The timing of such a system is hardly accidental. Irrigated agriculture already accounts for approximately 70 percent of global freshwater withdrawals, while arable land continues to shrink under pressure from degradation and rapid urbanization. The Food and Agriculture Organization estimates that global agricultural production must increase by about 50 percent by 2050 relative to 2012 levels to feed a growing population. Controlled-environment agriculture, including vertical farming in urban buildings, has emerged as one strategy to raise productivity while cutting resource consumption, but its energy appetite has remained a persistent obstacle, with energy representing between 10 and 40 percent of total production costs in commercial greenhouses.

Among soilless cultivation techniques, aeroponics stands out for its extreme water efficiency. Unlike hydroponics, where roots sit submerged in nutrient solution, or aquaponics, which couples plant cultivation with fish farming, aeroponics suspends bare roots inside a closed chamber and sprays them with a fine nutrient mist. Reported water savings reach 90 to 98 percent compared with soil-based cultivation, while direct exposure to oxygen enhances root respiration and nutrient uptake. The technique also reduces exposure to soil-borne diseases, allows precise moisture control, and has even attracted attention from space agencies for food production under microgravity.

Yet aeroponics has a critical vulnerability: it depends on continuous electrical power. Because roots hang in air rather than water, a power outage can desiccate a crop within hours. Commercial vertical aeroponic towers, such as the Tower Garden FLEX, the Nutraponics Pro AeroTower, and the Agrotonomy Tower Farm system, all rely on grid electricity and proprietary designs, and none include integrated filtration to protect their misting nozzles. Prices range from $765 to $5,250 per unit, and academic prototypes published in the literature typically omit fabrication files, making them difficult or impossible to reproduce.

TOTEM was designed to close these gaps. The system stacks eight mechanically coupled modules, each housed in standard 20-centimeter-diameter PVC components: growth, reservoir, pump, filter, inlet-drainage, control, power, and solar. The growth module is a 1.5-meter PVC tower holding 24 net cups arranged in six staggered rows, with modified 45-degree elbow fittings angling each plant site to optimize light distribution. Inside the chamber, a vertical distribution pipe carries pressurized nutrient solution past 24 misting nozzles that atomize it into fine droplets directed at the suspended roots.

The hydraulic loop is deliberately simple and closed. A 12-volt DC diaphragm pump draws solution from the reservoir and pushes it through an AZUD Modular 100 mesh filter, which captures suspended particles before they can clog the nozzles, a failure mode that plagues many commercial systems. Filtered solution travels up the internal pipe, is atomized across the root zones, and the excess drains by gravity back into the reservoir for recirculation. During the basil trial, this closed loop required only about 54 liters of nutrient solution for 24 plants over the entire 55-day cycle, an estimated 0.041 liters per plant per day, far below reference values of roughly 0.6 liters per plant per day for protected agriculture and 12.6 liters for open-field cultivation.

At the system’s electronic core sits an ESP32-WROOM microcontroller mounted on a custom printed circuit board alongside an LM2596 voltage regulator, an FOD852 optocoupler, and an RAS1220M relay that switches the pump. A waterproof DS18B20 digital temperature sensor tracks conditions inside the growth chamber while a water-level sensor monitors the reservoir, enabling basic fault detection such as low-solution alerts. The microcontroller executes an intermittent irrigation schedule, in the validation trial running the pump for 0.5 minutes followed by 29.5 minutes of rest, equivalent to 48 activation cycles per day. Over Wi-Fi, the controller transmits data to a remote server that logs performance history and serves a web-based graphical user interface, allowing users to adjust irrigation parameters and monitor the system remotely, a capability none of the surveyed commercial towers offer.

Energy autonomy comes from a 50-watt polycrystalline solar panel mounted on a three-meter galvanized steel mast, angled at 24 degrees and oriented southward for maximum insolation. Power flows through a 40-amp MPPT charge controller into two 12-volt, 12-amp-hour rechargeable batteries wired in parallel, providing 288 watt-hours of nominal storage and roughly 122 watt-hours of usable energy at a conservative 50 percent depth of discharge. That corresponds to approximately 2.7 days of autonomous operation without any sunshine. The designers sized the array against the worst month of the year in La Paz, Baja California Sur, where December delivers only 3.9 peak sun hours per day; even with a photovoltaic derating factor of 0.70, the panel supplies an estimated 136.5 watt-hours daily, comfortably exceeding the calculated demand of 44.9 watt-hours after accounting for the pump’s 19.2 watt-hours, the continuously active microcontroller’s 19.0 watt-hours, and 85 percent system efficiency.

The validation experiment grew basil, a fast-growing crop prized in controlled-environment agriculture for its sensitivity to water availability, under uncontrolled shade-greenhouse conditions. After transplanting, formative pruning at 30 days promoted lateral branching, followed by a first harvest at 45 days and a final harvest at day 55. Sampled plants averaged 517.97 square centimeters of leaf area, 31.33 leaves, an 18.8-centimeter shoot length, and a mean relative water content of 82.18 percent, indicating that intermittent misting maintained adequate hydration throughout. Chamber temperatures fluctuated naturally between 14 and 38 degrees Celsius, and the system completed every programmed irrigation cycle without interruption across the full cultivation period.

