Continuous ethanol fermentation at 70 C from straw and straw hydrolysates
The project concerns a thermophilic process with continuous ethanol removal. An early problem was in developing a defined medium for continuous aerobic and anaerobic cultures of the organism to allow accurate fermentation balances. A more serious problem was that strain LLD-15 reverted to lactate production under conditions that maximise ethanol production in continuous culture. However, development of a continuous system using membrane cell separation and recycle allowed reproducible and accurate growth and product kinetics over prolonged periods. Attempts to develop a host-vector system for the organism so as to use genetic engineering techniques to delete the LLD gene, and for other strain improvement strategies, showed promise but were not completed. However, a stable LLD-16 strain was achieved by diepoxybutane mutagenesis and screening fluoropyruvate resistance plus lack of reversion. Moreover, analogous mutagenesis and screening for fluoroacetate resistance yielded strains that make more ethanol and less acetate. It was discovered that even the unimproved LLD-15 strain has high ethanol productivity from xylose at 70 C in the cell-recycle system, suggesting an ethanol production price below 0.30 dollars/litre for sugars derived from hemicellulosic wastes. Together with recent Canadian developments in using steam-explosion of wood-chips followed by ethanol extraction to produce paper pulp, this could form the basis for an economical production process, yielding paper plus ethanol and using lignin as the plant fuel, eliminating water pollution and reducing CO(2) contribution to the Greenhouse Effect. Continued development and extension to sugar-cane bagasse, straw and sugar-beet pulp is therefore planned.
Bibliographic Reference: EUR 12716 EN (1990) 53 pp., MF, ECU 4, blow-up copy ECU 7.50
Record Number: 199011053 / Last updated on: 1994-12-01
Original language: en
Available languages: en