Composition of Municipal Solid Waste in the United States and Implications for Carbon Sequestration and Methane Yield

Eleven statewide waste characterization studies were compared to assess variation in the quantity and composition of waste after separation of recyclable and compostable materials, i.e., discarded waste. These data were also used to assess the impact of varying composition on sequestered carbon and methane yield. Inconsistencies in the designation of waste component categories and definitions were the primary differences between study methodologies; however, sampling methodologies were consistent with recommended protocols. The average municipal solid waste (MSW) discard rate based on the statewide studies was $1.90\text{kg}\text{MSW}{\text{person}}^{-1}{\text{day}}^{-1}$ , which was within the range of two national estimates: 2.35 and $1.46\text{kg}\text{MSW}{\text{person}}^{-1}{\text{day}}^{-1}$ . Dominant components in MSW discards were similar between studies. Organics (food waste, yard trimmings), paper, and plastic components averaged $23.6\pm 4.9\%$ , $28.5\pm 6.5\%$ , and $10.6\pm 3.0\%$ of discarded MSW, respectively. Construction and demolition (C&D) waste was $20.2\pm 9.7\%$ of total solid waste discards (i.e., MSW plus C&D). Based on average statewide waste composition data, a carbon sequestration factor (CSF) for MSW of 0.13 kg C dry $\text{kg}{\text{MSW}}^{-1}$ was calculated. For C&D waste, a CSF of 0.14 kg C dry kg C and D ${\text{waste}}^{-1}$ was estimated. Ultimate methane yields $\left(L_o\right)$ of 59.1 and $63.9{\text{m}}^3$ ${\text{CH}}_4$ wet Mg ${\text{refuse}}^{-1}$ were computed using EPA and state characterization study data, respectively, and were lower than AP-42 guidelines. Recycling, combustion, and other management practices at the local level could significantly impact CSF and $\left(L_o\right)$ estimates, which are sensitive to the relative fraction of organic components in discarded MSW and C&D waste.