Energy-efficient selective fractionation of lignin and bacterial hydrolysis of cellulose in corncob biorefinery for sustainable production of PHA and biohydrogen

In this biorefinery, a lignocellulosic biomass corncob (CC) was used as a feedstock for the production of polyhydroxyalkanoate (PHA) and biohydrogen. It was achieved through the fractionation of lignin via physicochemical pretreatment for the production of PHA, and bacterial hydrolysis of cellulose for the production of hydrogen. A delignification of 82.2% was obtained during the fractionation of CC using microwave-assisted alkaline pretreatment. The addition of NaOH reduced the microwave specific energy from 108 MJ/kg TS to 48 MJ/kg TS, thus making the process energy efficient. After fractionation, the lignin-rich supernatant was used for the production of PHA using a novel bacterium capable of utilizing lignin as its carbon source. A higher PHA concentration of 460.8 mg/L was obtained from a stock solution with a 70% lignin concentration. The delignified, cellulosic-rich CC residue was hydrolysed using a novel cellulase-secreting bacterium. A higher sCOD and glucose release (1600 mg/L and 1200 mg/L) were obtained in the delignified bacterially pretreated residue than the delignified (600 mg/L and 385 mg/L), and bacterial alone (1000 mg/L and 775 mg/L) pretreated CC. The hydrolysed cellulosic residue was subjected to dark fermentation, resulting in the production of 48.4 mL/g COD hydrogen on the 5.5th day of fermentation.