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A set of three ukiyo-e prints depicting Osaka's bustling shipping industry. by Gansuitei Yoshitoyo. 1854–1859.
This set of three prints from the 1850s depicts the harbor of Osaka, Japan. Illustration by Gansuitei Yoshitoyo

Why Shipping Shit Is a Good Idea

Ancient cultures knew the value of their excrement. Given the current environmental emergencies, it’s time we resurrect their wisdom.

Authored by

by Lina Zeldovich

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The following excerpt is from writer Lina Zeldovich’s first book, The Other Dark Matter, which focuses on the science of poo and the novel solutions to dealing with human excrement, an age-old problem. Zeldovich has written for Hakai Magazine since it launched in 2015. She has covered no-carbon cargo boats, the sale of killer whales in Russia, the US Navy’s use of dolphins, and the value of bird shit.

At some time during the Tokugawa period in Japan, between around 1600 and the mid-1800s, the magistrates in the coastal city of Osaka received air quality complaints. Residents who lived near the port objected to the foul smell that emanated from some of the docked ships. A thriving urban sprawl, Osaka welcomed many merchant boats, domestic and foreign, that delivered tea, rice, silk, fish, and other goods. But along with these boats came other vessels that ferried much less agreeable cargo: human waste.

These boats cleared the city of its daily shimogoe, as the Japanese called their sewage. In Japanese, the word shimogoe literally means “fertilizer from the bottom of a person” and is roughly translated into English as “night soil,” explains Kayo Tajima, a professor at Rikkyo University in Tokyo, whose research focuses on environmental economics and urban studies.

Brought to the wharves by the shimogoe collectors, the waste was loaded into the boats’ bellies. But instead of being dumped into the sea or onto a remote island, where the Japanese sent some of their other, less useful garbage, it was shipped to farmers outside the city of Osaka. The valuable shimogoe went on to nourish crops for the people who produced it. As the city grew, so did the amount of night soil it generated. More boats had to come to take away the mammoth loads. Eventually, the daily hauls generated such a stink that the city folk protested.

The magistrates considered the problem. On one hand, the complaints had merit. The Japanese culture valued cleanliness. On the other, banning the sewage ships from the port would cause not one but two major problems. First, it would cripple the city’s waste disposal system. Second, it would leave farmers without fertilizer and urbanites with food shortages, both of which would result in an uproar. After much deliberation, the magistrates ruled that “it was unavoidable for the manure boats to come into the wharves used by the tea and other ships.” In the end, the sewage haulers retained their rights to dock alongside other vessels.

To some, especially in the West, this decision may seem unhygienic at best. But to the Japanese, the ruling was logical. They maintained a very different view of human excreta than the Western world. Japan didn’t have an abundance of natural resources and large swaths of fertile land. Spread over a few small islands where mountain ranges occupied three-quarters of the landmass, Japan had to make do with what it had. A large portion of its harsh, rocky terrain couldn’t be used for agriculture at all. Unlike Europe, Japan lacked abundant grassy landscapes, which limited how many cattle it could sustain. Its soil, sandy and nutrient-poor, would bear very meager crops without fertilizer. So while European farmers could cut down forests to plant crops, which thrived in rich soil left behind by trees, the Japanese never expected much from a new plot. A Japanese saying, “A new field gives but a small crop,” epitomizes the agricultural challenges the culture faced.

As crops grow, they extract nutrients from the soil—including nitrogen, carbon, calcium, phosphorus, potassium, sulfur, and magnesium—to build their cell walls. If the soil is to produce crops year after year, these nutrients must be regularly replenished with the addition of organic matter from agricultural refuse like rice husks, animal remains like crushed bones, or digested food like manure, which contains all of the leftover nutrients.

In the soil, certain bacterial species feed on the carbon, freeing nutrients like nitrogen, potassium, and phosphorous for the plants. Other microbes convert nitrogen from the air into ammonia, a potent plant food. The latter, however, is a very slow process. Freeing nitrogen and other nutrients from agricultural refuse is somewhat quicker, yet it still takes time—weeks for leaves and months for twigs or corn husks. But manure, whether human or animal, is a partially digested organic material, so it’s already broken into smaller compounds and molecules, and that makes the microbes’ work easier. Composted manure, which microorganisms and earthworms have already chewed through, makes an even better fertilizer. The plants don’t have to wait for the nutrients to become available—their roots can just start sucking them up.

Japanese farmers didn’t know about the complex inner workings of the soil microbes, but they could certainly see that adding “humanure” to their land made crops flourish. “Japanese peasants didn’t keep big animals, they had very few horses and cows, so they didn’t have animal manure,” Tajima explains. “So they had to use what humans produced—shimogoe.”

Historically, only a handful of cultures around the world used humanure—and they all had one thing in common: poor soils that otherwise wouldn’t yield much. In China, excrement, or fenfu, was valued so highly that the fenfu men who gathered it priced it based on the parts of cities it was produced in. The wealthier people, who ate more nutritious food, generated more nutrient-rich fenfu. Even the emperors knew the value of shit. “Treasure night soil as if it were gold!” was the directive of an imperial treatise published during the early Qing dynasty in 1737. In Europe, only Flanders and the Netherlands, which weren’t blessed with fertile land, used humanure to boost crops. People stored it in sunken outdoor tubs, gathering it like “honey from the hives,” as one agricultural scientist noted later.

