(644d) Microbial Conditioning and Pretreatment of Grasses for Ethanol and Lignin Co-Products

Cellulosic ethanol continues to develop as a potential alternative transportation fuel. For its production, major process steps involve pretreatment to degrade or disengage lignin, saccharification to depolymerize cellulose to sugars, and fermentation of sugars to ethanol. Through DOE-supported projects, Novozymes and Genencor have dramatically reduced the enzymatic hydrolysis costs, leaving pretreatment as a significant remaining cost challenge to cellulosic ethanol commercialization. Aggressive research and development is pursuing alternative pretreatments to meet this challenge. In this matter, lignin plays a key role. It inhibits enzymatic hydrolysis of cellulose, and process designs typically consign its recalcitrant, low-value forms to boilers. However, lignin, in appropriate molecular weight ranges, is a suitable component of phenolic resin plastics.

Our objective is to combine microbial conditioning to improve pretreatment performance, allowing reductions in severity and complexity, reduced costs, and improved economics for the biomass grower. Furthermore, we aim to obtain a more useable lignin co-product.

In this work, we applied a wastewater sludge bacterial (consortium) and Phenerochaete Chrysosporium to Corn Stover, Switch Grass, Sorghum, and Giant Miscanthus for 20 and 28 days respectively. We measured enzyme activities for Phenol oxidase, Peroxidase and beta-Glucosidase during the period of fungal conditioning of the biomasses. The bacterial consortium was characterized for the active species responsible for conditioning. The conditioned biomasses were washed and analyzed for their composition. Sugar yields after 72 hours of enzymatic hydrolysis were determined using HPLC. Finally, a comparison of the impact of Ammonia Fiber Expansion (AFEX), Extrusion and Centrifugation, Dilute Acid Hydrolysis and Microbial Conditioning on enzymatic hydrolysis was made on the four feed stocks. The liquid portion of the conditioned material was analyzed for solubilized sugars and lignin. Findings include observations that bacterial conditioning liberated significant xylose and that fungal conditioning generated primarily the beta-Glucosidase enzyme.