The ammonium oxidation by potential electron acceptors(NO2-, Fe3+ and SO42-) in ANAMMOX sludge was studied by inoculating nitrite-dependent ANAMMOX sludge. The results showed that nitrite was the most suitable electron acceptor for ANAMMOX bacteria, which could completely react within a short time. Nitrate was converted into nitrite by ANAMMOX sludge using the organic as electron donor and then participated in ammonia conversion, in the absence of nitrite. Fe3+ and SO42- conversion occurred at the end of ammonium oxidation, but its direct or indirect participation requires further study. Microbial activity must be activated through addition of nitrite as electron acceptor before ammonia excess oxidation occurred. Aerobic ammonia oxidizing bacteria and nitrite oxidizing bacteria grew during this period. This phenomenon did not last, and the microbial production of H2O2 was speculated. Although the oxidation rate was slow, the phenomenon of ammonium excess oxidation was obvious. Therefore, the oxidation of excess ammonia was for sure present in ANAMMOX sludge. The order of electron acceptor use by ANAMMOX sludge was NO2-, NO3-, SO42- and Fe3+.
Keywords: ANAMMOX; ammonia oxidation; electron acceptor; nitrate; nitrite.