Stable partial nitrification of domestic sewage achieved through activated sludge on exposure to nitrite.

Partial nitrification is crucial for application of autotrophic nitrogen removal which is beneficial for treating carbon-limited wastewater. This study presents an alternative strategy for achieving partial nitrification of domestic wastewater treatment, by treating activated sludge of a nitrifying reactor on long-term nitrite exposure. Initially, the nitrifying reactor obtained complete nitrification. After the sludge of the reactor was treated with nitrite at concentration of 5-30 mg·L without feeding for 32 days, the nitrite accumulation ratio (NAR) above 90% was achieved in 30 days, and then the NAR stabled at 97.9% under low temperature of 16.6 °C. Further analysis showed that the activity decay rate of ammonium-oxidizing bacteria (AOB) (0.020 d) was lower than that of nitrite-oxidizing bacteria (NOB) (0.035 d) under nitrite stress. Meanwhile, the NOB were effectively suppressed while AOB were dominant. These observations supported the feasibility of achieving stable partial nitrification by treating sludge on long-term exposure to nitrite.