Biological co-production of ethanol and biodiesel from wheat straw: a case of dilute acid pretreatment

A process for co-production of ethanol and biodiesel from wheat straw was proposed. Dilute acid prehydrolysis of hemicellulose followed by enzymatic hydrolysis of cellulose were optimized to maximize recovery of total sugars. It was found that xylose yield obtained by super-dilute acid (0-0.1%) pretreatment under the experimental conditions was too low. By using moderate conditions (140-160 degrees C) with higher sulfuric acid concentration (0.3-0.6%), xylose recovery could be greatly increased to 60-70%. The relatively optimum conditions for dilute acid pretreatment were 0.5% H2SO4 at 140 degrees C for 1 h. 15.1 g L (-1) ethanol with approximately 58% of theoretical yield obtained by SSF of the pretreated solid. The hydrolyzate was directly converted to microbial lipid using a mutagenized Rhodosporidium toruloides. The extracted lipid was well converted to biodiesel with 90% conversion ratio under the catalysis of immobilized lipase. Mass balance showed that 0.80 g biodiesel and 10.1 g ethanol were produced from 100 g of wheat straw. This work thus can provide a novel idea for biological production of biofuels from lignocellulosic biomass.