Jiang et al. (2003) reported that addition of Ca2+ accelerated the aerobic granulation process. With addition of 100 mg Ca2+ l-1, the formation of aerobic granules took 16 days compared to 32 days in the culture without Ca2+ added. The Ca2+-augmented aerobic granules also showed better settling and strength characteristics and had higher polysaccharides contents. It has been proposed that Ca2+ binds to negatively charged groups present on bacterial surfaces and extracellular polysaccharides molecules and thus acts as a bridge to promote bacterial aggregation. Polysaccharides play an important role in maintaining the structural integrity of biofilms and microbial aggregates, such as aerobic granules, as they are known to form a strong and sticky non-deformable polymeric gel-like matrix.
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