Hemicellulose recovery and lignin removal through acid-alkali union pretreatment to improve the lactic acid production from garden garbage

Generally, pretreatment is essential to enhance the hydrolysis of lignocellulosic biomass. However, hemicellulose is easily lost during the pretreatment process. To avoid the loss of hemicellulose while removing lignin during the pretreatment process, an acid-alkali union pretreatment was performed to recover hemicellulose and remove lignin. Firstly, acid pretreatment was employed at 120 °C using 1% H 2 SO 4 and garden garbage for 1 h with the solid-liquid ratio of 1:7. Subsequently, alkali pretreatment was conducted at 120 °C using 1% NaOH and acid pretreated garden garbage for 1 h with the solid-liquid ratio of 1:7. The results indicated 75.1% hemicellulose recovery and 78.3% lignin removal through acid-alkali union pretreatment. Through enzymatic hydrolysis using acid pretreatment liquid and acid-alkali union pretreated garden garbage, cellulose, hemicellulose, and total sugar conversions reached 70.8%, 69.5%, and 70.3%, respectively. Enterococcus mundtii which could metabolize hexose and pentose simultaneously was used for LA fermentation. Eventually, because more xylose was metabolized and high initial xylose concentration reduced the byproduct yield (0.33 g/g), the LA concentration and yield reached 67.9 g/L and 0.71 g/g total sugar, which was 28.0% and 15.0% higher than that of single acid and alkali pretreatment, respectively. Graphical Abstract