N.P. Nghiem, C.M. Nguyen, C.M. Drapcho, T.H. Walker
sweet sorghum, biorefinery, fuel ethanol, value-added co-products
A biorefinery has been developed where all carbohydrate components of sweet sorghum are used as feedstocks. First, the juice is extracted from the stalks. The resulted straw then is pretreated using the soaking in aqueous ammonia (SAA) process to enhance subsequent enzyme hydrolysis for production of fermentable sugars. The SAA process is chosen for sweet sorghum straw pretreatment because it does not result in significant losses of cellulose and hemicellulose as in several other pretreatment processes. Following pretreatment the straw is hydrolyzed with commercial enzyme product containing high hemicellulase activity. The xylose-rich solution obtained after solid/liquid separation is used for production of value-added co-products using suitable microorganisms. The value-added co-products may include astaxanthin, succinic acid, lactic acid, butyric acid, itaconic acid, xylitol, and others. The residual solids are hydrolyzed with commercial enzyme product containing high cellulase activity with the juice extracted in the first step being used as make-up water. By combining the sugar in the juice with the glucose released from the residual solids by enzyme hydrolysis high ethanol concentrations can be achieved, which results in lower distillation cost than if pure water is used for enzyme hydrolysis and subsequent fermentation as normally performed in cellulosic ethanol production.