The authors are candid about limitations. The final nutrient solution pH drifted to 7.39, above the mildly acidic range typically targeted in soilless production, and the team recommends adding calibrated pH and electrical conductivity sensors with closed-loop control in future iterations. The single-cycle trial demonstrated feasibility rather than long-term endurance, and the growth measurements from three plants provide descriptive data rather than statistically rigorous agronomic comparison. Still, the study’s principal contribution lies in its radical transparency: complete STEP CAD files for every module, circuit schematics, PCB layouts, ESP32 firmware in C++, and web interface code are released under CERN Open Hardware License v2-S and GNU General Public License v3, accompanied by an itemized bill of materials totaling $719.51. With a footprint of just 0.078 cubic meters, less than a ninth of comparable commercial towers, TOTEM makes off-grid aeroponic farming something a workshop, a school, or a resource-limited community can actually build, repair, and adapt for itself.

Subject of Research: An open-source, low-cost, solar-powered aeroponic vertical farming system for sustainable urban agriculture

Article Title: TOTEM: A low-cost solar-powered aeroponic system for vertical agriculture

Article References: Von Borstel, F. D., Villa-Medina, J. F., Nieto-Garibay, A., & Gutiérrez, J. (2026). TOTEM: A low-cost solar-powered aeroponic system for vertical agriculture. HardwareX, 28, Article e00838. https://doi.org/10.1016/j.ohx.2026.e00838

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00838

Keywords: aeroponics, vertical farming, open-source hardware, solar power, urban agriculture, ESP32, water efficiency, controlled environment agriculture, basil cultivation, food security, IoT, sustainable agriculture

The traditional production of fertilizers poses serious concerns regarding its reliance on non-renewable energy sources. Natural gas, oil, and coal dominate this sector, leading to substantial energy consumption and greenhouse gas emissions. The redundant CO2 emissions generated during fertilizer production have driven the search for more environmentally friendly alternatives, and researchers believe that human urine, often dismissed as waste, is a significant untapped resource.

According to the findings published in the reputable journal Resources, Conservation and Recycling, urine possesses high levels of nitrogen, a key nutrient essential for promoting healthy plant growth in agricultural systems. This study was spearheaded by the Sostenipra group at ICTA-UAB, in collaboration with the GENOCOV group from the Department of Chemical, Biological, and Environmental Engineering. Their work collectively emphasizes the potential impact of nutrient recovery via human urine not just for agricultural productivity but also for significant reductions in CO2 emissions and water usage.

Human urine, referred to scientifically as "yellow water," is defined as a rich nutrient matrix, particularly in nitrogen content. Transforming it into fertilizer could result in a robust circular economy approach that enhances sustainability in urban agricultural practices while helping to mitigate the adverse effects of pollution from conventional farming techniques. The benefits extend beyond agricultural applications; by utilizing urine for fertilizer, critical issues such as water contamination of rivers and aquifers could also be significantly alleviated.

The feasibility of this approach has been assessed through experimental research conducted at the bioclimatic building at ICTA-UAB. This site features a pilot plant dedicated to nitrogen recovery, complemented by a state-of-the-art greenhouse situated on the rooftop. Within this controlled environment, researchers have meticulously evaluated the efficacy of the recovered nitrogen on hydroponic tomato crops, which serve as a model for broader agricultural applications. The process begins by collecting urine from waterless male urinals, stored in a specialized facility designed to handle this nutrient-rich waste.

Once collected, the urine is conveyed to a custom reactor where intricate biological processes are set into motion. In this phase, the urine is mixed with a base compound aimed at regulating acidity levels. Subsequently, microorganisms within the reactor convert urea into nitrate, transforming the nitrogen into a biologically available form that plants can easily absorb. The produced nitrate is then directed to nourish the hydroponic tomatoes cultivated in the greenhouse, demonstrating a tangible application of this concept.

Research results indicate that each cubic meter of treated yellow water can yield approximately 7.5 kg of nitrogen, sufficient to support the cultivation of nearly 2.4 tons of tomatoes. These findings open up new agricultural possibilities by illustrating how urban settings could efficiently recycle human-generated waste into valuable inputs for food production. Such a system not only promotes urban agriculture but also significantly lessens the dependency on traditional fertilizers derived from limited natural resources.

While the study remains at the laboratory scale, the researchers envision a compelling case for further scaling up their operations. By extending the nitrogen recovery network to connect all urinals within the building, the environmental and economic impacts of urine recovery could substantially improve. Ongoing research aims to evaluate additional factors, including the potential presence of pharmaceutical compounds consumed by humans, which may unintentionally find their way into crop tissues, providing a holistic understanding of the health implications involved.

The implications of this study extend far beyond mere agricultural practices. The efficient use of human urine as a nitrogen source supports a paradigm shift in resource management strategies, promoting sustainability and environmental stewardship. As cities continue to grow and face mounting pressure to provide for their inhabitants, innovative solutions like urine-based fertilizers could empower urban agriculturalists to minimize their ecological footprint while maximizing crop yield.

The concept of circular economies is gaining traction, reinforcing the need for sustainable practices in both rural and urban contexts. Resource recovery initiatives, such as utilizing human urine, highlight the importance of rethinking waste management and agricultural practices to foster resilience against climate change and resource depletion. This shift is not merely an environmental imperative but also an avenue toward safeguarding food security in a world increasingly challenged by resource scarcity.

In conclusion, the research conducted by ICTA-UAB paves the way for a sustainable future in urban agriculture, harnessing human waste to regenerate vital nutrients for food production. By embracing innovations such as nitrified urine fertilizers, agricultural systems can evolve to become more sustainable and resilient, ensuring that urban areas can thrive amidst the challenges posed by climate change, population growth, and environmental degradation.

Subject of Research:
Article Title: Urine luck: Environmental assessment of yellow water management in buildings for urban agriculture
News Publication Date: 19-Jan-2025
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Keywords: Sustainable agriculture, Urine, Nitrogen, Fertilizers, Natural resources conservation, Water, Human fertilization, Sustainability, Food production, Food resources, Chemical processes.