Australia has been finding ways to expand the use of recycled biosolids as it deals with ever-increasing volumes due to the country’s growing population. In 2017, it was estimated that 6% of the biosolids produced, or approximately 20,000 tonnes were either sent to landfills, stockpiled or discharged into the ocean.
Abbas Mohajerani, and Associate Professor at Australia’s RMIT University, is an expert in construction, pavements and roading materials. He has explored to possibility of using sustainable materials for construction for the past 15 years and his team has begun to look into the possibility of using recycled biosolids to create bricks.
To provide perspective, approximately 1.5 trillion bricks are produced worldwide annually. Traditionally, these are made from clay soil but recent trends have delved into incorporating recycled biosolids materials such as saw dust or rice husks to reduce their environmental impact.
Mohajerani’s team went to two local wastewater treatment plants and took samples of recycled biosolids from three existing stockpiles and mixed them with clay soil. Four different mixtures were developed consisting of 10, 15, 20 and 25% recycled biosolids content which were then dried and fired like traditional bricks. The team examined the physical, chemical and mechanical properties of their biosolids incorporated bricks, and compared them to the traditional clay bricks.
The results showed a lot of promise. All the recycled biosolids bricks exhibited lower thermal conductivity than the traditional clay bricks. This makes the bricks provide better insulation.
Another discovery was that the bricks needed less energy to produce because of the high organic content coming from the recycled biosolids. In their studies, they found that bricks with 25% biosolids took almost half the amount of energy to produce.
There where some problems with the bio-bricks however. The organic content tended to be burned off during the brick firing process resulting in porous bricks. There was a reduction in the density and a shrinkage in size compared to the control bricks. This made them weaker despite the fact that the bio-bricks showed higher than normal compressive strengths.
But Mohajerani remains cautiously optimistic about the product. He believes that the bio-bricks will be environmentally favorable and would significantly reduce all the negative environmental impacts that are associated with traditional clay bricks. Several hurdles need to be overcome before the idea of producing bricks from recycled biosolids becomes feasible for large scale production.
There are other studies being conducted on biosolids-based bricks. One in particular focused on producing bricks from human urine. The researchers from the University of Cape Town were able to make these bricks without needing to fire the bricks in an oven and can be produced at room temperature. They utilize a process called microbial carbonate precipitation. This uses a particular type of bacteria which is added to loose sand and it produces an enzyme called urease. The enzyme breaks down urine producing calcium carbonate that acts as a cement, solidifying the sand into bricks. The longer the time given for the bacteria to do its work, the stronger the brick.
It is only a matter of time before human waste becomes the main ingredient in brick production. Once all the impediments are worked out, bio-bricks will become mainstream and it would greatly reduce the environmental impact of traditional brick making.
If you are a municipality in Ontario and in need of a biosolids management solution, please feel free to contact us at 1 (877) 479-1388.