Metagenomics Approach and Canonical Correspondence Analysis of Novel Nitrifiers and ammonia-oxidizing Archaea in full-scale A2/O and oxidation ditch processes

Various microorganisms are involved in nitrogen removal in various activated sludge processes, and their group compositions depend closely on the operating parameters. Operating data on nitrogen removal efficiency and microbial groups were collected according to the operating parameters in the A2/O and oxidation ditch (OD) processes. The structure and function of microorganisms involved in nitrification were analyzed in the two typical biological nitrogen removal processes. Regardless of the season, ammonia-oxidizing bacteria (AOB, Nitrosomonadales) and ammonia-oxidizing archea (AOA, Thaumarchaeota, Crenarchaeota) were present at a higher ratio in the OD process comparing to the A2/O process and microorganisms involved in the comammox reaction (Nitrospira inopinata) were only found in the OD process. Abundance of diverse slow growing nitrifiers were observed in the OD process with a long hydraulic retention time (HRT) and a long solid retention time (SRT). The canonical correspondence analysis (CCA) of various environmental variables, samples, and taxonomic groups showed that Nitrosomonadales (AOB group), Crenarchaeota (AOA group), and Nitrospira inopinata (comammox group) were highly correlated with NH4+-N removal and Nitrospira was more involved in nitrite oxidation than Nitrobacter. Thaumarchaeota having amoA enzyme showed a weak correlation with nitrification. As a result of microbial community analysis on A2/O and OD, it was found that various microorganism groups involved in nitrification were found more in OD than A2/O, and thus it is possible to obtain stable treatment efficiency in OD.