Influencing factors on the activity of an enriched Nitrospira culture with granular morphology

Nitrospira is a common genus of nitrite oxidizing bacteria found in wastewater treatment plants. To identify the key factors influencing the composition of NOB communities, we conducted research using both sequencing batch reactor and continuous flow reactor under different conditions. The results showed that dissolved oxygen and nitrite concentrations may be key factors in the selective enrichment of Nitrospira. High throughput 16S rRNA gene sequencing revealed that Nitrospira was the dominant NOB under low DO and low nitrite concentrations, while Nitrobacter was the dominant NOB under high DO and high nitrite concentrations. We also cultivated flocculent and granule sludge with Nitrospira as the dominant genus. Compared to Nitrospira flocculent sludge, Nitrospira granule sludge had higher inhibition threshold concentrations for free ammonia and free nitrous acid. Nitrospira granular sludge was more likely to resist adverse environmental disturbances. Furthermore, the effects of environmental factors such as temperature, pH, and DO on the activity of Nitrospira granular sludge were also studied. The results indicated that the optimum temperature and pH for Nitrospira granular sludge were 36 and 7.0, respectively. Additionally, Nitrospira granular sludge showed a higher dissolved oxygen half-saturation constant about 3.67 mg/L due to its morphological characteristics. However, the majority of actual wastewater treatment conditions do not meet the optimal conditions for the Nitrospira granular sludge obtained in this study. Thus, it can be speculated that future development of aerobic partial nitrification granular sludge may automatically eliminate the influence of Nitrospira. This study provides a theoretical basis for a deeper understanding of Nitrospira and the development of future water treatment processes.