Effect of Different Ratios of Anaerobic Time and Aeration Time on the Operation of a Continuous-Flow Reactor with Partial Nitrification Granules

Abstract

A continuous flow reactor was inoculated at 25-28℃ with mature partial nitrification granular sludge. In order to avoid the granular sludge being crushed because of the sludge backflow through the peristaltic pump, a built-in sedimentation zone was used for internal backflow. The experiment investigated the influence of the different anaerobic time to aeration time ratio (1:1, 2:1, and 1:2) on the stability of a continuous-flow partial nitrification granular sludge system. The results showed that when the controlled anaerobic time to aeration time ratio was 1:1 and 2:1, the partial nitrification performance was good and the nitrite accumulation rates were 85.2% and 94.5%, respectively. When the controlled anaerobic time to aeration time ratio was 1:2, the partial nitrification performance gradually deteriorated, and the ammonia nitrogen removal rate and nitrite accumulation rate at the end of the stage decreased to 64.1% and 58.7%, respectively. Batch test results showed that intermittent aeration and continuous aeration can better inhibit the relative activity of NOB in the partial nitrification system to a certain extent. The longer the anaerobic time, the better the NOB activity inhibition. However, too long an anaerobic time will also lead to ammonia nitrogen removal rate. In the process of partial nitrification, the long-term stable operation of continuous flow partial nitrification process can be realized by 1:1 and coordinated control of other control conditions. An analysis of sludge performance indicated that in the anaerobic time to aeration time ratio range of 1:1-1:2, the longer the anaerobic time, the more stable the granular sludge structure. The shorter the anaerobic time, the smaller the selection pressure in the reactor, resulting in poor sludge sedimentation performance and partial disintegration of partial nitrification granular sludge. An EPS chemical analysis and a three-dimensional fluorescence spectroscopic analysis showed that the PN content was higher and the PN/PS value was higher when the anaerobic time and aeration time ratio was 2:1.