Euler-Lagrange Computational Fluid Dynamics simulation of a full-scale unconfined anaerobic digester for wastewater sludge treatment

For the first time, an Euler-Lagrange model for Computational Fluid Dynamics (CFD) is used to model a full-scale gas-mixed anaerobic digester. The design and operation parameters of a digester from a wastewater treatment works are modelled, and mixing is assessed through a novel, multi-facetted approach consisting of the simultaneous analysis of (i) velocity, shear rate and viscosity flow patterns, (ii) domain characterization following the average shear rate value, and (iii) concentration of a non-diffusive scalar tracer. The influence of sludge's non-Newtonian behaviour on flow patterns and its consequential impact on mixing quality were discussed for the first time. Recommendations to enhance mixing effectiveness are given: (i) a lower gas mixing input power can be used in the digester modelled within this work without a significant change in mixing quality, and (ii) biogas injection should be periodically switched between different nozzle series placed at different distances from the centre.