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- Title
The effect of discontinuous airlift mixing in outdoor flat panel photobioreactors on growth of Scenedesmus obliquus.
- Authors
Leupold, Marco; Hindersin, Stefan; Kerner, Martin; Hanelt, Dieter
- Abstract
Discontinuous airlift mixing was realized by injecting pressured air at time intervals with a frequency between 0.033 and 0.25 Hz (at 80 kPa; i.e., every 4-30 s; valve opening time 800 ms) into outdoor flat panel photobioreactors ( $$ 200\, \times \,100\, \times \,2.1\,{\text{cm}} $$). This caused a flow velocity between 2 and 20 cm s of the culture medium within the photobioreactor and the mixing time was between 38 and 103.5 s, requiring 0.175-1.340 L L min pressured air. In order to detect the effect on growth of Scenedesmus obliquus during outdoor experiments and to be able to compare obtained results, a batch run with an airlift frequency of 0.25 Hz was simultaneously used as control. Growth at different airlift frequencies was measured by the increase of cell dry weight (CDW) during 3-5 days and biomass yield on light energy was calculated. With increasing airlift frequencies, growth increased from 52 to 91 % compared to the control. When CDW was at around 1.0-1.5 g L, airlift frequency had no effect on growth, indicating that mass transfer gradients of nutrients and gas were not the limiting factors of growth. Above 1.5 g CDW L, growth increased with increasing airlift frequency and light limitation for a single cell occurred. This effect was observed during low and high irradiance and it is concluded that a higher mean flow causes a better light distribution, resulting in an enhanced growth. Biomass productivity and demand of pressured air are correlated logarithmically, which enables to save mixing energy during cultivation.
- Subjects
AIRLIFT bioreactors; PHOTOBIOREACTORS; SCENEDESMUS obliquus; AIR pressure; FLOW velocity; BIOMASS production
- Publication
Bioprocess & Biosystems Engineering, 2013, Vol 36, Issue 11, p1653
- ISSN
1615-7591
- Publication type
Article
- DOI
10.1007/s00449-013-0939-x