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.