Subject Top Page: Composting Emissions

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This page last reviewed on July 29, 2008

Compost Emissions Work Group

Background:

ARB has established a Compost Emissions Work Group (work group) to evaluate the emissions of volatile organic compounds (VOCs) and greenhouse gases (GHGs) from commercial composting operations.

Composting of organic waste material has become an important method of managing California's solid waste stream. There are nearly 200 compost and mulch producers in California who are permitted by the California Integrated Waste Management Board (CIWMB) through their organics material management program. Over 25 percent or approximately 10 million tons of organics are sent to landfills each year in California. The anaerobic decomposition of these wastes result in the emission of methane, a GHG that has a global warming potential twenty-one times that of carbon dioxide (CO₂). The CIWMB organics road map sets a goal of reducing 50 percent of the organic waste sent to landfills by the year 2020. This objective will contribute to the reductions in GHG emissions needed to meet the goals of California's Global Warming Solutions Act (AB 32). In order to quantify the reductions possible from diverting organics from landfills, CIWMB is conducting a Life Cycle Analysis (LCA) of GHG emissions from selected organics diversion alternatives.

Commerical composting is typically produced by spreading and layering the organic waste in large elongated piles called windrows (see picture above). The aerobic decomposition of this waste can result in emissions of some GHGs (methane and CO₂)_. If the composting process is well maintained, and the waste decomposes in primarily aerobic (with air) conditions, only small amounts of methane will result; CO₂emissions are considered "biogenic" by U.S. EPA and are not part of the overall GHG emissions inventory; VOC emission levels, however, can be significant. Best management practices (BMPs) can minimize these emissions along with some of the odors that result from decomposition.

VOCs contribute to the formation of ozone in the lower atmosphere, and in areas that are in "non-attainment" of the federal ozone standards, VOC emissions must be controlled. Some of California's 35 air districts have developed rules to reduce VOC emissions from various types of composting; these include: green waste (leaves, grass, yard clippings), food waste, chipping and grinding (wood waste), co-composting (with biosolids), etc. The first task of the Compost Emissions Work Group will be to evaluate the existing protocols and completed studies used for determining the emissions factors for local rule development. This process will help identify gaps in existing studies that can be used for development of a research plan. CIWMB will participate in the work group and will discuss methods of evaluating compost facility throughput using the State's Solid Waste Information System (SWIS). Additional topics will include evaluation of the emissions reduction potential of various BMPS, and an "emissions" reduction calculator that can be used to estimate facility-wide emissions based on throughput and facility-specific practices.

Workshops / Meetings:

This work group began meetings in May, 28 at Cal/EPA headquarters to evaluate data from emissions studies and establish emissions fractors for various types of compost production (Agenda) (Presentation). A list of studies to be considered by the work group can be downloaded on the Compost Emissions web page.

Contact Information:

For more information on the work group meetings, please contact Lea Yamashita at (626) 450-6240 and join our e-mail list.

Waste Management Sector