The co-existence of anammox genera in an expanded granular sludge bed reactor with biomass carriers for nitrogen removal.

Anaerobic ammonium oxidation (anammox)-based nitrogen removal saves aeration energy and organic carbon costs, attributed to its anaerobic and autotrophic nature. However, due to the slow growth of anaerobic ammonium oxidation bacteria (AnAOB), drawbacks including long startup time and sensitivity to toxins still hamper the application of anammox-based processes. To cope with the slow growth of AnAOB, various bioreactor configurations have been investigated for the capability of retaining anammox biomass, among which, the expanded granular sludge bed (EGSB) reactor is a promising option. In this study, two laboratory-scale EGSB reactors were used to gain insights of microbial population and their response to amending biofilm-carriers, aiming to enhance the biomass retention of AnAOB. The respective ammonium and nitrite removal efficiencies were up to over 90%, and the overall nitrogen removal efficiency (NRE) was stable at over 70%, in the EGSB reactor amended with carriers (CEGSB). Compared to the control EGSB, CEGSB's observed performance was more stable during the 236-day operational period. The abundance of AnAOB reached 22% in the EGSB and 49% in the CEGSB. It was also observed that Ca. Brocadia (14.25%) and Asahi BRW2 (33.19%) coexisted in the CEGSB. The dynamics of major metabolisms and functional genes involved in nitrogen conversion were further observed by FAPROTAX based on the taxonomic data, providing more insights into the functions of the microbial communities.