Analyzing greenhouse gas emissions from a multi-stage public swine manure-treatment facility in Korea: Comparison with 2019 Refinement of the IPCC-guidelines

Wastewater treatment facilities are major systems for managing swine manure in Korea. These facilities primarily use physical, chemical, and biological processes to remove harmful substances from manure and convert them into compost, liquid fertilizer or biogas. The 2050 carbon neutrality scenario in Korea aims to increase the proportion of manure purification treatment from 13% to 25% by 2030. As manure treatment facilities expand, it is crucial to quantify and monitor their greenhouse gas (GHG) emissions such as methane (CH₄) and nitrous oxide (N₂O) gas emissions. This study aimed to measure the GHG emissions from a swine wastewater treatment plant to develop a country-specific emissions factor for each treatment stage to determine the national GHG inventory. The facility evaluated in this study had tanks for sedimentation, manure retention, denitrification, and aeration (nitrification) and treats 121 tonnes of swine manure from approximately 24,335 pigs. Quantification of the total GHG emissions from the facility was conducted for 24h once per a month, using a CH₄/N₂O Analyzer. The total emission factors from this facility for CH₄ and N₂O were estimated 0.59 kg CH₄/head/year and 0.004 kg N₂O/head/year. Also, field-measured data showed 417 tCO₂-eq/year, whereas 2019 IPCC Tier 2 factors estimated 1,238 tCO₂-eq/year- a 66% overestimate. The results revealed that the initial treatment stages (sedimentation and manure retention tanks) were the primary emission hotspots. This significant overestimation highlights the critical need for adopting refined specific emission factors based on direct field measurements. In conclusion, it is crucial to ensure that sedimentation and manure retention tanks are gastight to reduce the GHG emissions from a facility. Likewise, direct stage-resolved monitoring is essential to prevent overestimating GHG emissions. Therefore, this study serves as a foundation for the development of effective carbon reduction strategies in manure treatment processes.