The impact of temperature and dissolved oxygen (DO) on the partial nitrification of immobilized fillers, and application in municipal wastewater

Abstract

To achieve the stable partial nitrification of municipal wastewater, activated sludge with high ammonia-oxidizing bacteria (AOB) content and low nitrite-oxidizing bacteria (NOB) content were immobilized in a polyvinyl alcohol filler. The effects of different levels of dissolved oxygen (DO) on the activity of AOB and NOB in the filler with temperature changes at the initial ammonia concentration of approximately 100 mg L⁻¹ were investigated. At 25 °C, when the DO concentration was greater than 5 mg L⁻¹, the O₂-limiting condition inside the filler was destroyed as the demand for oxygen in AOB was certain, and resulted in enhanced NOB activity. At 15 °C, the DO concentration was not a key factor in determining the NOB activity due to the negative effect of temperature on NOB activity. The immobilized filler reactor of municipal wastewater achieved a nitrite accumulation rate (NAR) of >86.7 and >82% at 24–26 °C and 14–16 °C, respectively. Low temperatures did not deteriorate the stable partial nitrification performance. The total nitrogen (TN) removal efficiency of the immobilized filler reactor was 21.7–26.1% and 10.3–15.3% at 24–26 °C and 14–16 °C, respectively. The TN removal efficiency and NAR in municipal wastewater were higher as compared to simulated wastewater, indicating that the organic carbon in municipal wastewater enhanced nitrate reduction by denitrification. High-throughput sequencing analysis showed that denitrifying bacteria and nitrifying bacteria were identified as the predominant bacteria genera, while the dominant species of NOB was Nitrobacter. This study is a viable approach to promoting partial nitrification in municipal WWTPs.