The effects of different temperature conditions on sludge characteristics and microbial communities of nitritation denitrification

The effects of different temperature conditions on nitritation denitrification are still unclear. In this study, two sequencing batch reactors (SBR) were used to explore the effects of stepwise cooling (28.2, 24.5, 20.6, 17.0 degrees C) and continuous low temperature (17.0 degrees C) on partial nitrification denitrification (PND). The PND performance, sludge characteristics, and microbial communities were evaluated. The results showed that PND completed start-up faster and achieved >80 % nitrite accumulation under stepwise cooling conditions, while a longer acclimation period was required under continuous low temperature conditions. Higher dissolved oxygen limits should be used for real-time control at low temperatures to achieve complete ammonia removal. Fitting using Arrhenius equation, it was found that PND was not significantly affected by temperature at 17-28 degrees C. However, the denitrification activity was significantly inhibited by temperatures below 17 degrees C. Bacteroidota phylum proliferated at low temperatures, while DGAOs proliferated only under stepwise cooling conditions, and they may contribute to efficient denitrification. Sludge bulking under sustained low temperature conditions eased with increasing PND activity, suggesting that sludge settling performance needs attention when activity is low.

Automated summary

This study investigated the effects of different temperature conditions on nitritation denitrification. The results showed that stepwise cooling facilitated a faster start-up of the process and achieved higher nitrite accumulation compared to continuous low temperature conditions. Additionally, lower temperatures significantly inhibited denitrification activity.