Influence of critical factors on nitrogen removal contribution by anammox and denitrification in an anammox-inoculated wastewater treatment system

Suitable environmental conditions facilitate the nitrogen removal in the wastewater treatment system. However, it remains unknown about how critical environmental factors regulating the activity of denitrification and anammox in the anammox-inoculated wastewater treatment system. In this study, the effect of temperature, pH, dissolved oxygen, organic matter, and substrates on denitrification and anammox activity was investigated with the nitrogen isotope pairing method. Results showed that the increase of temperature promoted the activities of both denitrification and anammox, and the activity of anammox was higher than that of denitrification at 25 degrees C-30 degrees C. Denitrification was more sensitive to acidic and alkaline pH values with the highest activity observed at neutral pH, but anammox has a more robust adaptability and the reaction rate remained relatively higher over a wider pH range. Moreover, anammox showed a stronger tolerance than denitrification to higher dissolved oxygen (DO) concentration. In addition, organic matter promoted the activity of denitrification significantly, while the anammox activity was inhibited by glucose, but enhanced by acetate, sodium formate and pyruvate. The denitrification and anammox reaction rates responding to nitrate were fitted well to Michaelis-Menten kinetics, but showing a linear relationship with nitrite. The results presented here offered useful information on how to regulate the environmental factors to improve the nitrogen removal efficiency from wastewater by facilitating the collaboration between denitrification and anammox.