Performance and microbial community of anammox in presence of micro-molecule carbon source

Because ammonium (NH4+-N) coexists with organic matter in some wastewaters, the possible adverse influences of organic matter become a major concern in the applications of anaerobic ammonium oxidation (anammox). In this study, the effects of acetate, as a representative of micro-molecule organic matter, on anammox were investigated. Efficient nitrogen removal was realized because denitrifying bacteria and anammox bacteria (AnAOB) had a better synergistic effect under the condition of chemical oxygen demand (COD) concentrations lower than 251 ± 7 mg L−1. Furthermore, the nitrogen removal efficiency (NRE) decreased to 82.02 ± 3.14% when COD was increased to 730 ± 9 mg L−1, and effluent free ammonia (FA) reached 21.93 ± 4.71 mg L−1 might be one of factors leading to inhibition. However, the nitrogen-removal contribution rate of anammox remained steady at 61.97 ± 2.84% at COD of 730 ± 9 mg L−1, which indicated that anammox was still dominant in the system. AnAOB, such as Ca. Kuenenia and Ca. Jettenia, and denitrifying bacteria, such as Denitratisoma and Thauera, were found to coexist in the reactor. Interestingly, Ca. Kuenenia presented in the trend of first decreased then increased with the increasing of organic matter concentration, which might be one of reasons that anammox played an important role in nitrogen removal at high COD concentration. •Effects of acetate on N and COD removal in an anammox reactor were studied.•Nitrogen removal performance was promoted at low COD concentration (≤251 ± 7 mg L−1).•Ca. Kuenenia first decreased then increased with increasing COD in the system.•Anammox and heterotrophic denitrification could coexist at COD of 730 ± 9 mg L−1.