Bamboo cutlery, plant fiber plates, trash cans and many other household items are all now labeled as home compostable and can be easily found in stores and online. In December, the New York-based Biodegradable Products Institute (BPI) announced certification standards for home compostable products and labels for bioplastic products that can be broken down in backyard trash cans. Since then, we have quietly certified the products of about 20 companies.
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Austrian company TUV has a similar label, OK Home, with hundreds of products already on the U.S. market.
Compostable bioplastics are primarily manufactured using the same processes as traditional plastics, using plant materials, fossil fuels, or both. Most are designed to decompose under controlled conditions in commercial facilities, where billions of microorganisms break down the material into water, carbon dioxide, and compost.
The idea behind compostable bioplastics is to reduce greenhouse gas emissions by diverting food waste (which is increasingly packed into biobags) from landfills to compost piles, reducing pollution from traditional single-use plastics.
However, some compostable products cannot fully decompose, and many commercial composters prohibit them.
Greenwashed products with misleading labels are also part of the problem. This is one reason why BPI launched the Home Compostable label, which certifies products that can decompose under the low temperatures typical of backyard bins.
“We thought it was important to begin testing claims about home compostability,” said BPI Executive Director Rose Yepsen.
Home composting could, in theory, help more people reduce plastic pollution by using compost in their own backyards. However, open questions remain regarding how these products degrade, and research and standards continue to evolve.
Tricia Vaidyanathan, scientific director at Beyond Plastics, said BPI’s standard is “a pretty good standard for home composting, but it’s not a health or environmental standard, so it leaves a lot to be desired,” adding that she was concerned about whether it “reflects what happens in someone’s backyard.”
A compostable bowl on an outdoor table in Walnut Creek, California. (Photo credit: Smith Collection/Gado/Getty Images)
What to look for in a BPI home compostable label
BPI’s new certification is similar to TUV’s OK Home label. BPI based its version on the French composting standard, but also on its own six-month study of how well home-compostable products already on the market break down in different backyard systems, climates, and varying degrees of management.
The study included more than 15 sites, ranging from volunteer-managed backyard piles to community compost operations, but the results were not made public, a BPI spokesperson said.
To earn BPI’s home composting certification, materials must meet two international standards for industrial composting set by the American Society for Testing and Materials (ASTM), but must be done at lower temperatures typical of backyard piles (25 degrees Celsius/77 degrees Fahrenheit), rather than the industrial temperatures of 55 to 60 degrees Celsius. A longer period is also allowed compared to 12 weeks for industrial composting.
Experts agree that materials that meet ASTM biodegradation standards should theoretically break down more easily than traditional plastics, and several studies back this up. But no one knows how long it will take for compostable microplastics, whether produced in commercial or home systems, to fully break down in soil.
As part of the BPI study, Ohio State University professor and compost researcher Frederick Michel tested 14 types of home-compostable materials, including butcher paper, single-use coffee capsules (K-cups), plates, straws, and compostable bags, in five different containers (two tumblers, an open heap, and an insulated container) to simulate how homeowners would add food scraps and manage the containers. fertilizer and fallen leaves. His lab received a BPI grant to study the product, but he is not otherwise affiliated with the organization.
One of Michel’s most interesting findings, he said, was that home composting systems were able to achieve, on average, only 5 degrees Celsius above ambient temperature. As a result, much of the test material did not completely degrade throughout the six-month study, except in the insulated container, which reached consistently high temperatures.
“The compostable bags didn’t completely decompose after six months, but they decomposed better when filled with food scraps. The K-cups only decomposed in an insulated container,” he says. “But all (the materials) have degraded to some extent, so I think if you do this for a year, it will break down over time.”
However, Michel said he was concerned that non-biodegradable coatings on compostable products, even a small portion of the total product, could generate persistent microplastics.
Real-world backyard composting challenges
San Francisco restaurants are marking their utensils, serving containers, and cups as compostable. (Photo credit: Lee Suzuki/San Francisco Chronicle via Getty Images)
Michelle’s results are consistent with the experience of composting practitioners. Some compost manufacturers estimate that home compostable products can take up to two years to fully decompose, and BPI also advises home compost manufacturers to allow 12 months for BPI-certified products to fully decompose and leave no detectable microplastics.
This is because people’s attention to backyard conditions and mountain management varies greatly. Generally speaking, “home compost very rarely achieves composting as well as commercial compost,” says Caleb Goossen, organic crops and conservation specialist with the Maine Organic Farmers and Gardeners Association (MOFGA). “It’s difficult to pile up enough material to retain heat.”
MOFGA maintains a small outdoor composting operation to compost bioplastic food service equipment used at the annual trade show, which draws 60,000 people over three days. MOFGA prefers reusable cups and plates, but Goossen said that’s not a realistic option for the fair.
MOFGA facility director Jason Tessier perfected the system through trial and error, using 180 yards of food scraps, manure, bedding and butcher waste from his dairy farm to compost 30 yards of compostable plates, cups and cutlery.
Many home composters won’t be able to take advantage of dairy inputs, which provide microbes and heat, Tessier said. “I think the typical home composter that I talk to has a really hard time maintaining the temperature and has a really hard time composting (these) products,” he said.
Several home composters shared different experiences. Ben Jankowski, a member of Pedal People, a Northampton, Mass., trash, recycling and composting group, said he occasionally puts bioplastics into two compost piles at his home. Each compost bin contains approximately 100 to 150 gallons of compost.
“I’ve been experimenting with it a little bit, and it seems to work pretty well, especially the BPI-certified ones,” he said. “They melt quickly.”
Jankowski’s household generates a lot of food scraps, to which he adds some of the leaves and compost he collects through Pedal People. “We might be a little fed up” of microplastics, he added. “I work with trash all day, so you’re probably going to produce some trash too. We need to minimize it as much as possible.”
Margot Wise, a certified community composter who runs a community compost hub in Holyoke and maintains a pile in her backyard, said she thinks it’s “great” that materials are being developed that can be composted at home or in the backyard, since so many people don’t have access to commercial composting equipment.
But education is a big challenge, she said, and it’s very difficult to give people clear instructions on what types of food scraps can go into local compost piles. There is so much confusion about which products can really be composted in the backyard that she is hesitant to allow them.
Rick Carr, senior farm manager and director of composting at the Rodale Institute, worked to compost bioplastic products both at his home and at the organization’s Pennsylvania site after the event. Carr maintains a separate pile for composting bioplastic serviceware and does not allow bag liners or other bioplastic items in organic compost.
“In my experience at any scale, you have not been able to break down these materials,” he said.
Home Compostables and Chemical Contamination
Scientists are far more concerned about the chemical additives and untested decomposition products released as household compostables decompose than microplastics. Therefore, most experts caution against putting bioplastics in backyard bins and spreading the compost in edible gardens.
Compostable bioplastics, which can be used for home and commercial composting, are primarily made from renewable resources such as corn, sugar cane, and seaweed, but most are made using the same processes as traditional plastics, with chemicals added to give them properties such as flexibility, durability, and color. Some are made from fossil fuels and are designed to break down.
Alternative films for wrapping leftovers, often made of polybutylene adipate terephthalate (PBAT), for example, fall into this category.
