Compost, food for thought

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Food for thought
Tossing the wilted kale you never got around to cooking may be a bigger contributor to climate change than throwing away a plastic takeout container. A recent study by Zero Waste Scotland found that the carbon footprint of home food waste is close to three times greater than that of plastic waste, largely because when food goes to the landfill it releases methane gas, which is even more damaging to the atmosphere than carbon dioxide.

Composting, which turns organic waste into fertilizer, is one solution to the food waste problem. Humans have been composting for as long as they have been farming. The first written reference (pdf) to compost dates to around the year 2300 BC. George Washington, the first US president and avowed gentleman farmer, spent a lot of time thinking—and writing—about compost at his Mount Vernon plantation.

But large-scale food waste collection and processing is expensive and requires participants to be diligent and well informed. Can cities get citizens to do their part or will the idea end up in the trash heap?

2 months: Time it takes for an apple core to decompose

450 years: Time it takes for a plastic water bottle to decompose, though plastics may never truly disappear

1.94 million: Tons of food composted in the US in 2014

29 million: Tons of food sent to landfills in the US in 2014

$1,500: Value of the food wasted each year by an average American family of four—that’s 2 million calories

2020: Year San Francisco plans to achieve zero waste

95%: Amount of food waste recycled in Seoul, South Korea today

1 billion: Number of people who could be fed on less than 25% of the food the US and Europe wastes

How composting works

While food scraps and other natural waste like dead leaves and lawn clippings will decompose on their own, composting creates optimal conditions to speed up the process. A good compost pile starts with the right mix of organic materials. The pile needs both nitrogen-rch “green” materials, like food scraps and manure, and carbon-dense “brown” materials, such as dry leaves and wood chips.

The scraps should also be small in size to maximize the surface area on which microorganisms can feast. A backyard compost pile is a mini ecosystem, with bacteria and fungi feeding on the organic matter; protozoa, nematodes, and mites feeding on the bacteria and fungi; and predatory nematodes, predatory mites, and other invertebrates feeding on the protozoa, nematodes, and mites.

A compost pile also needs moisture, either from rain or manual watering, and oxygen, which can be added by turning the pile regularly or installing aeration pipes. Lastly, the pile needs to be at least 140°F (60°C) to prevent rot.

Whether you make your own or buy commercially produced compost, the benefits (pdf) to your yard and the environment are myriad. Compost reduces the need for chemical fertilizers while adding nutrients to the soil, helping the soil retain moisture, and limiting erosion. And there’s evidence that healthy soil is crucial to addressing climate change.

Can composting scale?

Encouraging dedicated Earth-lovers to start compost heaps in their backyards is one thing, but getting millions of space-starved city dwellers to separate their food waste into special containers for dropoff or collection is quite another.

Seoul may be the best model for how city-wide composting can be achieved. Today 95% of food waste in Seoul is recycled, way up from less than 2% in 1995. Seoul has compelled residents to compost since 2013, and they are charged for food waste removal by weight or volume. This has the double benefit of decreasing the amount of food wasted in the first place, and helping to offset the cost of the program.

In the US, similar efforts have seen mixed results. Some communities have resisted construction of large composting facilities, while others haven’t been able to keep up with public interest. There’s also a question of education: Casual composters often toss in items that don’t belong, like plastic, which can ruin an industrial-size batch of fertilizer.

With much fanfare, New York City started phasing in an urban compost program in 2015, but in 2017 managed to recycle just 1.7% of its organic waste. In 2018 existing pickup service was reduced and expansion to additional neighborhoods delayed. Last year the cost of the program was $15.7 million, and the city earned just $58,000 from selling the composted material in 2017.

Still, some would argue the hefty price tag is worth the benefits. As Frank Franciosi, executive director of the US Composting Council, told Governing magazine, “Cities should look at this as an investment for future growth and sustainability. One must calculate the cost of doing nothing against the cost savings of valuable landfill space. What are the costs for increasing methane in our atmosphere?”

“When you go about the repository for the compost, at the mouth of the drain by the Stable, if the bottom should not be of good clay, put clay there and ram it well before you pave it, to prevent the liquid manure from sinking, and thereby being lost—this should also be done on the New sides which are to be walled up.”
—George Washington’s instructions for building a compost “repository” in a 1787 letter to his farm manager

An energy-producing alternative

A process called anaerobic digestion still requires dutiful trash sorting, but it is one alternative to the cost and space challenges of large-scale composting. With the help of bacteria, anaerobic digestion breaks down organic waste into fertilizer and biogas, which can power processing plants and be refined further for use as fuel.

The initial startup costs are greater, but anaerobic digesters have a smaller physical footprint than composting facilities (and tend not to smell as much). They also have a smaller carbon footprint. Trucking food scraps from cities to processing centers and powering the processing equipment requires fossil fuels, but the byproducts of anaerobic digestion can make the process more or less carbon neutral.

And biogas pays. A recent report from the New York City Independent Budget Office found if the city were to turn all of its food waste and used pizza boxes into biogas, it could make back $22.5 million (although that’s still less than the $30 million allocated to organic waste removal in 2019).

The concept is gaining traction. In one county in Sweden, biogas from anaerobic digestion powers garbage trucks, taxis, cars, and 200 city buses. California has 14 digesters in operation; one at the University of California, Irvine helps power the Irvine Ranch Water District. And in March, a town on New York’s Long Island approved an anaerobic digester that will be able to handle roughly 180,000 tons of food waste a year.

The future of composting

Composting your kitchen scraps seems old-hat when compared to these futuristic examples of extreme composting:

Compostable clothing: Feel better about dumping your old duds by buying compostable jeans and sneakers.
Compostable food packaging made from garbage: This meta concept entails wrapping food in material woven from agricultural waste, which can later be thrown in a compost heap.
Cooking with compost: A recipe for “compost potatoes” from chef José Andrés’s latest cookbook calls for used coffee grounds and “a few scoops from your compost bin.”
Compostable styrofoam: Turns out mealworms have a taste for styrofoam—and what they poop out can safely be used as compost.
Composting ourselves: In May, Washington state’s legislature approved the composting of human remains as an alternative burial option.

At-home composters can recruit the help of certain worms in a process known as vermicomposting. Worm bins are especially ideal for those without a yard or who live in climates where year-round outdoor composting isn’t a great option. This time-lapse video shows how the worms turn food scraps into fertilizer over the course of eight weeks:

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