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

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, 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 data of two scenarios of waste treatment systems were used for a multiscale estimation of CH4 emissions from swine farms in North Carolina. Scenario 1 (baseline) was the conventional lagoon-based swine waste treatment system. 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 and processed with aerobic in-vessel composting. 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 estimates showed an annual emission of 332.2 kg CH4 per 1000 kg swine mass for scenario 1 and 114.7 kg CH4 per 1000 kg swine mass for scenario 2 sustaining an overall 65.5% CH4 abatement ascribable to the solid-liquid separation system. Methane emissions potentials were upscaled at the county, and state levels. The multiscale estimates highlighted hotspots of swine lagoons CH4 emissions in the North Carolina region. Two counties, Duplin and Sampson, contributed 49% of the state-level swine lagoon emissions estimated as 117,227 Mg CH4/year. However, the solid-liquid separation, as a mitigation practice, could reduce the total emissions at the state-level by 76,723 Mg CH4/year. Hence, the spatial disparities highlighted through the multiscale scenarios analyses could help to plan strategies for CH4 emission avoidance and abatement through technology improvement such as solid-liquid separation modules.