Also Fang states that granules do not develop by the random aggregation of suspended bacteria, but that bacteria search for strategic positions for supply of substrates and for removal of products, as the layered microstructure of certain granules suggest. Once a nucleus is formed, bacteria start to proliferate leading to a growth of the size of the granule that only stops when the interfacial area between bacteria and the mixed liquor decreases to a critical level in relation to the initial hydrolysis or fermentation that takes place at the granule surface.

Vanderhaegen et al., although supporting the multi-layered granule structure proposed by McLeod et al., state that sugar fermentative acidogens form sufficient biomass and polymers to act as ‘nucleation’ centers in which the rest of the methanogenic associa-tions can develop.