Sustainable bricks made from recycled biosolids

Melbourne researchers have come up with a way to recycle the world’s stockpiles of treated sewage sludge and boost sustainability in the construction industry, all at the same time — by turning biosolids into bricks.

Biosolids are a by-product of the wastewater treatment process that can be used as fertiliser, in land rehabilitation or as a construction material. Around 30% of the world’s biosolids are stockpiled or sent to landfill, using up valuable land and potentially emitting greenhouse gases.

Researchers at RMIT University have now demonstrated that fired-clay bricks incorporating biosolids could be a sustainable solution for both the wastewater treatment and brickmaking industries. Lead investigator Associate Professor Abbas Mohajerani said the research sought to tackle two environmental issues — the stockpiles of biosolids and the excavation of soil required for brick production.

“More than 3 billion cubic metres of clay soil is dug up each year for the global brickmaking industry, to produce about 1.5 trillion bricks,” said Assoc Prof Mohajerani.

“Using biosolids in bricks could be the solution to these big environmental challenges.”

RMIT University Associate Professor Abbas Mohajerani, with a biosolids brick.

The research examined the physical, chemical and mechanical properties of fired-clay bricks incorporating different proportions of biosolids, from 10 to 25%. The results were published in the journal Buildings.

The research showed brick-firing energy demand was cut by up to 48.6% for bricks incorporating 25% biosolids. This is due to the organic content of the biosolids and could considerably reduce both the carbon footprint and costs of brick manufacturing companies. The biosolids bricks also had a lower thermal conductivity due to being more porous than standard bricks, transferring less heat to potentially give buildings higher environmental performance.

About 5 million tonnes of the biosolids produced in Australia, New Zealand, the EU, US and Canada currently go to landfill or stockpiles each year; using a minimum 15% biosolids content in 15% of bricks produced could completely use up this 5 million tonnes. Indeed, the results of a comparative life cycle assessment and an emissions study conducted as part of the research confirmed biosolids bricks offered a sustainable alternative approach to addressing the environmental impacts of biosolids management and brick manufacturing.

The biosolids-enhanced bricks also passed compressive strength tests, and analysis demonstrated heavy metals were largely trapped within the brick. Biosolids can, however, have significantly different chemical characteristics, so the researchers recommend further testing before large-scale production.

Top image caption: Fired-clay bricks incorporating biosolids require around half the energy of conventional bricks and have lower thermal conductivity, potentially giving buildings higher environmental performance.

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