An experimental study on microanalytical characterizations and service performances of landfill modified municipal sludge liner materials in contact with leachate

This study aimed to evaluate the long-term service performance of modified municipal dewatered sludge as a landfill liner barrier. Industrial calcium-containing solid waste was used as a modified material for sludge. The shear strength parameters (cohesion c, friction angle φ), compressive strength, and hydraulic conductivity of the modified sludge were studied using direct shear, uniaxial compression, and penetration tests. The leaching toxicity, hydration products, and microscopic morphology of the modified sludge were determined using atomic emission spectroscopy, X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The corrosion mechanisms of the landfill leachate and acid-base chemical solution on the modified sludge liner barrier were revealed. Under the long-term corrosive environment of the landfill leachate and acid-base chemical solution, the shear strength parameters, i.e., cohesion (c) and friction angle (φ) had values in the ranges of 0.51−3.79 MPa and 6.52−37.58° of the modified sludge, respectively. The uniaxial compressive strength reached 2.70−22.92 MPa, and the permeability coefficient ranged from 0.12 × 10−8 to 3.97 × 10−8 cm/s. After long-term corrosion by landfill leachate and an acid-base chemical solution, the modified sludge liner barrier still had significant bearing capacity and water-blocking properties. Under leachate corrosion, sulfate corrosion (such as ettringite and thaumasite formation) occurred, the modified sludge and some structures were damaged. Under an acidic chemical corrosion solution, alkaline substances, such as calcium hydroxide with hydrogen ions, underwent solvent-out crystallization and chemical dissolution reactions, which caused the decomposition of hydrated gel products such as C–S–H inside the specimen. Under alkaline chemical solution corrosion, the active components in the modified sludge underwent a hydration reaction to form ettringite, C–S–H, etc.