Formation of bacterial aerobic granules: Role of propionate

[Display omitted] •Propionate is used as main carbon source for aerobic granulation.•Propionate granules have strong structure but with delayed granulation.•Propionate shifted microbial community and increased cell hydrophobicity.•Propionate increased secretion of c-di-GMP to increase EPS production.•Feed with propionate is promising to cultivate strong aerobic granules. Propionate presents as one of the major volatile fatty acids in municipal wastewaters, which are not readily degraded as acetate by microorganisms. This study cultivated aerobic granules from column reactors with acetate, acetate/propionate mix (3:1 and 1:3) and propionate as carbon sources and noted that propionate-rich feed would delay granulation, but could generate granules with high structural strength. Propionate feed enriched strains fractionated into the hydrophobic phase, Sphaerotilus sp., Sphingomonadaceae and Thauera sp., in granules and altered hydrophobicity of Thauera sp. and Zoogloea sp. The enriched strains could secret high quantities of cyclic-di-diguanylate to increase production of extracellular polymeric substances (EPS). The hydrophobic cell surface and increased EPS quantity led to integrated propionate-fed granules. Feed with high propionate concentration is proposed as promising way to cultivate strong aerobic granules for practical use.