. One manifestation uses oxygenic photogranules (OPGs) which are dense, easily-settleable granular biofilms of cyanobacteria, which surrounding populations of heterotrophs, autotrophs, and microalgae. OPGs can remove COD and nitrogenous compounds without external aeration. To better grow and maintain biomass in the proposed wastewater process, this study seeks to understand the factors that contribute to successful granulation. Availability of initial inorganic nitrogen, particularly ammonium, was associated with successful cultivation of OPGs. In the first days of granulation, a decrease in ammonium coupled with an increase in a cyanobacterial-specific 16S rRNA gene, may suggest that ammonium was assimilated in cyanobacteria offering a competitive environment for growth. Though both successful and unsuccessful OPG formation demonstrated a shift from non-phototrophic bacterial dominated communities on day 0 to cyanobacterial dominated communities on day 42, the successful community had a greater relative abundance (46%) of OTUs associated with genera Oscillatoria and Geitlernema than the unsuccessful community (27%), supporting that filamentous cyanobacteria are essential for successful OPG formation. A greater concentration of chlorophyll b in the unsuccessful OPG formation suggested a greater abundance of algal species. This study offers indicators of granulation success, notably availability of inorganic nitrogen and chlorophyll a and b concentrations for monitoring the health and growth of biomass for a potential OPG process.
Highlights
Cyanobacteria are an extremely diverse phylum and exceedingly adaptive
Filamentous cyanobacteria are integral to the structural integrity of successful granulation (Milfrestadt et al in review), so their early and sustained growth is crucial for
At the end of a successful cultivation, filamentous cyanobacteria comprised the large percentage of the communities with operational taxonomic unit (OTU) 2 and 5 associated with filamentous genera Oscillatoria and Geitlernema accounting for 46% of the relative abundance
Summary
Cyanobacteria are an extremely diverse phylum and exceedingly adaptive. Within biofilms, there is evidence that they participate in the exchange of oxygen, carbon, and nitrogen species (Abed 2010; Muro-Pastor et al 2005; Stal 1995). Wastewater treatment facilities could save 25–60% of the operating costs of municipal wastewater treatment Though this is a promising process, the formation and propagation of OPGs within the treatment process is not yet fully understood, which remains a challenge in starting and sustaining the treatment process. The mechanisms for stimulating the strong granule-like formation is still unknown, studies have pointed to the stickiness of extracellular polymeric substances (Jakub et al 2013; Tuomainen et al 2006), filament entanglement (Weber et al 2007), gliding actions that form cohesive patterns (Tamulonis and Kaandorp 2014), and gliding actions that serve as a defense against extreme light conditions, or predation by microbial grazers (Edyta and Agnieszka 2002). Granulation of OPGs has generally been described and the essential role of filamentous cyanobacteria in the parallel structural development under both static and hydrodynamic conditions has been defined (Milferstedt et al in review). Understanding the conditions that lead to successful granulation is critical for consistently growing OPG biomass for both seeding reactors and sustaining new biomass growth within operating reactors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
