In situ continuous countercurrent cloud point extraction of microalgae cultures

Green microalgae are gaining increased interest due to their ability to accumulate high-value compounds such as pigments, oils, antioxidants, and aromatics. These hydrophobic compounds can be extracted from the culture by the means of the biocompatible surfactant-based in situ cloud point extraction. In this study, we developed a continuous cloud point extraction using the nonionic surfactant Triton X-114, in order to extract the lipophilic substances from a green microalgae culture and accumulate these in the surfactant-rich phase. Cinnamic acid was applied as tracer in order to determine the optimal operating conditions for the extraction in a stirred extraction column. This model substance shows satisfying partitioning in the micellar phase (10logPCA = 1.2 ± 0.2) and the maximal yield of 79.1 ± 0.2% in a corresponding batch experiment. The process window for the continuous extraction was developed based on three parameter ranges: feed-to-solvent ratio of 6-10, a total column capacity of 1-2 l·h−1, and a stirring speed of 20-60 rpm. Statistical experimental design utilizing a response surface method was applied to investigate the influence of the three process parameters mentioned above on the yield and productivity of cinnamic acid. The optimal conditions for the in situ extraction of the microalgae were validated with an Acutodesmus obliquus culture (cell dry weight  =  1g·l−1). A total amount of 0.2 ± 0.1 gAlgae product/kgCulture (0.2 ± 0.1 gAlgae product/gcell dry weight) accumulated in the extract phase. A good biocompatibility of the surfactant with the microalgae cells in raffinate was demonstrated by measuring the photosynthetic activity with a pulse amplitude measurement. This study demonstrated for the first time a successful application of a surfactant-based cloud point extraction of microalgae in a continuous mode. The presented results proved the potential of the in situ surfactant-based extraction of microalgae products as an alternative to conventional extraction techniques.