Written By: Jordan Monson; SLU Dietetic Intern
Did you know that human waste was once a valuable resource? For centuries, in cultures worldwide, composted human waste, often called “humanure” was valued for its ability to fertilize soil and improve crop yields. In 18th century Japan, for example, “night soil” was so prized that farmers would trade fresh produce for it or buy it, ensuring a sustainable nutrient cycle between urban and rural areas. This was even the cause of many squabbles, particularly between tenants and landlords, who often claimed rights to their tenants' waste. Because human waste was a valuable commodity, the farmland was fertile and the cities clean, unlike many other large cities at the time, where overflowing latrines, smelly gutters, and widespread diseases were the norm.
But these practices faded with industrialization, as the invention of modern sewage systems in the mid-20th century revolutionized sanitation and health, reducing diseases like cholera and dysentery. However, it also broke the nutrient cycle and the reciprocal relationship between urban and rural areas. Today, most waste travels miles through underground pipes to treatment plants, where it becomes sludge- most of which ends up in landfills. A small portion is recycled into fertilizers, but these biosolids often carry “toxic compounds, nanomaterials, hormones, dangerous pathogens… PCBs, flame retardants, heavy metals, and endocrine disruptors that all collect and are not filtered out by the sanitation process” which raises safety concerns, particularly if this sludge ends up back on agricultural land.
A Crisis for Soil, Sewage Systems, and Food Security
Sewage systems have played a vital role in improving public health by reducing waterborne diseases and improving overall urban cleanliness, but today, these aging infrastructures face significant challenges. In the U.S., 15% of wastewater treatment plants have reached or exceeded capacity, and over 23,000 sewer overflows occur annually. These overflows contaminate clean drinking water, harm aquatic life, and release methane, a potent greenhouse gas, contributing to climate change.
Simultaneously, agriculture is grappling with a fertilizer crisis. Since 2021, the price of nitrogen-based synthetic fertilizer has skyrocketed by 300% (and this was exacerbated by the outbreak of the Russian war in Ukraine in 2022, as Russia is a major producer of synthetic fertilizers), forcing farmers to either spend more or scale back on production. For consumers, this means higher grocery bills and reduced access to affordable food. Compounding this problem is the potential scarcity of phosphorus, a critical nutrient for growing crops. Most of the reserves of phosphorus are concentrated in just a few countries around the world, making global food systems vulnerable to geopolitical instability, as we have already seen some impact from.
Here’s where the potential of humanure becomes revolutionary. Human waste is a natural and renewable source of the nutrients plants need to grow- nitrogen (N), phosphorus (P), and potassium (K)- all conveniently found in what we flush away daily. Instead of burying phosphorus deep underground or extracting energy-intensive synthetic nitrogen, we could tap into this abundant, overlooked resource.
Rethinking Human Waste: The Nutrient Cycle
To understand the connection between human waste and agriculture, consider another reciprocal relationship between humans and plants found in the air. Just as we breathe out carbon dioxide for plants to absorb and return oxygen for us to inhale, nutrients cycle through us and return to the soil in forms ready for plants to use. These nutrients, excreted as waste, can feed plants, which in turn grow into nutrient-rich foods ready for us to eat again.
This nutrient cycle is a natural and sustainable solution that could replace synthetic fertilizers altogether. Synthetic options, while temporarily effective, require vast amounts of energy to produce and wash away easily from farmland into waterways. This runoff creates oxygen-depleted “dead-zones”, algal blooms, polluted drinking water, and acid rain. In contrast, humanure’s sticky organic properties help it bind to soil, preventing it from washing away and delivering nutrients more efficiently and long-term.
Risks of Synthetic Fertilizers
While synthetic fertilizers have played a significant role in increasing agricultural productivity, their drawbacks are becoming increasingly evident:
- Water Pollution: These fertilizers leach easily into water systems, causing algal blooms, oxygen-depleted “dead zones,” and contaminated drinking water that is unsafe for human consumption.
- Rising Costs: Synthetic fertilizer prices have surged, placing economic pressure on farmers and contributing to higher food prices for consumers.
- Soil Depletion: Long-term use of synthetic inputs weakens soil health by reducing its organic matter, compromising its ability to retain water and nutrients effectively.
