Quantification of CH4 and N2O Fluxes from Piggery Wastewater Treatment System for Emission Factor Development

Piggery farming is the largest source of livestock manure in South Korea, yet greenhouse gas (GHG) data from piggery wastewater treatment systems remain limited. This study quantified methane (CH4) and nitrous oxide (N2O) fluxes from a full-scale treatment facility to develop stage-, seasonal-, and diurnal-specific emission factors. Continuous laser-based monitoring using a PVC air-pool chamber was applied across raw wastewater storage, an anoxic nitrogen-conversion reactor, and strongly aerated nitrification units. Mean CH4 fluxes ranged from 1.1 to 15.6 mg s−1 m−2 peaking in summer, while N2O fluxes ranged from 0.01 to 17,971 mg s−1 m−2, with maxima in fall. Emissions were dominated by two functional zones: aerated basins where vigorous mixing enhanced CH4 stripping, and an upstream anoxic reactor where oxygen instability and nitrite accumulation produced extreme N2O peaks. Derived emission factors were 0.11 kg CH4 head−1 yr−1 and 45.2 kg N2O head−1 yr−1, equivalent to 3.1 and 12,300 kg CO2-eq head−1 yr−1. CH4 variability was controlled mainly by treatment stage and temperature, whereas N2O was governed by internal redox conditions. These results refine emission factors for inventories and underscore the need for improved aeration stability and denitrification control to reduce GHG emissions from piggery wastewater systems.