Initial nitrite concentration promote nitrite-oxidizing bacteria activity recovery from transient anoxia: Experimental and modeling investigations

Transient anoxia due to the periodic anoxic/aerobic operation is beneficial for the nitrite-oxidizing bacteria (NOB) suppression. A continuous reactor of modified University of Cape Town process treating municipal wastewater was equipped with alternating anoxic/aerobic zones to maintain nitritation. Higher nitrite accumulation ratio in the oxic zones was achieved through transient anoxia and shorter aerobic actual hydraulic retention time (15 min), but it steeply deteriorated from above 95.0% to 21.0% after elevated temperature (25 degrees C). Batch experiments indicated that the existence of initial nitrite at the starting of aerobic phase promoted the recovery of NOB activity from transient anoxia and inhibited the activity of ammonium-oxidizing bacteria. Furthermore, a supplemental modeling further confirmed that the specific growth rates of NOB (mu(NOB)) decreased at the anoxic phase and the recovery extent of mu(NOB) after anoxic exposure have a positive correlation with the initial concentrations of nitrite, leading to the failure of maintaining nitritation.