title: "The Third Toilet Revolution: An Urgent and Daunting Task" date: "2026-07-07" category: "ecology" author: "Zhigeng"

The Third Toilet Revolution: An Urgent and Daunting Task

On the road to a sustainable civilization, there are many unavoidable hurdles—and the toilet is one of them.

The Bill & Melinda Gates Foundation has been promoting a toilet revolution since 2011, investing tens of millions of dollars annually to solicit and develop solutions. Some progress has been made, but it remains limited.

History has witnessed two toilet revolutions, both of which advanced civilization. Today, humanity faces the daunting task of a third toilet revolution, one that directly concerns sustainable development and the future of our species. It will require extraordinary wisdom and courage to accomplish.

Some readers may already be dismissive: toilets—is it really that serious? The answer: yes, it is—and it's extremely serious.

I. From Open Defecation to Pit Latrines: The First Toilet Revolution

To be honest, calling this first one a "revolution" is a bit of a stretch. Many who discuss this topic skip it entirely. It was more of a natural occurrence that played a huge role, but calling it transformative is debatable. I keep it as the first revolution mainly for the sake of a complete historical narrative.

After humans settled down, they quickly discovered a serious problem: people need to excrete every day, but they couldn't keep doing it just anywhere, as they had in hunter-gatherer times.

Settlement meant a fixed home and a fixed radius of daily life. When a group of people stays in the same place for a long time, open defecation becomes a problem—sanitary hazards, odor pollution, insect-borne diseases... And so, the first toilet revolution in human history quietly took place: digging pits, building sheds, putting up walls—transforming defecation from "anywhere" to "a designated place."

Archaeological findings show that as early as around 3000 BCE, the ancient city of Mohenjo-daro in the Indus Valley had brick-built toilets and sewers. The Yinxu ruins in China also contain traces of pit latrines similar in nature [1]. The ancient Romans went even further, turning public toilets into social venues—marble benches, running water for flushing, even heating.

All these facilities shared a common underlying logic: collect waste and return it to the fields.

For thousands of years of agricultural civilization, human excrement was never "waste"—it was precious fertilizer. "A crop is only as good as its manure"—this Chinese farming proverb captures the core of the first toilet revolution perfectly: the toilet is not a garbage station; it is a fertilizer collection station.

In agrarian societies, farmers would regularly clean out pit latrines, mix the feces with plant ash for composting, and after it matured, apply it to the fields. During Japan's Edo period, cities even had a dedicated "night soil trade"—the money farmers paid for fertilizer was an important source of income for urban residents [2]. This cycle continued for thousands of years: people took food from the land, food became excrement, excrement returned to the land, and the land produced food again.

It was a perfect closed loop. And this loop was completely shattered in the second toilet revolution.

II. The Flush Toilet: Savior of Cities, Killer of Cycles

1. From Cholera to the Sanitation Revolution

Nineteenth-century London was a city floating on feces.

At the time, London had a population of roughly three million, producing over a hundred tons of excrement every day. Most of this waste was dumped into roadside cesspits and open drains, eventually flowing into the Thames. The "Great Stink" of 1858 filled the entire city with suffocating odors—even the curtains of the Houses of Parliament were soaked with the stench of sewage. More lethally, the contamination of water sources triggered successive cholera pandemics—between 1832 and 1866, tens of thousands died of cholera in London alone [3].

It was against this backdrop that the flush toilet and modern sewer systems stepped onto the stage of history.

The flush toilet's origins actually go back further. In 1596, the English poet Sir John Harington designed the world's first flush toilet for his godmother, Queen Elizabeth I—but without a supporting sewer system, the invention never gained widespread use. In 1775, Alexander Cumming received the first patent for a flush toilet; his S-shaped trap remains a core component of flush toilets to this day. In the 19th century, Thomas Crapper improved the valve and flushing mechanism, making the flush toilet more practical and reliable [4].

What truly allowed the flush toilet to change the world was London's sewer project. Between 1856 and 1865, engineer Joseph Bazalgette oversaw the construction of London's underground drainage system—spanning roughly 2,100 km and capable of handling hundreds of millions of liters of sewage daily. This was a miracle of engineering history, fundamentally transforming urban sanitation [3].

