Ahn proposed a similar granulation model as presented in. At the initial stage of granulation, aceticlastic methanogens (filamentous) and other organ-isms grow dispersed in the medium.By bridging and rolling effects due to the hydrodynamic behaviour of the UASB, small loose conglomerates mainly composed of the filamentous methanogens are eventually formed. Following on, acetogens attach to this conglomerate, in syntrophic relationship with the aceticlastic methano-gens, thus forming a small granule with a dense core.

Then, acidogens and hydrogenotrophs in syntrophic relationship with the acetogens adhere to the small granule and due to the extracellular polymers excretion by the hydrogenotrophs, the granule is allowed to grow.