Suppression of N₂O Greenhouse Gas Emission Volume using the Flow Equalization Function in Johkasou

Abstract

 Emission volumes of the greenhouse gas N₂O from small-scale johkasou are around five times higher than those from sewers. In this study, we focused on fluctuations in the flow rate of johkasou and compared the N₂O emission volumes of johkasou with a flow equalization function, for leveling out variations in volume of inflow over time, and of those without. The comparison showed that N₂O emission volumes from johkasou equipped with a flow equalization function are one sixth of those from johkasou without the function or lower. This is because fitting a flow equalization function alleviates the concentration of wastewater that is sent from the primary treatment to the secondary treatment This is believed to be able to minimize the decrease in oxygen reduction potential (ORP) at the secondary treatment. Furthermore, through this study, ORP appears to be a more appropriate indicator for controlling N₂O emission volumes in johkasou than dissolved oxygen (DO).