Successful start-up of the anaerobic ammonium oxidation (anammox) process in up-flow sludge blanket reactor was achieved by seeding denitrifying (R0) or mixed denitrifying-anammox granular sludge at a 3: 1 volume ratio (R1). The results demonstrated that R1 was successfully started-up on day 40 and had a nitrogen removal rate (NRR) of 0.55 kg N m(-3) d(-1). By contrast, it took 98 days to start up R0 (0.54 kg N m(-3) d(-1)). R0 and R1 achieved maximum NRRs of 5.70 and 12.02 kg N m(-3) d(-1), respectively. The biogranules from R1 generally possessed greater specific anammox activity (SAA), higher extracellular polymeric substance (EPS) and heme c content, larger granules and greater settling velocity. Quantitative PCR (qPCR) and high-throughput sequencing techniques were used to monitor the evolution of the bacterial community. These results demonstrated the feasibility of seeding mixed denitrifying-anammox granular sludge to start-up an anammox reactor. (C) 2016 Elsevier Ltd. All rights reserved.