N₂O accumulation from denitrification under different temperatures

The effects of temperature on nitrous oxide (N₂O) accumulation during denitrification and denitritation were investigated. Batch experiments were performed to measure N₂O accumulation at 25 and 35 °C. More N₂O accumulation was observed during denitritation at the higher temperature as compared with full denitrification and low temperature tests. The highest nitrite concentration tested in this study (25 mg/L NO₂ ⁻N and pH 8.0) did not show inhibitory effect on N₂O reduction. It was found that the major cause of more N₂O accumulation during denitrification at higher temperature was due to higher N₂O production rate and lower N₂O solubility. Specific nitrate, nitrite, and N₂O reduction rates increased 62, 61, and 41 %, respectively, when temperature rose from 25 to 35 °C. The decrease of N₂O solubility in mixed liquor at 35 °C (when compared to 25 °C) resulted in faster diffusing rate of N₂O from liquid to gas phase. It was also more difficult for gas phase N₂O to be re-dissolved. The diffused N₂O was then accumulated in the headspace, which was not available for denitrification by denitrifiers. The results of this study suggest higher temperature may worsen N₂O emission from wastewater treatment plants (WWTPs).