Pretreatment Development of Lignocellulosic Feedstocks for the Production of Bioproducts

Three different lignocellulosic feedstocks – switchgrass, sweet sorghum bagasse and pine wood chips, were analyzed for the production of bioproducts (sugars and enzymes). High sugar content of these feedstocks could be utilized either in the production of enzymes, biofuel and paper/pulp. Utilization of lignocellulosic feedstock in any production processes require preprocessing to remove phenolic compounds (lignin). Lignin acts as a barrier and protects the structure of polysaccharides from oxidation. Removal of lignin (delignification) leads to maximum utilization of lignocellulosic polysaccharides, mainly glucan and xylan in bioproducts production. The effect of pretreatment on ground switchgrass were evaluated through enzyme production and sugar production (through enzyme hydrolysis). A concentration of 4.5 wt% NH4OH (SAA-pretreatment) was applied. SAA-treated and untreated switchgrass (0.5-1.0 mm) were utilized for cellulase production using T. reesei Rut C-30. Enzyme activities of 1.34 FPU/mL and 0.37 FPU/mL were observed for SAA-treated and untreated switchgrass particles, respectively. A significant difference was observed between SAA-treated to untreated switchgrass particles. Temperature and pH controlled enzyme fermentation resulted in 1.80 FPU/mL of enzyme activity. The generated fermented cellulase broth was utilized for enzyme hydrolysis using SAA-treated switchgrass. The total enzymatic digestibility test resulted in 46 wt% and 54 wt% sugar recovery with 4.5 FPU of cellulase per g-biomass enzyme loading without externally added β-glucosidase and with externally added β-glucosidase (0.3 mL, enzyme activity=900 pNPG U), respectively. A separate enzyme hydrolysis study was performed on SAA-treated switchgrass using Accellerase® 1500 at four different enzyme loadings. The total conversion of SAA-treated biomass was observed at 44 wt%. These experiments suggested the importance of pretreatment in both cellulase production and enzyme hydrolysis. In the continuation, sweet sorghum bagasse was analyzed at 3 different pretreatment conditions: - 3.75 wt% NH4OH, 7.5 wt % NH4OH and 15 wt% NH4OH. All pretreatments were performed at 60oC for 15 hours. SAA-treated solids were hydrolyzed at enzyme loadings of 20 FPU per g of biomass, 40 FPU per g of biomass and 80 FPU per g of biomass. The enzyme hydrolysis resulted in 71 wt% / 55 wt% of glucan conversion/ total polysaccharide conversion, respectively, at 15 wt% NH4OH pretreatment and 80 FPU per g biomass. In addition, the biomass residue decreases to 50 wt% after the enzyme hydrolysis for 15 wt% NH4OH-treated bagasse at enzyme loading of 80 FPU per g biomass. Ground loblolly pine wood chips were evaluated using AHP-pretreatment and EHOs-pretreatment at 78 oC for 24 h. Enzyme hydrolysis of EHOs-treated and AHP-treated solids resulted in 91/41 wt% and 75/28 wt% of total cellulose / total hemicellulose conversion at 72 hours, respectively. The combined effects of ethanol concentration, potassium hydroxide (KOH) concentration, hydrogen peroxide (H2O2) concentration and temperature were found through enzymatic hydrolysis of pine wood chips. In 95% confidence interval, the maximum total polysaccharide conversion was predicted for 33.0 vol% ethanol + 3.8 wt% H2O2 + 3.5 wt% KOH, temperature = 67.4°C, pretreatment time = 24 h with. 69.1 wt%