The optimization of conditions for the start-up of anammox bacteria seeded with non-specific biomass

Abstract

Start-up of anammox bacteria mediated nitrogen removal from synthetic and reject water sources was investigated using a sequential batch reactor (SBR) inoculated with non-specific seed sludge (aerobic and anaerobic sludge types). The effect of anammox reaction intermediate hydrazine was also tested. A simplified SBR setup was implemented controlling pH and temperature at 7.5 – 8.3 and 30 ± 0.5 °C respectively. This condition was stabilized and adapted to favour the cultivation of anammox bacteria from scratch. The system was started with an initial ammonium concentration from inoculum sludge and was supplemented with synthetic and reject water at 10 mg L-1 to 110 mg L-1 with a hydraulic retention time (HRT) of 2 – 3 days during the entire period of start-up. The use synthetic ammonium and nitrite as nitrogen source as well as reject water created three distinct period of salinity: low, high and optimum salinity period. Reject water gave the optimum salinity period of less than 0.5 g L-1 with significantly higher nitrogen removal rate observed. Nitrogen removal efficiency of 87 % was achieved. Spiking with different concentration of hydrazine was carried out. 5 mg N2H4 L-1 indicated optimum concentration that enhanced anammox activity during batch testing, achieving specific nitrogen removal rate of 0.72 mg N/ g MLSS/d. Addition of trace hydrazine for short-term was able to enhance nitrogen removal rate (NRR) and nitrogen loading rate (NLR) by approximate 100 % after inhibition by high C/N ratio. Nitrogen loading rate increased during the entire start-up period of 193 days from 0.08 kg N m-3L-1 to 0.1 kg N m-3L-1. Specific nitrogen (NH4+ + NO2-) removal rate of 0.127 g N L-1 d-1 was achieved. The start-up of anammox bacteria in suspended granular biomass was successful after 65 days of operation, with hydrazine significantly accelerating anammox activity.