Response of anammox metacommunity to varying hydrodynamic wash

The responses of microbial community structures and bacterial interactions of anammox process to hydrodynamic wash was investigated. Based on the operation of three identical anammox reactors with the same nitrogen loading rate, we found that though the three reactors achieved comparable nitrogen removal performance during the whole operation period, the average specific anammox activities (SAAs) increased with decreasing hydraulic retention time (HRT), resulting in SAAs of 64.69, 73.99 and 119.12 mg-N/(g-VSS.d) at HRT of 4, 2 and 1 h, respectively. The bacterial diversity was observed to increase with decreasing HRT. Moreover, significant (P = 0.001) differences in microbial compositions were found among the three reactors, demonstrating that the hydrodynamic wash played an important role in determining the microbial community structure of anammox process. Taxonomic analysis revealed that the anammox-like bacteria in the reactors subjected to weaker hydrodynamic wash were consistently dominated by Ca. Jettenia, whereas a population shift from Ca. Jettenia to Ca. Brocadia was observed in the reactor with a strong hydrodynamic wash. Additionally, network analysis showed that hydrodynamic wash greatly altered the species-species interactions, and the ecological roles of individual OTUs and key microbial populations. Overall, the results obtained in this study highlight the importance of hydrodynamic wash in determining the bacterial activity, community structure and species interactions of anammox process.