Accelerated aerobic granulation using alternating feed loadings: Alginate-like exopolysaccharides

•Alternating OLR feeding is applied to accelerate aerobic granulation.•Increase in OLR stimulates the cells to secret c-di-GMP to produce ALE.•Excess ALE with subsequent shearing forms aerobic granules.•Fraction of building blocks in ALE does not affect granulation.

Alginate-like exopolysaccharides (ALE) likely contribute markedly to strength of aerobic granules. This study cultivated aerobic granules from propionate wastewaters using strategies with different organic loading rates (OLRs) (4.4–17.4 kg/m3-d). When the OLR increased suddenly, the constituent cells (Pseudomonas, Clostridium, Thauera and Arthrobacter) were stimulated to secret extracellular cyclic diguanylate (c-di-GMP) and produced excess ALE, which formed a large quantity of sticky materials that served as the precursor of aerobic granules. Formation of excess ALE was the prerequisite for accelerated granulation. Conversely, this study observed no enrichment of poly guluronic acid blocks in ALE during granulation.