On This Earth

A blog about clean water, interesting toilets and how we can do better for our beautiful world

Author: Laura Allen

Top 5 reasons why The Sewage Question still stands (A book review)

“It need hardly be stated that the removal of human excrements out of cities and towns has always been a question of the highest importance, both from considerations of public health and national economy.”

Nineteenth century engineer Frederick Krepp had a lot to say about sewage. In 1867, when he published The Sewage Question (Longmans, Green and Co press), cities around the world were desperate for a solution to their poopy problems. Krepp had a solution for them — the pneumatic air toilet. Though his preferred design didn’t replace the flush toilet, he left a fascinating book detailing the 19^th century’s wild explorations with sewage, with lessons ripe for our modern day problems.

The mid-1800s were the heyday of sewage solutions. At this time, flush toilets were newly popular, but there weren’t systems to manage the wastewater. So sewage overflowed in towns, poisoning the water, killing fish, spreading disease and causing smells so awful they shut down Parliament.

Illustration of the waterborne cause cholera from 18 Aug 1866 edition of the satirical magazine “Fun”

City government and private industry looked for solutions. They experimented, tinkered, invested huge amounts of money, and threw up their hands. Most of the book’s 200 pages seeks to answer the question at the front of everyone’s mind: “What is the cheapest and most efficient technical process for rendering human excreta useful instead of dangerous?”

Krepp discusses the social and economic impacts of poorly managed sewage and lessons from failed nations who neglected agriculture. To Krepp, sewage and agriculture were intrinsically linked: people ate food from the land and excreted nutrients, which should be returned to the land.

Reserves for a vacuum system in Amsterdam. PHOTO: City Archief Amsterdam

Next, he complains about water flush toilets and the high cost for town sewers. His critiques echo the same problems we face today in attempts to bring safe sanitation to the 40 percent of the world that lacks it.

The bulk of the book covers all the sewer schemes of the day — and there were many! Including air closets, earth closets, buckets and pneumatic carts.

Here are five take-away lessons from The Sewage Question:

1. Sewage has value. In the 1800s, the majority of people believed sewage had value; they understood nutrients had to be replaced from farmlands to have productive crops. The problem was how to get the nutrients back out once water was used to transport feces. Writes Krepp: “We have seen how bountiful the reward, if we obey the divine Laws of Nature, by applying to agriculture the most valuable mineral and organic substances daily ejected from our bodies and how severe the punishment if we neglect to do so..[and allow them to pollute]”

2. Proper treatment of feces is necessary for a healthy society. On page two, Krepp lays out his view of governments: they exist to secure life, liberty and happiness for people, which relies on public health. Healthy people, he points out, need abundant food, clean air and an unlimited supply of clean water. Feces must be properly managed to meet these needs. “All efforts at sound civil government must fail, unless they secure these primary conditions of human happiness,” he writes.

3. The economy is tied to nature’s laws. Krepp calls this the sublime laws of nature and cautions that neglect of these laws leads to national decay. He emphasizes nutrient cycling and the need to “return to the soil the minimal ingredients we take from it.”

4. It’s harder to remove nutrients from wastewater than to keep urine and feces separated from the start. Many of the schemes outlined in The Sewage Question attempt to turn wastewater into a dry fertilizer, with dismal results. They proved, in myriad ways, it’s harder to remove nutrients from liquid wastewater than it is to compost humanure manure from dry toilets.

One epic failure took place in Birmingham, a riverside town of 300,000 people. They created filter beds with gravel and sand, in attempts to remove poop from wastewater. But the filter beds became choked and useless and the sludge wouldn’t dry and so no one wanted it for their farms.

Tank at the sewage farm, near Barking, London. Published in The Illustrated London News, 26 September 1868.

5. Sanitation systems must manage excreta from the toilet all the way until it’s returned to the earth. Krepp’s preference was the pneumatic toilet invented by Charles Lierner, whom Krepp had a business relationship with. This system managed feces from the house, to tanks, to transport, to special farming tools that delivered it into the earth. He also spoke favorably about the dry toilet options, such as the earth closet system of Rev. Henry Moule.

You can read a free digital copy of The Sewage Question or purchase a reprint from Forgotten Books.

May our labour not prove in vain, but assist in opening and smoothing the road to new fields of honourable and useful enterprise!

-Frederick Krepp, May 22, 1877

This plough is designed to deliver humane manure into the soil from barrels. Credit: The Sewage Question pg. 128.

