The Science of the City: Composting, the fertile solution to food waste

This story by MIT Environmental Solutions Journalism Fellow Paul Ruffins was originally published in Streetcar Suburbs News, where it appears with additional photos. It is the second in a series of articles exploring landfills, food waste, and methane emissions in Prince George's County and neighboring jurisdictions.

 

At the U.S. Composting Council’s (USCC) January convention in Phoenix, Ariz., the entire first day’s workshop examined how organizations already composting garden and agricultural wastes could meet the challenges of incorporating food. According to the U.S. Department of Agriculture, farmers estimate that nearly 49% of the soil used to grow America’s most important crops is eroded or depleted of some nutrients. The production and use of nitrogen fertilizers for growing food accounts for about 5% of global greenhouse gas emissions, which is more than aviation and shipping account for combined. However, as the first article in this series explained in March, adding food waste makes compost more nutritious and diverts food from landfills, saving space while reducing the formation of greenhouse gases.

Most attendees of the convention seemed to agree that the industry’s biggest worry is contamination. The ubiquitous plastics, PFAS, and “forever chemicals” in the environment are ending up in compost, attracting the prospect of regulation and possibly posing a small risk to compost farmers themselves. In response, one presenter argued that it was absurd to consider banning PFAS in compost when they are still legal in cosmetics and dental floss. Nevertheless,  most of the officials, farmers, environmentalists and manufacturers who attended the convention seemed optimistic that the composting industry will continue its explosive growth of about 10.6% a year through 2029.

The USCC has long recognized the Maryland suburbs of D.C. as national leaders in food composting. In 2022, Ben Parry, CEO of Rockville-based Compost Crew, won its person of the year award. In 2024, the USCC honored Prince George’s County for its efforts to collect food waste from over 104,000 households (now over 180,000). The county and Compost Crew represent competing visions: large centralized operations versus farm and community-based composting.

In the 1980s, the Prince George’s County Organics Processing Facility (OPF) in Upper Marlboro was created to keep grass, leaves, lawn clippings, trees and other organic matter out of the landfill by turning them into mulch and a profitable compost sold as LeafGro. In 2013, OPF became the largest facility on the East Coast to incorporate food waste into a product called LeafGro Gold. The facility is operated by Maryland Environmental Services (MES) — a state-owned nonprofit corporation.

Steven Birchfield, operations manager of the food composting operation, explained that mulch can be made from any untreated shredded wood, including trees and forklift pallets, and is primarily used to retain moisture and prevent weeds. “Compost,” he said, “is legally regulated by the Maryland Department of Agriculture as a soil amendment. It’s similar to fertilizer because it adds nutrition to the soil and must be safe to be used on food crops.”

Making compost requires microbes that grow the best with a carbon-to-nitrogen ratio of approximately 30:1 by weight. Generally, brown and dry organic matter, such as autumn leaves and wood chips, is higher in carbon. Materials that are moist and green, like grass clippings, are higher in nitrogen. 

The Montgomery County Yard Trim Composting Facility, in Dickerson, is typical of a large operation that doesn’t incorporate food into its compost. The facility collects yard trim and grass in the summer, leaves during the fall, and wood year-round. It then mixes them in the right proportions, grinds them, and forms the mixture into long, narrow triangular piles, called windrows, about eight feet high. The windrows are then regularly turned and aerated to reduce the formation of methane.

In any type of composting, the biological reactions should cause the compost to heat up to between 140 F and 160 F, which is hot enough to kill pathogens and unwanted seeds. With the right amounts of moisture and oxygen, turned windrows create compost in about eight or nine months. Adding food can threaten nearby communities by generating terrible odors and attracting birds and vermin. This is why Montgomery County, College Park and other municipalities that make compost don’t include food.

In 2015, the USCC named Prince George’s OPF the best large-scale composting facility in America because it had adopted a then-state-of-the-art pilot program to create compost that contained up to 50% food waste. Instead of starting with windrows, OPF placed materials in static piles covered with a breathable Gore-Tex material and force-fed air through perforated tubes. In 2018, the food composting project expanded to include 12 waist-high Gore-Tex-covered concrete bunkers, which supply air through holes in the floor. After several weeks, the compost is moved and formed into conventional windrows for final processing. The entire process only takes about two months, and the staff says the Gore-Tex covers prevent problems from pests or odors. The OPF also produces compost without food, for a total of approximately 70,000 tons per year.

Making compost faster in less space is important because Maryland House Bill 264 requires organizations that produce more than 1,000 pounds of food waste a week, such as universities, grocery stores and restaurants, to divert this waste from landfills or incinerators if they are within 30 miles of a proper facility that will accept it. To encourage recycling and composting, Prince George’s Brown Station Road Sanitary Landfill, in Upper Marlboro, charges $77 a ton (increasing to $85 in July). The OPF only charges Prince George’s County municipalities $25 a ton, while most non-county municipalities and commercial customers pay $48. It recently purchased an $800,000 de-packaging machine to process expired food in plastic containers or cans, which will cost customers $60 a ton.

The Convertus composting facility, in Manassas, Va., which services Prince William County, handles 100,000 tons of food and yard trim a year using a newer process that both blows and sucks air through bunkers covered with partly processed compost (rather than Gore-Tex fabric) to prevent pests and odors. However, this facility is about 34 miles from downtown D.C., compared to the 23 miles from downtown to Prince George’s OPF. An extra 22 miles or more round trip (and a river crossing) is an expensive difference for trucks that only get about 6 mpg. Thus, the OPF also composts most of the food waste collected in Montgomery County, as well as some from the District.

“The Organics Processing Facility has been a great financial success,” explained Maryland Environmental Services project manager Thomas Brewer. “Between our tipping fees and selling all the Leafgro Gold we make, the food composting completely pays for itself.”

So, what are the advantages of smaller organizations, such as Compost Crew?

Compost Crew provides paid compost collection services throughout the DMV and has developed several small-scale Compost Outposts. Its partners include ECO City Farms’ three nonprofit organic farms. ECO City’s 3.5-acre Bladensburg farm features a concrete bunker for receiving and mixing materials, and a composting enclosure approximately the size of a shipping container. The enclosure consists of two cells, with holes in the floor aerated by solar-powered blowers. With some additional processing, ECO City can produce compost in about four months.

ECO City Compost Manager Tom Fazio explained that one advantage of his operation is helping local communities and businesses save fuel and tipping fees. “In the fall, we encourage towns like Bladensburg and Riverdale Park to drop their leaves here for free, rather than driving to Upper Marlboro. Local landscapers also drop off wood chips at no cost,” he said.

The biggest plus may be producing compost with less contamination. For example, the OPF is not supposed to accept yard waste in plastic bags, but sometimes residents hide plastic bags inside paper ones. Once a non-compostable plastic spoon or other contaminant goes through a grinder, it’s very difficult to get it out. ECO City, on the other hand, doesn’t accept yard trim or use grinders.

When Compost Crew’s organic solutions representative, Tim Jenkins, arrives at ECO City with a ton and a half of food scraps, it’s all from ecology-minded paying customers who are much more likely to sort their waste more carefully than the average citizen. Then it’s his responsibility to further remove any other contaminants he sees, such as ketchup packets. 

“I consider the Prince George’s composting facility [the OPF] to be a valuable partner because we often drop off food with them when we collect more than our small operations can handle at one time,” he said. “However, it’s simply unreasonable to expect a huge facility to deliver compost of the same quality as a small organic farm.”

Composting is only one approach to food waste. Our next article will explore biodigestion and waste-to-energy incineration, which is widely used in Europe.