Seasonal and Diurnal Variations of GHG Emissions Measured Continuously at the Viikinmäki Underground WWTP

Abstract

The gaseous emissions of an underground activated sludge treatment plant with total nitrogen removal have been measured on-line since 2012. The continuous Fourier transform infrared (FT-IR) measurement of CO₂, NO, NO₂, N₂O, NH₃ and CH₄ is situated in the single exhaust air pipe, thus covering the whole wastewater treatment process. The measurement data from 2015 showed that the seasonal and diurnal variations of N₂O and CH₄ are considerable. When comparing N₂O and CH₄ emissions as CO₂ equivalents to CO₂ formed in the activated sludge process, the impact of N₂O was dominant. The CH₄ emission was considerably smaller, and the emissions of NOx and NH₃ from biological treatment were small. The long term variations of N₂O or CH₄ production were not linked directly to load variations or other “apparent” factors such as temperature, nitrogen load, nitrogen reduction or anoxic volume. There was neither a clear seasonal pattern. The short interval variations of N₂O were similar to but not identical with CO₂ variations.