April 2, 2026
Lessons from the chinampas: How the Aztecs recycled human nutrients for a clean, green city

It’s a gray August morning on the banks of Lake Xochimilco, a maze of canals and tiny islands, just a few blocks away from the highways and high-rises of the southern edge of Mexico City. The sounds of Mexican pop music mix with shouts from a nearby soccer game as I wait for our tour guide to load the canoes. The land here was hand-built many centuries ago — the remnants of a highly productive urban farming system that once fed the dazzling city of Tenochtitlan. That Aztec capital city was sewerless, waste-free and sparkling clean, sustained by a city-wide system that recycled food scraps and human poop to fertilize these nearby farms.

Our guide Francisco Javier Juarez is a biologist from Mexico City and a member of Humedalia, a nonprofit that promotes cultural and wetland preservation. They also farm one of the islands, our destination. I step gingerly into the canoe and we wait for a brightly colored party boat to pass by before paddling across the main channel. We head east, past snowy egrets and night herons, soccer fields and food stalls. The waterways split and turn, a labyrinth of dark water threading through lush green islands.

This system of farming, called chinampas, developed in the Valley of Mexico around a thousand years ago. Farmers created islands by staking out rectangular sections in the shallow lake, then filling them with brush and fertile lake-bottom muck. Layer by layer, like lasagna, the islands rose from the water. Willow trees planted along the borders stabilized the new land. Chinampa farming was small-scale before the Aztecs came to power.

Francisco Javier Juarez explains how the chinampa farmland was formed.

The Aztec’s island city

In the early 1300s, a group of people we now call the Aztecs migrated here from the north. They arrived in the Valley of Mexico and found a blanket of shimmering lakes across hundreds of miles, and wetlands noisy with the trills of birds. The only land available for the newcomers was a marshy island in Lake Texcoco, so they settled there. To grow their city, they used chinampa technology. Farmers lived on the islands and crops grew year-round. The new land expanded the city and fed its people, who in turn provided the nutrients that fertilized the soil to grow more food.

By 1519, Tenochtitlan was a bustling city, home to as many as 200,000 people, then one of the largest cities in the world. It was so magnificent that when Europeans first laid eyes on it, they “scarcely knew what to think” and wondered “whether all that we beheld was real,” wrote Bernal Díaz del Castillo, a Spanish invader traveling with Hernán Cortés.

Model of how chinampa islands were constructed. At the Museum of Anthropology in Mexico City.

In Europe at that time, urban waterways were polluted by feces. From rivers in London to canals in Venice, Europeans drained sewage into the water. There, tides or rivers eventually swept away the polluted water, but not in the Valley of Mexico — it had no natural outlet. The Aztecs developed a mindset worlds apart from the “out of sight, out of mind” mentality which shaped the polluting sanitation systems of Europe (and America).

And Tenochtitlan sparkled. A thousand workers cleaned the city streets, washing dust into the lake — but never urine, feces or organic waste. The surrounding waters teemed with life: aquatic plants, insects, fish, axolotls. Farmers and fisherpeople canoed food to the markets. One enormous market served a dizzying array of foods, goods and services including “delicious bars of dried algae from the lake,” writes Camilla Townsend in The Fifth Sun: A New History of the Aztecs.

Artist’s idea of what the public bathrooms looked like. See the toilet on left side of the wooden bridge. This drawing shows one of the causeways connecting the city to the mainland. This one carried drinking water from springs all the way into the city. Image: Jean Torton

Markets for pee and poo

Markets were organized by merchandise type, with sections for luxury goods, wood products, fruits, vegetables, meats, pre-cooked food and so much more, including human excreta. Urine, collected in clay pots from homes across the city, was distributed in the largest market. Díaz del Castillo described this place in detail, including the human excrement for sale in canoes at the docks. He noted that toilets were placed along every road, “so that great care was taken that none of the last-mentioned treasures should be lost.” Public and private toilets collected feces for fertilizer or for tanning animal hides, and urine served as a mordant — a substance to help fix dyes into cloth.

Though the Spanish were awed by this place, they had not come to learn how to recycle urban nutrients and protect the environment — they wanted gold. Just two years after their first visit, Tenochtitlan was destroyed and the Spanish ruled. The European contact sparked a smallpox epidemic that quickly killed nearly half the population and led to a famine. This paved the way for Cortez’s military takeover of the city. He destroyed the drinking water system, burned the libraries and smashed the temples. On the ruins, he built what became the Mexico City we know today. Quickly, the canals around the city reeked, filled with garbage and sewage. Later, the Spanish started draining the lakes.

Now, most of the lakes and wetlands are gone. What remains is polluted by sewage and street runoff, harming the wildlife in Xochimilco. Invasive species displace native ones. Many, like the axolotl, hover on the brink of extinction.

