In Osaka, Japan, in the early-1700s, neighboring villages fought over rights to city residents' excrement. Much of Japan's soil, sandy and poor in nutrients, produced feeble crops and supported few animals, so farmers depended on human fertilizer to grow food. And they were willing to pay for it. Often in exchange for a fee paid to each household, farmers collected what was called night soil at regular intervals to fashion into fertile compost. Poop was precious. Defecating at a friend's house was considered an act of generosity — a gift. Landlords earned extra income by retaining collection rights from tenants: Often the bigger the household, the lower the rent. As the city of Osaka grew, so did the value of residents' waste, until prices climbed to such extremes in the early 1700s that some desperate farmers resorted to stealing it, despite potential prison time.
Roughly a hundred years later, London's River Thames was choked with human and animal waste, emitting noxious methane, ammonia, and the rotten egg smell of hydrogen sulfide. Seemingly more sewage than water, the river's banks swelled with refuse, interfering with marine navigation and making life miserable for many Londoners. Finally compelled to act, city authorities contracted boats to carry the sludge out to sea and dump it — at the approximate cost of a million pounds, or more than $170 million in today's U.S. dollars.
Why are these stories of human excrement so different? The key, according to science journalist Lina Zeldovich in "The Other Dark Matter: The Science and Business of Turning Waste into Wealth and Health," is that one culture regarded poop as trash, the other as treasure.
With plenty of flat land and rich soil, the British could afford to chuck out their excreta, and so they did. In the absence of the invertebrates and microbes in dirt that transform dung into harmless compost, Londoners' excrement flowed to the river and festered. And when cultivation exhausted the soil, British farmers simply tilled another square. But Japanese farmers could not. Limited land and livestock necessitated soil replenishment with nitrogen, phosphorus, and other nutrients — all of which are present in poop. So excrement was recycled into the same ground that created the food it came from.
Inspired by childhood memories of watching her grandfather turn septic waste into garden compost in Russia, Zeldovich takes readers on a historical tour of human sanitation, then positions the ideas and practices of the past in the present. Sanitation challenges to health, the environment, and the economy have grown globally, and the book highlights entrepreneurs working to solve these problems. Its last section describes the relatively recent discovery of the human microbiome and poop's life-saving role in human health. Throughout, the book presses the reader to reexamine how we understand human waste.
"We may think that we have solved the excrement problem in the Western world with our massive sewage plants," writes Zeldovich. "But the bitter truth is that we have solved only one problem — ensuring that our excrement no longer endangers our health."
Today, Zeldovich argues, we find ourselves at the intersection of Japan's need and Britain's overabundance. Increasing food demand strips our soil of nitrogen and other nutrients, while sewage pollutes land and water. We continue to frame poop as waste and ignore its value at our peril — creating a "ticking time bomb" that perpetuates a broken cycle of dirt, food, and fertilizer.
The closed cycle of the old Japanese system, in which waste is plowed back into soil, is not as ubiquitous in today's farmlands. In towns and countries without water treatment facilities, excrement can accumulate in streams and even people's yards. "The World Health Organization (WHO) estimates that 2.4 billion people on this planet still lack access to basic toilet facilities, and that nearly 1 billion still head for the bush," Zeldovich notes.
Modern sewage treatment removes pathogens but often leaves nitrogen, phosphorous, and minerals. Centuries ago farmers were forced to add waste back into their fields as soil became depleted, but in the early 1900s German scientists Fritz Haber and Carl Bosch discovered a way to pull nitrogen from the air to produce synthetic fertilizer. Easy to transport, less smelly, and effective, synthetic fertilizer quickly replaced poop.
In China, one of the largest global fertilizer consumers, about "80 percent of the nitrogen in Chinese bodies now comes from food produced with the aid of chemical fertilizers," Zeldovich writes. Nutrients from excrement in China and most other industrialized countries does not always return to fields. Instead, excess nitrogen and phosphorous is flushed into the water where it creates algal blooms and destroys marshes.
One such marsh is on a pond near the Quashnet River, on Cape Cod. A model of nitrogen overabundance, its "collapsing banks are so slippery you must be careful not to fall into the foul-smelling water, which looks dark blue and opaque like ink," Zeldovich writes.
Not long ago, scientists thought marshlands were infinite sponges, able to recycle as much nitrogen as we could pump into them by simply growing more plants. We now know that with enough pollution marsh plants grow shallow roots, banks erode, microbial communities turn sour, fish and crabs die, and as Zeldovich notes, "when pushed to the brink, the marshes can 'flip,' turning from carbon sinks into carbon emitters — speeding up the dreadful warming cycle and all the evils that come with it."
Fortunately, potential solutions abound. One is Loowatt, a small startup that began in Madagascar's capital city of Antananavrio, also known as Tana, that turns excrement into power and fertilizer. Sanitation is a pressing problem in Tana, where latrines are holes dug into the ground. After frequent rains, Zeldovich writes, "the filth rises up to the brim and then slowly flows over, oozing out into the yards, down the streets, and into people's living rooms."
To prevent flooding, Loowatt provides special toilets — for a monthly or pay-per-use rate — that encase eliminations in biodegradable plastic. Employees retrieve the poop-filled bags and deliver them to a processing facility, where the bags are broken and chewed up by machines, the sludge is mixed with food waste and heated to kill pathogens, and bacteria convert the mix into biogas and fertilizer.
Loowatt uses its biogas-generated power to pasteurize the sludge, and toilet biodigesters help to recharge customers' phones. The fledgling company converts 1,000 people's emissions into about 6 metric tons (more than 13,000 pounds) of liquid fertilizer a month, with aspirations to become the major sanitation provider to the city's 1.2 million people in five to 10 years. Loowatt toilets are already in use in the United Kingdom at festivals and other outdoor venues.
On a much larger scale, the Newtown Creek Wastewater Treatment Plant in Brooklyn, New York, "serves about 1 million people, [and] generates 2 million cubic feet of biogas every day," the book notes, while in Washington, D.C., the city's sewage treatment plant processes the contributions of 2.2 million people into Grade A fertilizer that is sold in stores.
In the Pacific Northwest, scientists are working to turn the city of Vancouver's poop into biofuel. When a program to convert algae into oil fell flat due to cost, scientists turned to cheap and abundant sewer sludge. Unlike fertilizer that must be transported back to farms, "poop-derived gasoline doesn't have to travel anywhere. It can be used right next to its original source…," Zeldovich writes.
The book's final section details the use of human waste as a diagnostic tool in medicine, including the fascinating science and history of fecal transplants and how one patient's impassioned speech changed the FDA's trajectory for regulation.
It would be easy for a book that focuses on obstacles to improving global sanitation, fixing the agricultural waste cycle, reducing pollution, and improving health to resort to paralyzing gloom. "The Other Dark Matter" does not shy from the enormity of the problems, yet suggests solutions are achievable, at scales from individuals to entire countries. Paced quickly with prose enlivened by the author's on-location reporting and personal experiences, the book is far from a grim slog through the world's sewers — it's more like an exciting tour in a biogas-powered balloon.
"Moving bowels is one big equalizing commonality that unites humankind regardless of ethnicity, color, religion, diet, or traditions," Zeldovich writes.
"Perhaps this generation won't be ashamed of their organic power," she adds. "They won't think of it as waste."
Jenny Morber works a freelance science journalist on an island near Seattle. Her work has appeared in Popular Science, Discover, Glamour, and National Geographic, among other publications.