A bio-refinery concept for production of bio-methane and bio-ethanol from nitric acid pre-treated corncob and recovery of a high value fuel from a waste stream

Abstract The present paper reports the bio-refinery concept on exploiting the pre-treated non-detoxified corncob hydrolysate for bio-gas production and simultaneously utilizing the delignified cellulosic residue for bio-ethanol and black liquor for extraction of lignin. Based on the optimized conditions, corncob was pre-treated with HNO 3 at 121 °C for 15 min at a solid concentration of 20% (w/v). Maximum sugar concentration achieved was 110.12 mg mL −1 . The resultant corncob hydrolysate for bio-gas production was investigated in three anaerobic hybrid rectors. The reactors were operated at an OLR of 1.000, 1.428 and 2.500 g COD L −1 d −1 and HRT of 10, 7 and 4 d. Maximum bio-gas production rate was in R 2 (18.7 Ld −1 ), followed by R 1 (18.41 Ld −1 ) and R 3 (12.06 Ld −1 ), respectively at 7 d HRT. The COD removal efficiency was 81.0, 83.3 and 79.0% in R 1 , R 2 and R 3 reactors, respectively. Simultaneous saccharification and fermentation studies were carried out at three different enzyme loadings (9, 15 & 21 FPU g −1 substrate) by Kluveromyces marxianus at 42 °C for 96 h. 1% NaOH pre-treated cellulosic residue yielded maximum ethanol concentration (33.14 mg mL −1 ) with 15 FPU g −1 substrate enzyme load and at 87 h. The extracted lignin has a calorific value of 21.05 MJ kg −1 .