Mechanical Characteristics and Micro-Mechanism of Modified Dredged Sludge Based on Calcium-Containing Solid Waste Used as Landfill Cover Materials

Abstract

In order to prepare a new type of landfill covering material for closure, we used industrial calcium-containing waste (construction rubbish, slag, desulfurized gypsum and fly ash) to modify the dredged urban sludge. Shrink, unconfined compression, shear and infiltration tests were performed to obtain the volume shrinkage, compressive strength, shear strength and permeability coefficient of the modified sludge, as well as the permeability coefficient under the action of wet and dry cycles. Comprehensive characterization of the modified sludge using X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy detection methods, resulted in the hydration products, molecular groups and microstructure characteristics of the modified sludge and revealed the modification mechanism of calcium-containing waste to sludge. After natural curing for 28 d, the volume shrinkage rate of the modified sludge sample was 2.6~8.3%, the unconfined compressive strength was 7.9~14.5 MPa, the cohesion force c was 179~329 kPa, and the internal friction angle φ was 42.59~53.60°. After six wet and dry cycles, there were no cracks in the modified sludge; the permeability coefficient of the modified sludge reached stability at 0.84–11.1 × 10−7 cm/s; and the permeability coefficient of MS7 sample was less than 1 × 10−7 cm/s, which met the engineering anti-seepage requirements of the landfill closure cover. The industrial calcium-containing waste by alkali formed C–S–H and C–A–S–H gelled geopolymer, which filled the gaps between soil particles to form a strong soil cement skeleton. Therefore, the mix ratio of sludge:construction waste:slag:fly ash:desulfurized gypsum was 50:22:15:8:5. Calcium-containing solid waste modified sludge can be used as a cover material for landfill closure.

Leaching Behaviour of Synthetic Leachate through a Sewage Sludge and Red Gypsum Composite as Intermediate Landfill Cover

“…With most studies focusing on the hydraulic conductivity and strength properties of the materials [21,22], there is scarce data available on the environmental impact, such as the leaching of hazardous chemicals from the mixtures. A six-month study conducted by the authors of [23] has demonstrated that the hydraulic conductivity of the SS:RG composite can be maintained at 10 −6 cm/s and the leaching of chemicals from the composite is within the regulated limits when flowing distilled water through the composite.…”

Evolution and Prospects in Managing Sewage Sludge Resulting from Municipal Wastewater Purification

“…Other studies have depicted the significant evolution of MWW, MSS management, and environmental remediation in China [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57].…”