Study on the effect of external hydrazine addition on Anammox bacteria during the starvation period

Abstract

As widely known, Anammox bacteria can easily undergo starvation due to fluctuation of feed in wastewater treatment plants which mostly were compromised due to the nature of the wastewater composition. Thus, three different types of starvation were studied namely, starvation with ammonium (Ra), with nitrite (Rn), and with hydrazine (Rh). The biomass for starvation test was obtained from an enriched Anammox reactor that has been stably running for 2 years where approximately 94% of nitrogen removal efficiency (NRE) was achieved before starvation. The amount of ammonium, nitrite and hydrazine added into the starvation reactors were 50 mg/l, 50 mg/L and 10 mg/L, respectively. Anammox bacteria in Rh showed better results during starvation compared to the other two. First of all, for decay rate after 15 days, the values obtained for Ra, Rn, and Rh were 0.032/day, 0.042/day and 0.019/day, respectively. In addition, the amount of Heme C extracted showed similar pattern when compared to the results of decay rate. The Heme C values obtained for Ra, Rn, and Rh after 15 days of starvation were 0.32 μg/L, 0.25 μg/L and 0.45 μg/L, respectively. This indicated that, availability of hydrazine helps to reduce the mortality rate of Anammox bacteria. To further enhance the finding, the amount of extra polymeric substances (EPS) available in the reactor during starvation was also studied. The PN/PS ratio obtained for Rn, Ra and Rh after 15 days were 7.35, 4.73 and 4.21, respectively. These values are higher compared to normal conditions which are around 0.8 1. This is because; none of the reactors could produce carbohydrates due to starvation process. PN/PS ratio results also show that addition of hydrazine helps reduce the adverse effects of starvation towards Anammox bacteria. Thus, addition of hydrazine reduces the adverse effects of starvation that Anammox bacteria are susceptible to.