Researchers from three institutes at the University of Stuttgart are developing a new type of building material - bio-concrete.
Scientists in Germany have successfully turned urine into bio-concrete, as part of a project aiming to revolutionize sustainable construction by creating building materials from waste.
The research team, led by Lucio Blandini, head of the Institute for Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart, utilized microbial biomineralization, a biotechnological process where bacteria convert urea found in urine into calcium carbonate crystals.
These large circular crystals with radial striations with smooth surfaces bind sand particles together, resulting in a robust and environmentally friendly bio-concrete chemically similar to natural sandstone.
The project, named SimBioZe, was initiated as the researchers recognized urine as an abundant yet underutilized resource, prompting them to explore microbial biomineralization as a sustainable alternative to traditional concrete production.
Supported by the state of Baden-Württemberg’s Ministry of Science, Research, and the Arts, the initial feasibility study successfully demonstrated the viability of converting urine into eco-friendly bio-concrete.
Green building material
While concrete remains the most widely used building material globally with approximately four billion tons produced annually, its hefty environmental price tag pushes the construction sector to seek more sustainable alternatives.
Producing cement, its key ingredient, requires heating limestone to temperatures of about 2,642 degrees Fahrenheit (1,450 degrees Celsius), consuming vast amounts of energy and releasing significant greenhouse gas emissions.
In a bid to address this environmental challenge, the research team developed bio-concrete as a promising substitute, through an innovative method that integrates into a ‘wastewater-bio-concrete-fertilizer’ value chain, transforming a common waste product into valuable construction materials and fertilizers simultaneously.
Maiia Smirnova, MSc, a research associate at ILEK, explained that bio-concrete is produced through biomineralization, a process in which living organisms produce inorganic material through chemical reactions.
“We mix a powder containing bacteria with sand, place the mixture into a mold, and then flush it with calcium-enriched urine over the course of three days in an automated process,” she continued. “The breakdown of urea by the bacteria, combined with adding calcium to the urine, causes crystals of calcium carbonate to grow.”
The process solidifies the sand mixture into bio-concrete, ultimately producing a solid that is chemically similar to natural calcareous sandstone. “Depending on the mold, elements can be created in various shapes and sizes, with a current maximum depth of 15 centimeters,” she added.
Trials yield outstanding results
According to the researchers, when using technical-grade urea, the bio-concrete achieved compressive strengths surpassing 50 megapascals (MPa), making it considerably stronger than previously available biomineralized materials.
Meanwhile, tests with artificial urine produced strengths of 20 MPa, while real human urine resulted in strengths of around 5 MPa, due to a decline in bacterial activity during processing. The researchers aim to enhance this further, targeting strengths of 30 to 40 MPa, sufficient for buildings up to three stories high.
“The production process for our bio-concrete consumes considerably less energy and causes fewer emissions than conventional cement production,” Blandini concluded in a press release. “But our approach is also sustainable because we embed the product in a circular value chain.”
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In the ‘SimBioZe’ project, researchers are using human urine to produce a sustainable building material. Credit: University of Stuttgart / ILEK / IMB / ISWA
The team is currently assessing the bio-concrete’s resilience under freeze-thaw conditions, determining its suitability for outdoor applications. The project’s second phase, recently funded for an additional three years, will focus on optimizing bacterial activity and further refining the production process.
In addition, to test real-world applicability, the scientists plan to construct a pilot facility at Stuttgart Airport. This facility will process urine collected from high-density public areas, transforming it into bio-concrete and extracting valuable fertilizers simultaneously. By creating a circular economy that reclaims nutrients and minimizes waste, the project exemplifies sustainable urban infrastructure.
The study has been published in the journal npj Materials Sustainability.
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