Bioethanol production from pretreated whole slurry rice straw by thermophilic co-culture

Abstract

In this study, an innovative approach is proposed for the valorization of all sugars (cellulosic and hemicellulosic) contained in a lignocellulosic feedstock, as is rice straw biomass (RSB), for the production of second-generation bioethanol. For this purpose, the whole slurry obtained after dilute sulfuric acid pretreatment at a biomass loading of 5% (w/v) was subjected to consolidated bioprocessing without previous solid-liquid separation and/or detoxification and the concentrated solution of carbohydrates recovered was fermented to bioethanol by a co-culture of thermophilic anaerobic bacteria. To bypass the inhibitory effect of undetoxified whole slurry on the lower fermentability of the co-culture, the concentration of different additives was optimized for improved buffering capacity, enhanced substrate-microbe interaction, and by-product elimination. The individual supplementation of 3 selected additives at optimum concentration; 20 mM calcium carbonate, 0.4% (v/v) polyethylene glycol, and 1% (w/v) sodium acetate resulted in enhanced ethanol yield of 130.83 mM, 106.37 mM, and 99.10 mM, respectively, compared to 75.03 mM ethanol yield in control. The combined effect of optimal dosage of these additives was able to improve the ethanol concentration and yield to 142 mM and 48% of the theoretical maximum respectively, suggesting about 88.58% increase compared to control medium without additives supplementation. The combined supplementation of additives proved to be an advantageous strategy for bioethanol production using undetoxified whole slurry biomass.