Utilization of drinking water treatment sludge with coal fly ash to make permeable bricks for low impact development

The use of aluminum coagulants for drinking water treatment generates a large amount of sludge that is typically destined to landfills, wasting valuable urban land with potential environmental risks. An innovative approach was presented to recycling aluminum-rich sludge from water treatment, alongside coal fly ash, into bricks for construction. By varying fly ash ratios (0–50 %) and firing temperatures (900–1200 °C), optimal conditions were determined: 1050 °C firing temperature and 30 %-50 % fly ash addition. The resulting bricks meet construction material standards, boasting compressive strength (>7 MPa), porosity (15–30 %), water absorption (10–20 %), and permeability (>1.0 × 10⁻² cm/s). Incorporating fly ash mitigates shrinkage and crack formation. Organic matter ignition in sludge during brick-making creates a porous structure, ideal for low-impact development like permeable pavements in sponge cities. This method promotes waste reduction, aluminum recycling, heavy metal stabilization, and sustainable urban development, offering a cost-effective solution for safe, permeable bricks.