The flush toilet's working principle seems simple: water stored in a tank → press to flush → water sweeps waste into the sewer pipe → merges into the municipal sewer network → transported to a treatment plant. The system appears flawless, and indeed it solved the most urgent problem of the time: getting feces out of the city.

2. The Other Side of the Achievement

But every technology comes at a cost. The flush toilet's cost is buried deep in the pipes, only slowly revealing itself decades later.

The first cost: water.

Each flush of a traditional toilet consumes 6–12 liters of clean drinking water. A family of four uses about 50–80 liters of water per day just for flushing. Over four billion people worldwide use flush toilets—the clean water consumed daily runs into hundreds of millions of tons. And this water, after sweeping away waste, becomes polluted water, waiting to be purified again.

You use clean water and discharge dirty water. Clean turns dirty in an instant, but making dirty water clean again requires enormous energy and resources.

The second cost: the loss of fertilizer.

The nitrogen, phosphorus, potassium, and other nutrients a person excretes in a day are roughly enough to grow the food that person needs for a day.

But in the flush toilet system, where do these nutrients go? They mix with several liters of water, travel through complex underground pipe networks, journey long distances to wastewater treatment plants. There, microorganisms degrade the organic matter, consuming vast amounts of oxygen and energy. The removal of phosphorus and nitrogen is especially challenging—most nitrogen is converted to nitrogen gas and released into the atmosphere, while phosphorus is chemically precipitated into sludge. And sludge treatment is itself a major problem.

The end result: nutrients that should have returned to the land are washed away by water, "eliminated" in treatment plants, never to return to the fields.

The third cost: soil impoverishment, and everything that follows.

When humans stop returning excrement to the fields, the land is forced to rely on chemical fertilizers. The advent of chemical fertilizers was once hailed as a great agricultural breakthrough—it multiplied grain yields several times over. But chemical fertilizers can only replenish nitrogen, phosphorus, and potassium—they cannot restore soil organic matter. The long-term result of relying solely on chemical fertilizers: soil compaction, declining microbial communities, and diminished water- and nutrient-holding capacity.

Compacted soil cannot grow nutritious crops. A substantial body of research confirms this: a research team at the University of California, Davis compared USDA nutritional data for 43 fruits and vegetables from 1950 to 1999 and found significant declines in protein, calcium, phosphorus, iron, vitamin B2, and vitamin C—calcium dropped an average 16%, iron 15%, and vitamin C 20% [5]. While the study notes that the causes of nutrient decline are multifaceted (including crop breeding that prioritizes yield over nutrition), deteriorating soil health is widely acknowledged as a key factor.

The data from this study only covers the last century in the United States. As cities expand and become mega-cities, and the urban population share surges, the disruption of organic matter cycling leads to even more severe soil impoverishment.

In sum: the flush toilet solved the problem of urban sanitation, made the growth of massive cities—and thus urban civilization itself—possible, but shifted the problem of soil nutrients to a hidden, neglected, and far more consequential place.

3. The Truth About Wastewater Treatment Plants

You might think: no problem, we have wastewater treatment plants.

Yes, modern cities all have them, and they genuinely perform an invaluable service. But their treatment outcomes are nowhere near as perfect as most people imagine.

Take China's standards as an example: the Grade 1A standard under the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB 18918-2002) specifies key indicators—chemical oxygen demand (COD) ≤ 50 mg/L, ammonia nitrogen ≤ 5 mg/L, total phosphorus ≤ 0.5 mg/L, suspended solids ≤ 10 mg/L. This effluent roughly corresponds to Class V or worse surface water (under the Environmental Quality Standards for Surface Water GB 3838-2002, Class V water is suitable mainly for agricultural use and general landscape purposes, with COD ≤ 40 mg/L and total phosphorus ≤ 0.4 mg/L). Achieving Class IV surface water standards (suitable for general industrial use and recreational waters without direct human contact, COD ≤ 30 mg/L, total phosphorus ≤ 0.3 mg/L) requires further advanced treatment—reverse osmosis, activated carbon adsorption, ozone oxidation—and this is about the highest standard a treatment plant can achieve, and is quite difficult to reach [6].

