Hydraulic, chemical and biological coupling on heavy metals transport through landfills liners

Abstract

Soil layers in landfill liners are usually considered non-reactive, and the biological activity in the barrier is neglected for the calculation of the liner life span. The purpose of this research is to highlight the relative importance of hydraulic conductivity, chemical retardation and biological clogging on the transport of heavy metals through landfill liners. Mass transport was computed considering semi-empirical equations to determine contaminant leakage through geomembranes imperfections, and Darcy's law and advection-diffusion equation were used to evaluate the transport through soil liners. Hydraulic conductivity values were modified considering its reduction due to biological effects, and different retardation factors were considered to evaluate heavy metal adsorption on soil particles. The effect of compacted soil barrier thickness in specific discharge and breakthrough time was evaluated. Obtained results showed that the use of a geomembrane results in higher breakthrough time for composite liners when the prevailing transport mechanism is advection. Results also indicated the importance of considering bioclogging on the coupled hydraulic and chemical flow that determine the breakthrough time.