Night soil is an old term for human feces and urine collected from cesspools, privies, and chamber pots, typically for use as agricultural fertilizer. The phrase itself is a Victorian-era euphemism, coined because the waste was usually carted away under cover of darkness to spare the sensibilities of city dwellers.1Journal of Global History. Nightsoil and the ‘Great Divergence’: human waste, the urban economy, and economic productivity, 1500–1900 While the practice sounds like a relic, the core idea behind it is making a serious comeback in sanitation engineering and sustainable agriculture, though with far more science applied to the risks involved.
How Night Soil Shaped Agriculture for Centuries
The systematic recycling of human waste into cropland was a defining feature of Chinese and Japanese farming for centuries, and researchers have long recognized it as a key factor in sustaining intensive agriculture without the synthetic fertilizers that would arrive much later.1Journal of Global History. Nightsoil and the ‘Great Divergence’: human waste, the urban economy, and economic productivity, 1500–1900 In East Asian cities, night soil had genuine economic value. Collectors paid households for the privilege of hauling it away, and the waste moved through organized supply chains to farmers in surrounding regions. European cities, by contrast, generally treated human waste as something to be disposed of rather than recovered, a divergence that some historians argue contributed to differences in soil fertility and agricultural productivity between the two regions.
Europe eventually developed its own night soil trade, particularly in the 18th and 19th centuries as urban populations boomed and sewage systems lagged behind. Farmers near London, Paris, and other major cities paid for cartloads of “poudrette” (dried night soil) to spread on fields. The practice declined sharply once waterborne sewage systems became standard and synthetic nitrogen fertilizers appeared in the early 20th century. But in many parts of the world where sewage infrastructure remains limited, the direct application of untreated human waste to fields never fully stopped.
Why Raw Night Soil Is Dangerous
The fundamental problem with spreading untreated human waste on food crops is that it can carry every pathogen a human body sheds. The list includes bacteria like Salmonella and E. coli, viruses like hepatitis A and norovirus, protozoan parasites like Giardia and Cryptosporidium, and helminth worms like roundworm and whipworm. Helminth eggs are especially tenacious because they can survive in soil for years.
A study in southeastern Turkey documented how broken sewer lines and direct application of night soil to garden plots contaminated both irrigation water and soil with viable helminth eggs. About 60% of the irrigation water samples contained parasite eggs, and the contamination spread readily to vegetable gardens and household yards.2Memórias do Instituto Oswaldo Cruz. Environmental pollution with soil-transmitted helminths in Sanliurfa, Turkey That kind of scenario is not unique to Turkey. Wherever untreated human waste reaches food-growing soil without adequate treatment or delay, people eating those crops face a real risk of parasitic infection.
Chemical and Pharmaceutical Contaminants
Pathogens are the oldest concern, but modern human waste carries baggage that night soil collectors in 1800s Beijing never had to think about. Pharmaceuticals, persistent organic compounds, and heavy metals all pass through the human body and end up in excreta. A 2024 review identified these contaminants as a key challenge for any fertilizer derived from human waste, noting that they can affect plant health, soil quality, and water resources.3Science of The Total Environment. Opportunities and challenges of using human excreta-derived fertilizers in agriculture: A review of suitability, environmental impact and societal acceptance
How much of a pharmaceutical dose actually ends up in the food you eat? A review of studies on crops grown in soil amended with wastewater, biosolids, and manure found that concentrations drop sharply at each step: from wastewater to soil, then from soil to plant tissue. Less than 1% of the initial pharmaceutical load typically shows up in the edible parts of crop plants. Leafy vegetables accumulate the most, while grains accumulate the least.4Environmental Chemistry Letters. Pharmaceutical contamination in edible plants grown on soils amended with wastewater, manure, and biosolids: a review That sounds reassuring, but “less than 1%” of a city’s collective pharmaceutical output still adds up over years of repeated application. The long-term effects of low-level chronic exposure through food remain an active area of research.