In other words, every drop of water flushed away by your toilet, after expensive treatment, returns to rivers as Class IV water or worse. And those nutrients that should have gone back to the fields are largely "consumed" during treatment—not only unrecoverable, but becoming pollutants in the rivers themselves. The massive quantities of sludge produced, extremely difficult to utilize, are often classified as "hazardous waste," requiring even more resources and energy to treat, becoming an even bigger problem.

III. The Iceberg Below the Waterline: The Rural Sewage Crisis

If the flush toilet is at best a mixed blessing in cities, in rural areas it is a disaster in the making.

For centuries, rural China's tradition was the dry pit latrine. Pit latrines certainly have their shortcomings—poor sanitation, strong odors, breeding flies and mosquitoes. So in the push for rural living environment improvement and the "toilet revolution," many places chose the simplest and most direct approach: replace dry latrines with flush toilets.

Sounds reasonable—isn't that what cities did? But the problem is: rural areas lack the city's drainage network and treatment plants.

What's the result? In many villages where toilets have been "upgraded," the feces and wastewater from flush toilets are discharged directly into village streams, seepage pits, or simple septic tanks. Simple septic tanks have limited degradation capacity and easily overflow when it rains. River eutrophication, groundwater contamination, soil pollution—the problems of flush toilets have simply been transferred from cities to more vulnerable rural ecosystems.

Even more ironic: for thousands of years of agricultural civilization, Chinese farmers were the ones who best understood "waste nothing"—human excrement in their hands was gold. And after flush toilets entered the countryside, gold turned into pollution. A recycling system that had worked in rural areas for millennia was severed by an invention from the city.

Similar problems are not unique to China. In India's national campaign to eliminate open defecation (Open Defecation Free), flush toilets were built in large numbers. Lacking supporting treatment infrastructure, vast quantities of untreated sewage were discharged directly into water bodies, causing even more severe non-point-source pollution [7]. Multiple African countries faced similar dilemmas in toilet construction under the UN Millennium Development Goals.

This is not a technical problem—it is a systemic problem. Solutions that work in cities become ill-suited when transplanted to rural areas. Simply applying urban sanitation standards to rural settings amounts to using the city's metabolic pattern to destroy the countryside's ecosystem.

IV. The Third Toilet Revolution: What's Missing Is Resolve

So, are there better solutions?

The answer is: yes—and quite a few.

Complete water regeneration and reuse, as practiced on crewed spacecraft and space stations, is too costly to be viable for broad application.

To date, the long-term funding and solicitation efforts of the Gates Foundation have not produced an ideal, revolutionary solution compatible with current urban construction realities.

Having spent years in various environmental protection circles, I've learned something: if we truly want to accomplish this revolutionary reform, the crux of the problem is not in the toilet itself. What's needed is a fundamental transformation of the deep technological pathways and standard systems of urban construction.

Solution One: Vacuum Toilets

The toilets you use on airplanes and high-speed trains are vacuum toilets, fundamentally different from conventional flush toilets:

Working principle: using vacuum negative pressure, a very small amount of liquid (about 0.3–0.5 liters, only 1/12 to 1/20 of a conventional flush toilet) draws waste into vacuum pipes and into collection containers. Because water usage is so low, the waste has very low water content; complex pipe networks and large water resources are not required, and the collected material can be more easily used for composting [8].

Maturity: the aviation industry has used this technology for over half a century—since the Boeing 707 first introduced vacuum toilet systems in the 1960s, the technology has undergone countless iterations and is extremely reliable. The Swedish company Jets (now part of the Swedish environmental group Envac) has decades of application experience in vacuum drainage systems for ships and eco-communities. The Hammarby Sjöstad eco-community near Stockholm trialed vacuum drainage in its early planning, achieving significant water savings compared to traditional gravity drainage systems [9].

What's the hold-up? Technically, there is almost no barrier. The real obstacle is that the entire urban construction standards system is built around the flush toilet. Building water supply and drainage design codes (such as China's Standard for Design of Building Water Supply and Drainage GB 50015), residential design standards, renovation industry standards... each link interlocks with the others; changing one link pulls the entire chain. This is the power of path dependency.

