Optimization of Acid-Catalyst Hydrolysis Process in Lactic Acid Production from Rice Husk by Using Lactobacillus bacteria

Abstract

Lactic acid is an important component of manufacturing polylactic acid (PLA), which can be produced with high-lignocellulosic biomass, still few of them have utilized that. The production process starts with Alkaline Hydrogen Peroxide (AHP) pretreatment, acid-catalyzed (H2SO4) hydrolysis followed by post-hydrolysis, and fermentation using a mixture of Lactobacillus brevis + Lactobacillus rhamnosus and single Lactobacillus delbrueckii bacteria. The effectiveness of pretreatment results was analyzed by using Thermal Gravity Analysis (TGA), which resulted in the removal of lignin and cellulose are 32.60% and 43.18%, respectively. Lignin reduction results are supported by Scanning Electron Microscope (SEM) for morphology analysis; it is shown the surface of rice husk becomes rough and cracks after pretreatment. Cellulose reduction was analyzed by using X-Ray Diffraction (XRD) and shown the Crystallinity Index (CrI) decrease after chemical pretreatment. The optimum operating condition of hydrolysis was also studied using Face Centered Composite Design (FCCD) by Response Surface Methodology (RSM), and get the optimum conditions at a 4 M H2SO4 for 30.7 minutes 63.1 . Followed by post-hydrolysis for 10 minutes at 121 , it resulted in sugar concentration of 15.3056 g/L, which was analyzed by using dinitrosalicylic-acid (DNS) with Root Mean Square Error of 0.78009. The last process is fermentation which is carried out at 125 rpm 37 , for 48 hours. Through High-Performance Liquid Chromatography (HPLC) analysis, the lactic acid concentration of a single bacterium and a mixture was 24.595 and 24.975%, respectively. Similar research has been previously carried out using palm waste raw materials with the enzymatic hydrolysis method without optimization of RSM. This study investigates the effect of AHP pretreatment in the lignin removal process, the effectiveness of acid-catalyzed hydrolysis in the optimized sugar reduction through FCCD, and compares lactic acid concentrations obtained from the fermentation process with L. delbrueckii and culture L. rhamnosus + L. brevis.