Use of Zymomonas mobilis immobilized in doped calcium alginate threads for ethanol production

Zymomonas mobilis immobilized in doped calcium alginate (Ca-alginate) threads was successfully employed for the production of ethanol in immobilized cell reactors operated with both vertical and horizontal flow. Polyethylene oxide (PEO) as a dopant for Ca-alginate threads was used to increase thread porosity. The influence of the direction of the flow into the reactor and the use of a dopant on the effectiveness of microbe immobilized Ca-alginate threads to produce ethanol was studied and results were compared to the widely used 2% Ca-alginate beads. Threads were able to obtain a similar ethanol yield to beads achieving 90.7% in vertical and 88% in horizontal flow reactors, while beads obtained 91% and 74.7%, respectively. The addition of PEO decreased the lag phase of the threads in both the horizontal and vertical flow reactors compared to a Ca-alginate standard over a 24 h period. The horizontal flow reactor's ethanol yield increased from 10.5% to 41.2% with the addition of PEO while the vertical flow reactor's ethanol yield increased from 15.5% to 69.6%. Additionally, doping with PEO lead to higher ethanol yield. This study demonstrates the use of threads for immobilization of microbes and the effectiveness of PEO as a dopant. •Zymomonas mobilis was immobilized in alginate threads.•Threads used in vertical or horizontal flow reactors obtained similar ethanol yield.•Alginate threads doped with polyethylene oxide showed increased ethanol yield.