The ability of aerobic granular sludge (AGS) technology to biotransform contaminants of emerging concern (CECs) is largely unknown. AGS supplemented with either acetate, 2-propanol, glycerol, or a 1:1:1 mixture of all three, were cultivated to investigate the link between carbon supplements and biotransformation of six CECs. Carbon substrate had a significant effect on the microbial community composition, as assessed by 16S rRNA gene sequence analyses. Substrate degradation requiring a larger number of catabolic reactions (i.e., glycerol and the mix) was associated with greater microbial richness. The biotransformation of CECs was 45.9% greater in communities supplemented with glycerol (60.3 +/- 30.2 mu g L-1 VSS-1) compared to acetate (20.9 +/- 29.7 mu g L-1 VSS-1). Database surveys of metabolic reactions indicate that microbial communities supplemented with glycerol have the greatest capacity for the degradation of aromatic compounds, while those supplemented with acetate community have the lowest.