CONVERSION OF MIXED WASTE OFFICE PAPER TO ETHANOL BY GENETICALLY-ENGINEERED KLEBSIELLA-OXYTOCA STRAIN P2

Unsorted, mixed waste office paper (MWOP) is an excellent substrate fo r conversion into fuel ethanol using a recombinant strain of Klebsiell a oxytoca which ferments cellobiose and cellotriose to ethanol at near theoretical yields, eliminating the need for supplemental beta-glucos idase. This organism was tested with commercial fungal cellulase in op timized simultaneous saccharification and fermentation experiments (SS F) using MWOP as a substrate (pH 5-5.2, 35 degrees C). Similar rates a nd yields were obtained with dilute acid-pulped (hydrolysis of hemicel lulose) and water-pulped MWOP on a dry weight basis although viscosity was reduced by the acid pretreatment. In simple batch fermentations, 40 g/L ethanol was produced after 48-72 h with 100 g/L MWOP and 1000 f ilter paper units (FPU) of cellulase/L, a yield of 550 L of ethanol me tric ton. Cellulase usage was further reduced by recycling SSF residue s containing bound enzymes in multistage fermentations. This approach reduced the requirement for fungal cellulase while retaining rapid eth anol production and high ethanol yield. In our optimal design, broths containing an average of 39.6 g/L ethanol were produced in three succe ssive stages with an average fermentation time of 80 h (567 FPU of fun gal cellulase/L; 6.1 FPU/g of substrate). This represents a yield of 0 .426 g of ethanol/g of substrate, 539 L/metric ton, 129 gal/U.S. ton. MWOP contains approximately 90% carbohydrate. Thus the combined effici ency for saccharification and fermentation to ethanol was 83.3% of the theoretical maximum.