Optimization of nitrogen removal performance of partial nitrification AO process based on PVA-SA immobilized particles

Partial nitrification activated sludge immobilized with polyvinyl alcohol-sodium alginate (Polyving Akohol-Sodium Alginate, PVA-SA) was used to treat domestic wastewater and achieve stable partial nitrification in a continuous flow AO (Anaerobic/Oxic) reactor. Using the response surface method, the effects of hydraulic retention time (HRT), internal recirculation ratio and filling rate on nitrite accumulation ratio (NAR) and total nitrogen removal nitrogen removal efficiency (NRE) were investigated, and a quadratic regression model was successfully established. The results showed that the system had the best performance in nitrogen removal with NAR and NRE reaching 86.22% and 86.56% when HRT, internal recirculation ratio and filling rate of aerobic section were controlled as 6.43h, 2.93, and 25%, respectively. In addition, it was observed by live and dead bacteria and Fluorescence In Situ Hybridization (FISH) that the live cells were mainly distributed in the range of 0~500µm on the surface of the particles, while the dead bacteria were distributed in the range of 0~300µm. FISH fluorescence was gradually decreased in intensity with the increase of depth. Finally, 16S rRNA sequencing results showed that the relative abundance of Nitrosomonas increased from 0.013% to 5.02% and Nitrospira increased from 0.055% to 1.99% in the immobilized particles of the long-term run compared with that of the partial nitrification activated sludge. The proportion of NOB in the nitrifying bacteria was reduced, while the proportion of AOB was increased, which contributed to the stabilization of nitrogen removal effect of partial nitrification. This study provides a promising technology for the engineering application of partial nitrification in municipal wastewater plants. © 2024 Chinese Society for Environmental Sciences. All rights reserved.