Insights into deterioration and reactivation of a mainstream anammox biofilm reactor response to C/N ratio

In-depth knowledge of the deterioration and reactivation of the anaerobic ammonium oxidation (anammox) induced by carbon-to-nitrogen (C/N) is still lacking. Herein, the anammox performance was investigated in an anaerobic sequence biofilm batch reactor fed with low-strength partial nitration effluent in the range of C/N ratio from 0.5 to 3. The anammox was hardly deteriorated at C/N lower than 1.5, while became worsen if C/N was above 2.0. The specific anammox activity (SAA) experiments showed an 85% decrease of SAA at C/N of 3.0 compared with the maximum value (C/N:0). However, anammox capacity was rapidly recovered once influent C/N was adjusted back to zero. Moreover, C/N also highly affected the composition, structure and function of extracellular polymeric substance of the anammox biofilm. High-throughput sequencing revealed a close correlation between C/N change and microbial structure shift. Finally, the potential inhibition and restoration mechanism of the C/N-dependent anammox were proposed based on metagenomic analysis. This research provides some insights into the reinstatement of a mainstream anammox biofilm process after it is interrupted by high C/N influent.