LABORATORY INVESTIGATION OF ETHANOL-PRODUCTION FROM MUNICIPAL PRIMARYWASTE-WATER SOLIDS

Ethanol can be produced from a number of renewable resources such as s tarches, sugars, or lignocellulosic materials. Lignocellulosic waste m aterials such as municipal wastes or wastepaper are defined as such be cause they contain cellulose in combination with lignin. The cellulose component in these materials can be converted to ethanol in a two-ste p process where the cellulose is first converted to glucose sugars by hydrolysis (saccharification); the resulting sugars can in turn be con verted to ethanol by fermentation. A preliminary investigation was per formed to assess the conversion of the cellulosic component of municip al primary wastewater solids to ethanol. Primary wastewater solids col lected from two full-scale facilities were tested. A laboratory experi mental set-up was designed in order to perform the necessary conversio ns. The primary wastewater solids were characterized to contain 10% ce llulose and 26% lignin. Conversion of the cellulose to glucose was ach ieved by Trichoderma reesei cellulases in enzyme hydrolysis. These exp eriments demonstrated that higher substrate concentrations, temperatur es and enzyme concentrations resulted in higher rates of reaction. Con version of the glucose to ethanol during fermentation was accomplished by the action of yeasts from Saccharomyces cerevisiae. The two conver sion processes were then combined in the same vessel to obtain simulta neous conversion in a process known as simultaneous saccharification a nd fermentation (SSF). SSF experiments employed the cellulase system f rom Trichoderma reesei QM9414 and Saccharomyces cerevisiae in the same vessel and achieved ethanol concentrations between 1.5 and 2.3 g/l fr om nutrient media containing 100 g/l primary wastewater solids. This c orresponded to overall conversion efficiencies of cellulose to ethanol in the range of 17-60% based on theoretical values. (C) 1997 Elsevier Science Ltd.