Solution Two: Source-Separating Toilets

"Source separation" means collecting urine and feces separately. The idea is ingenious: urine makes up the vast majority of excrement volume (about 90%), but feces carry a higher risk of organic matter and pathogens. Collected separately, urine can be directly diluted as liquid fertilizer (rich in nitrogen, phosphorus, and potassium), while feces can be dehydrated and composted.

International practice: the Tanum eco-village in Sweden has operated a urine-separating toilet system since the 1990s, running for over 20 years with positive resident feedback, and the urine fertilizer has been received and used by local farms [10]. Eawag, the aquatic research institute of ETH Zurich, has long studied source-separation technology and implemented a full cycle of urine collection and nutrient recovery in the "Ecological Quarter" project in the city of Biel [11]. A friend dedicated to phosphorus recovery told me that since phosphorus is excreted mainly through urine, source separation is especially advantageous for phosphorus recovery.

German exploration: a research team at the Technical University of Berlin developed the "Sanitation 21" demonstration project, installing source-separating toilets and a greywater (household wastewater excluding toilet discharge) treatment system in a Berlin student dormitory, achieving roughly 70% water savings and over 80% nitrogen recovery [12].

Chinese practice: research institutions such as the University of Science and Technology of China and Beijing University of Civil Engineering and Architecture have piloted source-separating toilets in rural areas, but adoption has been limited due to cost and usage habits.

Solution Three: Biodegradation / Composting Toilets

Various technological approaches using microbial degradation of organic matter have also been practiced.

Japanese experience: Japan is one of the countries with the most mature research and application of composting toilets. The microbial degradation toilets developed by the Japanese company Biolu use wood chips and specific microbial consortia to break down waste—virtually zero emissions, no water required, no sewage pipes needed. These systems have seen long-term use in mountain huts in Fuji's national parks and remote areas of Aomori Prefecture [13].

Swedish practice: the Swedish company Clivus Multrum has been manufacturing composting toilets since 1939, with products widely used in locations lacking sewage infrastructure, such as national parks and ferry terminals. The compost product, after 1–2 years of maturation, can be used as a soil amendment.

Developing-country exploration: the Bill & Melinda Gates Foundation's "Reinvent the Toilet" project, launched in 2011, has invested hundreds of millions of dollars supporting dozens of research teams worldwide to develop sewer-free toilets suitable for developing countries. Most of these toilets are based on biodegradation, chemical treatment, or membrane technology, with the goal of treating human waste on-site into a resource that can be safely used [14].

I had an old friend who devoted years to using engineered bacterial composting and fermentation to create an integrated solution for the three major problems of toilet waste, non-chemically-polluted rural wastewater, and non-chemically-polluted rural garbage. He named the toilet he developed—with multiple patented technologies—"Soul of the Forest," drawing on the idea that in a forest, there is no garbage, no pollutants—only organic matter in circulation.

In the "Soul of the Forest" toilet, all interior surfaces and walls are hollow and breathable, filled with engineered bacteria that degrade the toilet's odors and floor liquids; the toilet bowl also receives specially introduced engineered bacteria; an air-seal technology prevents odors from rising upward from the bowl.

Sadly, this old friend passed away before his ambitions could be realized, leaving the "Soul of the Forest" prototype to wither in the wind.

As I write this, I offer my deepest condolences to "Old Landlord" (my late friend's online nickname)—Mr. Wang Guangsheng, General Manager of Hebei Woye Biotechnology Co., Ltd.—who recently passed away from illness, having dedicated himself tirelessly to toilet improvement and the promotion of ecological toilets.

Path Dependency Is the Strongest Opponent

Three alternative solutions—none faces insurmountable technical obstacles. So why haven't they been adopted widely?

Reason one: the flush toilet is already deeply embedded in the entire urban and building system. Hundreds of thousands, millions of kilometers of underground pipe networks, hundreds of millions of renovated bathrooms, entire building water supply and drainage design codes—an industry and standards system built entirely around the flush toilet. The difficulty of separating toilet wastewater from other domestic, industrial, and medical wastewater for separate discharge is almost unimaginable.

