Composting is a great way to keep organic wastes out of the landfill and reduce emissions of greenhouse gases. But not everyone can compost at home. And people who do can’t compost meat, bones, dairy, or any kind of grease or oil. Municipal composting and commercial composting (also known as industrial composting) can handle these wastes.

Municipal and commercial composting use the same processes. Cities and counties operate municipal composting facilities and private corporations operate commercial composting facilities. In addition, some places have community composting, where small companies pick up small quantities of food waste using small trucks or even bicycles.

Organic materials such as food waste, yard waste, and paper products make of about 56% of the municipal solid waste stream.

Industrial composting now handles about 8.5% of America’s organic waste. I have found no statistics for municipal composting. The only difference between municipal composting and industrial composting is who operates the facility. Plus, industrial composting companies don’t collect material from households. Some may offer drop-off facilities.

Composting basics

Whenever something dies, nature provides insects, worms, bacteria, and fungi to consume it. And then excrete their own wastes. We call it composting when humans construct piles of organic wastes to concentrate this decomposition in one place. We can almost think of compost as worm poop.

Effective composting requires a balance of two different kinds of feedstock. So-called green materials (grass, food waste, and manure) contain a lot of nitrogen. Brown materials (dry leaves and wood chips) contain a lot of carbon but little nitrogen.

It also requires grinding, chipping, or shredding these materials to increase the surface area. Smaller particles provide more space for microbes to feed. But it’s possible to get them too small, which prevents air from flowing through the pile.

Without oxygen, anaerobic bacteria take over. Anaerobic digestion of organic wastes can be a good thing when done deliberately with proper equipment. When it happens in a landfill or compost pile, it stinks and emits lots of methane into the atmosphere.

All composting, at home or otherwise, requires building and maintaining an internal temperature of abut 120-170º F and about 40-60% moisture level.

Processes of municipal and commercial composting

Either municipal or industrial composting takes place on a large scale to make it a community-wide effort. The community also benefits from having access to the compost. In the case of municipal composting, the compost may even be free for residents.

While some large-scale composting operations have achieved recognition as meeting organic standards, many of them carry some risk of contamination from herbicides, heavy metals, or other toxins. Also, the heavy equipment necessary to turn windrows usually runs on fossil fuels and therefore increase the plant’s carbon footprint.

Municipal composting and commercial composting one of three basic techniques.

Windrow composting

Windrow composting entails building piles between 4-6 feet tall and about 14-16 feet wide. It is necessary to turn these piles, just like a home compost pile, except that it takes heavy equipment to do it. Windrow composting has both advantages and disadvantages:

• It generates temperatures high enough to compost grease and animal products, which you can’t compost at home.
• Even if the outside temperature is below freezing, the interior of the pile can reach a temperature of 140º F.
• Weather conditions influence the best shape of the piles and may make it necessary to shield them from excess rain, hot external temperatures, or low humidity.
• Windrow composting generates leachate, which can contaminate ground and surface water without collection and treatment.
• Windrows can stink without careful odor control.
• It is necessary to test finished compost in a laboratory before it can be sold. It may have heavy metals or other contaminants that would render it useless.

Static pile composting

Static pile composting uses a network of pipes and blowers to aerate the piles instead of turning them. It works quickly. it’s not good for composting any kind of animal products.

• The controlled air supply allows larger piles than the windrow technique and therefore occupies less land.
• It can be done indoors, which makes it less influenced by weather conditions.
• Static aeration makes odor control less complicated.
• It’s not good for composting any kind of animal products.
• Installation and maintenance of the necessary equipment is expensive.

In-vessel composting

In-vessel composting involves feeding materials into some kind of barrel, drum, or concrete-lined trench. It also produces compost very quickly and can use animal products in the feedstock.

• But it can take longer for the compost to cool off than it takes to make it.
• It can accommodate a wide range of sizes. Some vessels are small enough for a school or restaurant kitchen, but they can also be very large.
• Even the largest vessels use much less land and manual labor than windrows.
• It produces little odor or leachate.
• The weather doesn’t affect in-vessel composting.
• It is a very expensive method and requires more technical expertise than other methods.

Municipal composting and a little history

In 1960, Sam Yorty became mayor of Los Angeles promising more convenient trash pickup. After the city finally banned backyard paper incineration, residents had to separate their wastes into solid trash, wet garbage, and paper. And they had to deal with three different companies to haul everything away.

Yorty provided one pickup of commingled wastes. It turned out to be a costly convenience, an environmental catastrophe that the US still hasn’t recovered from. Food waste now represents almost a quarter of the volume of municipal solid waste.

The municipal composting program in Davis, California, which began in about 1972, was among the first. The first private commercial composting companies started at about the same time. They started to become more commonplace in the 1980s as concern over rapidly dwindling landfill capacity began to grow.