Antibiotic Resistance Genes in the Soil
A less obvious risk is that human waste carries antibiotic resistance genes, the genetic instructions that let bacteria shrug off drugs. When sewage sludge or biosolids are spread on agricultural land, those resistance genes can persist in the soil and even end up on harvested vegetables. One field study found that vegetables grown in soil treated with raw or digested sewage sludge carried resistance genes that were not present on vegetables from untreated control plots. The effect was strongest in the season the sludge was applied and faded by the following year, suggesting that timing and pre-treatment matter.5PubMed Central. Impact of fertilizing with raw or anaerobically digested sewage sludge on the abundance of antibiotic-resistant coliforms, antibiotic resistance genes, and pathogenic bacteria in soil and on vegetables at harvest
Elevated levels of resistance genes have been detected in soil for several months following the application of manure or biosolids.6PubMed. Levels of antibiotic resistance genes in manure, biosolids, and fertilized soil Another study confirmed that fertilizing with dairy manure or human biosolids increases resistance gene abundance in the bacterial fraction of the soil, though interestingly it did not increase resistance genes carried by bacteriophages (the viruses that infect bacteria).7PubMed Central. Abundance of Antibiotic Resistance Genes in Bacteriophage following Soil Fertilization with Dairy Manure or Municipal Biosolids, and Evidence for Potential Transduction The concern here is broader than night soil alone. Any time animal manure or human biosolids reach agricultural soil without adequate treatment, they carry this resistance burden. But human waste is especially concentrated in the pharmaceuticals people take, which is why it gets particular scrutiny.
Microplastics Along for the Ride
Sewage sludge, the modern industrial descendant of night soil, turns out to be a significant pathway for microplastics into farmland. A study comparing fields that received different application rates of sludge-based compost found a stark dose-response relationship. Fields receiving the higher application rate had roughly 546 microplastic particles per kilogram of soil, compared to about 5 per kilogram in fields that received no sludge compost at all. Microplastics were also found inside earthworms living in the amended soil, suggesting the particles move through the food web.8PubMed. An Overlooked Entry Pathway of Microplastics into Agricultural Soils from Application of Sludge-Based Fertilizers This is a genuinely new dimension of the night soil question that historical practitioners never faced. Every time someone washes synthetic clothing or uses products containing microbeads, those particles flow into wastewater. If the resulting sludge goes onto farmland, the microplastics go too.
The Nutrient Case for Human Waste
For all the hazards, the reason people keep returning to this idea is straightforward: human excreta contain substantial amounts of nitrogen, phosphorus, and potassium, the same nutrients found in commercial fertilizer. Roughly half of the nitrogen and most of the phosphorus in municipal wastewater come from urine alone. Throwing all of that into rivers via conventional sewage treatment is a massive waste of resources and a major source of water pollution. It also means we mine and manufacture those same nutrients from scratch, using energy-intensive industrial processes.
Research into fertilizers derived from processed human excreta shows genuine promise. Nitrified urine fertilizers, produced by converting the ammonia in urine into more stable nitrate forms, have performed comparably to commercial organic fertilizers in crop trials.9Frontiers in Environmental Science. Recycling fertilizers from human excreta exhibit high nitrogen fertilizer value and result in low uptake of pharmaceutical compounds Composted human feces can also supply meaningful nitrogen, though the amount depends heavily on how the composting is done. Active composting at warmer temperatures produces material with significantly more available nitrogen and better crop yields than passive, low-temperature methods.10Resources, Conservation and Recycling. Human excreta as a resource in agriculture – Evaluating the fertilizer potential of different composting and fermentation-derived products
Making It Safe Through Composting
Composting is the oldest and most widely accessible treatment method. The basic principle is that sustained high temperatures generated by microbial activity can kill pathogens. North American regulatory guidelines call for all compost material to remain above 55°C for at least three days to achieve pathogen kill. But a review of the scientific literature found that this standard does not always work in practice. Pathogenic bacteria, protozoa, and helminth eggs survived in a significant number of studies even when the prescribed temperatures were apparently met, often because the heat was unevenly distributed throughout the pile.11Journal of Environmental Engineering and Science. A review of the effectiveness of current time–temperature regulations on pathogen inactivation during composting
Adding biochar to compost piles has emerged as a way to improve the process on several fronts at once. In one study, biochar achieved a decomposition rate similar to rice husks and corn stalks but lost less nitrogen during composting, and the resulting compost delivered a higher proportion of its nitrogen to plants.12PubMed. Suitability of biochar as a matrix for improving the performance of composting toilets A separate composting trial found that adding biochar cut nitrogen losses by roughly half and reduced organic matter losses as well, all while maintaining temperatures above 60°C long enough to indicate pathogen-free compost.13PubMed. Nutrient dynamics during composting of human excreta, cattle manure, and organic waste affected by biochar Biochar also reduced non-CO₂ greenhouse gas emissions from composting by roughly half to two-thirds, cutting methane and nitrous oxide output substantially.14PubMed. Biochar addition reduces non-CO(2) greenhouse gas emissions during composting of human excreta and cattle manure
Urine-Diverting Toilets and Dry Sanitation
One of the more practical innovations in this space is the urine-diverting dry toilet, which separates urine from feces at the source. Keeping them apart makes treatment easier because urine is relatively sterile when it leaves the body and carries most of the nitrogen, while feces carry most of the pathogens and can be treated separately through composting or desiccation.