Reason two: cost and attitudes. The unit cost of vacuum toilets is higher than flush toilets; source-separating toilets require users to change habits ("Are you okay with separating?") ; composting toilets require regular maintenance. These "extra costs" seem uncompetitive against the existing system—because the existing system shifts most of the cost of treating excrement onto municipal budgets and the natural environment; the user never feels the real cost.

Reason three: lack of urgency. Soil degradation is a slow process. If soil organic matter drops by 1% today, no one feels hungry. If the nutrients in vegetables have already decreased by 5%, 25%, even 50%, no one connects their hospital visit to it. But the reality is pressing—if this situation remains unchanged, the costs, from personal health to civilizational progress, will be staggering. (See our previous issue: "Have You Really Eaten Enough?—The Consequences of Hidden Hunger")

V. The Essence of the Third Toilet Revolution: From Linear to Circular

The flush toilet is a product of industrial civilization, and the underlying logic of industrial civilization is linear: extract → use → discard.

Take clean fresh water from nature, use it to transport excrement, then spend enormous sums and vast energy to "purify" the water to a barely-returnable level. Substandard effluent and the sludge with nowhere to go cause irreversible pollution; nutrients taken from the land never return to it.

What the third toilet revolution seeks to change is this linear chain.

What it seeks to restore is the circular wisdom of agricultural civilization—the difference being, this time, it will be achieved with modern technology.

Vacuum suction, source separation, biodegradation... the essence of these technologies is making different trade-offs between "flushing away" and "keeping."

The flush toilet chose "flushing away"—sweeping excrement and all its problems into the pipes, then playing ostrich, burying its head in the sand and pretending the problem is solved. What the third revolution chooses is "keeping"—keeping the water, keeping the nutrients, keeping the possibility of a cycle.

This is not a technological failure—quite the opposite. The flush toilet has been a tremendous success in terms of hygiene and has enabled the success of urban construction. It is a systemic design failure: treating a system designed for "removal" as the only viable system, while ignoring that the costs of "removal" are bouncing back in another form.

Soil compaction, fertilizer dependency, groundwater contamination, surface water eutrophication, declining nutrient density in human food—these seemingly unrelated problems, traced to their source, all connect to that ceramic fixture we flush several times a day.

This is not a failure of technology. This is a failure of civilization. And correcting this failure requires a new revolution.

VI. The Third Toilet Revolution: Who Will Make It Happen?

Transforming a system deeply embedded in the fabric of cities requires the synergy of three forces:

First, cognitive awakening. Most people have never thought about what happens "after the flush." Change will only happen when a person realizes that their excrement contains all the nutrients needed to nourish a tomato plant—when they know that each flush consumes enough fresh water to supply a family in an arid region with a day's basic drinking water—when each flush brings a sense of unease.

Second, policy guidance. It's worth noting that some countries have already elevated nutrient recovery to a legal requirement, not merely a technical exploration.

Sweden, for instance, is at the forefront of phosphorus recovery legislation. As early as 2018, the Swedish Environmental Protection Agency (Naturvårdsverket) submitted a special report on "Sustainable Sludge Management" (Hållbar slamhantering) to the government, proposing mandatory phosphorus recovery from sludge. In 2021, Sweden passed legislative amendments requiring treatment plants above a certain scale to recover phosphorus from sludge, setting a target of 60% phosphorus recovery by 2030 [15]. Under the new regulations, large treatment plants (serving populations of 20,000 person-equivalents or more) are required to develop phosphorus recovery plans, and new facilities must include phosphorus recovery processes. Sweden's phosphorus recovery pathway focuses on extracting phosphorus from the ash of incinerated sludge—chemically treating the ash to produce phosphate fertilizer. This approach has been demonstrated at treatment plants in cities like Helsingborg. Another important aspect of the regulation is progressively tightening the conditions for direct agricultural use of sludge, with the ultimate goal of transitioning from "land application of sludge" to "industrial recovery of phosphorus resources."

Germany has moved even faster. In 2023, Germany amended its Sewage Sludge Ordinance (AbfKlärV 2017), explicitly requiring that from 2029, all treatment plants serving populations over 100,000 must recover phosphorus from sludge or incinerated sludge ash; from 2032, this obligation extends to plants serving over 50,000. The regulation also requires a phosphorus recovery efficiency of at least 50%, with the recovered phosphorus product usable for fertilizer production. The German Federal Ministry of Education and Research (BMBF) has also provided long-term funding for sustainable sanitation research projects such as "Sanitation 21" and "WATERKNOT." The experience of both Germany and Sweden shows that the most critical driver for moving phosphorus recovery from R&D to large-scale application is not technological breakthroughs but legislative mandates [16].

