Impact of the nitrifying community dynamics on the partial nitritation process performed by an AOB-enriched culture in a granular sludge airlift reactor

Altres ajuts: Clara Reino acknowledges the Xunta de Galicia (Spain) and the CRETUS Institute of Santiago de Compostela for her postdoctoral fellowship (ED481B-2019-008)One of the main challenges for the full-scale implementation of the autotrophic biological nitrogen removal process is to achieve a stable long-term partial nitritation under the mainstream conditions of urban wastewater treatment plants. Here, the performance of partial nitritation process under mainstream conditions was investigated based on the change of the nitrifying community developed. A lab-scale airlift reactor was operated for 430 days with a granular sludge highly enriched in ammonia oxidizing bacteria (AOB) performing partial nitritation treating a mainstream-mimicked synthetic influent. The changes in solid retention time (SRT), dissolved oxygen (DO) concentration and temperature strongly affected to the microbial community developed, especially to the dynamics of the nitrite oxidizing bacteria (NOB) population, which triggered to instabilities in the partial nitritation process. The extremely high values of SRT applied (SRT = ∞) and long-term exposure to low temperature (10 °C) promoted the growth of NOB Nitrotoga genus and development of nitratation activity; and the subsequent variability in temperature (between 10 and 30 °C) and in DO concentration (between 0.4 ± 0.1 and 1.4 ± 0.3 mg O2 L−1) influenced the competitiveness between nitrifiers and the growth of species previously undetected in the culture, as Nitrospira genus. Anaerobic ammonia oxidizing bacteria were also identified during cultivation and assisted to the repression of the NOB activity at 25-15 °C. The results of the present study uphold that understanding the niche differentiation and competitiveness of NOB will be key to develop strategies for NOB repression in order to make possible full-scale implementation of partial nitritation process at mainstream conditions