Chemical mutagenesis approach was used for the improvement of H-2 yield using Thermoanaerobacterium thermosaccharolyticum. A H-2 yield of 3.12 mol mol(-1) glucose was observed which was about 13.5% higher as compared to wild type. An inverse relation was observed between the NADH/ NAD(+) ratio and the rate of H-2 production. Bioelectrochemical analysis showed an overall increase in reducing equivalent in mutants. Continuous H-2 production with mutant using starchy wastewater showed maximum H-2 production rate of 500 mL L-1 h(-1) at a dilution rate of 0.25 h(-1) and organic loading rate (OLR) of 8.75 g L-1 h(-1). The spent medium was mostly comprised of acetate (0.62 +/- 0.3 g L-1), butyrate (1.26 +/- 0.34 g L-1) and ethanol (0.10 +/- 0.02 g L-1). It was subsequently used as substrate for the biomethanation process to improve overall gaseous energy recovery. Highest methane production rate, methane yield and COD removal of 51.4 +/- 0.4 mmol L-1 d(-1), 82.6 L kg(-1) CODadded, and 66%, respectively were observed at an OLR of 14 g L-1 d(-1) thereby improving overall gaseous energy recovery by 53.6%. (C) 2015 Elsevier Ltd. All rights reserved.