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    EFFECTS OF LEACHATE ON COMPACTED CLAY LINER AND TEMPORARY COVER LAYER OF LANDFILL SYSTEMS STABILIZED WITH SODIUM LIGNOSULFONATE
    (2024-06) Awam, Awass H M
    This thesis aims to investigate the potential of sodium lignosulfonate (NLS) for stabilizing compacted clay liners against the adverse effects of leachate in municipal solid waste landfill structures. In addition, the potential use of NLS as a temporary cover layer was investigated using column model test. To do so, a series of tests, including particle size distribution, Atterberg limits, compaction, unconfined compressive strength, bender element, SEM, XRD, XRF, FTIR, pH, and EC, heavy metal concentration tests, were performed. In addition, the leaching behavior of the temporary layer stabilized with NLS was examined using the small column test designed for the study. In this research, for the untreated compacted clay liner, five scenarios were determined: (1) mixing the clay with water and testing it in a dry condition, (2) mixing the clay with leachate and testing it in a dry condition, (3) mixing the clay with water and testing it in a wet condition by soaking in water, (4) mixing the clay with water and testing it in a wet condition by soaking in leachate, and (5) mixing the clay with leachate and testing it in a wet condition by soaking it in water. All these methods are also performed on NLS stabilized compacted clay liner, with testing conducted at various curing times, including 7, 28, and 90 days. For leaching behavior, the effects of various variables on pH, EC, flow rate, and heavy metal concentration were examined, including operation mode, leachate recirculation, thickness of temporary cover, curing time, and type of materials. The results verified that, even in the worst-case scenario of soaking in leachate, the addition of 1% NLS significantly enhanced the performance of CCLs, reducing the voids percentage by 85.5% and increasing both strength and shear wave velocity by 52% and 40%, respectively. SEM-EDX and FTIR findings confirmed the potential of NLS, even in the presence of leachate, to create electrostatic attraction among the clay particles, develop polymer chains around them, and promote the formation of denser microstructures. Among various variables, the operation modes and leachate recirculation were found to be very effective in changing the results of heavy metal concentrations in the landfill system, including a temporary cover layer made of a mixture of clay and 1% NLS. A higher temporary cover thickness led to a significant reduction in the amounts of Cd, Cu, and Zn. It was confirmed that curing time did not show substantial effects on changing the results of column model tests. Therefore, in the case of controlling heavy metals concentration, 7 days of curing can be considered adequate and optimum. It was found that the model with NLS alone as a temporary cover could perform better in terms of controlling heavy metal concentrations such as Zn, Ni, Cu, and Cd. The results of the current project can illustrate the effects of leachate on the environmental, mechanical, physical, and dynamic responses of compacted clay liners in landfill systems, thereby enhancing designers' insights for future designs. Additionally, the project explores the potential of NLS, an industrial byproduct of a paper factory, to enhance the properties of both the compacted clay liner and the temporary cover layer, leading to recycling and reusing NLS for new applications.