Influences of Water Temperature, Nitrogen Load on Nitrification Activity and N₂O Emission in Biological Wastewater Treatment Process

Abstract

Activated sludge processes coupled with membrane filters were operated at 10, 20 and 30°C to study the influences of the water temperature, and various kinds of the nitrogen load conditions on nitrification and emission of N₂O, known as the greenhouse gas. The results obtained were as follows: Lower temperature, higher nitrogen concentration in the influent and shorter HRT caused the decrease of the nitrification efficiency and the increase of N₂O conversion ratio. In addition, the effects of the nitrogen load was higher at low water temperature than high temperature. Under the same condition of the nitrogen load per MLSS, the runs with low MLSS concentration achieved high nitrification rate and low N₂O conversion ratio than those with high MLSS concentration. It was suggested that oxygen diffusion was insufficient in the runs with higher MLSS concentration because of the larger-sized flocculation of the microorganisms, and so that effective oxygen supply was very important to improve the nitrification efficiency under such operational condition.