Skip to main content

High temperature ethanol fermentation of lignocellulosic wastes

Objective

The overall objective is to develop a laboratory scale pilot plant to test a novel process, using a novel thermophile, for continuous ethanol production from a range of cheap and abundant agricultural wastes.
A laboratory scale pilot plant is being developed to test a novel process, using a novel thermophile, for continuous ethanol production from a range of cheap and abundant agricultural wastes.
The stage reached is that a suitable mutant thermophile has been selected and tested on pure xylose feedstocks in an open system that uses an anaerobic catalytic stage with cell recycle via hollow fibre ultrafiltration in which there is no cell growth. Long term continuous operation is achieved by feeding fresh cells grown on xylose aerobically to compensate for the death rate of cells in the catalytic reactor. The results show sucrose volumetric productivity although ethanol yields on xylose are slightly below those of the best yeasts on glucose. Ethanol costs are predicted to be well below those for petrochemical ethanol.

The lack of a nonreverting strain has been the biggest handicap to the research. However despite this, significant progress has been made. The existing LLD-15 and LLD-16 strains were used in the open system to provide useful results on relative fermentability of various components in the real feedstocks. These have shown that almost all the sugar in various mixtures is efficiently fermented and no sign of toxicity from other components has been detected. The cell recycle system can be used over long periods even with these reverting strains to obtain product yields at moderate feedstock concentration and new neutral pH.

It is likely that an LLD-deletion strain will shortly be available via the recombinant deoxyribonucleic acid (DNA) strategy enabling the feedstocks to produce reasonable ethanol yields at very high volumetric ethanol productivities, particularly in the closed system.

The encouraging data from dilute acid hydrolysates of corn cobs and from enzymic hydrolysates of beet pulp suggest that the former strategy will be applicable to a range of high lignin wastes such as straw or wood chips, and the latter to low lignin wastes such as beet pulp, citrus wastes or enzymic retting of flax or rape straws.
This process has so far been developed entirely at Imperial College, London, with partial CEC assistance from the Non-Nuclear Energy programme. The stage reached is that a suitable mutant thermophile has been selected and tested on pure xylose feedstocks in an Open System that uses an anaerobic catalytic stage with cell-recycle via hollow fibre ultrafiltration in which there is no cell growth. Long term continuous operation is achieved by feeding fresh cells grown on xylose aerobically to compensate for the death rate of cells in the catalytic reactor. The results already show that although ethanol yields on xylose are slightly below those of the best yeasts on glucose, sucrose or maltose, the more rapid metabolism of this organism allows a much higher volumetric productivity. Using data on costs of xylose from steam exploded wood or straw derived by the Institut Francais du Petrole from their pilot plant at Soustons, ethanol costs well below those for petrochemical ethanol were clearly predictable, even wh n based on oil prices below 20 dollars per barrel.

The specific objectives of the project are to continue the process to pilot plant stage and make progress in the following areas:

bacterial strain improvement;
development of the Closed System;
development and testing of feedstocks derived from wood and straw wastes;
development and testing of feedstocks derived from sugarbeet wastes.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
Address
South Kensington Campus
London
United Kingdom

Participants (3)

CENTRALE RECHERCHE SA
France
Address
Grande Voie Des Vignes, Ecole Centrale Paris
92295 Chatenay Malabry
Institut Français du Pétrole
France
Address
1-4 Avenue Du Bois Préau
92506 Rueil-malmaison
NATIONAL UNIVERSITY OF IRELAND, GALWAY
Ireland
Address
University Road
90 Galway