Microwave-assisted sequential green liquor-inorganic salt pretreatment for enhanced sugar recovery from sorghum leaves towards bioethanol and biohydrogen production

Abstract

A two-stage green liquor-inorganic salt pretreatment was developed to enhance sugar recovery from sorghum leaves (SL) for biofuel production. Process inputs included green liquor (GL) concentration, MgCl2 concentration and microwave power intensity. A coefficient of determination (R2) of 0.86 was achieved with optimal conditions of 31% (v/v) GL, 1.46 M MgCl2 and 600 W resulting in fermentable sugar yield of 0.719 g/g. This was followed by simultaneous saccharification and bioethanol production using the pretreated SL giving rise to maximum bioethanol concentration of 12.16 g/L. Thereafter, bioethanol fermentation effluent was channelled towards biohydrogen production and a peak H2 fraction of 31.85% (78.44 ml H2/g sugar) was obtained. These findings demonstrate the sequential valorisation of SL, GL, and bioethanol fermentation effluent towards a sustainable, cost effective and eco-friendly lignocellulosic biorefinery concept.