Searching for more sustainable building materials, scientists have found a way to transform human waste into bricks which can be used for building.
The research used treated sewage biosolids, not a recipe for adding raw human feces to household building materials. Tested mixtures contained 10–25% biosolids with clay. The 30% figure described an estimated unused share of biosolids, not an observed global waste reduction achieved by this experiment. The study was announced by RMIT University in January 2019.
The study, published in the journal Buildings, explained:
“Millions of tonnes of leftover biosolids are increasingly stockpiled every year around the globe. Biosolids are a product of the wastewater sludge treatment process. Stockpiles necessitate the use of large areas of increasingly valuable land. Biosolids have many beneficial uses and are currently utilized in agricultural and land rehabilitation applications. However, it is estimated that 30 percent of biosolids are unused and stockpiled.”
For the study, prototypes of those bricks were made and tested to compare with traditional building materials. The prototypes passed compressive-strength tests, but that is not blanket approval under every building regulation. RMIT noted that biosolids vary chemically and recommended further testing before large-scale production. The creation of the bricks also uses less energy than traditional building materials, and they're better for insulation as well. Adding that extra material would also cut down on the amount of clay and sand which is used for building.
Abbas Mohajerani with a biosolids brick
In the book, The World in a Grain: The Story of Sand and How It Transformed Civilization, the author Vince Beiser claims that the world is running out of the sand to keep up with the current demand of products from concrete to computer chips.
The dredging projects to harvest sand and clay has also a notably detrimental impact on the environment as some of the best clay for buildings is taken from beneath waterways, causing significant damage to the local wildlife and ecosystem.
Professor Abbas Mohajerani, a civil engineer in RMIT’s School of Engineering and one of the lead researchers in the study, noted that this new process could help alleviate two separate environmental issues simultaneously, both the overabundance of biosolid waste and the soil excavation required for traditional building materials.
Image credits: RMIT University
Separate the recipe from the scale-up scenario
A percentage in the brick mixture and a percentage of waste diverted describe different things. A 25% biosolids recipe says what goes into a tested mixture. It does not mean the process has already removed a quarter of the world’s sewage waste. RMIT’s 2019 announcement discussed a separate adoption scenario for using currently stockpiled or landfilled material. That scenario depended on manufacturers adopting the process.
The university reported a reduction of up to 48.6% in firing-energy demand for its 25% biosolids bricks. Firing is a defined manufacturing step. A claim about that step should not silently become the same percentage reduction in every cost or environmental impact associated with a building. RMIT’s dated announcement gives the scope of the result.
What would make a comparison useful?
For an illustrative comparison, imagine two suppliers offering the same number of usable bricks to the same site. The relevant questions include what each brick can do, how much material is rejected, and what processing and transport each supply chain requires. Counting only the recycled ingredient would leave much of that comparison unanswered.
Likewise, strength and heat transfer are separate properties. A material can perform differently on each, so “better brick” needs a stated purpose. The research is interesting because it turns a disposal problem into a testable materials question. Its value is clearest when the tested formulation, manufacturing stage, and remaining production questions stay visible.
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For another material story where testing conditions matter, explore Plant-Based Six-Pack Rings: Packaging Promise and Limits.
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