Other Europeans didn’t share that view. They were lucky to have vast expanses of land and enough cattle to supply manure. And when their old fields grew barren, they could often clear more land. They didn’t need the fertilizer from their own bottoms, so they never learned to appreciate it. And, as science, medicine, and technology came of age, the value of human excrement, already low, dropped precipitously.

Medical research found that many deadly bacteria naturally dwelled in sewage, so who in their right mind would put this toxic muck on their farm fields? And when humans finally learned how to produce synthetic fertilizer in the early 20th century—which came in odorless neatly packed bags and without dangerous pathogens—humanure was doomed.

Historians aren’t sure when the last of the shimogoe boats left Japanese harbors, but they were eventually replaced by modern sewage pipes. Every developed industrial nation built these systems to end the epidemics of cholera, dysentery, typhoid, and other infectious diseases that swept through many cities in the 19th and early 20th centuries. And end the epidemics they did. Only they helped create a whole new set of problems because humans cannot stop eating or excreting. And as the human population grew so did the amount of sewage it dished out. That changing geography of excrement created a major nitrogen imbalance, which some scientists call the redistribution of nutrients on the planet.

To understand this in action, start at your local supermarket. The next time you go grocery shopping, note where your food comes from. If you live in a colder climate, most of it isn’t local. In Canada and the northern United States, your strawberries probably come from California or Florida, your asparagus from Mexico or Chile, and your bananas from Ecuador or Costa Rica. Your salmon probably comes from Alaska or British Columbia, your beef probably originates in Alberta or Texas, and your pork sausages aren’t stuffed by your local butcher, either. Most of the food that gets put on our tables these days is shipped, trucked, flown, and in some cases, even helicoptered to us from far away.

As it grew, your food extracted nutrients from the soil in which it was planted. Then it was shipped to you—using fossil fuels. Next, you eat the food—and you excrete the unused nutrients, which ultimately end up in a local body of water, probably closer to your house than you think. So we are continuously taking nutrients from some parts of the planet and discharging them in others. The result? Depleted, barren soils in some places, and overfertilized, stinky, dying creeks and marshes in others.

Today, farmers in North America and beyond spend billions of dollars on synthetic fertilizers, trying to keep their soil fertile year after year. But when we continuously ship corn from South America and strawberries from California to other places—to be eaten and turned into waste—we deplete soils, and then use synthetic industrial fertilizers to replenish their nutrients. What we completely leave out of the equation is that our waste—the potent fertilizer we produce regularly—goes to fertilize all the wrong places: not the farm fields, but our rivers, lakes, coastal marshes, and the ocean. And because we don’t ship our shit back to where the food came from, this problem will only get worse. Some scholars have called this changing geography of excrement a metabolic rift—meaning that body wastes are generated too far from where the food that fed those bodies comes from.

That redistribution of nutrients on the planet ruins the nutritional balance of ecosystems, explains Canadian epidemiologist David Waltner-Toews. “You’re taking all this biodiversity out of one ecosystem and creating these piles of shit somewhere else,” Waltner-Toews says—hence farm soils turn to dust while waterways suffocate from toxic algal blooms and marshes fall apart. As a result, our continuously depleted farmlands require more and more fertilizer to produce food. With our changing climate, unpredictable weather, droughts, floods, and heatwaves, barren soils only add to our already pressing food security problem. We solve this problem by putting in more fertilizer, but we don’t have a good way of trapping the excess of nutrients on the other end. Instead, we release nitrogen-rich effluent into the water while the remaining biosolids, aka sludge, are burned or put in landfills, rather than into the fields.

There is no doubt that sewage disposal methods in modern industrialized countries are more hygienic overall than they were centuries ago. Our waste doesn’t decay in pit latrines. It doesn’t leach into drinking water. We no longer have cholera epidemics. But we haven’t gotten anywhere near the recycling prowess the Chinese, Japanese, and Flemish exhibited centuries ago. Today, even those nations have adopted the industrial methods of sewage disposal that have brought with them larger, more global, and more nuanced problems. No matter what humans do, our shit comes back and bites us in the rear. It really does look as if we can’t win the waste war.

Can the solution be found in growing food locally as much as possible and supplying city residents with composting bins? Or should we load our sewage into barges and ship it to Florida and California to scatter on the fruit orchards? If oil tankers can ship oil across the ocean, why can’t shit tankers ship shit?

That’s exactly what the visionary shit thinkers are thinking. Prompted by the Gates Foundation’s Reinvent the Toilet Challenge, scientists and entrepreneurs all over the globe are finally looking at excrement in the same way as our thriftier ancestors did several centuries ago—as a resource, not as waste. There’s no single one-size-fits-all remedy for our sewage problem, but some poop upcycling efforts are already happening. There is a Madagascar-based start-up that converts poo to biogas and fertilizer. There’s a Kenyan venture that singes it into charcoal briquettes. A Canadian company blends sewage into a smoothie that is dispersed on fields. An American wastewater treatment plant converts it into garden dirt neatly packaged into square bags with cute logos, which local gardeners can buy as organic fertilizer they made themselves—a modern-day shimogoe.

When was the last time you dropped into your local sewage plant? You may be in for surprises—scientists, innovators, and ecologists are using our unwanted dark matter to generate electricity, cook dinner, and fertilize veggie patches. The rest of us just need to stop holding our noses and dive in.

Adapted from The Other Science Dark Matter: The Science and Business of Turning Waste into Wealth and Health by Lina Zeldovich, to be published by University of Chicago on November 19, 2021. Copyright © 2021 by Lina Zeldovich.