Francisco Javier Juarez stands in front of the chinampa. Willows line the banks, holding soil in place.

And yet, even polluted this place is magical. We pass fields of dark, fertile soil where marigolds bloom gold and corn stalks tower over squash vines. Chiles, amaranth, lettuce and sunflowers fill the fields. Pink trumpet flowers droop to the water’s edge, kissing their reflection under the bright sky. The biodiversity is stunning: this area holds two percent of the entire world’s biodiversity and eleven percent of Mexico’s.

Today there’s about one percent of the original chinampas left, and of those a small fraction are still farmed. The rest are soccer fields, party huts and food stands. “It’s kind of sad,” Juarez says, “some of the ancient techniques are getting lost, but not all of them.” He reminds us that this is living history. The whole area is recognized as a UNESCO World Heritage Site, and the Mexican government designated it a historic site, on par with the pyramids of Teotihuacan.

Visiting a chinampa

We reach Humedalia’s chinampa and climb onto the banks. The farm buzzes with flowers and veggies, herbs and sunflowers. There is a bathroom, too, a simple structure made from cob with a urine-diverting dry toilet inside. The dry toilet keeps feces out of the lake, but the humanure is not recycled as fertilizer, Juarez tells me. He’s not familiar with the practice.

After wandering the farm, our group gathers in their outdoor classroom to learn about the wetlands and legends of this land. Juarez is animated as he talks about axolotls and chinampas and preserving the Nahatl (NA-wat) language, the indigenous language here. Smoke from the wood cookstove drops tiny ashes in my lap and carries the aroma of our lunch. We share delicious food made with ingredients grown on this farm, sitting under a roof thatched with reeds from the chinampa.

A dry toilet contains human feces and prevents pollution of the lake.

I imagine what it was like back when nutrients cycled at a grand scale in Tenochtitlan — moving from farm to food to fertilizer and back to the farms. This lesson feels very much alive, surviving in the soil beneath my feet. It’s one of balance and sustainability, a glimpse of how urban life can be interwoven into a thriving, healthy ecosystem.

Before we leave, Juarez takes us to the nursery to choose a start. He shows us how to dig into the soft brown soil for the transplant. I choose a sunflower plant: It’s small and delicate, with promise of the big, beautiful flower to come.

A 3D reconstruction of Tenochtitlan by Thomas Kole. CC BY 4.0

January 17, 2026
Sewer sludge is the new black: An eco-friendly process converts it to useful products and curbs carbon emissions

The smooth concrete floor of Remy Wines in Dayton, Oregon, has a special ingredient, one that helped make its construction carbon-neutral — processed poop.

The concrete floor of Remy Wines’ warehouse contains OurCarbon, a climate-friendly product made from sewer sludge. Photo: Remy Wines

This product started out as biosolids from a wastewater treatment plant. But instead of being used as fertilizer or dumped into a landfill — the fate of most biosolids — it was transformed by microbes and scorching heat into a type of biochar. This process zapped pollutants in the sludge and bound up carbon, a benefit for the climate. The end result, it turns out, is a unique and useful product.

When John Mead was hired to design an eco-friendly concrete floor for Remy Wines’ new 5,000-square-foot warehouse, he turned to this carbon-negative product — called OurCarbon. He was looking for a secure way to offset the carbon emissions from the rest of the construction. Mead knew carbon offsets from places like tree plantings are at risk of burning up in a forest fire. But when they’re embedded in concrete, “the carbon is not going anywhere,” says Mead.

OurCarbon is a stable product that will not break down to release greenhouse gases. Eco-conscious contractors like Mead can add it into the cement mix as a carbon ‘inset.’

Image: Bioforcetech Corporation

The reinvention of waste

Even though biosolids are full of nutrients, they are often viewed as waste products. They can contain undesirable chemicals and heavy metals. In 2022, the state of Maine banned their use as fertilizer. Sometimes it’s too costly to transport them to farms. Landfilling is not a good option either, because it wastes nutrients and creates methane, a potent greenhouse gas. That’s why the company Bioforcetech created a way to reduce the weight and volume of biosolids to one-tenth the original amount, while using no extra power.

Their system dries out wet biosolids with heat from bacteria, instead of natural gas. Then, the dried slurry goes through a process called pyrolysis. This happens in an ultra hot chamber — temperatures of around 1200 degrees F (700 degrees C) — without oxygen. The system creates few emissions, and in the end, any pharmaceuticals, microplastics and ‘forever chemicals’ called PFAS are obliterated, and heavy metals are bound up in the product.

