Eco-efficient reuse of alum-based water treatment sludge into structural sintering bricks

Water treatment sludge (WTS) disposal in landfills and estuaries has significant negative environmental effects. This study aims to produce a cleaner approach to recycling solid waste sludge from water treatment plants into eco-friendly construction materials. This approach involves the production of structural sintering clay bricks using WTS as a substitute for clay in the manufacturing process. Various mixtures of WTS content ranging from 10 to 50% and sand content of 10 and 20% were investigated. The Brick samples were shaped in the form of cubes and then fired in an oven at 700 oC for 3 h. Subsequently, several tests were conducted on the fired brick samples, including compressive strength, bulk density, water absorption, apparent porosity, efflorescence, freeze and thaw analysis, and microstructure investigation. The properties of WTS indicate a high concentration of silica, aluminum, and iron, which contribute to the improved properties of the fired bricks. It was observed that the bricks' compressive strength decreased from 29.8 to 8 MPa as the WTS content increased from 10 to 50%. In parallel, increasing the WTS content resulted in a decrease in bulk density from 1.005 to 0.75 g/cm3, an increase in apparent porosity values from 20 to 35%, and a higher water absorption from 12 to 37%. Furthermore, the addition of sand by 10 and 20% to the bricks leads to enhancements in both the mechanical and microstructure properties of the sintered bricks. Moreover, the efflorescence analysis of bricks is at a slight level. It can be concluded that WTS can be reused in the manufacturing of structural sintering clay bricks, providing a cleaner and more sustainable method of disposal for water treatment sludge.