From toilet to brickyard: Recycling biosolids to make sustainable bricks
A by-product of the wastewater treatment process, biosolids not only use up valuable land and have the potential to emit greenhouse gases, but 30% of the world’s biosolids are stockpiled or sent to landfill. A solution? A fire-clay brick that incorporates biosolids, giving a much more sustainable option for both the wastewater treatment and brick-making industries.
Published this month in the journal Buildings a team at RMIT University proved that as well as conserving half the energy it takes to make a conventional brick, biosolid bricks will be cheaper to produce and effectively give buildings higher environmental performance due to lower thermal conductivity in the brick.
The EU produces over 9 million tonnes of biosolids a year, while the United States produces about 7.1 million tonnes. In Australia, 327,000 tonnes of biosolids are produced annually. 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 use up this 5 million tonnes.
There were two main environmental issues that the research aimed to resolve, according to lead investigator Associate Professor Abbas Mohajerani. The stockpiles of biosolids and the excavation of soil required for brick production.
“Using biosolids in bricks could be the solution to these big environmental challenges. It’s a practical and sustainable proposal for recycling the biosolids currently stockpiled or going to landfill around the globe,” he says.
Not only did the research test the physical, chemical and mechanical properties of fired-clay bricks incorporating different proportions of biosolids, but the bricks also passed comprehensive strength tests. Because biosolids can have significantly different chemical characteristics, the research team recommended further testing before any large-scale production.
Research also 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 the carbon footprint of brick manufacturing companies.
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.