A one-dimensional reactive multi-component landfill leachate transport model

A one-dimensional reactive multi-component landfill leachate transport model coupled to three modules (geochemical equilibrium, kinetic biodegradation, and kinetic precipitation–dissolution) is presented to simulate the migration of contaminants in soils under landfills. A two-step sequential operator splitting method is applied to solve the coupled transport equations and the biogeochemical reaction equations. The geochemical module is based on the equilibrium speciation model (MINTEQA2), which uses ion-association equilibrium–constant approach to represent the various geochemical reactions. The biodegradation module describes the sequential biological degradation of organic compounds by multiple functional bacterial populations. Analytical equations based on macroscopic approach are used to model changes in porosity and permeability caused by biomass accumulation and mineral precipitation in soils. The model has been evaluated by comparing the model results with the widely used one-dimensional mixing-cell model PHREEQM for acidic mine tailings discharge in a carbonate aquifer. The composite leachate transport model is applied to a hypothetical landfill to simulate the effect of biological degradation of organic matter on the local inorganic geochemistry and also to demonstrate the effect of microbial activity on the evolution of porosity reduction of soils under the landfill.