Potential re-use of sewage sludge as a raw material in the production of eco-friendly bricks


Wastewater (sewage) treatment plants generate a high volume of sludge that, although it is classified as class II-A (not inert) non-hazardous waste, is commonly disposed of in sanitary landfills. Hence the environmental urge to assess its valorization possibilities. The present study describes the use of a sewage sludge as raw material in the production of red ceramic bricks by extrusion, focusing on the technological changes brought about by the presence of the sludge during the plastic forming process, in terms of the plasticity of the mixture and its subsequent extrudability. To quantitatively identify the best moisture conditions for the extrusion of high-quality products, shear strain amplitude sweep (torsional) tests were conducted on green (moist) prismatic samples produced with different moisture and sludge contents. For sewage sludge contents up to 10 wt%, the optimal moisture content was identified at 31-33 wt%. Higher water demand was identified for 15 wt% of sludge, for which optimal extrusion results required 35 wt% moisture. The total linear shrinkage after drying and firing, as well as the water absorption, were within the limits required for ceramic bricks for all the sludge contents. The results for compressive strength of the fired bricks also demonstrate that the incorporation of up to 15 wt% sewage sludge into the clay mixture is highly feasible for the production of extruded ceramic bricks.



subject category

Environmental Sciences


Zat, T; Bandieira, M; Sattler, N; Segadaes, AM; Cruz, RCD; Mohamad, G; Rodriguez, ED

our authors


Authors are grateful for the financial support from Sao Gabriel Saneamento S.A. and Pauluzzi Ceramicas Santa Maria Ltda. Grants from CAPES (T.Zat and M.Bandieira), FAPERGS (N. Sattler) and the CNPq (E. D. Rodriguez, PQ 309885/2020-5) are gratefully acknowledged. The authors also wish to thank the UFSM, FATEC, Laboratorio de Magnetismo e Materiais Magneticos, Grupo de Estudos e Pesquisas em Pavimentacao e Seguranca Viaria, Laboratorio de Materiais de Construcao Civil, Instituto de Materiais Ceramicos at the Universidade de Caxias do Sul and the Laboratorio de Inovacao em Cimentos Ecoeficientes (at Universidade Federal de Rio Grande do Sul).

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