A multi-component two-phase flow algorithm for use in landfill processes modelling

•Details are provided of the algorithm for a landfill liquid and gas sub-model.•Results of applications in the context of leachate recirculation are presented.•Example values are provided for the flow sub-model parameters.•The sub-model tracks multi-component gas and liquid phases simultaneously.•Saturation patterns do not appear to be influenced greatly by gas generation.

This paper describes the finite difference algorithm that has been developed for the flow sub-model of the University of Southampton landfill degradation and transport model LDAT. The liquid and gas phase flow components are first decoupled from the solid phase of the full multi-phase, multi-component landfill process constitutive equations and are then rearranged into a format that can be applied as a calculation procedure within the framework of a three dimensional array of finite difference rectangular elements.The algorithm contains a source term which accommodates the non-flow landfill processes of degradation, gas solubility, and leachate chemical equilibrium, sub-models that have been described in White and Beaven (2013).The paper includes an illustration of the application of the flow sub-model in the context of the leachate recirculation tests carried out at the Beddington landfill project. This illustration demonstrates the ability of the sub-model to track movement in the gas phase as well as the liquid phase, and to simulate multi-directional flow patterns that are different in each of the phases.