Bricks incorporating biosolids could be a sustainable solution for both the wastewater treatment and brickmaking industries, claim Australian researchers. They say making bricks from biosolids required around half the energy of conventional brick manufacture.
Biosolids are a byproduct of wastewater treatment. Globally, around 30% are stockpiled or sent to landfill, but they can be used as fertiliser, in land rehabilitation or as a construction material. The EU produces over 9m t/year of biosolids, while the US produces 7.1m t and Australia, 327,000t.
The research sought to tackle two environmental issues: stockpiles of biosolids and the excavation of soil required for brick production, explains lead investigator Abbas Mohajerani, a civil engineer in RMIT University’s School of Engineering in Melbourne. ‘More than 3bn m3 of clay soil is dug up each year for the global brickmaking industry, to produce about 1.5 trillion bricks. Using biosolids … is… a sustainable proposal for recycling the biosolids currently stockpiled or going to landfill around the globe.’
The research examined the physical, chemical and mechanical properties of fired-clay bricks incorporating from 10 to 25% biosolids (Buildings, doi: 10.3390/buildings9010014). All the biosolid-enhanced bricks passed compressive strength tests. Leachate analysis before and after firing demonstrated that between 43 and 99% of heavy metals tested were trapped inside the fired bricks. As biosolids can have significantly different chemical characteristics depending on the wastewater and the treatment procedure, the team recommends further leachate analysis before any large-scale production.
They showed that the energy required for brick firing was cut by almost 50% for bricks incorporating 25% biosolids, because of the higher organic content of biosolids. Scanning Electron Microscopy also showed that the biosolids bricks are more porous than standard bricks, giving them lower thermal conductivity, which could improve the environmental performance of buildings.
The team proposes the inclusion of a minimum of 15% biosolids content into 15% of brick production in order to fully recycle approximately 5m t/year of leftover biosolids in Australia, New Zealand, the EU, the US and Canada. ‘This is a practical and sustainable proposal for recycling all the leftover biosolids worldwide,’ they say. ‘Utilisation of only 15% of biosolids in brick production would reduce the carbon footprint of brick manufacturing whilst satisfying all the environmental and engineering requirements for bricks.’