Modelling contaminant transport in fly ash–bentonite composite landfill liner: mechanism of different types of ions

Abstract

Generated hazardous or toxic waste posses a serious threat if dumped into ponds or low lying areas which leads to contamination, this necessitates the effective landfill liner system. Mainly compacted clayey soils are used as an engineered barrier. Recently, composite materials have gained popularity as landfill liner materials, including the use of waste materials amended with low permeable soils. Though, studies on the composite optimum mix and its corresponding thickness are very scarce. Here, we evaluated the unconfined compressive strength and hydraulic conductivity of fly ash-bentonite composites. Efforts were also made to determine the thickness of landfill liner composite using a finite difference method (i.e. MATLAB). The results reveal that composite consists of 30% bentonite and 70% fly ash is suitable for landfill liner, which meets strength and permeability criteria. Numerical simulation for five major contaminants shows that the composite plays a crucial role in reducing the leaching of heavy metals and suggests an optimum thickness in the range of 126-154 cm. Overall, the findings of the study indicate that fly ash-bentonite composite can be used to solve real-life challenges in a sustainable way. Landfill liner is a low-permeable barrier, which acts as a partition between the waste and its surrounding environment. Well constructed landfills are more secure than open dumping 1. The fundamental factor influencing the nature of compacted clay liners is their low permeabilities, which should be as less as 1.0 × 10-7 cm/s suggested by RCRA (Subtitle D). To avoid contamination of groundwater (due to permeation of leachate), generally clayey soils are compacted to achieve desired permeability. Sand-bentonite composites are also used as engineered barriers or liners to prevent leaching of contaminants 2. Other than hydraulic conductivity, strength also needs to be considered in assessing landfill liner material. Earlier studies and environmental guidelines proposed a minimum unconfined compressive strength (UCS) of 0.20 MPa to utilize as a landfill liner material 3. Few studies reported that waste-bentonite composites satisfy the strength criteria when a correct mix proportion used 3,4. The utilization of wastes like fly ash solves the problems associated with waste management and also saves the extensive exploitation of natural materials 5,6. Fly ash and bentonite can replace the sand-bentonite liners because of lack of available natural sand and an increase in the cost, which is widely used in other construction activities. Fly ash is known for its pozzolanic reactions, and that solidifies and gains strength over time when cured. Therefore, the curing period prompts an increase in strength and reduction of hydraulic conductivity. Recent studies have examined the amendment of fly ash to the soil, found the enhanced geotechnical properties such as cation exchange capacity, shear strength, and hydraulic conductivity 3,7,8. Problems in landfill lining system of a waste containment facilities can be escalate...

Modeling Contaminant Transport of Nitrate in Soil Column

“…It was observed in Figure 4 that predicted values were lower than the measured values. Also, there was a sharp decrease in nitrate concentrations at 0.561ppm and 0.098 at a distance of 1.8m but slight decreases was observed at different distances and this could be attributed to soil type, adsorption or dispersion in the soil [1]. The correlation coefficient r of the predicted model and measured values P1, P2 were found to be 0.894 and 0.484 respectively.…”

“…It was observed in Figure 9 that predicted values were lower than the measured values. Also, there was a sharp decrease in nitrate concentrations at 0.682 ppm, 0.165 ppm for M and P1 respectively at a distance of 1.8 m. But there were slight decreases at different distances which this could be attributed to soil type, adsorption or dispersion in the soil [1]. Also, the correlation coefficient r of the modified model P1 was 0.769 while the experimental data fitted in existing model P2 was 0.620.…”

“…With the increasing population growth and the industrial and agricultural development, the amounts of wastes generated are increasing day by day in Nigeria thereby polluting the air, water and soil which becomes a threat to human health. The increasing solid waste and their disposal sites like landfills are not only causing groundwater contamination and soil pollution but also leaving many productive lands as waste lands [1]. It is also possible for untreated waste from septic tanks and toxic chemicals from underground storage tanks to contaminate groundwater.…”

“…Modelling contaminant transport of metal ions through soil was carried out by [1]. The result revealed that the finite difference method using Crank-Nicolson scheme was found to be the most accurate method for estimating the contaminant transport parameters.…”

Some Numerical and Analytical Solutions to an Enzyme-Substrate Reaction-Diffusion Problem

“…In addition, finite difference methods for solving the unsteady and steady state problems are provided. Finite difference method has been shown to be powerful for solving various problems [31,32,33,34,35], which also include mathematical chemistry areas [36,37,38,39,40,41,42,43,44,45].…”