title: Fast start-up and enhancement of CANON process for the low-strength wastewater treatment: tactic and action of ultrasonic
design: the CANON (Completely Autotrophic Nitrogen-removal Over Nitrite) process was successfully started-up for mainstream wastewater treatment, and the stable operation of CANON process were achieved through ultrasonic enhancement. In accordance with the optimal parameters determined in batch tests which controlled (DO<0.3mg/L , HRT< 4.0 h, and pH=7.5) as three critical factors to repressed the NOB (Nitrite-Oxidizing Bacteria), thus the promotion of AnAOB (Anaerobic Ammonia Oxidizing Bacteria ) could obtained sufficiently NO2--N. The CANON process was quickly started up within 21days. Microbial community analysis revealed that the Candidatus brocadia and Candidatus Kuenenia were accounted for 27.07% and 11.52% respectively at stabled inhibition. The Nitrosomonas was also significantly enriched to 12.15%. Moreover, through ultrasound (intensity of 0.3w/cm2, act on time 4 min/d), the CANON process(~50mg N.L-1) was got with the average ammonia nitrogen removal rate and total nitrogen removal efficiency approximately 95% and 76.7% under steady state, respectively. The 16S rRNA analysis showed that the abundance of dominanted phylum has remarkablely conversion after ultrasonic enhancement. The relative abundance of AOB were increased form 12.15% to 24.14%,and the NOB were decreased from 2.97% to 1.64%. In general, a certain intensity of ultrasound provides an effective promotion for AOB and suppression for NOB. Further moreintermittent ultrasound(intensity of 0.3w/cm2, act on time 4 min/d) could enhanced the enrichment of AOB and ANAMMOX bacterias. The results provide technical assistance for the starting-up and stably performance in the mainstream CANON system.