What actually happens in a municipal landfill?

Landfills receive over half of all U.S. municipal solid waste (MSW) and are the third largest source of anthropogenic methane emissions. Life-cycle assessment (LCA) of landfills is complicated by the long duration of waste disposal, gas generation and control, and the time over which the engineered infrastructure must perform. The objective of this study is to develop an LCA model for a representative U.S. MSW landfill that is responsive to landfill size, regulatory non-methane organic compound (NMOC) thresholds for landfill gas (LFG) collection and control, practices for LFG management (i.e., passive venting, flare, combustion for energy recovery), and four alternative schedules for LFG collection well installation. To add complexity, the U.S. EPA lowered the NMOC threshold from 50 to 34 Mg yr-1 to force more landfills to collect their gas.

Material production required for construction and operation contributes 68−75% to toxicity impacts, while LFG emissions contribute 50−99% to global warming, ozone depletion, and smog impacts. Material use dominates ecotoxicity and human health cancer and non-cancer effects due to the use of clay, sand, and heavy equipment. These activities release heavy metal emissions (Zn, Cr (VI), and Ni) to the water body, which together contribute ~94% to ecotoxicity. The steel production process required for a building and heavy equipment use also releases large zinc emissions to groundwater due to treatment of tailings from mining ores.

The current non-methane organic compound regulatory threshold (34 Mg yr−1) reduces methane emissions by <7% relative to the former threshold (50 Mg yr−1). Requiring landfills to continue collecting LFG until the flow rate is <10 m3 min−1 reduces emissions by 20−52%, depending on the waste decay rate. In general, for landfills already required to collect gas, collecting gas longer is more important than collecting gas earlier to reduce methane emissions.

In this work, a state-of-the-art landfill LCA was developed to represent how a landfill actually works in consideration of size, waste composition, decay rate, and practices and regulations of gas collection and control. The findings indicate that capital goods should be included due to their significant contribution to toxicity-related impacts. The stricter NMOC threshold exerts little influence on improving the gas collection efficiency. For landfills that have already been required to collect gas, collecting longer is more important than collecting earlier to reduce fugitive methane emissions. Wet regions could improve food waste diversion policies while arid regions could collect and control LFG for longer than currently required by federal law.

Page updated

Google Sites

Report abuse