[Rapid Start-up of One-stage Autotrophic Nitrogen Removal Process in EGSB Reactor for Wastewater with Low Concentration of Ammonia].

Biofilm coming from a reactor in which One-stage Autotrophic Nitrogen Removal Process exists was selected as inoculum in an expanded granular sludge bed reactor. A potential fast start-up procedure was tested in this research. Wastewater with low ammonium concentration between 60-100 mg·L was applied. The results showed that a One-stage Autotrophic Nitrogen Removal Process was successfully established in 83 days under the following conditions: temperature at (30±2)℃ , pH at 7.8-8.2, dissolved oxygen (DO) at 0.2-1.1mg·L and upflow velocity at 2.0-4.0m·h. After the 83-day operation, the removal efficiencies of NH-N and TN were 99.4% and 80.7%, respectively. By controlling the reflux ratio and increasing the NH-N load, the reactor could maintain a stable state of low DO concentration. Nitrification and anaerobic ammonium oxidation became main reactions that maintained efficient and stable nitrogen removal performance. In addition, nitrite-oxidizing bacteria (NOB) were inhibited. In the start-up process, the average particle diameter of granular sludge increased from 174 to 296 μm. Moreover, scanning electron microscopy showed that the surface of granular sludge was smooth, and most microorganisms were bevibacteria and cocci. Finally, a fluorescence in situ hybridization experiment showed that ammonium oxidation bacteria and anaerobic ammonium oxidation bacteria were distributed on the surface and in the inner space of granular sludge, respectively. The research indicated that a stable autotrophic nitrogen removal granular sludge system was quickly established in the sludge bed.