The material that comes out the other end of the system looks like what you might find on a black-sand beach. “It’s not really a biosolid,” says Garrett Benisch, the Director of Design Development at Bioforcetech. It’s not a classic biochar either – it has more ash and less carbon than wood-based biochars, he says. This new product can be used to store carbon, and qualifies for carbon offsets in buildings, like at Remy Wines.

“When we divert from the landfill we have a monstrous change in avoided emissions from methane,” says Benisch. It’s like taking up to seven cars off the road for a year per ton of OurCarbon.

Biosolids are transformed into this black, sand-like material that is free of harmful chemicals. Photo: Bioforcetech Corporation

From concrete to fashion

It turns out the jet-black OurCarbon can also be used to replace black ink. The black ink color used in everything from t-shirts to key boards is called carbon black, and it comes from fossil fuels. The production of standard black ink color produces tons of CO₂, Benisch points out. OurCarbon makes black ink that’s just as good. So far, it’s been used to color shirts, furniture, digital print ink, and foam in shoes.

Back at Remy Wines, Mead used OurCarbon to replace some of the sand in the cement mix. He’s happy with the results, yet this won’t be a solution to offset carbon emissions from the cement industry as a whole. There will never be enough of the product, he says, even if all the biosolids in the country were converted. For now, Mead believes it’s good to use this product, because it brings attention to the need to decarbonize cement and find secure sources of carbon offsets.

Interest in these systems is spreading. So far, Bioforcetech has installed 18 systems to dry biosolids with bacteria and three are producing OurCarbon, with more on the way.

And the win for Benisch is happening: “I’m most interested in changing business as usual,” he says, “as well as fixing this carbon and using it.”

The black dye from OurCarbon is used to dye fabric, shoes and more. Photo: Bioforcetech Corporation

*A version of this post was first published on the Ocean Sewage Alliance website.

August 23, 2025
This urban oasis in Tijuana thrives on sewage, first cleaned by microbes and wetland plants

The line between the two properties looks as if someone drew it with a fat, green crayon. On one side, the eroding Tijuana hillside is brown, dry and denuded. On the other side, trees and plants weave the hillside into a thriving ecosystem, a shelter for birds and pollinators. The difference between the two sites? Sewage.

This green oasis is called Ecoparque — or “Eco Park” in English. It’s a neighborhood-sized ecological wastewater treatment system plus an education center. EcoParque is a project of COLEF, El Colegio de la Frontera Norte (College of the Northern Border).

Ecoparque is an oasis of greenery on this Tijuana hillside. Photo: Yasmin Ochoa

For over 30 years, wastewater from a nearby sewer line has flowed into Ecoparque, where it’s cleaned and then used for irrigation. The recycled water has helped to reforest the site, stabilize the hillside and grow over seven acres of greenery. EcoParque is Tijuana’s fourth-largest green space.

Gabriela Muñoz Meléndez attributes the long-term success of the project to the work of “lots and lots people!” from COLEF and the larger community. Meléndez, an engineer from COLEF, oversees Ecoparque’s wastewater system and designed its most recent update.

An answer to Tijuana’s water woes?

Most water flowing through Tijuana is managed in a nonsensical way, explains Meléndez. Water originates from the Colorado River, travels through aqueducts and is pumped up over a thousand meters — a process that is both expensive and energy-intensive. Then, the water is used once, dumped into overloaded wastewater treatment systems and ends up polluting beaches on both sides of the US-Mexican border, just south of San Diego, California. “We can do better,” she says.

Trees shade the roads and paths at Ecoparque. Photo: Samuel Pérez

Ecoparque is a living example of what doing better can look like. Shady paths lined with jacarandas and mesquite trees wind up the hill, past agave cactus and purple penstemon flowers. Stone-lined terraces create productive plots of land and hold the soil in place. Benches, shaded by grape arbors, overlook the city. Kids visit on field trips to learn about water reuse and composting, renewable energy and recycling, native plants and urban agriculture. This is all possible thanks to sewage.

This wastewater treatment at EcoParque is decentralized, meaning it’s small and designed to manage a fraction of the city’s total wastewater. It also uses very little energy, since the wastewater flows by gravity and is used on the same site. In contrast, water and wastewater in the rest of Tijuana are pumped multiple times.

Cleaning wastewater with microbes and plants

Wastewater in the Ecoparque system is treated in three steps. First, it flows through screens to remove trash and large debris. Next, the dirty water enters a biofilter — essentially a big box filled with plastic bits that are colonized by bacteria, which eat contaminates in the wastewater and aerate it. Then, the effluent flows into a tank called a clarifier, where leftover solid bits sink to the bottom of the tank and are removed. After that, the water travels through a wetland, passing over stones and gravel, where microbes remove nutrients and bacteria. The wetland is planted with canna lilies: not only pretty, with red, yellow and orange blooms, but they also capture coliform bacteria. The last stage is a large, open-water pond, added in 2020, to improve the water quality coming out of the system.

