Enhancing multistage anammox biofilm system by ultrasonic irradiation: performance and microbial community characteristics.

The multistage anammox biofilm system constructed on anaerobic baffled biofilm reactor was enhanced by ultrasound irradiation. The optimal ranges of ultrasonic working parameters for enhancing the specific anammox activity (SAA) were explored. When the ultrasonic frequency, power and irradiation duration were in the range of 35∼55 kHz, 60∼100 W and 1.0∼3.5 min, SAA increased by 35.57%∼43.96%. Then, the long-term effect of ultrasound on the multistage anammox biofilm system was further studied. The optimal ultrasonic parameters with 40 kHz, 90 W and 3 min per week were adopted and the remarkable enhancing effect was attained. Furthermore, the ultrasonic enhancing mechanism was uncovered. The EPS analysis indicated that the introduction of ultrasound increased EPS and its PN/PS to promote the formation and renewal of anammox biofilms. The bacterial community analysis revealed that Candidatus Kuenenia emerged as the predominant bacteria in the mature biofilms of the control group while Candidatus Brocadia predominated in the mature biofilms of the ultrasonic group. The microbial community succession was redirected under the function of ultrasonic irradiation, which was helpful to improve the anammox performance. Moreover, the ultrasonic irradiation increased the abundance and biodiversity of AnAOB. This study offers the significant theoretical basis for construction of the ultrasound-strengthened multistage anammox system.