Three types of VFA degrading granules (1980): In this granulation theory, two bacterial genera are proposed to be of predominant importance to granule formation: Methanothrix and Methanosarcina.From the research developed in 1980, De Zeeuw explains the formation of the different types of granules developed in labora-tory UASB reactor start-up experiments from digested sludge as seed material and VFA as substrate.The cha-racteristics of the formed granules were the following:

(A) Compact spherical granules mainly composed of rod-shaped  bacteria resembling Methanothrix soehngenii in short chains or single cells (rod-granules)

(B) More or less spherical granules mainly consisting of loosely intertwined filamentous bacteria attached to an inert particle (filamentous granules) . The prevailing bacteria resembled Methanothrix soehngenii.

(C) Compact spherical granules composed predomi-nantly of Methanosarcina-type bacteria.