Hydrogen and ethanol fermentation of various carbon sources by immobilized Escherichia coli (XL1-Blue)

• Hydrogen and ethanol fermentation of Escherichia coli XL1-Blue were demonstrated.
• Immobilization and the biomass concentration inside the beads are key factors.
• E. coli XL1-Blue efficiently utilizes the beverage wastewater.

In this study, hydrogen and ethanol production by a facultative anaerobic bacterium Escherichia coli XL1-Blue immobilized in calcium-alginate beads have been investigated. Batch fermentations were carried out at mesophilic temperature (35 °C) and an initial cultivation pH of 6.5. Firstly, the influence of biomass concentration in terms of dry cell weight (expressed in g DCW/L, range 0.2–1.0) was investigated using fructose (5 g/L) as a carbon source. The peak hydrogen yield (HY) of 1.17 mol-H2/mol-fructoseutilized was obtained at an initial cell concentration of 0.4 g DCW/L. The hydrogen production potential of other simple carbon sources (glucose and xylose) was evaluated at this optimized cell concentration and peak HY values were attained as 0.96 mol-H2/mol-glucoseutilized and 0.69 mol-H2/mol-xyloseutilized, respectively. In addition, utilization of the beverage wastewater (BWW) showed the peak cumulative hydrogen production and ethanol concentration of 120 mL and 5.65 g/L, attained at the substrate concentration of 20 g(glucose equivalent)/L. However, peak HY (1.65 mol-H2/mol-glucose eqivalent utilized) was observed at low substrate concentration of 5 g(glucose equivalent)/L. The percentage of sugar utilization of BWW was ranged between 80 and 96.