Fast start-up of the cold-anammox process with different inoculums at low temperature (13 °C) in innovative reactor

[Display omitted] •Fast start-up of anammox process treating domestic sewage at low temperature (13 °C) was achieved.•The microbial communities of three enriched reactors are similar.•The enriched anammox species were different in the three reactors.•The Ca. Brocadia sinica confirmed the fast anammox start-up.•The hydraulic flow of the CAMBR insures the accumulation of anammox bacteria. Three innovative reactors (CAMBR) through optimally combining with the Anaerobic Baffled reactor and Membrane bioreactor were applied to start up the cold-anammox process at low temperature (13 °C) through inoculating flocculent nitrification sludge (R1), anaerobic granular sludge (R2) and flocculent denitrification sludge (R3), respectively. Results showed that anammox process was started successfully with over 90% total nitrogen removal rate in R1, R2 and R3 after 75d, 45d, and 90d, respectively. Microbial community revealed that Ca. Brocadia and Ca. Jettenia were the dominant anammox bacteria in R1, R2 and R3, accounting for an abundance of 0.08%, 12.18%; 3.17%, 0 and 0.08%, 0.38%, respectively. Three anammox species, Ca. Brocadia caroliniensis, Ca. Brocadia sinica and Ca. Jettenia asiatica were annotated based on the phylogenetic tree, suggesting the anammox species with larger maximum growth rate contributed to the rapid start-up of the cold-anammox process. This study reinforces the potential application of mainstream anammox.