Several key factors influencing nitrogen removal performance of anammox process in a bio-filter at ambient temperature

Anaerobic ammonium oxidation (Anammox) was a recent discovery of new energy-efficient, microbiologically mediated nitrogen removal process, which was mainly used for the treatment of rich ammonium wastewater of low C/N ratio in a high operating temperature of 35–40 °C. But the growth rate of anammox bacteria was extremely low and it was easily inhibited by many factors, which becomes a bottleneck problem in the application of this efficient nitrogen removal process in the actual wastewater treatment at ambient temperature. So, influence of several key factors (i.e., COD, methanol, hydrazine, hydroxylamine, pH, nitrate, and phosphate) on the nitrogen removal performance of the anammox process was researched to optimize the operation of the anammox process in a bio-filter, and the total nitrogen removal rate (R _TN) and the linear correlation coefficient between the total nitrogen removal rate (R _TN) and influent total nitrogen load (L _TN) of it were assessed with the real municipal wastewater at ambient temperature. The results demonstrated that (1) the influent of COD <100 mg/L had no visible inhibition on the anammox process in the bio-filter, and the recommendation of COD <80 mg/L was suitable for the operation; (2) short-term shock load of methanol would give significant inhibition on the anammox bacteria, which could be restored by adding a small amount of hydrazine and hydroxylamine, but the recovery process was extremely slow; (3) when the influent total nitrogen load increased suddenly, and the removal capacity of the bio-filter was not enough, the temporary mixed dosing of hydroxylamine and hydrazine could enhance the nitrogen removal performance; (4) the anammox activity was very sensitive to the influent pH, and the best range of pH values was 7.3–7.6; (5) the nitrate of 23.56–463.14 mg N/L had no obvious effect on the nitrogen removal performance; and (6) the phosphate itself had no significant inhibition on the anammox bacteria physiologically and ecologically, but it could form a great deal of deposits, which would lead to the bio-filter plugging.