On the effect of biogas bubbles in anaerobic digester mixing
Soroush Dabiri, Prashant Kumar, Christian Ebner, Wolfgang Rauch
Abstract
A mixing strategy capable of handling a suitable agitation within digester tanks is a necessity in order to assure continuous contact of substrates and degraders inside bioreactors. As mixing is an energy demanding process, the energy needed for a proper mixing contributes to overall efficiency of digesters. In the current study, the aim is to assess the incorporation of biogas bubble creation into the mixing of anaerobic digesters of wastewater treatment plants (WWTP) tanks with and without an external vertical mixer, in order to analyze the possibility of considering bubble creation as an imperative factor in the mixing scenario. Computational fluid dynamics (CFD) prepares the opportunity to simulate the creation biogas bubbles within a stirred tank of anaerobic digester, in a combination of an Eulerian and Lagrangian platform. The amount of dead volume, average velocity, velocity gradient and bubble particle trajectories are analyzed and discussed.\n\nOur key findings are as follows: biogas bubble creation contributes to the reduction of dead volume inside the digester tank, once there is no external rotating mixing, or once the amount of mixer rotation speed is low. However, either in low or in high mixer rotation speed the biogas bubble creation does not have a considerable effect of velocity gradient.