Composting is not for everyone.
I notice this when I travel home to visit my parents in Florida, or pretty much anywhere outside of Vermont or other states that mandate trash collection. Curbside collection is rare; many see it as a chore. Even for those, like me, who enjoy turning leftovers into rocket fuel for the garden, composting can turn into a foul-smelling, sulfurous mess.
But what if you could make your food waste disappear by simply digging a hole in the ground, dumping it, and walking away? No more dirty trash. Less climate pollution. While researching ways to make compost, I discovered an easy way to return almost all organic waste, from vegetable scraps to chicken bones to pet waste, back to nature: the solar digester.
These biodigesters don’t produce compost, the rich, fluffy organic matter that goes back into the soil. Instead, these biodigesters—usually plastic cones half-buried in a little soil—use the action of microorganisms and the heat of the sun to convert organic matter into its elemental components, primarily carbon, water, carbon dioxide, and micronutrients, says Yichao Rui, a soil scientist at Purdue University’s College of Agriculture. “Nematodes, bacteria, and fungi all work together to break down all this organic matter,” he says. “Large and small soil organisms mainly digest and eat them,” returning plant and animal material to the soil and air components.
It’s a simple, easy, and non-dirty solution to keeping organic waste out of the trash and landfills. 58 percent of methane gas emitted by municipal landfills comes from rotting food.
So in January of this year, I ordered my own “green cone,” buried it in the ground, and began testing it by putting in loads of food waste each week. Here are the results:
The growing food waste problem
According to the Environmental Protection Agency, the average American household tosses 300 to 400 pounds of food waste into the trash each year, which, when buried deep in airless landfills, turns into methane, a potent greenhouse gas, further contributing to global warming.
States and federal agencies want to wean themselves off this global warming substance. They start by trying to prevent food waste by encouraging less wasteful shopping, storage, donation and upcycling (reusing it as animal feed, for example). But there will always be waste, and an increasing number of states are treating food waste like recyclables: a valuable material that should never end up in the trash.
On July 1, 2020, Vermont became the first state in the United States to ban most food waste from being disposed of in the trash or landfill. Most trash collection companies offer food waste pickup services, or residents can compost at home (residents who compost at home are not required to compost meat and bones, but they can). State officials estimate that more than half of food waste is diverted from landfills. According to the University of Vermont, 85% of Vermont residents compost, most of which is done in the backyard. Only about one-fifth rate their composting as “hard or very hard.”
Dana Gunders, executive director of food waste reduction group ReFED, says more states are following Vermont’s lead and introducing food waste regulations. Most policies focus on large corporations initially, but once composting and distribution facilities are in place, restrictions on households are feasible. Ten states, including Massachusetts, New York and Washington, DC, currently restrict the disposal of organic waste. “I think new scientific research showing that about 10 percent of methane gas in the U.S. comes from food in landfills is driving interest in organic waste bans and diversion targets,” Gunders says.
What is a solar digester?
Solar digesters are still relatively unknown. Josh Kelly, solid-waste program manager for the Vermont Department of Natural Resources, says the most popular products so far are the Soil Saver ($52), an insulated compost bin for cold climates, and the Barrel Composter ($38), a compost bin or drum that can be turned to mix the contents.
But as organic waste bans spread, solar digesters are likely to play a bigger role.
Perhaps the most popular design is the green cone. This digester (which retails for $200 or is subsidized by many waste-treatment agencies) is a 2-foot-tall cone that sits on top of a plastic mesh basket that holds food waste. The cone concentrates the sun’s heat, and the food waste is sometimes dusted with bacterial cultures, or “accelerant powder,” to speed up decomposition.
The plastic mesh basket allows soil microbes and invertebrates to coexist, and the large air chamber creates aerobic conditions to reduce odors. Because it is buried underground, it will exclude most animals, but if burrowing animals are a problem we recommend using wire mesh.
How much food waste can it handle? Two pounds per day, or the equivalent of one or two households’ worth of food waste, says Carl Walkomski of Tar River Trading Post, Green Corn’s U.S. distributor. Walkomski says that the combination of an internal temperature of up to 130 degrees and regulated microorganisms allows it to quickly process almost any organic material, even bones and pet waste (using special bacterial cultures). Once every few years, whatever’s left in the basket is thrown out. Woody biomass, such as branches and yard waste, and industrially compostable plastics are not recommended.
How well did my solar digester work?
One warm spring morning, I set up Green Cone in my backyard and started filling it with food waste. Over the next few months, it ate everything I threw at it. The trash never got more than a few inches high. At one point, it even got some unwanted help: a burrowing animal got into the basement basket. I fixed it with some cheap chicken wire, and it’s still there to this day.
Can anyone use a solar digester? You need to dig a hole in well-drained ground with plenty of sunlight. If you have waterlogged or clay soil, you’ll need to raise the cone so the digester chamber stays moist but not waterlogged. In winter, as long as there’s sunlight, the decomposition will slow down but not stop. If it’s too expensive (Warkomski says the high manufacturing costs in Canada, the US and the UK, and the use of high-quality recycled plastics make it more expensive), you can share it with another family member or DIY it yourself if you have the time.
Composting isn’t hard, with a solar powered digester it’s super easy, weeks can go by without throwing anything away, recycling can handle the bulky items, my Green Corn takes care of the rest.
