The dark fermentation process promises a sustainable route for biohydrogen production. But the low substrate conversion efficiency hinders its commercial feasibility. The present study aims towards simultaneous hydrogen and butanol production to enhance the net energy recovery. Process parameters optimization revealed that pH of 6.5, temperature of 37 degrees C and inoculum size of 7% (v/v) were suitable for obtaining maximum hydrogen and butanol yields by C. saccharoperbutylacetonicum. Starch and xylan were observed to be preferred carbon sources suggesting effective utilization of C-5 and C-6 sugars. The maximum hydrogen yield of 264.3 mL g(-1) starch and 216 mL g(-1) xylan and butanol yield of 0.27 g g(-1) starch and 0.24 g g(-1) xylan were obtained with overall energy recovery of 85.61% (starch) and 75.22% (xylan), respectively. The present research work indicates the potency of bi-phasic fermentation to boost energy recovery from starch/xylan based feedstock. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.