Start-up of the nitrogen removal process in an anaerobic up-flow reactor inoculated with aeration tank sludge

Anaerobic ammonium oxidation (anammox) has been considered a promisingly alternative to traditional nitrification/denitrification to remove nitrogen in an autotrophic process, without using an external carbon source, requiring low energy consumption and sludge production. The start-up of the anammox process in a stirred anaerobic up-flow reactor was seeded with aeration tank sludge, and fed with medium containing ammonium and nitrite at the ratio1:1. The reactor was running for 369 days, with an initial instability period of 117 days, when nitrite was removed, and nitrate accumulated. Further on, the reactor was not fed with nitrite, and nitrate decrease in the effluent. Afterwards, a transition period (140 days) was followed by a stable one (112 days). The average ammonium removal was 48.0% in the transition stage, to decrease to 33,6% in the stable period. No nitrite was noticed in the effluent. The presence of anammox community in the reactor related to Candidatus Brocadia fulgida was detected. These results have been combined with molecular techniques to evaluate shifts on microbial community structure and composition within the reactor. Acknowledgments: Project UNNOWN (PTDC/BTA-BTA/31098/2017), co-financed by COMPETE 2020, Portugal 2020 and the European Union through the ERDF, and by FCT through national funds.