CFD multiphase modelling for evaluation of gas mixing in an anaerobic digester

Biogas production from municipal and industrial solid and liquid waste has captured the attention of engineers and managers both in the UK and globally due the substantial benefits for achieving environmental protection, energy generation and Green House Gas emission reductions. However, there are number of problems involved in scaling up experimental anaerobic digestion (AD) plants to field level plants. One such problem associated with AD is mixing, which is a vital component to segregate synthesized gas and biomass from digester liquid, to enhance homogeneity and to ensure adequate contact between bacteria and substrate in the AD. Such situations are well suited to Computational Fluid Dynamic (CFD) analysis, where models can be calibrated and validated using the pilot plant and can then be used to accurately simulate the performance of the large-scale reactors. The aim in this work has been to further understand and enhance the use of bubble mixing approaches to improve the performance of future bioreactors. A computational model has been developed to simulate the complex flows occurring in a digester. The paper discusses CFD simulations of a lab scale AD for evaluating mixing characteristics that provides understanding required for developing accurate simulations of mixing conditions in the large-scale systems with the reactor contents simulated for both Newtonian and non-Newtonian cases