On the other hand, higher anaerobic and overall COD removal levels were observed in the granular SBR cycle. In fact, the COD removal profiles showed a fast COD decrease during the first 30 min of anaerobic reaction (Fig. 5), suggesting a fast carbon source uptake for intracellular polymer storage. This metabolism may be associated with the presence of polyphosphate accumulating organisms(PAO), which are key microorganisms for the successful formation and stability of aerobic granules [11]. In contrast with the flocculent SBR, similar COD removal profiles were obtained for GSBR1and GSBR2 cycles. Thus, it can be assumed that the inhibitory effect of the azo dye (and/or its bioconversion intermediates) towards anaerobic COD removal was not observed in the studied granular SBR, which is consistent with the increased tolerance of AGS totoxicity previously reported