Single-stage partial nitrification/anammox process performance restoration by bio-augmenting nitrifiers with or without nitrite oxidizing bacteria suppression

Abstract

The use of low dissolved oxygen (DO) is common to suppress the growth of nitrite oxidizing bacteria (NOB) in the partial nitrification/anammox (PN/A) process. However, this approach can negatively impact the activity of ammonium oxidizing bacteria (AOB) and reduce the oxygen consumption rate, disrupting the essential low DO environment required for anammox bacteria (AMX) and leading to a decline in PN/A performance. We innovatively harnessed the strategy of common nitrifiers (AOB + NOB) bioaugmentation in an impaired single-stage PN/A reactor after operation for a period of time. The results demonstrated an immediate improvement, with the total nitrogen removal efficiency increasing from approximately 60 % to 80 %. This enhancement was attributed to decreased NOB activity and increased AMX activity, which occurred at reduced DO level (0.24 to 0.12 mg O2/L) following nitrifiers bioaugmentation. Partial nitrification (PN) and PN/A batch experiments with nitrifiers bioaugmentation further supported these findings. This strategy pioneered a fresh perspective that the diversion of nitrite from NOB to AMX was the pivotal underlying mechanism. Mathematical simulations complemented these results by demonstrating that nitrifiers bioaugmentation broadened the optimal oxygen supply window.