Estimating methane emissions from swine waste treatment lagoons and the reduction through solid-liquid separation: a multiscale case evaluation

Authors: Sohoulande, Clement; Vanotti, Matias; Szogi, Ariel

Submitted to: Cleaner Waste Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2024
Publication Date: 2/3/2024
Citation: Sohoulande Djebou, D.C., Vanotti, M.B., Szogi, A.A. 2024. Estimating methane emissions from swine waste treatment lagoons and the reduction through solid-liquid separation: a multiscale case evaluation. Cleaner Waste Systems. 7. Article 100133. https://doi.org/10.1016/j.clwas.2024.100133.
DOI: https://doi.org/10.1016/j.clwas.2024.100133

Interpretive Summary: Methane is a significant greenhouse gas emitted by livestock operations across the United States. In particular, the swine production industry of North Carolina, where agglomeration of the production and the use of open-air lagoon systems for waste treatment causes substantial methane emissions and alter the environmental quality. Yet the possibility of reducing methane emissions from these lagoons represents an avenue to sustain environmental quality. However, quantitative estimates of methane emissions potentials at county, watershed, and regional levels are needed to envision effective emissions reduction initiatives. In this study, updated guidelines of the Intergovernmental Panel on Climate Change (IPCC) and fifteen-month data of two scenarios of waste treatment systems were used to evaluate methane emissions from swine farms in North Carolina. Scenario 1 (baseline) was the conventional lagoon-based swine waste treatment system, and scenario 2 (project activity) was the conventional lagoon-based system retrofitted with a solid-liquid separation module that diverted solid waste from reaching the anaerobic lagoon. Both scenarios are feeder-to-finish swine operations. The farm-scale evaluations showed an annual emission of 332.2 kg of methane per 1000 kg swine mass for scenario 1 and 113.2 kg of methane per 1000 kg swine mass for scenario 2, sustaining an overall 65.9% methane abatement ascribable to the solid-liquid separation system. Methane emissions potentials were estimated at county, state, and watershed scales. The multiscale estimates across the North Carolina region highlighted hotspots of swine lagoons methane emissions. Two counties, Duplin and Sampson, contributed 49% of the State-level swine lagoon methane emissions, estimated as 117,227 Mg per year. Likewise, the swine lagoon methane emission from one sub-watershed, the Six Runs Creek, counts for 12.1 % of the State-level total emission while its covers only 0.5% of the state area. However, the solid-liquid separation, as a mitigation practice, could reduce the total methane emissions at the State-level by 77,252 Mg per year. Hence, the multiscale scenarios analyses highlighted spatial disparities that could help plan strategies for methane emission avoidance and abatement through technology improvement such as solid-liquid separation modules.

Technical Abstract: With an estimated global warming potential of 27 to 30 over 100 years, methane (CH4) is a significant greenhouse gas emitted by livestock operations across the United States. In particular, the swine production industry of North Carolina where agglomeration of the production and the use of open-air lagoon systems for waste treatment, cause substantial emissions of CH4 and alter the environmental quality. Yet the possibility of reducing CH4 emissions from these lagoons represents an avenue to sustain environmental quality. However, quantitative estimates of methane emissions potentials at county, watershed, and regional levels are needed to envision effective emissions reduction initiatives. In this study, updated guidelines of the Intergovernmental Panel on Climate Change (IPCC) and fifteen-month full-scale evaluation data of two scenarios of waste treatment systems were used for a multiscale evaluation of CH4 emissions from swine farms in North Carolina. Scenario 1 (baseline) was the conventional lagoon-based swine waste treatment system, and scenario 2 (project activity) was the conventional lagoon-based system retrofitted with a solid-liquid separation module that diverted organic compounds from reaching the anaerobic lagoon. Both scenarios are feeder-to-finish swine operations and the related in-situ data utilized are monthly animal population and weight, liquid waste temperature, and 5-day biological oxygen demand (BOD5). The farm-scale evaluations showed an annual emission of 332.2 kg CH4 per 1000 kg swine mass for scenario 1 and 113.2 kg CH4 per 1000 kg swine mass for scenario 2 sustaining an overall 65.9% CH4 abatement ascribable to the solid-liquid separation system. Methane emissions potentials were estimated at county, state, and watershed scales. The multiscale estimates across the North Carolina region, highlighted hotspots of swine lagoons CH4 emissions. Two counties, Duplin and Sampson, contributed 49% of the state-level swine lagoon emissions estimated as 117,227 Mg CH4/year. Likewise, the swine lagoon CH4 emission from one sub-watershed, the Six Runs Creek (HUC 0303000605), counts for 12.1 % of the state-level total emission while its covers only 710.8 km2 (0.5% of the state area). However, the solid-liquid separation, as a mitigation practice, could reduce the total emissions at the state-level by 77,252 Mg CH4/year. Hence, the multiscale scenarios analyses highlighted spatial disparities which could help to plan strategies for CH4 emission avoidance and abatement through technology improvement such as solid-liquid separation modules.