Methane generation and capture at U.S. operating landfills

Brief article submitted to Editor of Waste Management World, Dec. 15, 2023

by Prof. Nickolas J. Themelis

U.S. landfills are a major contributor to methane emissions but, until 2021, the amount of CH4 generated per ton of MSW landfilled was not known. For example, in a 2021 NPR report, Dr. Susan Thornelowe, foremost EPA scientist on landfiils, and some other scientists stated that the older EPA estimates of landfill methane emissions were two to four times lower than the actual number.  To answer the CH4 generation question, Columbia University, in 2020-2021 analysed the EPA developed spreadsheets of:
a) 1,164 operating MSW landfills which in 2018 received 316 million metric tons of waste.
b) 396 operating landfills which have installed equipment to capture biogas and use or flare the methane in the biogas; they reported these data to the EPA Landfill Methane Outreach Program (LMOP). The only assumptions we had to make were to convert the reported biogas daily flows to yearly flows (by multiplying by 365) and the reported power generation data to methane yearly consumption (2,000 tons CH4 per MW-year; at assumed engine thermal efficiency of 40% and 365-day operation of the power generators). This study resulted in the average rate of methane capture, for the 396 landfills, of 0.024 tons of methane per ton of MSW landfilled in the LMOP landfills in 2018 (see this spreadsheet on the web).

The other conclusion of our study was that, on the average, the generation of methane at U.S. MSW landfills was 0.05 ton CH4/ton waste landfilled. Of this amount, the LMOP operating landfills captured a maximum (because of 365-day assumption) of 0.024/0.05 = 48%.
I was one of the reviewers of EPA's 2022 GHG Inventory. The last draft (Nov. 2023) of this Report estimates the generation of landfill methane in 2022 to be 12.0 million metric tons and the deposition of MSW in landfills to be 210.0 million metric tons (Section 7.6, Table 7.4 and Table A-220). Dividing these two numbers yields 0.057 ton CH4/ton waste landfilled, which is in fair agreement with the Columbia estimate of 0.050.

published: , 2|2024
Keywords: Landfilling, Pollution Control, United States of America