Development of a photobioreactor with volumetric illumination via resonant inductive coupling

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Microalgae could be sources for a multitude of products in pharmacy, medicine, fine chemistry, and food industry. The most important process parameter for the growth of phototrophic microorganisms is light, which is not dispersible in water and is absorbed drastically by the cultivated organisms. This leads to a highly inhomogeneous light distribution over the reactor cross section, which results in drastically differing light supply in different parts of the reactor. Therefore a high surface to volume ratio is necessary to achieve a high specific light supply and consequently a maximum productivity. The major limitation of existing photobioreactors (PBRs) is the lack of convenient scale-up solutions. The main goal of this project is to engineer a stirred tank reactor with a homogeneous internal illumination for cultivation of phototrophic microorganisms. This will be achieved by using wireless light emitters (WLEs), powered wirelessly via resonant inductive coupling. The light will be generated by light emitting diodes (LEDs) with an appropriate spectral wavelength pattern. The WLEs will have nearly the same density as the cultivation medium to guarantee a statistical homogeneous distribution inside the whole fluid and thus lead to a uniform light pattern inside the reactor. The reactor will be surrounded by a primary transmitting coil, connected to a frequency generator and a power amplifier, to provide a frequent electromagnetic field inside the reactor. The WLEs will consist of a secondary coil connected to a capacitor and a LED encapsulated in a plastic sphere. The frequent magnetic field of the transmitting coil will induce a current inside the multiple receiving coils and will power the LED. The new reactor system will be compared to the PBR systems at the Institute of Bioprocess Engineering, focusing on growth behavior and the yield of valuable products. Furthermore, a scale-up from small-scale 1 L reactors to a 50 L reactor will be done and evaluated. The reactors will be constructed according to the DECHEMA guidelines for bioreactors from 1991. This will prove the principle scaling-up possibilities of this novel illumination method. Besides the goals in the field of engineering, basic studies regarding the influence of frequent electromagnetic fields (EMF) on microalgae have to be done. There are only few results on the EMFs influence on phototrophic microorganisms published. The knowledge of potential side effects of EMF is fundamental to the application of the new reactor concept, as the microorganisms are exposed to that field during the whole cultivation process. Preliminary work concerning this project showed no significant influence of two selected frequencies on the model greenalga Chlamydomonas reinhardtii, but nevertheless, a more detailed analysis of the influence of different EMF on more phototrophic microorganisms is necessary to provide a valuable and reliable tool to industrial photobiotechnology.