Clay Culture: Biosolid Bricks Lisa McDonald

Appears in the May 2021 issue of Ceramics Monthly.

Most people know about the overwhelming plastic waste polluting our world (as evident by public pressure successfully convincing companies to ditch plastic straws). Far fewer people, though, know about biosolids waste.

Biosolids are nutrient-rich organic materials that come from dewatered and appropriately treated wastewater sludge, which itself comes from the wastewater treatment process. While many biosolids are used as fertilizers or in land rehabilitation projects, other biosolids end up in landfills or stockpiles, where they then contribute to greenhouse gas emissions.

Fortunately, even though the general public may not be aware of biosolids, the construction industry is. Studies on keeping biosolids out of stockpiles by reusing them in construction materials include incorporating biosolids in road embankments and concrete.

1–3 Biosolids-enhanced bricks were created using biosolids from Melbourne’s Eastern Treatment Plant (ETP 22) and Western Treatment Plan (WTP 10 & WTP 17-29). Photos: Abbas Mohajerani, Buildings, CC BY 4.0.

One great new option under investigation is the use of biosolids to make bricks. Because brick composition is quite flexible, bricks are capable of incorporating a high percentage of waste. And, with about 1500 billion bricks produced globally each year, that offers a lot of opportunities to incorporate waste. Already, researchers have tried incorporating other troublesome waste materials into bricks, including cigarette butts, paper-processing residue, and glass.

Researchers at the Royal Melbourne Institute of Technology University (RMIT) in Australia are one group currently investigating the use of biosolids in bricks.

“More than 3 billion cubic meters of clay soil is dug up each year for the global brick-making industry,” Abbas Mohajerani, lead investigator and associate professor in RMIT’s School of Engineering, says in an RMIT University news release. “Using biosolids in bricks could be the solution to these big environmental challenges.”

Mohajerani has previously worked on using cigarette butts to make asphalt pavement and bricks. In the current experiment on biosolids, Mohajerani explains the research addresses two environmental issues—stockpiles of biosolids and excavation of soil required for brick production. They tested feasibility of the concept by incorporating 10–25% of biosolids into fired clay bricks, and then examined each brick’s physical, chemical, and mechanical properties.

The researchers found biosolids-enhanced bricks passed compressive strength tests and largely trapped heavy metals within the brick after firing. Additionally, bio-bricks showed lower thermal conductivity than traditional bricks, thereby enhancing the bricks’ insulating abilities. However, the most significant finding in terms of environmental impact had to do with brick production—brick firing energy fell 12.4–48.6% for bricks incorporating biosolids with organic contents of 7.1–27.79%.

“Based on the results found in this comprehensive study, this paper proposes the inclusion of a minimum of 15% biosolids content into 15% of brick production in order to completely recycle the approximately 5 million tonnes of annual leftover biosolids production in Australia, New Zealand, the EU, Canada, and the US,” the researchers write in the paper.

We can use up all leftover biosolids by only modifying 15% of brick production? Sign me up—as long as there is no accompanying smell!

10, 11 Storage conditions of biosolids. Photos: Abbas Mohajerani, Buildings, CC BY 4.0.

The open-access paper, published in Buildings, 2019, 9 (1), is “A proposal for recycling the world’s unused stockpiles of treated wastewater sludge (biosolids) in fired-clay bricks” (DOI: 10.3390/buildings9010014).

Originally published in Ceramic Tech Today, February 1, 2019.

the author Lisa McDonald is associate managing editor and science writer at The American Ceramic Society. Prior to this position, McDonald worked at the American Institute of Physics: FYI and the ATLAS Experiment at CERN. She has a master’s in science communication and specializes in communicating science to nonspecialist audiences.