Nitrogen Removal and Performance Deterioration in Digested Effluent Treatment by Partial Nitrification-Anammox (Pna) Process Based on Aeration Sedimentation Integrated Microaerobic Reactor (Asimr)

Abstract

In order to study the adaptability of aeration sedimentation integrated microaerobic reactor (ASIMR) to partial nitrification-anammox (PN/A) process, the reactor was inoculated with nitrified sludge and anammox sludge, and the nitrogen load of the influent was increased by gradually shortening the hydraulic retention time (HRT) to study the nitrogen removal performance of ASIMR treated digested effluent under different HRT conditions. When the HRT was 4.45 hours and the influent nitrogen load rate (NLR) was 3.98 kg·(m3·d)-1, ASIMR achieved the highest nitrogen removal performance, with the ammonia nitrogen removal rate (ARE) and total nitrogen removal rate (NRE) of 90.5% and 79.2%, and the total nitrogen removal rate (NRR) could reach 3.15 kg·(m3·d)-1. When HRT decreased to 3.60 hours with a NLR of 4.76 kg·(m3·d)-1, the nitrogen removal performance of ASIMR began to deteriorate, with ARE and NRE decreasing to 35.9% and 12.4%, and NRR decreasing to 0.59 kg·(m3·d)-1. The main reasons for the decrease in nitrogen removal performance were as follows: 1) high hydraulic load in the sedimentation zone led to the loss of nitrifying sludge, which in turn reduced the efficiency of ammonia nitrogen removal. The accumulation of free ammonia (FA) inhibited the activity of nitrogen removal functional bacteria, resulting in a decrease in nitrogen removal performance; and 2) the lack of Fe in influent water prevented anaerobic ammonia oxidizing bacteria (AnAOB) from synthesizing sufficient heme C, affecting the expression of nitrogen removal related genes, leading to the inhibition of AnAOB activity. Overall, ASIMR which did not need sludge reflux and can achieve excellent nitrogen removal at HRT greater than 4.45 hours, is suitable for the application of PN/A process in actual wastewater treatment projects.

Keywords: Swine wastewater, Microaerobic reactor, Partial nitrification-anammox (PN/A) process, nitrogen removal