A simulated textile wastewater containing the azo dye AR14 was supplied to two anaerobic/aerobic SBR systems, one inoculated with activated sludge flocs and the other with aerobic granules. The flocculent SBR system operated in 8-h cycles but this duration could be reduced to 6 h in the granular system, mainly due to the excellent settling properties of the aerobic granules. After around 40 days of operation with a SRT of 15 days, the mixed liquor of the flocculent SBR (FSBR1 and FSBR2) reached a TSS content of 5 g L−1. In the granular SBR (GSBR1 and GSBR2), the dense and fast settling aerobic granules progressively accumulated in both SBR, reaching a TSS content of 13 g L−1with negligible biomass washout levels. Consequently, SRT values higher than 30 days were attained in the granular SBR. A comparison between the overall dissolved COD removal yields of the four SBR during 41 days of operation is presented in Fig. 1