PRODUCTION OF ETHANOL FROM STRAW AND BAMBOO PULP BY PRIMARY ISOLATES OF CLOSTRIDIUM-THERMOCELLUM

Clostridium thermocellum strains SS8 and GS1 grew poorly on crude biopolymers but fermented them easily after alkali treatment. With 1% alkali-extracted rice straw (AERS) and delignified bamboo pulp (DBP), the ethanol-to-substrate (E/S) ratios were almost the same as those obtained when using filter paper. Increasing the substrate concentrations decreased the percentage substrate degraded and the E/S ratio and concomitantly increased the amount of reducing sugars accumulated. A maximum amount of 8.6 g ethanol/l was produced by strain SS8 out of 37.5 g DBP degraded. Strain GS1 accumulated reducing sugars at substrate concentrations > 50 g/l, thereby accounting for about 70% of AERS degraded. This strain produced cellulase on both cellulose and cellobiose. Both the strains grew in the presence of 1.5% (v/v) ethanol. Strain SS8 fermented starch, but the ethanol yield was low compared to that from cellulose. About 75% of starch degraded accumulated as reducing sugars at a substrate concentration of 40 g/l. The inhibitory effects of ethanol (2 to 4%) were less drastic when growing cultures were challenged than when they were formed in situ. The effect of ethanol depended upon the phase of the culture.