Polymers can either immobilize the anaerobic sludge or reinforce the strength of the already existing granules by coating the granule surface with a thin layer of polymer [68,184]. Both synthetic and natural polymers have been used to assist anaerobic bacteria to aggregate together and form granules (Fig. 6); for example the extract of Moringa oleifera seeds (a natural polymer) in the feed favors aggregation of coccoid bacteria and growth of microbial nuclei