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STUDY OF THE USE OF PACHYSOLEN TANNOPHYLUS FOR THE PRODUCTION OF ETHANOL.

Objective

THE AIMS OF THE PROPOSED R&D WORK ARE TO DEVELOP A NEW BIOREACTOR FOR ETHANOL FERMENTATION AND TO APPLY THIS TECHNOLOGY TO NOVEL ETHANOL FERMENTATIONS IN ORDER TO IMPROVE ETHANOL YIELD AND PRODUCTIVITY.

THE DEVELOPMENT OF THE NEW BIOREACTOR WILL BE BASED ON THE ENCOURAGING RESULTS OBTAINED IN PRELIMINARY EXPERIMENTS BY THE TWO INSTITUTES. EMPLOYING THE TECHNOLGY OF PACKED BED REACTORS, A SYSTEM USING NONCLARIFIED MOLASSES AND TRADITIONAL PACKING MATERIAL SHOWED A FIVE-FOLD IMPROVEMENT IN THE FERMENTATION RATE OVER A BATCH FERMENTER AND GOOD LONG TERM STABILITY. WITH A SYNTHETIC GLUCOSE MEDIUM AT A CONCENTRATION OF 150 G/L GLUCOSE, AND A NOVEL PACKING MATERIAL, VOLUMETRIC PRODUCTIVITIES EXCEEDING 80 G/L*HR,, WERE ACHIEVED. THE LONG TERM STABILITY WAS HOWEVER LOWER. THE WORK UNDER THIS MARGINAL COST CONTRACT IS ONE PART OF A THREE PART PROJECT AIMED AT OBTAINING DATA FOR THE DESIGN OF A LARGE SCALE PILOT PLANT BASED ON THIS TECHNOLOGY. THE THREE PARTS WILL BE CARRIED OUT CO-CURRENTLY.

THIS PART OF THE PROGRAM WILL CONCENTRATE ON THE NOVEL YEAST PACHYSOLEN TANNOPHILUS, WHICH IS CAPABLE OF FERMENTING PENTOSES, DERIVED FROM HEMI-CELLULOSE, TO ETHANOL. IT IS THEREFORE BETTER SUITED TO THE FERMENTATION OF RAW MATERIALS LIKE STRAW- AND/OR WOOD- HYDROLYSATES THAN SACCHAROMYCES CEREVISIAE, WHICH IS INCAPABLE OF FERMENTING THE PENTOSE FRACTION.W- HYDROLYSATES. PREVIOUS WORK HAS INDICATED THAT P. TANNOPHILUS WILL FERMENT, BUT NOT GROW ON, XYLOSE UNDER ANAEROBIC CONDITIONS. THE YIELD OF ETHANOL ON XYLOSE WAS ALSO HIGHER UNDER ANAEROBIC CONDITIONS THAN UNDER AEROBIC CONDITIONS, REACHING 42% ON SUBSTRATE UTILISED UNDER ANAEROBIC CONDITIONS AND ONLY 30% UNDER MICRO-AEROPHOLIC CONDITIONS, CF 45 TO 50% FOR GLUCOSE BASED MEDIA. THE BATCH FERMENTATION RATES, BOTH ON SYNTHETIC XYLOSE AND AUTHENTIC WOOD HYDROLYSATE, WERE HOWEVER VERY LOW COMPARED WITH S. CEREVISIAE ON GLUCOSE OR SUCROSE BASED MEDIA. FERMENTATION TIMES AS LONG AS 7 DAYS WERE FOUND TO BE REQUIRED BY P. TANNOPHILUS WHEN USING SOFT-WOOD HYDROLYSATE AS THE MEDIUM. THIS GAVE SPECIFIC ETHANOL PRODUCTION RATES OF0.07 AND 0.03 G ETHANOL/G CELLS*HR, AND VOLUMETRIC PRODUCTIVITIES OF 0.12 TO 0.05 G/L*HR. THIS LOW PRODUCTIVITY RENDERS SUCH FERMENTATION SYSTEMS ECONOMICALLY NON-VIABLE. HOWEVER, IF THE SAME IMPROVEMENT CAN BE OBTAINED AS WITH GLUCOSE OR MOLASSES BASED MEDIA BY THE APPLICATION OF PACKED BED TECHNOLOGY, CONSIDERABLE IMPROVEMENT IN THE ECONOMICS OF THE FERMENTATION WOULD BE OBTAINED, AND THE USE OF THESE NATURAL RAW MATERIALS FERMENTATION SUBSTRATES MAY BECOME ECONOMICALLY VIABLE COMPARED WITH GLUCOSE BASED MEDIA.THE R&D WORK WILL BE CARRIED OUT ON A LABORATORY SCALE FERMENTER TO OBTAIN DATA FOR ECONOMIC AND KINETIC EVALUATION OF THE PROCESS. DUE TO THE EXPENSE OF THE RAW MATERIAL REQUIRED, THE CONCENTRATION OF XYLOSE IN THE MEDIUM WILL BE 30G/L, WHICH IS CLOSE TO THE TOTAL SUGAR CONCENTRATION OF A MOST INVESTIGATORS. PRELIMINARY EXPERIMENTS WILL BE CARRIED OUT TO INVESTIGATE THE CAPABILITY OF P. TANNOPHILUS TO ADHERE TO FIBREOUS PACKING MATERIAL, IF LOW ADHERENCE IS FOUND, TRADITIONAL PACKING MATERIAL WHICH TRAPS THE YEAST IN INTERSTITIAL VOIDS WILL BE USED IN THE FERMENTER. THE OPTIMUM OPERATING CONDITIONS WILL BE INVESTIGATED FOR THIS FERMENTATION BY INITIALLY VARYING THE PH OF THE MEDIUM AND THE FERMENTATION TEMPERATURE.
PARTICULAR EMPHASIS WILL BE PLACED ON ANY INTERACTIONS BETWEEN OPTIMUM PH AND TEMPERATURE. THE PERFORMANCE OF THE FERMENTER WILL BE MONOTORED BY THE ETHANOL YIELD AND PRODUCTION RATE. HAVING OBTAINED THE BEST CONDITIONS THE EFFECT OF DILUTION RATE AND PACKING DENSITY, IF USING FIBROUS MATERIAL, WILL BE INVESTIGATED USING A SEMI-DEFINED XYLOSE MEDIUM.
AFTER THE OPTIMUM CONDITIONS HAVE BEEN OBTAINED, THE MEDIUM TERM STABILITY (UP TO 30 DAYS) OF THE FERMENTER WILL BE INVESTIGATED. IF LOW STABILITY IS EXPERIENCED AT OPTIMUM CONDITIONS FOR ETHANOL PRODUCTION RATE, EXPERIMENTS WILL BE CARRIED OUT TO OBTAIN A REASONABLE COMPROMISE BETWEEN STABILITY AND PRODUCTION RATE.
PROVIDED SUFFICIENT TIME IS AVAILABLE, THE INVESTIGATIONS WILL THEN SWITCH TO THE USE OF SYNTHETIC SOFT-WOOD HYDROLYSATE AS THE BASIS OF THE MEDIUM. THIS WILL ESTABLISH THE PERFORMANCE PROFILE FOR A

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

University of Strathclyde
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