Flush Once, Power Twice: Turning Toilets Into Resource Hubs
What if what you flush away today could help grow the food on your plate tomorrow?
Welcome to circular sanitation, where waste becomes your most valuable asset.
Time to Rethink the Flush
For over a century, we’ve relied on the same basic model: flush it with drinking water, pipe it far away, and hope someone else takes care of it.
But as urban populations keep growing and climate patterns shift, that model is showing its cracks.
- Release of potent greenhouse gases: wastewater, including sewers and treatment, contributes around 3% of global human-made emissions (CO₂, CH₄, N₂O)
- Contamination of industrial discharge and urban runoff, including heavy metals and persistent pollutants like PFAS
- Failure under climate stress: heavy rainfalls overwhelm sewers, raw discharge
- Highly linear: water, energy, and nutrients are wasted and never return to the supply system
Did you know?
A single pee can help grow three carrots. Every flush contains nitrogen, phosphorus, potassium, organic matter, and water – resources worth €2,470 per year for a family of four if using a circular sanitation system.
How the Loop Closes
Circular sanitation closes the loop, recovering these resources for local reuse while reducing costs, environmental impact, and dependence on imported products like industrially-made fertilizers.
Together with ToiletsForAll, we took a closer look at the key players driving innovation in this field and developed a comprehensive vision for the (not-so-distant) future of sanitation, bringing all the puzzle pieces together into one big picture.
1. Separation & Collection
Smart toilets separate urine and feces; kitchen/garden organics are gathered via shared disposal points.
2. Resource Recovery
Urine is processed into safe liquid fertilizer and distilled water. Feces, kitchen waste and garden residue generate biogas in an anaerobic digestion tank, leaving behind nutrient-rich digestate.
Learn about the value
Urine Nutrient recovery
At the front end, toilets apply the teapot effect, a clever hydrodynamic principle, to separate urine without changing the look or feel. At the back end, an urine nutrient recovery system transforms it into a safe, effective urine fertilizer.
Modern agriculture is pushing beyond planetary boundaries, largely because it depends on fossil-fuel-based fertilizers. Nitrogen from the Haber-Bosch process consumes massive energy and drives carbon emissions, while phosphorus mining depletes finite resources and damages ecosystems. Our urine contains nitrogen, phosphorus, and potassium, and can completely replace synthetic fertilizers. Recovering these nutrients eliminates dependence on fossil fuels and global fertilizer markets. The bonus? About 90% of the remaining liquid becomes valuable distilled water. Closing this nutrient loop can restore food production within safe planetary limits and make agriculture self-sufficient and resilient.
Feces and Organic Waste Recovery
Feces are flushed using a vacuum toilet system that cuts water use dramatically. Combined with kitchen waste collected through a shared disposal point, the mix heads into an anaerobic digestion tank. This setup generates biogas for household energy and leaves digestate behind, ready to become humus and soil conditioner. However, the journey of feces to the collection and treatment site can vary. Instead of a vacuum system, some alternatives include low-water flush toilets with water reuse combined with anaerobic treatment. Others, depending on community preference, may opt for dry toilets paired with aerobic composting to turn feces into high-quality humus directly on site.
Feces (like urine) contain phosphorus, potassium, nitrogen, plus organic matter and micronutrients. Add carbon-rich material like sawdust or leaves, and you’ve got humus in the making, a powerhouse for soil fertility. In a digestion tank, mixing feces with kitchen or garden waste boosts biogas production, generating household energy, reducing dependence on external inputs, and maximizing nutrient cycling. Humus and soil conditioners help keep soil healthy, prevent erosion, and make water use more efficient, while also restoring soil resilience, boosting yields sustainably, and cutting reliance on chemical fertilizers.
3. Reuse & Redistribution
Biogas powers heat/electricity; fertilizer nourishes rooftops and urban greens; water is reused; surplus can be sold.
Understand the Economic Impact
On Individual Level
A family of four can turn €2,470 a year from household waste into a €120,000 retirement boost.
Circular sanitation can generate €2,470 per year for a family of four. Invested wisely, and thanks to the power of compound growth averaging 8% annually, this steady contribution could grow into a €120,000 portfolio in 20 years, providing additional financial security for retirement and turning what was once waste into real wealth.
