Anaerobic batch fermentation experiments were conducted in 1L bioreactor (New Brunswick’s BioFlo®/CelliGen® 115) with a working volume of 0.8 L at a temperature of 37 ◦C and an initial pH of 6.8. During fermentation, the pH was adjusted to 5 with NaOH solution (2 M). High purity nitrogen was continuously sparged in the reactor at a flow rate of 75 mL/min. In the control experiment, xylose (60 g/L) was used as a carbon source and then replaced by 3.5× diluted flocculated hydrolysate containing 0.30 g/L of phenolic compounds. The final concentration of sugars in the FHWH was raised to 60 g/L by adding synthetic xylose and the total concentration was determined by high performance liquid chromatography (HPLC). Alfalfa juice, 4.4 folds diluted to a nitrogen content of 0.90 g/L, was used as a nitrogen source. The solutions were then sterilized separately at 121 ◦C for 15 min. Prior to inoculation with 5% (v/v) of active growth inoculum, 8 mL of filtered and sterilized stock solution consisting of buffer, vitamins and minerals were added to the medium (Ezeji et al., 2007). During fermentation, 5 mL samples were periodically withdrawn to analyze sugars, ABE and acids concentration. All fermentation experiments were conducted in duplicates and the results are expressed as an average.