A longitudinal study in a refugee camp in Ethiopia tested how well sealed dry toilet vaults inactivated pathogens over time. After 12 months of storage under warm, dry, alkaline conditions, 95% of the vaults had E. coli levels below the safety threshold, up from 30% at the start. Roundworm egg viability dropped by more than 99.8% within six months. Adding hydrated lime to push the pH above 12 appeared to speed the process further.15Science of The Total Environment. An environmental evaluation of urine-diverting dry toilets in Hiloweyn Camp, Dollo Ado, Ethiopia
Lab studies have explored how to optimize dry treatment using various additives. Desiccation, ammonia content, and high pH were all found to contribute to pathogen kill, with different organisms responding to different factors. The most effective additive combinations could inactivate 7 log units (meaning a 99.99999% reduction) of target bacteria and viruses within about 83 days.16PubMed Central. Inactivation of pathogens in feces by desiccation and urea treatment for application in urine-diverting dry toilets Thermophilic composting of the separated feces, when done with the right ratio of sawdust and proper insulation, can drive E. coli below detection limits within two weeks.17Journal of Water, Sanitation and Hygiene for Development. Engineering design of passively aerated urine-diverting dry toilet chambers based on thermophilic composting of human feces
Extracting Clean Fertilizer from Urine
Rather than composting everything together, newer approaches focus on extracting specific nutrients from urine in purified form. Struvite precipitation is the most developed technique: by adding magnesium to stored urine, phosphorus crystallizes out as struvite, a slow-release mineral fertilizer. Pilot plants in Vietnam have achieved phosphorus removal rates of 98%, producing struvite with heavy metal concentrations well below regulatory limits. Nitrogen can be recovered separately through air stripping and captured as liquid ammonium sulfate, with recovery rates above 90%.18CLEAN – Soil, Air, Water. Nitrogen and Phosphorus Recovery from Human Urine by Struvite Precipitation and Air Stripping in Vietnam
These extraction methods produce fertilizers that look and behave like conventional mineral products, without the pathogen and pharmaceutical baggage of raw or minimally treated waste. A pilot facility demonstrated the same struvite and ammonium sulfate recovery process at a larger scale.19Chemosphere. Recovery of phosphorus and nitrogen from human urine by struvite precipitation, air stripping and acid scrubbing: A pilot study The end products are essentially indistinguishable from mined phosphorus or synthesized ammonium sulfate, which neatly sidesteps the “ick factor” that raw night soil cannot escape.
Anaerobic Digestion and Biogas
Another modern treatment pathway involves anaerobic digestion, where microorganisms break down organic matter in the absence of oxygen and produce methane-rich biogas in the process. Human feces can be co-digested with food waste and other organic materials to boost methane yields. Research has confirmed effective methane production from human feces, toilet paper, and food waste both individually and in mixtures, with food waste contributing the highest methane potential.20Fuel. Anaerobic co-digestion of food waste, human feces, and toilet paper: Methane potential and synergistic effect The remaining digestate, after the methane has been captured, still contains nutrients and can be further treated for use as fertilizer. This approach has the appeal of producing energy and fertilizer from the same waste stream.
