Fluid-dynamics characteristics of a vortex ingesting stirred tank for the production of hydrogen from organic wastes fermentation

In this work, a novel stirred tank for the production of H2 by the biological fermentation of organic wastes is presented. The bioreactor design must ensure effective mixing of the liquid phase, full contact between the substrate and the biofilm and energy efficient biogas recovery. A vortex-ingesting dual impeller stirred vessel equipped with a central draft tube containing the packing support for the attached-growth process is proposed. The local hydrodynamics features of the system have been investigated experimentally at different working conditions by Particle Image Velocimetry and Digital Image Processing for determining the velocity fields of the two phases, the bubble size distribution and the central vortex shape. The results confirm that the reactor is suitable for the selected application and that it can ensure the external gas recirculation towards a membrane separation unit for the hydrogen recovery and purification, without additional energy requirements with respect to that provided for stirring