- Climate Harm: The production and transportation of synthetic fertilizers emit significant greenhouse gases, exacerbating climate change and undermining global food security.
- Lower Crop Quality: Soils degraded by overuse of synthetic fertilizers produce less nutritious crops, impacting human health and reducing the overall quality of food.
Benefits of Humanure
Humanure addresses these challenges by leveraging natural processes to enhance agriculture while minimizing environmental harm:
- Environmental Impact: Recycling nutrients from human waste prevents harmful runoff and protects water sources, soil, and surrounding ecosystems. Its use helps mitigate the environmental damage caused by synthetic fertilizers.
- Economic Opportunity: By reducing dependence on costly synthetic inputs, humanure can stabilize farming expenses and support sustainable, locally driven food systems.
- Human Health & Nutrition: Crops grown in nutrient-rich, naturally fertilized soil are healthier, often containing higher levels of vitamins and minerals, which benefits both individual and public health. Initial studies are also showing improvements in crop yield with the use of humanure.
- Climate Resilience: Humanure’s low-energy processing reduces greenhouse gas emissions, while its application supports carbon sequestration in healthy soils—an essential strategy for combating climate change and securing future food production.
A Solution Rooted in Sustainability
Humanure not only addresses the environmental risks posed by synthetic fertilizers but also offers a viable path toward a more sustainable, circular agricultural system. Its ability to enhance soil health directly influences crop quality and resilience, making it a cornerstone of sustainable food security efforts. By rethinking waste as a resource, we can move away from extractive, harmful practices and embrace methods that regenerate both ecosystems and food systems for future generations.
Sustainable Solutions in Action
Rich Earth Institute (Vermont) The Rich Earth Institute is at the forefront of transforming human waste into valuable agricultural resources. By conducting groundbreaking research, promoting education, and advancing innovative technologies, they focus on urine-diversion programs. These programs harness the nutrient-rich potential of urine—particularly nitrogen, phosphorus, and potassium—found in the waste of those in industrialized areas with "highly digestible diets" Their work highlights how human waste can be safely and effectively reintegrated into agricultural systems.
A spinoff from Rich Earth Institute, Bright Water Tools, builds on this mission by creating systems that separate water from toilet waste, turning it into non-potable reusable water and natural fertilizers. These tools help reduce wastewater management costs, prevent harmful runoff, and provide sustainable nutrient sources for agriculture and landscaping.
Washington D.C. Wastewater Treatment Plant: The Blue Plains Advanced Wastewater Treatment Plant is a leading example of large-scale waste reuse. This facility repurposes biosolids, energy, and nutrients from wastewater into valuable products. Their “Class A biosolids,” sold under the brand name Bloom, serve as a slow-release recycled fertilizer. Additionally, the plant employs thermal hydrolysis to extract energy from waste, reducing its carbon footprint while powering its operations.
Paris Pee Diversion Project: A broader effort can be seen across France to integrate green practices into upgrading its aging sewage systems. In the SVP eco-neighborhood, low flush toilets and dry urinals connect to a separate urine-connection network with on-site treatment plants that turn urine into concentrated fertilizers to be used locally. The La Fumainerie project in Bordeaux has been experimenting with composting feces and using dry toilets.
Sanivation: Operating in Kenya, Sanivation addresses inadequate sewage systems by creating waste-to-energy solutions. Their projects include converting fecal sludge into briquettes, which serve as efficient, low-emission fuel alternatives. By improving urban sanitation, reducing pollution, and creating jobs, Sanivation not only mitigates environmental issues but also enhances the quality of life for underserved populations.
S.O.I.L: In Haiti, SOIL (Sustainable Organic Integrated Livelihoods) offers a model for addressing sanitation and agricultural challenges simultaneously. Their initiative, EkoLakay, provides urban households with container-based toilets, which are collected weekly. The waste is then composted into eco-friendly fertilizers, revitalizing Haiti’s depleted soils. This program simultaneously promotes public health, creates local employment, and supports sustainable farming.
Looking Ahead
From small-scale community programs to city-wide wastewater treatment innovations, these projects underscore the transformative potential of human waste when managed sustainably. By implementing these systems globally, we can protect natural resources, bolster food security, and advance climate resilience, ensuring a healthier future for both people and the planet.
