The microbial community of activated sludge is remarkably efficient in removing a wide range of pollutants from sewage using oxygen as terminal electron acceptor. Treating water, however, comes at a high economic and environmental price largely caused by the energy demand for aeration (~2% of the electricity consumed in developed countries). Ecological engineering may help us develop more resource-saving strategies for wastewater treatment. We have recently generated oxygenic photogranules that treat wastewater without the need for external aeration. Photogranules are a step in a promising direction. During granulation, phototrophic, filamentous and gliding cyanobacteria are strongly enriched from an activated sludge community in which the initial cyanobacteria abundance is close to the detection limit. The cyanobacteria end up as the most abundant community members in the green outer layer of the granules. The brownish interior of mature granules contains a specific bacterial community sharing functional traits of the initial sludge. We are interested in the role of cyanobacteria in granulation. We expected that a cyanobacterial enrichment from a mature granule possesses all required properties to granulate an activated sludge matrix. Indeed, the granulation property could be propagated when augmenting fresh activated sludge with the enrichment, but only for a limited number of transfers after which granulation failed. Here, we demonstrate how engineering the cyanobacterial amendment affects granulation success. Our results let to a conceptual understanding of granulation, emphasizing the importance of the initial cyanobacterial growth kinetics as control lever. Formation of photogranules is an interesting model system for studying community assembly.