Comammoxand Unknown Candidate AOB Contribute to Nitrite Accumulation in an Integrated A-B stage process that Incorporates Side-stream EBPR (S2EBPR)

Abstract

In a pilot-scale A-B process integrated with side-stream enhanced biological phosphorus removal (EBPR) for treating municipal wastewater, an average of 7.62 ± 2.17 mg-N/L nitrite accumulation with nitrite accumulation ratio of 49% was achieved by partial nitrification, which was verified through relative higher ammonia oxidation activity (1.94 ± 0.89 mgN/gSS/h) than nitrite oxidation rate (1.06 ± 0.99 mgN/gSS/h). Nitrospira dominated the ammonia oxidizing community in a B-stage nitrification tank throughout the operation periods with one to two orders of magnitude higher than canonical aerobic oxidizing bacteria (AOB). The higher ammonia oxidation activity along with increased amoB/nxr ratio in nitrite accumulation period suggested the contribution of comammox Nitrospira as AOB. Phylogenetic investigation suggested that AMO and HAO were embedded in heterotrophic organisms that belong to the family Comamonadacea and the order Rhodocyclaceae. These organisms may function as heterotrophic nitrification. The integration of S2EBPR provides PAOs suitable environment, such as low ORP and favorable VFA concentrations and composition, but also exerts additional selective pressure on NOB activity than AOB, which may be beneficial for main-stream partial nitrification.