Sewage Sludge Valorization in Fired Clay Bricks: Physical Properties and Radiological Assessment

Abstract

Sewage sludge resulting from wastewater treatment process by infiltration/percolation using a matrix of adsorbent (coal ash waste/sand) was found to contain harmful elements. As an alternative approach for a sustainable valorization of this sludge, the present study intends to study the possibility of partially substituting clay in fired clay brick for sludge. Different bricks were manufactured incorporating a varied rate of sludge (5%, 10%, 15%, 20%, and 25%, by dry weight), as well as a reference brick that includes only the conventionnel raw materials. To evaluate their suitability as engineering building materials, the bricks specimens have been submitted to a set of trial experiments; linear drying shrinkage; absorption by capillarity, bulk density, mechanical resistance strength; and radiological proprieties. Bulk density and compressive strength were found to be inversely proportional to the amount of sewage sludge, and the results are respectively ranged from 1,882.81 to 1,921.87 kg/m³, and from 5.78 to 16.1 MPa. Specimens meet the Moroccan norm that requires a minimum of 5 MPa in compressive strength resistance for brick type class RC 50. Sludge/clay bricks favor the reduction of linear shrinkage, and specimens including up to 25% of waste sludge are improved on an order of 38.04% compared to the reference. The radiological assessment of sludge bricks ensures their safety since they are far below the required limits (less than 10 mSv · y⁻¹). According to results, incorporating up to 25% of sludge in bricks is suitable for building purposes.