Humans produce a lot of waste, but when we throw something away, how much do we know about where it goes and how it is handled? This is the third in a five-part series exploring what could happen.
Despite the proliferation of plastics over the past century, biodegradable organic materials remain the largest component of the US waste stream. But for a substance so ubiquitous, it is difficult for cities to cope with it.
Some organic materials, such as clean paper, can be recycled. Still, organic materials such as paper products, garden scraps, and food waste make up a 56% of municipal solid waste (MSW). Some people avoid producing food waste by composting it at home. But not everyone has the time or space to compost. Also, home composting systems are not always able to process all organic waste in the home.
Although the word “industry” has negative connotations in the environmental industry, there are benefits to scaling up when it comes to composting. Thanks to industrial-scale composting facilities, approximately 8.5% of America’s organic waste is composted. In some communities, like Seattle, Mandate composting. But these cities are in the minority. Many more do not even offer composting services. Here’s how municipal composting works where it exists.
What is composting?
Composting is a natural process of decomposition of organic materials optimized by a controlled environment. The basic biological processes are the same whether they occur in backyard piles or in industrial settings. An ideal compost pile has a carbon to nitrogen ratio of approximately 30:1. During periods of active composting, temperatures remain in the range of 120 to 170 degrees Fahrenheit (49 to 77 degrees Celsius). Moisture levels are kept between 40% and 60% to support the growth of naturally occurring microorganisms that break down the waste.
private commercial composting It started in the 1970s. Most of the early businesses were small companies, primarily servicing businesses such as farms and timberlands. One of the first municipal composting projects began in Davis, California in 1972. But things really started to take off in the 1980s, when concerns about rapidly filling up landfills spurred the development of recycling programs. Cities can now reduce solid waste by up to 50% during the growing season by composting organic waste.
Compared to home composting, industrial-scale commercial composting facilities can process much larger volumes of waste, including waste from residents who don’t have the time or space to compost themselves. Industrial composting facilities utilize a wider variety of raw materials than a single household would produce and have the tools and expertise to optimize the composting process.
How industrial composting works
If you compost locally, you may be automatically provided with a special collection bin, but you will need to sign up for ‘garden waste’ or ‘green waste’ as a separate service. There may be cases. In either case, keep organic waste separate from food scraps and recyclables. As with garbage, private transport companies typically collect yard waste in large dump trucks. But rather than transporting waste to a transfer facility or landfill, these trucks deliver organic materials to commercial composting facilities.
These facilities can be quite large, often housed in shed-like structures to minimize odors and keep rainfall away from the compost pile. Think bulldozers instead of pitchforks. There are three main ones commercial composting methods:
- Windrow: The waste is piled up in long rows called “windrows” and the piles are rotated for regular ventilation. The ideal pile height is 4 to 8 feet and the width is 14 to 16 feet.
- Inside the container: The waste is placed in drums, silos, or concrete-lined trenches where environmental conditions are mechanically controlled and physically rotated or mixed. This is the most flexible method regarding batch size and raw materials.
- Aerated static pile: The waste is mixed in a large pile and loosely layered with bulking agents such as branches, wood chips, or shredded newspaper to allow air to pass through the pile. A network of pipes beneath the pile blows air into and sucks air out of the pile.
Active composting typically takes only a few weeks, but large compost piles can take months to cool and be ready for use. Finished compost is often sold to the public to help offset program costs. However, compost may also be used in public landscapes.
What is compostable?
Yard waste services obviously include grass clippings and wood debris.
Depending on the composting process used and the capacity of the program, curbside composting programs often also include food waste and food-stained paper (which, unlike clean paper, cannot be recycled). But even the most robust municipal composting programs cannot accept all types of organic waste. For example, pet waste is high in nitrogen and contains pathogens that are difficult to eradicate. there was commercial experiment and Composting pet wasteHowever, this material poses an unacceptable risk to municipal composting programs.
Compostable plastics, also known as bioplastics, also pose technical challenges. Many products meet ASTMI standards for compostability unbreakable Under conditions in commercial composting facilities, compost is rarely kept at high temperatures for the time needed to break down the plastic.
Don’t put plastic in your compost bin unless it’s labeled as compostable and Composting services explicitly state that they accept compostable plastics. Even labeled bioplastics should be thrown in the trash unless you’ve verified that your local composting program accepts them. Just as wishcycling contaminates recycled materials, wish-composting contaminates compost.
compost problem
Contamination is the biggest problem for municipal composting programs. Regular trash is the most common pollutant. Non-biodegradable items don’t necessarily harm the composting process, but separating food scraps from compost can be tedious and inefficient. And no one wants to buy compost that contains plastic pieces and other debris. Composting only serves as a form of recycling if the resulting product is marketable.
As the City of Seattle discovered, it’s difficult to control compost quality when you can’t control the inputs. Consumers who purchased this compost in the 1980s reported that it killed certain garden plants. of issue tracked to a herbicide called clopyralid. Washington state has banned the use of herbicides on lawns and its composting program has been reinstated. However, municipal composting materials will still include materials treated with chemicals.
Compostables can also be exposed to other contaminants. For example, leaves that fall on your driveway may have picked up motor oil before being collected for composting. As a result, many municipal compost products are not eligible for the organic label. The American Composting Association states, “Test guarantee seal” to provide consumers with some assurance about the quality of their compost.
Compost progress
Since 2020, there has been a notable increase in community composting programs across the United States, both through grassroots efforts and government support.
Read Part 4 of this 5-part series: How waste incineration works
Editor’s note: This article was originally published on October 29, 2019 and updated in January 2025.
