Nitrous Oxide Emitted from Actual Wastewater Treatment Plants with Different Treatment Methods

Abstract

Nitrous oxide, which has 310 times the greenhouse effect of carbon dioxide, is known to be emitted from wastewater treatment processes. However, the state of emissions at actual plants and the mechanism of generation are not well understood, and measures to control emissions have not yet been established. Therefore, we investigated the generation of nitrous oxide at 10 plants with different treatment methods. We found high emissions from the conventional activated sludge process, but lower emissions from the membrane separation activated sludge process and nitrogen removal method with step feeding. In addition, molecular techniques such as denaturing gradient gel electrophoresis suggest that a wastewater treatment plant using an anaerobic/aerobic process produces high N₂O emissions.