Enhancement in yeast separation and recycling in continuous bio‐ethanol fermentation process in Blenke cascade

Abstract

AbstractBackgroundContinuous ethanol fermentation productivity strongly depends on yeast concentration. Therefore apparatuses, which can handle high cell concentrations, separation and recycling of adapted yeasts are of high interest.In our work, an enhanced sedimentation rate (ESR) settler for a Blenke cascade system, avoiding large electrical power consumption, was designed. To improve the sedimentation rate, the ESR settler was connected in series with a small conventional gravitational settler. Yeast recycling was executed in two modes, direct and activation modes. Yeast cell samples taken from both cascade and settler were counted and tested for cell viability using methylene blue staining technique and a haemocytometer. The samples were cultured on agar plate with yeast extract peptone dextrose broth and analyzed by HPLC to determine ethanol, residual sugars content and by‐products (of yeast and bacterial origin).ResultsThe results showed that, using ESR settler in series with a small conventional gravitational settler, more than 85% of the yeast cells were sedimented and were recycled by the direct or activation mode. The ethanol productivities were Qp = 19.45 ± 0.13 and Qp = 20.31 ± 0.11 g L−1 h−1 for direct and activation recycle mode, respectively. Continuous fermentation, yeast recycling and sedimentation were contamination‐free processes.ConclusionWith an ESR settler, more adapted yeast can be recycled into the continuous process. High ethanol productivity can be achieved by an activation recycling mode. © 2013 Society of Chemical Industry