Determination of greenhouse gas emission factors for Taiwan’s pig manure management systems

Methane (CH4) and nitrous oxide (N2O) gases are emitted from pig manure management (PGM) systems. In Taiwan, a three-step process is generally adopted for PGM: solid–liquid separation, anaerobic/anoxic digestion, and aerobic treatment of wastewater containing manure solids and pig urine. In this study, the Intergovernmental Panel on Climate Change tier 2 methods were used to determine the emission factors (EFs) for CH4 and N2O emissions in Taiwan’s pig manure management systems. The average daily amounts of volatile solids (VS) and total nitrogen (TN) in solids and liquids derived from local pig manure per pig were evaluated. CH4 and N2O production was measured through batch digestion (in glass bottles) at 25 ± 1°C of manure solids and liquids, respectively. Furthermore, the amount of TN in manure solids and liquids was used to estimate direct and indirect N2O emissions. The estimated annual CH4 generation factor before recovery adjustments was 21.7 kg/head.year, and the estimated N2O emission factor was 0.163 kg/head.year. The CH4 value does not represent net atmospheric emissions after methane collection, utilization, or flaring.Implications: This study provides a method for estimating greenhouse gas emissions from the anaerobic treatment of pig manure wastewater, which can serve as a basis for estimating greenhouse gas emissions from waste treatment. Additionally, basic data on greenhouse gas emissions from pig manure management are provided.