[Effect of Fe2+ and Fe3+ on the activity of ANAMMOX]

The effect of the change in concentration and valence of iron ion on the ANAMMOX sludge activity was studied by inoculating ANAMMOX sludge. The concentration experimental results showed that the ANAMMOX sludge activity was stimulated and gradually increased when the influent iron ion concentration increased from 0 to 5 mg x L(-1). Iron hydroxide precipitate was formed with the pH value increased due to the alkalinity of the ANAMMOX product when the influent iron ion concentration was higher than 5 mg x L(-1), while the biological activity was not inhibited. There was no significant difference in the effects of the concentration change of iron ions with different valence effects on the ANAMMOX sludge activity. The long-term experimental results showed that the nitrogen removal rate (as N) of anammox reactor R1 was increased from 0.28 kg x (m3 x d)(-1) to 0.65 kg x (m3 x d)(-1) with Fe2+ in influent, which was 1.28 times as high as that in the ANAMMOX reactor R2 containing Fe3+ in influent, after 71 cycles of cultivation. Therefore, Fe2+ could better meet the growth needs of ANAMMOX bacteria. The results also showed that Fe3+ easily led to the excessive conversion of ammonia in the ANAMMOX reactor. The conversion ratio between nitrate and ammonia was 1.17 in reactor R2, which was significantly lower than that in the reactor R1, with a conversion ratio between nitrate and ammonia of 1.24.