Experimental investigation of fluid dynamics in a gravitational local recirculation photobioreactor

Microalgal and cyanobacterial growth rate does not exert its full potential in high sunlight due to intrinsic limits of the photosynthetic systems that get 'electronically-flooded', thus leading to extensive thermal dissipation and photoinhibition. It is well known, however, that supplying high light in short pulses significantly reliefs this problem and much research is devoted into the development of photobioreactors which exploit this basic feature of photosynthetic systems. The present work deals with an experimental fluid dynamic analysis of the flow developed in a wavy-bottomed cascade photobioreactor for microalgal or cyanobacterial culture. A short but representative section of the equipment was analysed by suspended particle tracers and fast cinematography. The acquired image sequence was post-treated by using a specially designed software implementing the Feature Tracking technique. The effect of the installation and operating mode of the photobioreactor was tested at multiple overflowing liquid flow rates. A local recirculatory zone was found to establish in each trough and its size, local speed, and recirculatory period were characterised as a function of liquid flow rate. Local recirculation establishes owing to gravity only, so that this type of reactor could be rightfully denoted as 'gravitational local recirculation' (GLR) photobioreactor. Copyright © 2013, AIDIC Servizi S.r.l.