Evaluating desert landfill carbon sequestration efficiency and changing solid waste disposal policies.
Landfill carbon sequestration is often overshadowed by the amount of methane and CO2 generated: without effective gas recovery systems, landfills can be net greenhouse emitters. As the organic waste decomposes, a significant amount of sequestered carbon is released into the atmosphere. The general approaches for reducing GHG emission have been improving the gas recovery, reducing waste generation, and alternative chemical/mechanical degradation processes (including composting). Back-of-the-envelope calculation has always shown that landfills cannot effectively sequester carbon.
The recent extreme weather pattern and climate change, however, has exacerbated the water withdraw in certain parts of the world, causing more and more extremely dry periods. Desertification and wildfire has caused dramatic reduction in biomass; at the same time, the rate of decomposition of organic material has also been gradually decreasing, depriving the soil with nutrients.
Because deserts are getting more arid, landfills in desert climate has been expanding to compensate for the decreased rate of decomposition. A side effect of the phenomena is the reduction of outgassing. The emission rate of methane and CO2 in desert landfills can be dramatic lower than that of a regular landfill, making it an effective carbon sequestering system.
In many countries, landfills follow one-size-fits-all policies: they are designed with the same requirement, the same leachate and gas recovery systems, and the same operating practices. The recent climate shift should prompt policy changes that revisit the carbon sequestering ability of landfills in desert climates, and redesign desert landfills to improve the sequestration cost efficiency.
Category of the action
Reducing emissions from waste management
What actions do you propose?
1. A better understating of waste decay rates and landfill gas modeling in desert climate
When designing landfills, the waste decay rate directly affects the gas recovery system and landfill size. There have been a number of researches done to estimate the decay rate over the years, but there has not been any significantly advancements in the field. The rate of decay, as simplification of waste moisture content, bacteria availability, PH, temperature, humidity, precipitation, and other variables, should be unique for different landfills. For landfills in arid conditions, the average rate of decomposition can be 3-4 times lower than that of wet conditions; this number should be even lower as extreme weather patterns increases water withdrawal. We should gain a better understanding of how landfills are changing with the weather. The gas generation model follows a simple first-order decay equation, but the decay equation should be corrected from year to year based on precipitation and temperature.
2. Changing the design of landfills in arid conditions
Because the rate of decay is changing, the form and function of landfills should change with it. The gas recovery system of landfills can be improved to reduce cost/increase efficiency. The size, location restrictions, composite liners requirements of the landfill should evolve with it as well.
3. Improving the carbon sequestration credit system
Researches need to be funded, and changes are not sustainable unless there is profit to be made. Changing the carbon sequestration credit system can give tax incentives to solid waste disposal companies to make changes. Very much like cap-and-trade, a carbon credit can be given to municipal and industrial landfills in arid conditions.
4. Changing waste movement pattern
Moving waste from wet condition to arid condition can reduce the GHG generation. Aided by improved rate of decay model, the sequestration efficacy can be improved by changing the waste movement pattern.
Who will take these actions?
1. The very first step need to be taken by researchers to pitch a proposal on alternative landfill modeling in arid conditions.
2. Government regulatory agencies need to take the next step and fund more in depth researches.
3. Industry lobbying will take place to argue for/against carbon sequestration credit for landfills. Solid waste disposal companies will be key players in the policy change.
4. More solid waste will be directed to landfills in desert climates to reduce GHG emission.
Where will these actions be taken?
1. Landfills near large cities in desert climates should be analyzed first:
a. Las Vegas, Nevada, U.S.
b. Ürümqi, Xinjiang, China.
c. Dubai, UAE.
d. Somewhere in Outback Australia (I'm not super familiar with Australia)
2. Cities that are connect to arid regions, where solid waste can be directed to desert landfills.
What are other key benefits?
When the rate of decomposition is low, the landfills in arid conditions will keep growing. Even though they sequester more carbon, growing landfill is always a problem. There is no additional benefit.
How much will emissions be reduced or sequestered vs. business as usual levels?
The rough estimation of GHG reduction lies in the decreased rate of decomposition. If 10% more solid waste is directed to desert landfills by the year 2030, the total GHG generation from solid waste will be reduced by 3-6%.
What are the proposal’s costs?
The proposal comes with every negative side effects of growing landfills:
1. risk of ground water pollution will be higher and more concentrated, as more waste migrate to desert regions.
2. higher carbon emission from waste movement, as waste are directed to arid conditions for sequestration credit.
Short term: better landfill modeling and more in depth understanding of the problem.
Medium term: a shift of landfill location toward arid conditions, reduction of GHG
Long term: landfills become saturated, carbon sequestration meets the margin of diminishing return. Landfills are mined for resources.
Ideologically, this is the opposite of recycling. This proposal aims to expand the landfills with low GFG generation.
IPCC, Climate Change 2007: Working Group III: Mitigation of Climate Change, Chapter 10: Waste management
Frank Ackerman, William Moomaw, and Robin Taylor, Greenhouse Emissions from Waste Management. A survey of data reported to UNFCCC by Annex I countries, 2003.
EPA, 2015. Landfills, Municipal Solid Waste. [Online]
Available at: http://www.epa.gov/solidwaste/nonhaz/municipal/landfill.htm
[Accessed 12 6 2015].
Podolsky, M., Lindsay, C. & Akkeren, B. V., 1995. Carbon Sequestration in Landfills. [Online]
Available at: http://epa.gov/epawaste/conserve/tools/warm/pdfs/ICF_Memo_Carbon_Sequestration_in_Landfills.pdf
[Accessed 15 6 2015].
Richardson, G., 2015. Landfill Design & Operation. [Online]
Available at: http://www.epa.gov/osw/nonhaz/municipal/landfill/bio-work/richards.pdf
[Accessed 12 6 2015].