Composting and climate change
Composting is a biological process that transforms organic waste, such as yard trimmings and food scraps, into a stable nutrient-rich substance known as compost or humus. This process plays a crucial role in agricultural and environmental practices by enriching soil, aiding in erosion control, and serving as a landfill cover. Various composting methods exist, ranging from simple backyard systems to large-scale industrial operations, each catering to different quantities and types of organic waste.
In the context of climate change, composting offers significant environmental benefits. By diverting organic waste from landfills, it helps reduce greenhouse gas emissions, particularly methane, which is produced in large quantities in waste disposal sites. Composting also enhances soil quality, increases carbon content, and lowers the need for synthetic fertilizers, which require substantial energy to produce. However, it is important to note that composting itself can generate some greenhouse gases, such as nitrous oxide, during the decomposition process. Ongoing research is exploring ways to minimize these emissions while maximizing the climate benefits of composting. Overall, composting not only supports sustainable waste management but also contributes positively to climate change mitigation efforts.
Subject Terms
Composting and climate change
Definition
Composting is a natural biological process that breaks down organic materials into a stable organic substance called compost. Compost is created by combining organic wastes, such as yard trimmings, food wastes, and manures, in piles or containers. Microorganisms, primarily bacteria and fungi, decompose and form compost, a nutrient-rich material that is also called humus. Humus is dark brown or black in color and is free of most and weed seeds. Compost can either be added to soil as fertilizer or be used to support plant growth. Composting is used in landscaping, horticulture, and agriculture as an organic fertilizer to enrich soils. Compost is also used for erosion control, wetland construction, and as landfill cover. Industrial composting systems are increasingly being utilized as landfill alternatives, making them an important tool for waste management.
Composting methods range from simple backyard or onsite systems to large, commercial-scale agricultural and worm-composting centers. Composting can be either aerobic (occurring in the presence of oxygen) or (without oxygen). Aerobic methods are generally more efficient at decomposing organic matter. Homeowners and other small-quantity generators use backyard composting systems to degrade such wastes as yard trimmings and food scraps. Larger operations utilize aerated, or turned, windrow composting, in which organic waste is piled in rows called “windrows” and aerated by periodically turning the piles. Windrow composting is suited for large quantities of waste, such as that generated by food-processing businesses including restaurants, cafeterias, and packing plants. The process can accommodate diverse wastes, including animal by-products.
In aerated, static-pile composting, organic waste is placed in one large pile rather than rows and is aerated by layering the pile with bulking agents, such as wood chips or shredded newspaper. This method is suitable for large quantities of yard waste, food scraps, and paper products, but not animal by-products or grease. It is often used by landscapers or on farms. In-vessel composting uses a container—such as a drum, silo, or similar vessel—and can be used to process large amounts of waste in a limited area. Most organic waste, including meat, manure, biosolids, and food scraps, can be decomposed using this method. Worm composting, or vermicomposting, uses worms in a container to break down organic matter. Red worms, rather than nightcrawlers or garden worms, break down food scraps, paper, and plants and generate rich compost called “castings.” Vermicomposting also produces “worm tea,” a nutrient-rich liquid fertilizer that can be used in gardens or for houseplants. Vermicomposting is well suited for apartments or small offices.
Significance for Climate Change
Composting organic material has many environmental benefits, including some that mitigate some of the harmful effects associated with climate change. In general, composting leads either directly or indirectly to a reduction in the amount of greenhouse gases (GHGs) released into the atmosphere. Composting reduces the use of inorganic fertilizers and pesticides, diverts waste from landfills, restores soil quality, and increases carbon content in soils. By regenerating nutrient-poor soils, compost increases the water-hold capacity of soils and decreases the amount of inorganic fertilizer required to grow healthy crops.
Inorganic fertilizers require a great deal of energy to produce, so reducing the demand for such fertilizers reduces energy production and consumption. Composting, moreover, slows down the depletion of existing organic matter from soils while simultaneously adding organic matter and carbon to the soil. Increasing carbon sequestration within soils contributes substantially to reduced GHG emissions. Composting also helps decrease plant diseases and pests, which reduces the amount of pesticides required. Composting also diverts organic wastes that would otherwise end up in landfills or other disposal sites. Reducing organic wastes in disposal sites reduces the amount of methane, a very potent GHG, emitted from such sites.
Although composting decreases methane emissions from landfills, some GHGs, including carbon dioxide, methane, and nitrous oxide, are produced during composting. During the intense microbial activity that occurs during composting, a significant loss of nitrogen as nitrous oxide and other nitrogen-based gases occurs. Although the worms used in composting decompose organic material very efficiently, nitrous oxide is emitted during digestion. Large, commercial-scale worm-composting plants generate GHGs in amounts comparable in to those generated by landfills of the same scale. Nitrous oxide is believed to be many times more powerful than carbon dioxide or methane in contributing to global warming. While research on the management of GHGs during the composting process remains limited, the use of biochar to change the chemical atmosphere in the compost has shown some promise to reduce GHG emissions.
Bibliography
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Culen, Gerald R., et al. Organics: A Wasted Resource? An Extended Case Study for the Investigation and Evaluation of Composting and Organic Waste Management Issues. Champaign, Ill.: Stipes, 2001.
Ebeling, Erich, ed. Basic Composting: All the Skills and Tools You Need to Get Started. Mechanicsburg, Pa.: Stackpole Books, 2003.
Hoover, Darby and Dr. Daniel Roth. "Compost Is a Climate Solution." Natural Resources Defense Council, 5 Dec. 2023, www.nrdc.org/bio/darby-hoover/compost-climate-solution. Accessed 9 Dec. 2024.
Lens, Piet, Bert Hamelers, and Harry Hoitnik, eds. Resource Recovery and Reuse in Organic Solid Waste Management. London: IWA, 2007.
Scott, Nicky. Composting: An Easy Household Guide. White River Junction, Vt.: Chelsea Green, 2007.
Yin, Yanan, et al. "Research Progress and Prospects for Using Biochar to Mitigate Greenhouse Gas Emissions During Composting: A Review." Science of The Total Environment, 798, 2021. doi:10.1016/j.scitotenv.2021.149294. Accessed 9 Dec. 2024.