All About Composting
Important things you should know about composting (plus a little more)
What is composting?
Composting is the natural process of recycling organic material such as leaves, food scraps, etc., and converting it into valuable, nutrient-dense fertilizer (1). The natural process of decomposition is rather lengthy, but using composting methods speeds up the process for suitable environments for microorganisms (1). Composting can be utilized in various ways to discard organic material, whether on an industrial-scale or at home. Composting not only helps keep food and garden scraps out of the waste stream and out of landfills, but it provides various benefits to the environment as well (1)!
What are the benefits of composting?
Reduces the amount of waste thrown out
The majority of food and garden scraps thrown out collectively make up more than 28% of what is typically thrown out into our landfills (1). Food waste is a significant contributor to environmental stress, but the methods to process such waste are incredibly costly (1). The average cost for a single municipal solid waste landfill in the United States was approximately $55 per ton in 2019 (1). The United States is capable of generating massive amounts of waste, and in 2017 had produced over 267 million tons of municipal waste, with two-thirds of it going into landfills or incinerators, resulting in billions of dollars being spent solely on waste management (1). The west coast generates the most amount of waste than any other region compared to the average amount within the United States. In 2019 it cost $73.03 per ton within the west coast alone (2). There is no current data available on total food waste since 2018. The average municipal solid waste in the United States produced in 2018 was 292.4 million tons (3).
Eliminates large portion of methane and carbon emissions from landfills
Organic material, when it decomposes, goes through the process of aerobic decomposition, where microorganisms that need oxygen so it can efficiently break down organic material. When such materials go to a landfill, it is more than likely going to be compacted under massive amounts of other types of waste, resulting in the amount of oxygen being limited or completely cut off for these decomposers (1). This leads to anaerobic decomposition, where microorganisms break down organic material without the need for oxygen, resulting in a by-product known as biogas being produced (1). Biogas is a by-product consisting of approximately 50% methane and approximately 50% carbon dioxide, with methane being 28-36 times more potent at trapping heat in the atmosphere than carbon dioxide does (1). Most landfills today can trap methane emissions with methane capture systems, but they do not effectively capture all of the gas emitted from the landfills (1). Landfills are considered to be the third-largest source of human-generated methane emissions within the United States. Not only this, but our entire solid waste infrastructure is centered around landfilling, which means that only 6% of food waste is composted correctly (1).
Improves soil health and reduces risks of soil erosion
Compost has the capability to improve large-scale agricultural systems since it contains three crucial nutrients needed for healthy crops: nitrogen, phosphorus, and potassium (1). Including several other small traces of elements like calcium, zinc, and iron (1). Using compost can increase the soil’s water retention capacity, productivity, and resiliency (4).
Reduces water usage
The agricultural industry is a significant consumer of water within the United States, accounting for approximately 80% of national water usage (1). Irrigation systems are a great way to alleviate the amount of water used but are not entirely cost-effective for most large-scale farmers (1). Using compost increases the soil’s water retention, with a 1% increase in soil organic matter remedying the soil to hold 20,000 gallons more water per acre (5). This allows for farmers to not waste or use as much water and still maintaining higher crop yields.
Reduces personal food waste
The average American family throws out approximately $150 worth of food per month, which has increased by 50% since the 1970s (1). The most common foods waste by American households are fruits and vegetables (1). It has also been shown that most United States retailers and consumers dispose of more than 60 million tons or approximately $160 billion worth of produce annually (1).
A brief description of decomposition and the carbon cycle
Photo Credit: Kellan Parker
The natural process of decomposition is a prolonged process involving the breakdown of raw organic materials converted into compost by microorganisms. Both chemical and biological processes are required for decomposition to create compost, whether through the natural cycle or human-generated process (6). Two main methods can yield compost, aerobic decomposition/stabilization and anaerobic decomposition (6). Anaerobic decomposition, otherwise known as fermentation, occurs in areas with limited or no oxygen available to microorganisms within the environment (6). Microorganisms that do not require oxygen typically rely on nitrogen, phosphorus, and other nutrients to survive (6). The final product within anaerobic decomposition is humus (compost) (6). Aerobic decomposition occurs in environments with oxygen present and is the most common process found in nature (6). These microorganisms also utilize nitrogen, phosphorous, and some carbon as nutrients, but most carbon is used up and expelled as carbon dioxide (6). Typically, two-thirds of the carbon is released as CO2, whereas one-third is combined with nitrogen and absorbed into microorganisms (6). There are various types of decomposers found within the soil and compost piles and can be split into chemical and physical decomposers. Chemical decomposers such as bacteria, actinomycetes, protozoa, and fungi, make up the mass majority within a compost pile (6). Chemical decomposers are typical microorganisms and appear with the materials used to make up compost (6). Physical decomposers such as mites, flies, worms, snails, slugs, spiders, and ants are much larger and will move their way through the compost to find their ideal food choices (6). The decomposition process is a carbon cycle component since the most essential element recycled by decomposition is carbon (7). The carbon cycle is crucial for life to exist since it allows plants to undergo photosynthesis by combining carbon dioxide and water to create glucose (7). Plants will use glucose to grow and thrive until it dies, where the carbon and other nutrients within the plant rot and are recycled back into the system once again (7).
