What emits more greenhouse gas emissions, composting or landfilling organic material? How can you determine the quantifiable difference?
This is a question waste management specialists have to consider as they attempt to comply with GHG mitigation legislation and curb their emissions.
Life Cycle Analysis (LCA) is a common tool that quantifies the environmental footprint of a product or service from “cradle to grave.” The output is usually in the form of Greenhouse Gas (GHG) Emissions in the unit Metric Tons CO2 Equivalent (MTCO2E) but can also include a wide variety of outputs such as effect on acid rain production, eutrophication, or human health in the case of a Life Cycle Impact Assessment (LCIA) (ie. the WRATE model).
HOW DOES THIS RELATE TO COMPOSTING?
City, state, and local decision makers use LCA to plan waste management strategies, reduce GHG emissions, and make infrastructure decisions. For instance, the European Union (EU), California, Vermont, and New York banned organic materials from landfills to reduce methane emissions.
But how much does composting really reduce GHG emissions compared to landfills? GMT CEO and Founder, Michael Bryan-Brown ran the numbers and shared his results at U.S. Composting Council (USCC) 2020 in Charleston, SC.
HOW HE DID IT
Michael used the EPA Waste Reduction Model (WARM) to perform his calculations, which determines the GHG emissions of using alternative waste management practices (source reduction, recycling, combustion, composting, anaerobic digestion) when compared to a baseline (landfills).
WHAT DID HE FIND?
Landfilling vs. Composting
Landfilling vs. Composting GHG Emission Analysis
Using the WARM model, Michael found that landfilling 300,000 tons per year of mixed organics (2:1 yard trimmings to food waste) contributes ~ 18,000 MTCO2E into the atmosphere while composting the same amount of material removes ~ 46,000 MTCO2E from the atmosphere.
When focusing on methane emissions, which are 28 times more potent than CO2 on a 100-year scale and 86 times more potent on a 20-year time scale, the WARM model found methane seepage out of landfills to be 100,000 MTCO2E as opposed to about ~1,000 MTCO2E from composting. The WARM model also found that composting stores more CO2 in the soil and produces very low methane production, while landfilling shows high carbon storage, and lower dinitrogen monoxide (N2O) release (a potent greenhouse gas).
Landfilling vs. Anaerobic Digestion
Landfilling vs. Anaerobic Digestor GHG Emissions Analysis.
When comparing landfilling and anerobic digestion, landfilling produces ~ 18,000 MTCO2E while anaerobic digestion removes ~ 18,500 MTCO2E. This illustrates that the anaerobic digestion process generates more methane emissions compared to composting yet were still minimal. Additionally, due to the landfilled material from anaerobic digestion process, carbon storage was also present.
Composting vs. Anaerobic Digestion
Composting vs. Anaerobic Digestor GHG Emissions Analysis.
Using the WARM model, Michael found both methods to remove MTCO2E out of the atmosphere with composting more than three times more effective at ~ -17600 MT CO2E compared to anaerobic digestion which is estimated to reduce MTCO2E by ~ -5,800.
The results from the WARM model showed that composting is the superior method to process food waste when quantifying GHG emissions because it removes ~ 46,000 MTCO2E from the atmosphere and the process emits significantly less MTCO2E into the atmosphere compared to landfilling and anaerobic digestion. However, it is important to recognize the assumptions of a model, and thus it’s limitations as a tool. Some factors that are not illustrated in the WARM model include:
- The impacts of manufacturing industrial fertilizers that compost replaces
- The effect of carbon capture from increased soil fertility and carbon pump from increased root biomass (UC Davis Research & Marin Carbon Project)
- The GHG emissions differences between Aerated Static Pile (ASP) and Windrow Composting
- GHG emissions accrue over the long-term, not just within a year
Accounting for the Energy Required to Make Compost
Windrow and Aerated Static Pile (ASP) vary in their energy inputs based on facility operations, but grinding, handling, screening, and the electricity required to run the Aerated Static Pile (ASP) System combine to produce 30 lbs MTCO2E per ton processed.
The Benefits of Using ASP over Windrow Methods
Anaerobic conditions in composting can lead to increased methane emissions. When measuring methane emissions from compost, gas meters showed 5% methane from 409 static piles. These results reemphasize the importance of aeration when designing compost piles, supplied by the ASP method. Windrow composting lacks forced aeration, which reduces the speed of compost production and increases Volatile Organic Compound (VOC) and N2O emissions.
Call to Action
Life Cycle Analysis is a helpful tool in the industry not only to analyze the GHG emissions released during a product’s lifespan but to help governments decide which waste management strategy provides the most payback in regard to GHG emissions. Plus, composting systems are more affordable than landfills. A past client of Green Mountain Technologies, Salinas Valley Solid Waste Authority paid $2 million in total for their facility lasting upwards of 25 years, while a new landfill will cost $5 million only lasting 5 years. Reach out to us here to start planning your next composting system!
The next question on the docket:
Using LCA, would you expect recycling bottles and cans or composting to remove more GHG emissions? Comment below.
1 “Greenwaste Compost Site Emissions Reductions from Solar‐Powered Aeration and Biofilter Layer.” San Joaquin Valley Technology Advancement Program, 14 May 2013.
Written by Theo Fehsenfeld, GMT Project and Business Development Assistant