Wastewater flows through this biofilter as part of the treatment process. Photo: Ecoparque

The climate in Tijuana is hot and dry, which makes recycling water an attractive option. One treatment plant, called San Antonio de los Buenos, was designed to recycle water. But for the past 10 years it’s been inoperable, discharging untreated wastewater into the ocean. Too much sediment in the water damaged the plant, and repair costs were too high, explains Meléndez. This plant had to be rebuilt and is set to come online this year.

This highlights another lesson from Ecoparque: the benefits of integrated planning. Restoring green space, like at Ecoparque, reduces erosion, which, in turn, reduces sediment runoff that mucks-up the centralized wastewater treatment plants. Plus, being around green spaces is good for people.

Grape vines shade this bench that overlooks the city. Photo: Ecoparque

Big and small solutions are needed

Even without the sediment, managing all the wastewater in Tijuana is an enormous challenge. The agencies responsible for providing drinking water and treating sewage are unable to keep up with the rapid and unplanned urbanization in the city. And another part of the problem, points out Meléndez, is that American companies come to Tijuana expecting water and someone else to treat their prolific wastewater. Similarly, Americans move to Tijuana — to save money or retire — and also expect clean water, but they don’t pay Mexican taxes. “To solve the water pollution problem it will take resources and cooperation,” she says. Mexico has ideas and solutions, but can’t do it alone.

Some of the needed resources and solutions are coming to the region. In December, the US government unlocked 250 million dollars to fix Tijuana’s ailing South Bay International Wastewater Treatment Plant. This is one of three major projects designed to prevent most of the summer beach closures currently happening in the region due to sewage pollution.

Ecoparque is the fourth-largest green space in Tijuana. Photo Credit: El Colef, CC BY-SA 3.0 via Wikimedia Commons

With over half the world’s waterways polluted by wastewater, sewage solutions of all sizes are needed. The centralized treatment plants can clean millions of gallons of water a day, but the high cost to build and operate limits their reach. Neighborhood-sized systems, however, with lower costs and lower-energy consuming technology, are more flexible.

A photographer once brought a drone to Ecoparque. When Meléndez saw the images — of lagoons and trees standing in a sea of houses and traffic — it was moving, she said, “to see this green space very bravely standing there… an example of how cities could be different.”

*A version of this article was first published on the Ocean Sewage Alliance website.

August 20, 2025
You flushed, they decked out City Hall: How this Oregon community grows wood from wastewater leftovers

From ancient times to modern-day, some places manage water and excreta in a smart way. Recently, I visited one — the Biocycle Farm in Eugene, Oregon.

Flush the toilet in this town, and here’s a surprise: your contribution may be transformed into an eco-friendly building material — poplar trees. This climate-friendly practice recycles nutrients, keeps local rivers clean and could one day spark a new economy.
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June 24, 2024
This building gets the gold: Here’s how it converts human urine into an eco-fertilizer

From the outside, the PAE Living Building in Portland, Oregon, is nondescript. Its gray colors and rectangular shape blend into the historic district. But this five story, office building gets the gold for recycling. Rainwater, greywater and even urine, are all reused. And it’s the first building in the world to create carbon-neutral fertilizers from our body’s waste.
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May 20, 2024
A better way to go? Here’s 7 takeaways from a toilet museum
“Half the world needs a toilet while the other half needs a better one.”

That’s according to the Bill and Melinda Gate’s Foundation. It’s critical the 3.5 billion people who currently lack safe sanitation options get them. But what’s wrong with the rest of our toilets? A few things, it turns out:
- Flush toilets hog precious water and flush nutrients down the drain.
- They often pollute the environment and can spread disease.
- Wastewater treatment plants and the infrastructure needed to maintain them are expensive.
- And there are better options.
Last month, I visited the exhibit, “A Better Way to Go: Toilets and the Future of Sanitation.” It’s at the Discovery Center in Seattle, curated by the Bill and Melinda Gate’s Foundation. Here’s a peak at what’s inside.
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April 28, 2024
Fit for a pharaoh: Lessons from ancient Egyptian toilets

The ancient Egyptians were technology superstars. Their towering pyramids, mummified dead, and exquisite art still impress. Another earthly treasure they left behind is more practical — it’s their toilets. These urban, waterless toilets kept poop out of the nearby river. Did they also protect people from diseases that plagued other cities?
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April 20, 2024