Instead of flushing resources away, they turn their household waste into a powerful financial engine.
How the numbers add up:
A family of four in Hamburg can turn household waste into €2,470 per year through fertilizer, distilled water, rooftop-grown food, and utility savings. Instead of spending it, investing €205 per month in a diversified fund like the S&P 500 could grow the contributions of €49,400 over 20 years into a €120,000 portfolio (8% p.a.).
There’s more.
By choosing a decentralized toilet system, homeowners could avoid mandatory sewer connection fees: at least €3,345 (Hamburg Wasser) plus excavation costs. That’s several thousand euros saved before the system even starts running.
These assumptions come from real data, biogas yields, rooftop harvests, current energy rates, market-tested fertilizers, and German rooftop stats.
(Yes, we crunched the numbers so you don’t have to.)
Sources
Fertilizer Import Data: World Bank WITS, 2023. Germany imported 203.6 million kg of mineral/chemical fertilizers valued at $124 million.
Urine Production & Nutrient Content: Urine; based on 550L average annual urine production per adult with typical nutrient concentrations of 7.3g/L N, 0.67g/L P, 1.8g/L K.
Investment Returns: S&P 500 historical data shows compound annual growth rate of 6.2% (price only) to 9.8% (with dividends reinvested), 1926-2024.
Hamburg Water/Sewer Costs: Hamburg Wasser official tariffs (hamburgwasser.de). Connection fees vary by property; consult Hamburg Wasser for specific quotes.
Note: Figures are illustrative estimates for educational purposes.
| Urine-based fertilizer | €1,095/year |
| Distilled water | €680/year |
| Digestate | €5/year |
| Electricity & heat savings | €84/year |
| Water & wastewater savings | €202/year |
| Rooftop-grown food value | €404/year |
*Illustrative; not investment advice.
On Societal Level
Germany could cut €109.1 million* in annual fertilizer imports with recycled nutrients from just 35% of its population.
Germany has the potential to fully cover its entire annual agricultural fertilizer needs using nutrients sourced from just 29 million residents. This would make the country self-sufficient, eliminating the need for imported fertilizers.
By cutting *$127.5 million in fertilizer import costs (World Bank’s WITS, 2023), these funds could instead be invested in circular sanitation and fertilizer infrastructure, reducing dependence on energy-intensive nitrogen processing and phosphate mining, which deplete natural resources. The societal impact would be significant, creating jobs, promoting sustainability, and fostering community involvement in a truly circular agricultural system.
How the numbers add up:
In 2023, Germany imported 209.6 million kilograms of mineral and chemical fertilizers. Because urine-based fertilizers are less concentrated, they would require about 10 times more volume, which is roughly 1.6 billion liters to replace industrial fertilizers.
On average, one adult could produce 54.75 liters of urine-based fertilizer per year. That means it would take around 29 million people, which is just 35 percent of Germany’s population, to cover the country’s entire fertilizer demand.
So What Does it Look Like?
Pretty normal, actually.
Same comfort, same ease of use, just smarter behind the scenes.
Body outputs are separated, collected and treated to preserve their value. Urine becomes nutrient-rich fertilizer. Feces and kitchen waste are turned into biogas and compost.
The entire process is clean, odorless, and seamlessly integrated into the spaces we live and work in.
Proven Tech, Built to Adapt
The technologies behind this system have been carefully selected for their proven effectiveness. However, each component is modular, so things can be swapped, scaled, or adjusted to fit different community needs, climates, and setups.
Discover certified systems that are operating throughout Europe.
Has developed systems that safely transform urine into Aurin, an EU-approved liquid fertilizer, while also removing pharmaceuticals and hormones in the process. Active installations in Switzerland (Fribourg BlueFactory and Zurich pilot) demonstrating real-world feasibility.
Already producing certified, high-quality humus fertilizer from dry toilets. Implemented at the Eberswalde plant in Germany, closing the nutrient loop and promoting sustainable agriculture.
Vacuum toilets and nutrient recovery systems are effectively operating in urban environments. This district successfully implements vacuum toilets, anaerobic digestion, and nutrient recovery processes at scale.
The upcoming LEED v5 recognizes and rewards sustainable practices such as onsite water reuse and circular sanitation systems, creating real incentives for developers to invest in these solutions.
