Bio-concrete from urine: Researchers develop sustainable building material

Researchers at the University of Stuttgart have used microbial processes to produce environmentally friendly bio-concrete from urine as part of a “wastewater-bio-concrete-fertilizer” value chain. With the project extension granted by the Baden-Württemberg Ministry of Science, Research, and the Arts, the focus now shifts to product optimization and practical testing.

Concrete is booming. Around 4 billion tons of cement are processed into concrete and used worldwide every year. With serious consequences for the environment.

“Conventional cement is typically fired at temperatures around 1,450 degrees. This consumes a lot of energy and releases large quantities of greenhouse gases,” says Professor Lucio Blandini, Head of the Institute for Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart.

Environmentally friendly microbial production process

Researchers from three institutes at the University of Stuttgart are developing a new type of building material—bio-concrete. Thanks to its high compressive strength, it can not only replace traditional sandstone and, in some cases, cement-based concrete. It can potentially also be produced entirely from waste materials and therefore has a significantly lower ecological footprint.

The researchers are using a plentiful yet previously overlooked raw material: human urine. They have successfully tested their method in a feasibility study. The work is published in the journal npj Materials Sustainability.

“Bio-concrete is produced through biomineralization. This is a biotechnological process in which living organisms produce inorganic material through chemical reactions,” explains Maiia Smirnova, research associate at ILEK.

“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. The breakdown of urea by the bacteria, combined with adding calcium to the urine, causes crystals of calcium carbonate to grow. This solidifies the sand mixture into bio-concrete.

“At the end of the process, a solid is produced 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.”

The first samples produced show promising material properties. By using technical urea, the team has achieved a compressive strength of over 50 megapascals—significantly surpassing the strength of previously available building materials produced through biomineralization.

With urea in artificial urine, a compressive strength of 20 megapascals was achieved. Using real human urine, the value was five megapascals, as bacteria lose their activity in the course of the biomineralization period of three days. This must now be improved.

According to the scientists, a strength of 30 to 40 megapascals in the biomineralized material would be sufficient for constructing two- to three-story buildings. They are currently carrying out freeze-thaw tests to determine whether the material can be used outdoors.

Aiming for a circular economy: From waste product to building material

“The production process for our bio-concrete consumes considerably less energy and causes fewer emissions than conventional cement production. But our approach is also sustainable because we embed the product in a circular value chain,” says Blandini.

The researchers have developed a concept that shows how urine could be separated and processed from the partial wastewater flow in places with a high volume of people, such as an airport, in order to use it as a raw material for the production of bio-concrete. At the same time, this process could recover secondary valuable substances from the wastewater to produce fertilizer for agriculture.

“By manufacturing two products at the same time, we enhance the environmental benefits,” says Smirnova.

Second project phase: Optimization of the manufacturing process and practical testing

Following a successful completion of the preliminary studies, the project has now been extended for three years by the Baden-Württemberg Ministry of Science, Research and the Arts. In further laboratory tests, the researchers want to identify substances in human urine that have a negative effect on the activity of the bacteria and therefore the quality of the bio-concrete.

The manufacturing process is to be optimized on this basis. The team, together with the Centre for Organic Farming at the University of Hohenheim, is also focusing on simultaneous fertilizer production.

Once the laboratory tests are completed, the concept will be tested under real-world conditions: A pilot facility is planned at Stuttgart Airport, where urine will be collected and processed into bio-concrete and fertilizer.

Provided by
Universitaet Stuttgart