Fig1: The carbon cycle allows for decomposers to break down organic material and release CO2 into the atmosphere to start the process over again. Credit: M. Mayes, Oak Ridge National Lab.
Different types of composting methods
Composting requires three specific materials to have a healthy and stable compost by maintaining a well-balanced carbon ratio to nitrogen. “Brown” matter, this can include items such as dead leaves, wood chips, etc., “green” matter, such as grass clippings, fruit scraps, and coffee grounds, and water (9). Brown matter primarily consists of carbon, whereas green matter consists of nitrogen (1,9). Typically, carbon-to-nitrogen’s ideal ratio is 25-30 parts carbon for every one part of nitrogen (1).
There are various types of composts out there; it primarily depends on one’s location, climate, and space to determine which compost is best for specific areas. Using bins is the simplest and cheapest method for small-scale or at-home composting. There are two types of simply compost bins, closed and open containers (1). Closed containers help retain heat and moisture (1). Closed compost bins typically have opened bottoms placed directly on soil to allow for accumulated nutrients to seep into the soil (1). It is best to have openings within the container to ensure proper airflow (1). Open bins require less maintenance and are better for composting yard waste, and do not necessarily require a container to hold it (1). Trench composting results in placing organic waste into the soil and burying it (1). One of the benefits of trench composts is not only that it is a simple method that solely relies on physical decomposers to do the work, but it also allows you to compost small amounts of cooked food waste (i.e., meat, grains, and dairy) if it is buried deep enough not to let animals dig it up (1). Vermicomposting, otherwise known as worm composting, is excellent for year-round limited space and can be done indoors and outdoors (1). Worm composting requires little maintenance and produces natural, odorless castings that create nutrient-dense fertilizer (1). EMO composting or Effective MicroOrganisms is another indoor system that can be used by anyone (8). This system commonly uses the Bokashi system and creates a nutrient-dense juice that is valuable for gardens (8).
What to compost
fruit and vegetable scraps
eggshells
coffee grounds and filters
teabags
nut shells
shredded newspaper
cardboard
paper
yard trimmings
grass
houseplants
leaves
sawdust
wood chips
cotton and wool rags
hair and fur
fireplace (wood) ashes
What not to compost
coal or charcoal ashes
dairy products (i.e. milk, butter, yogurt)
egg yolks and whites
diseased plants
fats, greases, and oils
meat and fish scraps and bones
pet waste
pesticide treated yard trimmings
References:
Hu, Shelia. “Composting 101.” NRDC, 20 July 2020, www.nrdc.org/stories/composting-101#whatis.
Tiseo, Published by Ian, and Feb 4. “Cost to Landfill MSW by U.S. Region 2020.” Statista, 4 Feb. 2021, www.statista.com/statistics/692063/cost-to-landfill-municipal-solid-waste-by-us-region/.
Sustainable Materials Management (SMM). “ Advancing Sustainable Materials Management: 2018 Fact Sheet Assessing Trends in Materials Generation and Management in the United States.” U.S. Environmental Protection Agency (EPA), 2018, www.epa.gov/sites/production/files/2021-01/documents/2018_ff_fact_sheet_dec_2020_fnl_508.pdf.
O'Connor, Claire. “Using Compost to Improve Soil Health and Crop Productivity.” NRDC, 15 Dec. 2016, www.nrdc.org/experts/claire-oconnor/using-compost-improve-soil-health-and-crop-productivity.
Hudson, B.D. (1994). Soil organic matter and available water capacity. Journal of Soil and Water Conservation, 49(2), 189-194.
Texas A&M AgriLife Extension Service. “Chapter 1, The Decomposition Process - Earth-Kind® Landscaping Earth-Kind® Landscaping.” Aggie Horticulture®, Feb. 2009, aggie-horticulture.tamu.edu/earthkind/landscape/dont-bag-it/chapter-1-the-decomposition-process/.
Kowalski, Kathiann. “Recycling the Dead.” Science News for Students, 3 Dec. 2019, www.sciencenewsforstudents.org/article/recycling-dead.
“8 Methods of Composting.” Direct Compost Solutions, 14 Mar. 2021, directcompostsolutions.com/8-methods-composting/.
“Composting At Home.” EPA, Environmental Protection Agency, 10 Feb. 2021, www.epa.gov/recycle/composting-home.