What Happens to the Soil Over Time
A question that matters for any farmer considering these products is whether repeated application of human-waste-derived fertilizer changes the soil itself. A four-year field trial comparing different organic amendments found that soils treated with composted household waste and sewage sludge had higher microbial biomass and more active microbial communities than soils given only synthetic fertilizer or no fertilizer at all. The microbial community remained functionally robust throughout the trial. The cumulative heavy metal input from even an accelerated application schedule remained well below ecotoxicological limits, suggesting that decades of use could be possible without compromising soil health, as long as guidelines are followed.21Soil Biology and Biochemistry. Effects of fertilization with urban and agricultural organic wastes in a field trial – Waste imprint on soil microbial activity
Container-Based Sanitation in Cities Without Sewers
In dense urban areas of lower-income countries, conventional sewage systems are often too expensive or physically impossible to build. Night soil collection in these settings has evolved into what is now called container-based sanitation, where households use specially designed toilets with sealable containers. A service picks up the filled containers on a regular schedule, replaces them with clean ones, and brings the waste to a centralized treatment facility. This model has been tested in places like Cap-Haitien, Haiti, where it provides a viable sanitation option in neighborhoods that cannot support pit latrines or sewer connections.22PubMed Central. Container-based sanitation: assessing costs and effectiveness of excreta management in Cap Haitien, Haiti
Compared to pit latrines, container-based systems can dramatically improve nutrient recovery potential while reducing environmental emissions. One analysis of an urban informal settlement found that replacing pit latrines with container-based facilities increased nitrogen recovery two- to four-fold and cut emissions by roughly half to three-quarters, though operating costs were higher.23PubMed. Navigating Multidimensional Social-Ecological System Trade-Offs across Sanitation Alternatives in an Urban Informal Settlement The trade-off between cost and environmental benefit is the central tension for scaling these systems.
Will People Actually Accept It?
The biggest barrier to closing the loop on human waste is often not technology but psychology. A multinational survey of nearly 3,800 people across 16 countries found more openness than you might expect. About 68% favored recycling human urine as fertilizer, 59% said they would eat food grown with urine-based fertilizer, and only 11% believed the health risks could not be managed through treatment. Acceptance varied substantially by country, and the strongest predictors of willingness were people’s perceptions of the risks and benefits rather than simple disgust.24Science of The Total Environment. Willingness among food consumers to recycle human urine as crop fertiliser: Evidence from a multinational survey
Retailers, though, tend to be more cautious. A study of Swedish grocery stores found that while retailers were not outright opposed to stocking food grown with human-excreta-derived fertilizers, they were unlikely to champion the idea unless consumer demand pushed them.25City and Environment Interactions. Acceptance of human excreta derived fertilizers in Swedish grocery stores Clear regulations and public outreach appear to be necessary ingredients for broader adoption. A 2024 review concluded that public acceptance is achievable when paired with transparent safety standards and education about the benefits and proper processing methods.3Science of The Total Environment. Opportunities and challenges of using human excreta-derived fertilizers in agriculture: A review of suitability, environmental impact and societal acceptance
The Gap Between Ancient Practice and Modern Engineering
What separates a 19th-century night soil collector from a 21st-century resource recovery engineer is mostly knowledge of what can go wrong and the tools to prevent it. The ancient practice got the big picture right: human waste contains valuable plant nutrients, and dumping them into rivers is wasteful and polluting. But doing it safely requires either enough time and the right conditions for natural pathogen die-off, or active treatment that eliminates biological and chemical hazards before the material touches food-producing soil.
The modern toolkit includes thermophilic composting with biochar to speed pathogen kill and retain nutrients, urine-diverting systems that simplify treatment by separating the two waste streams, struvite precipitation that pulls out clean phosphorus fertilizer, and anaerobic digestion that captures energy while stabilizing the solids. Each of these approaches addresses different pieces of the problem, and in practice they are often combined. A urine-diverting toilet paired with composting of the feces and struvite recovery from the urine, for example, can handle both waste streams while producing two distinct fertilizer products and minimizing the risk profile of each.
The ancient name may have fallen out of use, but the substance itself never stopped being relevant. Around 4.2 billion people worldwide still lack safely managed sanitation, and the phosphorus reserves we mine for conventional fertilizer are finite. Whether the solution looks like a high-tech nutrient recovery plant in northern Europe or a well-managed composting toilet in a refugee camp, the basic proposition is the same one farmers understood centuries ago: what goes in one end of the human body still has value when it comes out the other.