Agro Waste Materials as Renewable Feedstock for Biological Production of Lactic Acid

Abstract

Environmental sustainability, long-term economic and national energy security concerns have motivated research over the last 25 years into renewable, domestic sources of fuels and chemicals. Development of renewable resources has significantly increased interest in the recovery of fermentation products, such as organic acids, feed or food additives, and industrial chemicals from agro-wastes and one such product is lactic acid. The interest in the fermentative production of lactic acid has increased due to the prospects of environmental friendliness and of using renewable resources instead of petrochemicals. The world market for lactic acid is projected to reach 259 thousand metric tons by the year 2012. The process for converting lignocellulosic material to lactic acid involve two step process with complete conversion of sugars through pretreatment & then enzymatic hydrolysis, followed by fermentation to produce lactic acid. The objective of the project work is to produce Lactic acid from the renewable resource such as agricultural waste biomass residues specifically, cane bagasse and wheat straw/wheat stover in laboratory conditions. Agriculture waste biomass was basically a lignocellulosic material represents an abundant renewable carbon resource for the production of valuables fuels & chemicals for both short- and long- term sustainability. Lactic Acid is a commercial viable chemical product with wide applications in food, pharmaceutical, leather, textile industries and as chemical feedstock. Novel applications in synthesis of biodegradable plastics have increased the demand for lactic acid. Microbial fermentations are preferred over chemical synthesis of lactic acid due to various factors. In the thesis, the Lactic Acid production from Bagasse and Wheat Straw via fermentation route using Lactobacillus cacei & Lactobacillus bulgaricus as the microorganism was being studied. The different pretreatment process such as 0.5% H2SO4, 1.5% H2SO4 and 1.0% NaOH was being carried out to separate and remove most of the hemicellulose portion of the biomass, to obtained C5 sugars and degrade lignin so as to enhance the enzymatic hydrolysis. In enzymatic hydrolysis cellulose is hydrolyzed to C6 sugars using cellulase enzyme (Trichoderma reesei) having 100FPU/mL activity. The substrate obtained after both the hydrolysis went for fermentation to produce lactic acid. According to the results of experiments, maximum glucose (92%) & xylose (98%) conversion is achieved after treating biomasses with 0.5% H2SO4 in the High Pressure Reactor at 150°C for 30min and simultaneously carrying out enzymatic hydrolysis. Substrate obtained after enzymatic hydrolysis shows maximum lactic acid production using Lactobacillus cacei culture for both cane bagasse & wheat straw The maximum lactic acid concentration of 11.2 gl-1 in case of glucose as substrate & 3.5 gl-1 in xylose for both the biomasses was observed.