Design principles of photo‐bioreactors for cultivation of microalgae

Abstract

The present hype in microalgae biotechnology has shown that the topic of photobioreactors has to be revisited with respect to availability in really large scale measured in hectars footprint area, minimization of cost, auxiliary energy demand as well as maintenance and life span. This review gives an overview about present designs and the basic limiting factors which include light distribution to avoid saturation kinetics, mixing along the light gradient to make use of light/ dark cycles, aeration and mass transfer along the vertical or horizontal main axis for carbon dioxide supply and oxygen removal and last but not least the energy demand necessary to fulfil these tasks. To make comparison of the performance of different designs easier, a commented list of performance parameters is given. Based on these critical points recent developments in the areas of membranes for gas transfer and optical structures for light transfer are discussed. The fundamental starting point for the optimization of photo-bioprocesses is a detailed understanding of the interaction between the bioreactor in terms of mass and light transfer as well as the microalgae physiology in terms of light and carbon uptake kinetics and dynamics.

The Application of Transparent Glass Sponge for Improvement of Light Distribution in Photobioreactors

“…The second step is based on an idea of nature inspired design published by Posten [10]. An additional effect on efficiency could be reached by enlargement of the inner surface of the reactor for light dilution and supply.…”

“…Both aspects intend to distribute the light over a larger reactor surface and avoid dark volume elements and to use the incident sunlight as efficient as possible (volumetric and areal productivity P V and P A ). An optimization of the incident angle of sunlight hitting the reactor surface is a further option for possible developments [10][11][12].…”

“…horizontal and vertical tubular reactors in many different configurations or flat plate reactors with a small layer thickness also in special arrangements. Moreover specific configurations like the Flat Panel Airlift reactor (Subitec) or cheap low-ceiling designs made of plastic foils (Soilx and Proviron) [9][10][11] are proposed. All this configurations try to improve the surface to volume ratio (SVR) of the photobioreactor as well as the surface to footprint ratio (SFR).…”

Cultivation of Microalgae Euglena Gracilis: Mixotrophic Growth in Photobioreactor

“…Chlorophyll reaction center with photo system I (P 700) and photo system II are sensitive to the light source wavelength. Therefore lipid syntheses were promoted by light source with maximum wave length similar to photo system I and II [8][9][10]. Even so, there is still limitation by the self-shading effect, that is, light penetration decreases as the algal mass increases in the reactor and in the both batches biomass cell number decrease during second autotrophic cultivation period (Figure 1a & 1b).…”

Dependency of Microalgal Production on Biomass and the Relationship to Yield and Bioreactor Scale-up for Biofuels: a Statistical Analysis of 60+ Years of Algal Bioreactor Data

“…This makes system scaling more unpredictable, and no practical scale-up methods exist although several design parameters have been identified, e.g., light, CO 2 , mixing, etc. [247][248][249][250][251][252][253][254][255][256][257]. Since production decreases with bioreactor volume, smaller bioreactors (10 2 -10 3 L) may be more practical, especially if they are designed to provide high surface areas for high illumination [257,258].…”