Research on Partial Nitritation and Anaerobic Ammonium Oxidation Process

*Wenqiang Wang, Dong Li, Shuai Li, Huiping Zeng and Jie Zhang*

## **Abstract**

In recent years, the partial nitritation and anaerobic ammonium oxidation (PN/A) process has been widely appreciated by many countries around the world. As an autotrophic nitrogen removal process, this process can save more than 60% of the aeration energy consumption, reduce 80% of the residual sludge yield, and do not need to add additional carbon sources. However, this process is faced with several kinds of problems. This paper summarizes several effects of operating parameters on the inhibition of NOB in municipal wastewater treatment, implications of the reactor configuration and operation, and fixed film processes vs. suspended growth systems. The fixed film processes based on Anammox granular sludge and AOB flocculent sludge are alternative. Finally, a new strategy of continuous flow PN/A process with partial nitrification flocculent sludge and Anammox granular sludge was proposed.

**Keywords:** Anammox, wastewater treatment, PN/A, granular sludge, mixed reactor

## **1. Introduction**

Anaerobic ammonia oxidation (Anammox) bacteria play a key role in the Earth's nitrogen cycle [1]. Compared with Anammox, the traditional biological denitrification technology widely used today has some shortcomings, such as high energy consumption, the need for additional organic carbon sources, and the inability to control the production of greenhouse gases [2]. Therefore, compared with the traditional nitrification and denitrification systems, Anammox technology has the advantages of no aeration, extra organic carbon source, and low surplus sludge yield, making Anammox a research hotspot for environmental protection. In the application of actual municipal wastewater [3], it is found that the lack of nitrite electron acceptor in actual wastewater is the main bottleneck of the application of Anammox in mainstream wastewater treatment. In addition to the artificial addition of nitrite, most of the current Anammox coupling processes focus on partial nitritation and anaerobic ammonium oxidation (PN/A) [4]. In practical application, partial nitritation (NH4 + -N → NO2 − -N) can provide NO2 − -N for Anammox, thus forming a PN/A

process. First, about 55% of the ammonia nitrogen in the wastewater is oxidized to nitrite under the action of ammonia oxidizing bacteria (AOB), and then the generated nitrite and the remaining ammonia nitrogen generate nitrogen under the action of anaerobic ammonia oxidation bacteria (AnAOB), to achieve the removal of TN. The total reaction equation [5] is:

$$\mathrm{NH\_4^+} + \mathrm{0.85O\_2} \rightarrow \mathrm{0.11NO\_3^-} + \mathrm{0.44N\_2} + \mathrm{0.14H^+} + \mathrm{1.43H\_2O} \tag{1}$$

In recent years, PN/A process has been widely appreciated by many countries around the world. As an autotrophic nitrogen removal process, this process can save more than 60% of the aeration energy consumption, reduce 80% of the residual sludge yield, and does not need to add additional carbon sources [6, 7]. However, this process is faced with the problems of long age and insufficient retention capacity of AnAOB sludge, competition of AOB from NOB, and high C/N ratio leading to massive reproduction of HB in sludge.

This paper summarizes several effects of operating parameters on the inhibition of NOB in municipal wastewater treatment, implications of the reactor configuration and operation, and fixed film processes vs. suspended growth systems. Finally, a new strategy of continuous flow PN/A process with partial nitrification flocculent sludge and Anammox granular sludge was proposed.
