Bricks made from recycled sewage sludge

Researchers from RMIT University of Melbourne, Australia, demonstrated that fire-clay bricks incorporating biosolids, a by-product of wastewater treatment, could be a sustainable solution for both wastewater treatment and brickmaking industries.

Biosolids are organic wastewater solids that are left over after sewage sludge treatment. While the material can be used as fertiliser, land rehabilitation or as construction material. However, about 30 per cent of the world’s biosolids are stockpiled or sent to the landfill. There, they use up land and emit greenhouse gasses.

The team from RMIT demonstrated that using bricks made of biosolids requires only about half the energy of conventional bricks. Additionally, the bricks are cheaper to produce and have a lower thermal conductivity, providing better insulation.

Annually, more than 3 billion cubic metres of clay soil is dug up to produce bricks. By replacing part of the clay with biosolids, this number could be reduced.

The researchers examined the physical, chemical and mechanical properties of fired-clay bricks with different proportions of biosolids, ranging from 10 to 25 per cent. The bricks all passed compressive strength tests. Heavy metals present in the biosolids remained trapped inside the bricks. When the bricks incorporate 25 per cent biosolids, the firing energy demand was cut with nearly 50 per cent.

The bricks wit biosolids are more porous than standards brick, which gives them lower conductivity.

The research, funded by RMIT University, Melbourne Water and Australian Government Research Training Program scholarships, is published in the “Green Building Materials Special Issue” of Buildings.

Photos: RMIT University