Estimation of the spatial distribution of substances in Anaerobic Digestion Tanks with CFD

Abstract

[EN] Anaerobic digestion (AD) is used in wastewater treatment plants (WWTPs) to decompose organic matter. Highly efficient AD tanks are able to mix biochemical substances within the tank, and – in order to assess such spatial distribution of substances - a proper modelling method is necessary. Computational fluid dynamics (CFD) is a simulation tool for modelling fluid flows in WWTPs, but there is a lack of studies on CFD modelling of hydrodynamics together with an integrated modelling of bio-kinetics due to the complexity of biochemical reactions in AD processes. The current study aims at estimating the distribution of biochemical components within an AD tank. For doing this, an integrated modelling of hydrodynamics and bio-kinetics is conducted, in order to assess mixing quality. The novelty of the work is the derivation of a new AD-related solver in an open source CFD platform. As the first step, the hydrodynamics of the fluid flow in our WWTP are estimated through iterative solution of fluid flow equations, and subsequently, by fixing the obtained velocity vector field, bio-kinetic equations are applied to the flow field. The bio-kinetics in our solver are based on ADM1, the state of the art transient model for AD process. The validation of our developed solver is done by comparing the results to a fully-mixed digester in an experimental setup. Then, the results of our hydrodynamic modelling are shown as the velocity profile and streamlines. Subsequently, regarding bio-kinetics, the concentrations of substances are estimated and plotted during the simulation time. In order to evaluate the distribution of the organic material within the tank, the uniformity index for the substances is analysed.