Switzerland similarly amended its Environmental Protection Act in 2016, requiring all treatment plants to recover phosphorus from sludge and incinerator ash. Switzerland's regulations cover not only large treatment plants but also set clear timelines and technical roadmaps for phosphorus recovery from sludge incineration ash [17].

It should be said that these policies focus on the wastewater treatment stage (i.e., "after the flush"), and in their deeper logic, they share a certain consistency with the circular thinking that is the purpose of the third toilet revolution—they represent considerable progress. Yet they remain patches on the flush toilet technological system, limited in effect. Sludge incineration, even if it recovers phosphorus, only produces it for chemical fertilizer—the precious organic matter in sludge is lost forever.

Third, technological innovation and cost reduction. Vacuum toilets need to be cheaper, source-separating equipment needs to be easier to maintain, composting treatment needs to be more stable. These are all specific technical problems—but all are solvable. The Gates Foundation's "Reinvent the Toilet" project has already proven that when sufficient resources are focused on technological breakthroughs, progress is rapid.

Those who have persisted in reading this far likely agree with this article's perspective. Please share it so more people become aware and awakened. When enough people agree, the possibility of change grows.

References

[1] Liu Dunzhen. A History of Ancient Chinese Architecture (2nd ed.). China Architecture & Building Press, 1984. (discussion of ancient residential sanitation facilities) [2] Hanley, S. B. (1997). Everyday Things in Premodern Japan: The Hidden Legacy of Material Culture. University of California Press. (discussion of urban waste utilization in the Edo period) [3] Halliday, S. (1999). The Great Stink of London: Sir Joseph Bazalgette and the Cleansing of the Victorian Capital. The History Press. [4] George, R. (2008). The Big Necessity: The Unmentionable World of Human Waste and Why It Matters. Metropolitan Books. [5] Davis, D. R., Epp, M. D., & Riordan, H. D. (2004). Changes in USDA food composition data for 43 garden crops, 1950 to 1999. Journal of the American College of Nutrition, 23(6), 669-682. [6] GB 18918-2002, Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants. / GB 3838-2002, Environmental Quality Standards for Surface Water. [7] World Bank. (2018). The Hidden Costs of Inadequate Sanitation: A Review of the Literature. Water Global Practice Discussion Paper. [8] Otterpohl, R., Grottker, M., & Lange, J. (1997). Sustainable water and waste management in urban areas. Water Science and Technology, 35(9), 121-133. [9] Pandey, P. K., et al. (2014). Vacuum sewer systems: A review of design, operation and maintenance. Journal of Environmental Management, 146, 33-43. [10] Jönsson, H., et al. (2004). Guidelines on the Use of Urine and Faeces in Crop Production. EcoSanRes Publication Series. [11] Larsen, T. A., & Gujer, W. (1996). Separate management of anthropogenic nutrient solutions (human urine). Water Science and Technology, 34(3-4), 87-94. [12] Otterpohl, R. (2002). Options for alternative types of sewerage and treatment systems directed to improvement of the overall performance. Water Science and Technology, 45(3), 149-158. [13] Winblad, U., et al. (2004). Ecological Sanitation (2nd ed.). Stockholm Environment Institute. [14] Bill & Melinda Gates Foundation. (2011). Reinvent the Toilet Challenge: Strategy Overview. BMGF. [15] Naturvårdsverket. (2020). Hållbar slamhantering: Redovisning av ett regeringsuppdrag. Rapport 6926. Swedish Environmental Protection Agency. [16] AbfKlärV (2017). Klärschlammverordnung: Verordnung zur Neuordnung der Klärschlammverwertung. Bundesgesetzblatt Jahrgang 2017 Teil I Nr. 65. [17] Bundesrat der Schweiz. (2015). Änderung der Gewässerschutzverordnung betreffend die Phosphor-Rückgewinnung. BBl 2015 6749.