2D SPH simulation of an anaerobic digester

Abstract

Understanding the hydrodynamics within the anaerobic digester tank of a wastewater treatment plant is of high importance to ensure sufficient mixing and subsequently a homogeneous distribution of the substrates. In this paper, we demonstrate a two-dimensional computational fluid dynamics simulation of a real-world case study focusing on both, the methodology and the operation of mixing. For this work, DualSPHysics, a Lagrangian solver, has been explored as an alternative to the more commonly used Eulerian solvers in studying the slow-moving dynamics inside a digester tank. This choice of a Lagrangian solver is primarily due to the inherent accounting for advection within the formulation, thus allowing for subsequent modelling of anaerobic digestion processes. A comparison has been made between the simulations from the two methods (Eulerian and Lagrangian), highlighting the benefits and the shortcomings of using smoothed particle hydrodynamics. Concerning operational mixing, the case relies on a draft tube, the effect of which on the velocity profiles has been studied based on the presence of low-velocity zones and Lagrangian coherent structures. Removing the draft tube results in an increase in low-velocity zones by 21.38% while the amount of dead volume increases from 0.52 to 1.2%.