Impact of substrate concentration on anammox-UBF reactors start-up.

Two up-flow blanket filter (UBF) reactors were employed to treat synthetic wastewater with different substrate concentrations and nitrogen load rates (NLR) for 178days. During days 0-60, higher influent NLR of R2 (0.21-0.58kg·m3·d) slowed down the formation of anammox sludge compared with the lower NLR of R1 (0.18-0.31kg·m3·d). Difference in sludge color and nitrogen conversion rate indicated greater anammox activity of R2 than R1. During days 61-178, R1 and R2 achieved the maximum nitrogen removal rates (NRR) of 1.213 and 1.684kg/(m3·d) under the NLRs of 1.924 and 2.502kg/(m3·d), respectively. Furthermore, high-throughput sequencing showed that R2 (43.5%) had a higher proportion of anammox bacteria than R1 (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 R2.