Potential of kaolin-palm oil fuel ash mixture as sustainable landfill liner material

Abstract

Contamination of groundwater due to leachate percolating through landfill liner is a potential hazard to human health and the environment. Effective mitigation approaches and imperative research on alternative liner materials could reduce contamination. In this study, an investigation on the potential of kaolin premixed with pulverized palm oil fuel ash (PPOFA) as an alternative mineral liner material is proposed. The investigation was carried out in two stages. Initially, physico-chemical and mechanical characterizations were performed on these materials separately. Then, PPOFA was mixed in stages of 0, 10, 20, and 30 percent by dry mass of the kaolin and were compacted using Standard Proctor. Result from the compaction test showed that 15 percent of PPOFA was found to be the optimum dose for the formulated liner matrix. In the second stage, material characterizations were repeated on the formulated liner matrix followed by performance criteria tests. These tests included heavy metal removal efficiency, chemical sorption, leaching, hydraulic conductivity and column tests. The criteria examined were compared with the standards and previous related research. All the tests were conducted without pH adjustment and were duplicated. Based on sorption tests, Freundlich and Langmuir isotherm models were developed and validated using linear regression and correlation coefficient R. The performance tests recorded high metal ion removal efficiencies of 59 to 99 percent at solution equilibrium pH ranging from 7.64 to 3.00. Freundlich sorption capacities ranged from 0.2063 to 25.64, while the Langmuir monolayer sorption capacity, ? ranged from 22.3714 to 52.6316 mgg-1. Besides that, the modelled Freundlich (qeFred) and Langmuir (qeLang) isotherm were relatively well fitted to the experimental (qexpt), with correlation coefficients (R) greater than 0.84. Leaching occurred at very low concentrations ranging from 0.003 to 0.19 mgL-1 and hydraulic conductivity tests obtained values ranging from 3.14 to 3.66 ?10-6 cms-1. Finally, the column test showed that the hydrodynamic dispersion coefficients ( * L D ) and retardation factors ( d R ) ranged between 1.16? 10-3 to 1.11?10-5 cm2s-1 and 17 to 337 respectively. The proposed kaolin- PPOFA liner matrix has been proven to be a promising alternative liner material in ameliorating groundwater contamination from the leachate generated in the landfill.