Recycling of municipal sewage sludge from Brazilian wastewater treatment plants for the manufacture of environmentally friendly ceramic bricks

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This research assessed the recycling feasibility of sewage sludges from Brazilian wastewater treatment plants for producing ceramic bricks. The process of treating sewage generates a large amount of sludge, primarily organic, that is frequently disposed of in landfills. This sludge can contain heavy metals and pathogens, depending on its origin. In this sense, this study evaluated the use of two different types of sludge (ranging from 0 to 10 wt% in place of clay) as starting materials in the production of ceramic bricks by microstructural and physico-mechanical analyzes. The results show that the addition of sludge decreases the apparent density of the bricks and increase the susceptibility of efflorescence formation, which is due to the higher porosity that is generated during the firing process. Although water absorption is increased, the levels remain within the commercial standards for bricks. On the other hand, the presence of sludge softens the presence of harmful elements such as Al, Ba, Fe, and Zn in the final product. The compressive strength and linear shrinkage of the bricks are not significantly affected by the addition of sludge. It was noticed that including up to 6 wt% of sewage sludge in the clay mixture for producing ceramic bricks is a viable and sustainable recycling solution with low environmental impact. The addition of 10 wt% sewage sludge significantly reduces the compressive strength and density and increases the water absorption of the bricks.