The potential of sludge from wastewater treatment plants to improve the mechanical properties of bricks

This paper aims to study the effect of adding sludge from wastewater treatment plants (WWTPs) in Eastern Algiers on swelling clay brick as a natural substitute for a degreaser to valorize it and minimise the risks related to its storage. First, physico-chemical analyses for clay and dried sludge were carried out using X-ray fluorescence (XRF), Scanning Electron Microscopy (SEM) analysis, Atterberg limits, and laser granulometry. Cylindrical brick specimens were prepared by compaction at 10 MPa, incorporating 0%, 5%, 10%, and 15% of dried sludge depending on the weight of the clay, then fired at 600 °C, 800 °C, and 1000 °C. Brick density, mass absorption, porosity, and compressive strength were evaluated at different temperatures for each sludge dosage. The results show that adding dried sludge to swelling clay improves compressive strength and reduces shrinkage. In contradiction to what has been published in the literature. The addition of 5% sludge to the weight of the clay in the brick composition fired at 800 °C resulted in the highest compressive strength of 32.26 MPa, twice the control bricks' compressive strength. Therefore, using sewage sludge from WWTPs in brick production is an essential sustainable development choice that benefits both the environment and the economy.