Post-treatment of anaerobic digester effluents by simultaneous partial Nitritation, Anammox and Denitrification process

A simultaneous partial nitrification, anammox and denitrification (SNAD) process was developed for the treatment of anaerobic digestion effluents. Seed consortium developed from a full scale running SNAD system was applied in the treatment of effluents in an oxygen limited lab scale SNAD-SBR type (8L) reactor run at moderate temperature (25°C). High total ammonium (96%), total nitrogen (88%) and organic matter (58%) removal efficiencies were obtained with ammonia loading rate 0.15 kgTAN /m3/d in the presence of about 400 mg TAN/L and a C/N of 0.5 at 2.5 - 3 days hydraulic retention time. This study showed that, under steady-state conditions, nitritation, anammox, denitrification and nitratation processes co-existed in the SBR, synchronizing each other and establishing a relation, which depended on the operative reactor conditions. At 25°C, both oxygen limiting conditions (DO < 0.3 mgO2/L) and high free ammonia concentrations (3.5 – 10 mg FA/ L) are required in order to properly inhibit NOBs. An influent C/N lower than 2 is required in order to avoid a proliferation of denitrifiers over anammox bacteria. The change of the influent characteristics and the shock in the operating DO, nitrogen loading rate of the SNAD system greatly affected the relation of these processes. However, the system was always able to recover its efficiency after 3- 4 time the HRT.