Optimized bioreactor setup for scale-up studies of extreme halophilic cultures

Adaptation to highly saline conditions required halophilic organisms to develop unique features. The mounting interest in those features has resulted in a number of potential applications for moderate and extreme halophiles. However, industrial exploitation has been reported only for few instances. With the aim to bring concepts from laboratory to pilot-scale a customized bioreactor for halophilic cultures was developed. The setup combined a bubble column reactor (BCR) with a membrane module for cell retention. The BCR was compared to a conventional stirred tank reactor (STR) in terms of physiological and hydro-dynamical parameters. The results showed that the BCR is preferable in terms of energy efficiency. The BCR reached a maximum kLa of 84 h−1 at ambient pressure, which equals an oxygen transfer rate (OTR) of 6 mmol/(L*h) in medium with 150  g/L NaCl. To reach this mass transfer a STR required more than 3-fold the amount of energy. Cultivation of the extreme halophilic archaeon Haloferax mediterranei showed suitability of the BCR for continuous halophilic processes. To reduce cost and ecological impact of this process a highly saline industrial waste stream from a chemical production process was used as source for NaCl. The BCR presented in this study allows continuous and competitive cultivation of halophilic organisms at high volumetric rates and high biomass productivities as required for large scale industrial applications.