The effect of bentonite/cement mortar for the stabilization/solidification of sewage sludge containing heavy metals

Abstract This study examines stabilization/solidification (S/S) techniques using a bentonite/cement mortar. These techniques are usually applied for the stabilization of sewage sludge, containing heavy metals such as Cu, Zn, Pb. Due to the high organic content of sludge, bentonite had been added in order to stabilize the system. For this purpose, 4 × 4 × 16 cm mortar prism samples were prepared. Their composition was: 50% w/w sewage sludge (primary sewage sludge from Psyttalia Athens and secondary biological sewage sludge from Metamorphosis Athens), 30% w/w cement CEMI 42.5 and finally 20% w/w bentonite. The samples were cured for 28 days at 25 °C and compressive strength was tested. Highest strength and lowest leachability were the criteria for selection of the optimum product by the S/S technique. An extensive study using several characterization techniques focusing on hydration reactions was carried out. The instrumental analysis included: X-ray diffraction analysis, thermal analysis (TGA, DTA), electron scanning microscopy (SEM), infrared analysis (FT-IR) as well as tests for the toxicity characteristic leaching procedure (TCLP). The S/S products had been proven throughout the study as a viable solution for stabilizing heavy metals. They can be used in many applications such as in landfill liners, slurry walls and building blocks.