Two up-flow blanket filter (UBF) reactors were employed to treat synthetic wastewater with different substrate concentrations and nitrogen load rates (NLR) for 178 days. During days 0-60, higher influent NLR of R-2 (0.21-0.58 kg.m(3).d) slowed down the formation of anammox sludge compared with the lower NLR of R-1 (0.18-0.31 kg.m(3).d). Difference in sludge color and nitrogen conversion rate indicated greater anammox activity of R-2 than R-1. During days 61-178, R-1 and R-2 achieved the maximum nitrogen removal rates (NRR) of 1.213 and 1.684 kg/(m(3).d) under the NLRs of 1.924 and 2.502 kg/(m(3).d), respectively. Furthermore, high-throughput sequencing showed that R-2 (43.5%) had a higher proportion of anammox bacteria than R-1 (37.8%) and less species. These results showed that after going through a higher NLR acclimation process during start-up period, stronger resistant capability against high impact nitrogen load and greater anammox activity were obtained by R-2. (C) 2017 Elsevier Ltd. All rights reserved.