Utilization of water treatment plant sludge in structural ceramics

Industrial solid waste generated by a water treatment plant (WTP) at a pulp mill was used for manufacturing construction bricks. The sludge from the WTP was mixed with three types of waste obtained via recovery of chemicals generated by the same pulp mill and with waste obtained by crushing and grinding granite rock. The formulation of these mixtures was based on the grain size distribution of the residues and the proportions of calcium, sodium, and potassium oxides in the mixtures. Specimens of these mixtures were then fired at 850, 950, and 1050 °C in order to obtain crystalline phases (anorthite, albite, gehlenite, and mullite) that would confer good mechanical properties. The technological properties of the specimens were evaluated after drying and firing. The statistical analysis of technological properties of the proposed mixtures suggests that sludge can be used as a substitute for clay in the formulation of clay masses and the mixtures B, C, D, and F at 850 and 950 °C, should be tested in the ceramic industry on a pilot scale in order to evaluate their suitability for the production of interior coatings or acoustic bricks. The utilization of WTP sludge in brickmaking eliminates an environmental problem, several economies related to the replacement of a natural raw material are generated. Finally, by using WTP sludge in the manufacturing of acoustic bricks and other products, it is shown that cleaner production practices promote innovation in the pulp mill and the red ceramic industry, leading to environmentally friendly practices.