Modification of residual soil with palm oil fuel ash as potential landfill liner

Abstract

In Malaysia, wastes that being disposed of to landfill sites have increased tremendously. This leads to another environmental problem where the leachate penetrates through the landfill barrier system and contaminates the groundwater source. In this study, palm oil fuel ash (POFA) is employed to modify residual soil samples collected from campus of Universiti Teknologi Malaysia (UTM) to enhance the potential of the soil material as the landfill liner. Soil classification, specific gravity, compaction, permeability and zinc adsorption tests were performed on soil sample with 0%, 5%, 10%, 15% and 20% POFA added. Soil sample collected was categorized as gravely silt with very high plasticity (MVG) with liquid limit of 74%, plastic limit of 40.79%, plasticity index of 34.79% and specific gravity of 2.77. As for compaction test, Standard Proctor was applied with optimum moisture content and maximum dry density obtained. The permeability was directly proportional to void ratio of the soil. The lowest permeability was shown in 15% POFA modified soil, which is 6.65x10-9 ms-1, whereas soil with more than 15% POFA added had exhibited higher permeability. Zn adsorption tests were conducted on the untreated soil and the lowest permeability soil sample, which was 15% POFA modified soil sample. The result showed that the soil sample modified with 15% POFA had exhibited better adsorption capacity compared to the untreated soil sample and agreed well with Langmuir isotherm. However, the 15% POFA modified soil did not meet the standard of permeability (less than 1x10-9 ms-1) that stated in the landfill liner material specifications.