Monoseptic cultivation of phototrophic microorganisms - development and scale-up of a photobioreactor system with thermal sterilization

The use of phototrophic microorganisms as sources of biological active substances in photoautotrophic and mixotrophic cultivation modes requires an adequate cultivation system with thermal sterilization. A corresponding photobioreactor system in the 10, 25 and 100 1 scales was developed. This Medusa-photobioreactor system represents a concept based on the air-lift loop principle, whose working volume is irradiated by external light sources. The incident irradiation can be varied by a light control system. An effective CO2/O-2 gas exchange is enabled due to the efficient supply with process gas by several gas supply nozzles within the system and a large degassing surface. Using a model to describe the growth characteristics of the organisms, the volumetric irradiation coefficient I-DX was defined as scale-up parameter. On this basis the scale-up from 1 1 bubble columns to the 10 and 100 1 scales was realized. The scale-up was performed successfully with Chlorella salina as model organism. A maximum biomass concentration of 7.89 g (dry weight) l(-1) at a maximum specific growth rate of 0.058 h(-1) and a yield of 35 mg l(-1) h(-1) was obtained in a batch cultivation in the 100 1 scale under photoautotrophic conditions with an initial biomass concentration of approx. 0.03 g l(-1). (C) 2003 Elsevier Science B.V. All rights reserved.