Incorporation of paper sludge in clay brick formulation: Ten years of industrial experience

In this paper, binary mixtures of clay and paper sludge under different formulations were produced and their physico-chemical properties were studied. Increasing the paper sludge content in the clay mixture provides the material with improved properties regarding its thermal and acoustic insulation, but in turn it decreases its mechanical strength. However, this fragility of the material is compensated by an increased ductility. Regarding metal leaching, the studied ceramics have no environmental restrictions as far as their use as building material is concerned, as the obtained results were virtually identical to those for the blank samples (100% clay). Results showed that the presence of dichloromethane (373.2 μg m− 3) and propanone (61.2 μg m− 3) in the samples with added sludge was relatively relevant with respect to concentrations in samples made of 100% clay. All monocyclic aromatics detected showed a concentration level far below their odor threshold. In general, thus, it can be concluded that volatile organic compound (VOC) emissions during firing of the new ceramic material do not involve any particular problem. Finally, the experience obtained after more than 10 years of industrial production of this new mixed ceramic product was also analyzed. This analysis allowed confirmation that clay brick production with incorporation of paper sludge waste is a feasible solution from a technical point of view. As a key outcome, this fact has helped the reduction in a large proportion the amount of sludge produced by the Spanish paper industry ending up in landfills.