Howard County, Maryland initiated a pilot composting facility in 2013.  It occupies about 2% of the county’s 25-acre landfill. The county has a population of about 320,000 people. Farmland takes up about a quarter of its area.

Its aerated static pile system started operating in 2020 with an annual capacity of about 3,000 tons of material. Agricultural waste including horse manure, provides much of the feedstock. Eventually, the county plans to offer curbside pickup of food scraps.

Diverting organic waste from the landfill saves not only space but the expense of transportation. The county sells finished compost locally for $23 per cubic yard. The project neatly proves that municipal composting can work outside of large-population areas.

The problem of collecting organic waste

Food waste amounts to 8% of greenhouse gas emissions in this country. In response, some American cities have started to explore municipal composting: adding compostables to their trash and recycling collections. It’s easier said than done.

New York City has offered neighborhood compost collection for years and hasn’t found how to scale it up. Not only is the collection difficult. So is developing facilities large enough to handle the volume of what’s collected. And since the program in voluntary, not enough of the public has bought into the concept to make it cost-effective.

San Francisco has operated its curbside compost collection for 25 years now. From the start, it concentrated more on food waste than the more common yard waste collection. It has succeeded mostly by taking incremental steps to grow the program. In 2009, San Francisco made compost collection mandatory. It now diverts 80% of its waste from landfills.

Unfortunately, the public acceptance of San Francisco’s organic collection has made people feel more comfortable about contributing to food waste. The volume of food waste has increased over the years as people no longer feel guilty about sending it to the landfill. But it still emits greenhouse gases while it rots awaiting collection.

California tries to undo Yorty

Beginning in January 2022, California began to enforce a law that requires separation of organic waste from other trash. That’s right. Now Californians have to separate their wastes into three different containers: trash, recyclables, and organic wastes (including food waste and yard waste). San Francisco and other Bay Area communities have been doing it for years.

Residents in the rest of the state will have various start dates. Some of them may be wondering why they have to put up with the inconvenience. Have they been told that they’re part of a plan to undo a more than 60-year-old mistake?

The state plans to divert the organic waste either to composting facilities or anaerobic digestion facilities. At the latter, it plans to capture the natural gas and use it. It can power the trash trucks, for example. California landfills will no longer emit as much methane once the project rolls out statewide.

But they can’t entirely undo Yorty’s damage. Before 1960, all households and businesses separated organic waste from everything else. Presumably, the haulers either composted or burned it. Now, it’s commingled with everything else anyone throws out.

Composting municipal solid waste without source separation leads to problems with contamination. Customers who bought compost from the city of Seattle, Washington in the 1980s reported that it killed some of their garden plants. After the problem was traced to a particular herbicide, the state of Washington banned it.

Still, composted municipal solid waste can still have enough chemicals in to disqualify it from use for organic gardening. Even leaves removed from driveways might be contaminated with motor oil.

The problem of bioplastics for commercial composting

Municipalities and private companies face all the same problems with the quality of feedstock.

Only 15% of commercial composting facilities in the US accept any kind of compostable packaging. In Canada, only 10 of 97 composting facilities accept even fiber packaging. Only one accepts bioplastics. Part of the problem is that fiber packaging often has a polyethylene lining that cannot break down in even the hottest of compost piles.

Bioplastics may one day become compatible with industrial composting, but they haven’t yet.

The Composting Manufacturing Alliance, the industrial composting industry’s trade group, sets useful standards for compostable packing, including food service ware. It performs field testing of feedstocks sent to commercial composting facilities. Its website identifies the products each member facility accepts.

The Biodegradable Products Institute certifies certain packaging as compostable in municipal or commercial composting programs. So far, of course, no bioplastic is compostable at home.

The Center for Environmental Health and Clean Production Action have developed the GreenScreen Certified label to identify which food service ware products contain only safe ingredients. It applies to both compostable and non-compostable packaging.

Standards exist for municipal and industrial composting but not for home composting. Such standards will be necessary before it will be possible to identify which disposable products will break down there.

Related posts:

Garbage to garden: composting basics
Trench composting at home: an infographic

Sources:

Are compostable products the best choice? / Renga Subramanyam, Earth 911. August 13, 2021
Compostable products: industry initiatives & optimal choices / Renga Subramanyam, Earth 911. August 20, 2021
How commercial composting works / Gemma Alexander, Earth 911. January 20, 2022
Municipal composting facility proves economics and feasibility of large-scale processing / EA Engineering, Science, and Technology. October 21. 2021
The quest to make composting as simple as trash collection / Linda Poon, Bloomberg. October 14, 2021
Types of composting and understanding the process / US EPA. April 21, 2022
What you need to know about California’s new composting law — a game changer for food waste / James Rainey, Los Angeles Times. December 26, 2021