SEM was used to further observe the inner structures and the outer morphology of the aerobic granules (Supplementary data, Fig. SD 2).
A closer observation on the surface of granules developed at all temperatures exposed the compact structure composed of various types of non-filamentous coccal-shaped bacteria which were tightly linked to one another.
Simultaneously, the bacteria cluster also led to the appearance of numerous cavities which contribute in enhancing transportation of substrate and oxygen into the inner cores of the granules.
Similar observation by Rosman et al. (2013) reported these cavities can promote transferring of the metabolic products in and out of the granules.