Key Operating Parameters Affecting Partial Nitritation Efficiency in the Nitritation Reactor Packed with PVA/Alginate Carrier

Abstract

Objectives:The purpose of this study was to investigate key operating parameters for partial nitritation in the nitritation reactor packed with PVA (polyvinyl alcohol)/alginate carrier.Methods:Partial nitritation was conducted in a 2 L reactor packed with PVA/alginate carrier of 30%. Dissolved oxygen (DO) concentration was considered as the main operating parameters. Raw reject water was used as the influent, and the ammonium concentration of the influent was adjusted with dilution at the beginning of operation. The DO concentration in the reactor was maintained at 3~4 mg O<sub>2</sub>/L. The activity test of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) was conducted periodically. The effect of the operating parameters applied in this study was verified through analysis of microbial community.Results and Discussion:The stable performance for partial nitritation was achieved at operation time of 17 days. Thereafter, the reject water containing 683.6±73.5 mg NH4<sup>+</sup>-N/L was introduced without dilution. Although the DO concentration was maintained at 3~4 mg O<sub>2</sub>/L, stable partial nitritation was achieved for a long time, resulting in effluent NO<sub>2</sub>-N/NH<sub>4</sub><sup>+</sup>-N of 0.94±0.07 and maximum nitrite production rate of 2.24 kgN/m<sup>3</sup>/d. This was confirmed to be due to DO diffusion limitation inside PVA/alginate carrier, whereby the NOB activity could be effectively inhibited. Microbial community analysis also showed that NOB fraction inside the carrier was reduced to 0.09%. It indicated that partial nitritation using the PVA/alginate carrier was effective for selective inhibition of the NOB.Conclusions:In the case of using the whole cell entrapment technique, effective inhibition of NOB was possible by keeping the DO concentration inside the carrier low despite the fluctuation of DO in the reactor. The results of these findings may help improve the stability of the process in the field.