A novel Lattice-Boltzmann model to simulate gas mixing in anaerobic digestion is developed and de- scribed. For the first time, Euler–Lagrange multiphase, non-Newtonian and turbulence modelling are ap- plied jontly with a novel hybrid boundary condition. The model is validated in a laboratory-scale frame- work and flow patterns are assessed through Particle Imaging Velocimetry (PIV) and innovative Positron- Emission Particle Tracking (PEPT). The model is shown to reproduce the experimental flow patterns with fidelity in both qualitative and quantitative terms. The model opens up a new approach to computational modelling of the complex multiphase flow in anaerobic digesters and offers specific advantages, such as computational efficiency, over an analogous Euler-Lagrange finite-volume computational fluid dynamics approach.