6 samples were collected from an anoxic chamber in the ADNMED (Anaerobic Digestion, Nitrification and Mixotrophic Endogenous Denitrification) system.

Anaerobic processes are a cost-effective alternative for sewage treatment. However, the effluent from anaerobic systems usually lacks organic compounds for denitrification, hindering nitrogen removal. The ADNMED (Anaerobic Digestion, Nitrification and Mixotrophic Endogenous Denitrification) system comprises a triple chamber configuration that was shown to provide high quality effluent regarding carbon, nitrogen and sulfide. This study presents an optimization of the ADNMED system treating domestic wastewater. Hydraulic retention time (HRT) was reduced to 7 h in the anaerobic chamber, 7 h in the anoxic and 5 h in the aerobic chambers (stage A). To improve the nitrogen removal efficiency (47 ± 19%), sewage was directly added to the anoxic chamber to provide extra organic electron donors for denitrification (stage B). The addition of sewage at a flow rate equivalent to 10% of the feed flow increased nitrogen removal efficiency to 61 ± 12%. Illumina® sequencing revealed a restructuring of the microbial community in the anoxic chamber, according to the availability of the endogenous electron donors for denitrification. At stage A, denitrification was mainly coupled to degradation of recalcitrant compounds, while the addition of sewage in the anoxic chamber during stage B stimulated the establishment of fermentative bacteria. Therefore, ADNMED system was capable of adapting to a wide-range of operational conditions, with no harm to the final effluent quality. These results support the ADNMED system as a robust and low-cost alternative for treating domestic sewage.