Why it Beats Linear Sewers
Circular sanitation moves beyond the linear model to a fully circular system that recovers water, nutrients, and energy locally. This approach:
Less climate pollution
Cuts emissions and avoids the worst hot‑spot gas.
Use the waste
Turns toilet waste into fertilizer, clean water and biogas.
Saves money
Lowers bills and can create new income from resources.
Cleaner results
Kept away from dirty runoff, with fewer toxic chemicals.
Saves water
Up to 90% less water with vacuum toilets.
Easier to build
Smaller pipes, shallow trenches – works in floods or droughts.
Ready to Own Your Sh*t?
Be Part of the Momentum
Do you want to see this project get attention? Help us spread the word and co-create the next steps.
For People & Communities
Circular sanitation won’t scale without awareness. If this resonates with you:
- Share this page with your network
- Start conversations in your community
- Challenge the status quo: “Why are we still flushing wealth away?”
- Spread the word on social media
- Engage with us – give input, ask questions, share ideas
The loop won’t close itself. But together, we can make it happen.
For Companies & Cities
We’re assembling a consortium of forward-thinking companies to scale circular sanitation globally.
- Be at the forefront of the €109M+ market opportunity in Germany alone
- Access pilot programs and early implementation opportunities
- Shape standards and certifications as the industry evolves
- Connect with municipalities, developers, and governments
Early partners will define the standards.
About INDEED Innovation
As a global design and innovation firm, INDEED empowers organizations to pioneer circularity. We combine deep expertise in product, service, and strategic design with innovative thinking to help you create impactful, future-proof solutions. This guide distills that experience, designed to accelerate your journey into Circular Design.
About Toilets for All
Toilets for All is a Swiss foundation which contributes to closing the huge gap in access to clean and dignified toilets for the world’s population (SDG 6.2), focusing on schools. We aim to achieve this goal through different collaborative actions, acting as an enabler for both entrepreneurs and funders, but also legislative organisations, select communities and government bodies, and focusing on the sector of circular off-grid sanitation for schools and related hygiene efforts.
FAQ Circular Sanitation
This comprehensive FAQ answers all your questions about our circular sanitation vision.
Urine separation toilets (also called urine-diverting toilets) use the “teapot effect” – a hydrodynamic principle that automatically separates urine from feces without changing how the toilet looks or works. This is the foundation of circular sanitation systems, which are being developed to turn human waste into resources. The separated urine would be processed into fertilizer while feces combined with organic waste would generate biogas. The technology exists in products from companies like VunaNexus and is proven in pilot sites like Hamburg’s Jenfelder Au district. Our project envisions integrating these technologies into complete building systems.
Yes, human urine can safely be used as fertilizer and contains nitrogen, phosphorus, and potassium – the same nutrients in synthetic fertilizers. Companies like VunaNexus already produce Aurin, an EU-approved urine-based fertilizer that removes pharmaceuticals and hormones during processing. One person’s urine could fertilize enough soil to grow three carrots per use. Our vision shows Germany could replace 100% of fertilizer imports (€109.1 million annually) using urine from just 35% of the population. The technology is proven – we’re working to scale it into integrated circular sanitation systems for buildings and cities.
Vacuum toilet systems can reduce infrastructure costs by up to 50% compared to conventional sewers due to smaller pipes and simpler installation. They save up to 90% water and up to 57 million liters over a building’s lifetime. Homeowners could avoid sewer connection fees (€3,345+ in Hamburg). Our circular sanitation vision projects that a family of four could generate €2,470/year in resource value (fertilizer, water, biogas, food), potentially growing to €120,000 over 20 years if invested. The technology is proven in projects like Jenfelder Au – we’re developing the complete integrated system.
The most sustainable toilet systems recover resources instead of wasting them. Our circular sanitation vision combines proven technologies: vacuum toilets (90% water savings), urine separation (fertilizer production), and anaerobic digestion (biogas generation). Unlike simple composting toilets, this integrated approach would provide fertilizer, water, energy, and savings (€2,470/year per family) while maintaining modern comfort – no behavioral changes required. Companies like VunaNexus, Finizio, and districts like Jenfelder Au in Hamburg already prove these technologies work. We’re developing the complete building-scale system.