Communication Wave-Mixed and Orbitally Shaken Single-Use Photobioreactors for Diatom Algae Propagation Nicolai Lehmann 1, *, Heiko Rischer 2 , Dieter Eibl 1 , and Regine Eibl 1 DOI: 10.1002/cite.201200137 Although vertical column, flat-plate, tubular, bubble column and airlift photobioreactors are widely used for the cultivation of diatoms, it has been shown that bubble-induced hydrodynamic stress created in these types of bioreactor can damage cells. Therefore, three single-use surface-aerated bag bioreactors, known for their outstanding results in cultivating shear- sensitive mammalian cells, were for the first time investigated for their suitability in growing the model microalgae Phaeo- dactylum tricornutum. All of the systems, which were additionally aerated with CO 2 and equipped with illumination sys- tems providing different light qualities, guaranteed a 22- to 43-fold increase in cell density within seven days, without any addition of cell protection agents or changes in cell morphology. Maximum cell density and dry biomass were achieved in the orbitally shaken 2D-bag by using cool-white fluorescent tubes. Schlagwörter: Diatom, Growth characteristics, LED, Orbitally shaken, Phaeodactylum tricornutum, Single-use bioreactor, Wave-mixed Received: August 06, 2012; revised: September 02, 2012; accepted: September 28, 2012 1 Problem Diatoms are one of the largest and most important groups of microalgae [1, 2] and are regarded as a potential source of high-value products such as polyunsaturated fatty acids, na- tural colorants, biopolymers and therapeutic agents [1 – 5]. Controlled in vitro production processes using diatoms are performed in photobioreactors such as vertical-column, flat- plate, tubular, bubble column and airlift [6,7]. However, se- veral authors reported that diatoms can be damaged by shear stress induced by mixing and aeration [8, 9]. Inter- estingly, it has been shown that Phaeodactylum tricornutum is especially sensitive to aeration-induced hydrodynamic stress [9, 10], arising from the bursting of small bubbles on the medium surface of bubble column and airlift photobio- reactors. To date, the suitability of surface-aerated single-use bio- reactors operating with a ready to use, pre-gamma radiated, light-transmissive flexible plastic bag instead of a sterilized glass vessel has not been described for P. tricornutum. Such surface-aerated single-use bioreactors include wave-mixed bioreactors and orbitally shaken systems [11, 12]. A key com- ponent of both bioreactor types is the 2D- or 3D-cultivation bag, which is either moved on a rocker or a shaker unit and is fixed and shaped by a support container (collecting pan or vessel) [12]. The medium containing the cells is efficiently mixed by rocking or shaking the bag, which continuously renews the medium surface and provides bubble-free sur- face aeration. Power input and oxygen transfer in these sin- gle-use bioreactors can be adjusted and controlled via rocking- or shaking rate, rocking angle, shaker diameter, fil- ling level and aeration rate [13, 14]. As described by Werner et al. [15] wave-mixed and orbitally shaken systems are cha- racterized by homogeneous energy dissipation. It is assu- med that shear-sensitive cells tolerate this better and it results in reduced cell damage. The phenomenon of homo- geneous energy dissipation was already described for airlift bioreactors in the late 1990s [16]. But thereby cell damage from bubble aeration, extensive foaming and resultant flota- tion can occur. In contrast, in wave-mixed and orbitally shaken single-use bioreactors, shear stress from bubble aeration is not a concern and it is even possible to perform the cultivation without the addition of antifoam agents, something which will simplify downstream processing of diatom-based bioactive substances. In the subsequently described growth experiments two wave-mixed single-use bag photobioreactor prototypes and one orbitally shaken single-use bag photobioreactor were used. They are equipped with illumination systems provi- ding differing light qualities: cool-white fluorescent tubes (particularly strong at the blue and red ends of the light spectrum), white LEDs, and white and red light LEDs. Pho- ton flux densities of between 56 and 1712 lmol m –2 s –1 are Chemie Ingenieur Technik Chemie Ingenieur Technik 2013, 85, No. 1–2, 197–201 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.cit-journal.com – 1 Nicolai Lehmann (nicolai.lehmann@zhaw.ch), Prof. Dr. Dieter Eibl, Prof.Dr. Regine Eibl, Zurich University of Applied Sciences, School of Life Sciences and Facility Management, Campus Grüen- tal, 8820 Wädenswil, Switzerland; 2 Dr. Heiko Rischer, VTT Techni- cal Research Centre of Finland, Tietotie 2, 02044 VTT, Finland. Diatom 197