Dynamics of ethanol production from whey and whey permeate by immobilized strains of Kluyveromyces marxianus in batch and continuous bioreactors

We investigated the bioconversion of whey and whey permeate into ethanol by Kluyveromyces marxianus immobilized in Ca-alginate, in both batch and continuous cultivations. Different strains of K. marxianus and cultivation media were tested in batch mode and the effects of dilution rate (D) and substrate concentration were investigated in continuous bioreactors. In shaker cultivations, the highest ethanol yield (0.51 g g−1) and ethanol productivities (0.77–1.15 g L−1 h−1) were obtained by strains CBS 6556, CCT 4086, and CCT 2653 in raw (not supplemented) whey permeate. These strains were immobilized in Ca-alginate beads and cultivated in batch fluidized-bed bioreactors, where the highest ethanol productivity (2.53 g L−1 h−1) was observed for strain CCT 4086. The effects of D (0.1–0.3 h−1) and whey permeate concentration (CWP, 60–180 g L−1) were also investigated in continuous fluidized-bed bioreactors using K. marxianus CCT 4086, and the highest ethanol productivity (6.01 g L−1 h−1) was achieved at D of 0.3 h−1 and CWP of 150 g L−1, whereas the highest ethanol yield (0.51 g g−1) and concentration (42.8 g L−1) were observed for D 0.1 h−1 and CWP of 90 g L−1. Two continuous fluidized-bed bioreactors operated in sequence were tested, showing increased ethanol productivities and concentrations to 6.97 g L−1 h−1 and 70.4 g L−1, respectively. Continuous immobilized-cell bioreactor showed promising results to improve the performance of ethanol production from whey fermentation processes. [Display omitted] •Screening of yeasts and media showed high ethanol conversion from unsupplemented substrates.•High concentrations of whey and permeate were possible to be fed into bioreactors.•Yield, productivity, and residual sugar depend upon D and substrate concentrations.•A 2-stage continuous immobilized cells bioreactor was highly efficient in sugar conversion.•Ethanol productivity and concentration peaked at 6.97 g L−1 h−1 and 70.4 g L−1, respectively.